# CRI of White LEDs



## UnknownVT (May 5, 2010)

CRI (Color rendering index) of white LEDs have been low in the region of CRI=70, compared to fluorescent lights even with the average consumer grade CFL from GE manages CRI=82.

Some consider that white LEDs seem better than the low CRI may indicate -
so much so that the CIE (International Commission on Illumination) had a paper out since 2007 suggesting that white LEDs should be assessed visually using the Gretag Macbeth ColorChecker chart.

The Macbeth chart is the photographic industry standard for testing the color accuracy of digital cameras and film - digital camera tests these days use software to analyze the test photo results - some criticize the Macbeth chart for not having a wide enough gamut to use visually - yet that is precisely what the CIE are proposing - to use the Macbeth chart for visual assessment for the CRI of white LEDs.

The abstract of the paper is on the CIE website:
CIE TC 1-62

on searching for a copy of CIE TC 1-62 I also came across these:

Labsphere
" _What is the TC 1-62 Colour Rendering of White LEDs?

The present color rendering system gives a poor rating for white LEDs yet the color appearance of white LEDs is better than color rendering index would suggest. This is a potential barrier to introduction of white LEDs into main stream applications so TC 1-62 was established to investigate, *by visual experiments*, color rendering properties of white LED light sources and to test the applicability of the CIE color rendering index to white LEDs._ "

Then -
pdf VISUAL OBSERVATION OF COLOUR RENDERING
from Colour and Multimedia Laboratory of the University of Veszprém, Hungary 
- where they followed the CIE TC 1-62 recommendation and used the Macbeth chart for the experiment
the *visual experiments* look very interesting - 
their comments on the 4000K tests

" _As can be seen, there are huge differences in ordering the lamps according to visual or calculated colour difference. The exceptionally good visual performance of the traditional Cool White lamp is hard to understand, one reason might be that most of the test samples contained only very little long wave radiation. It is also of interest that the small peak wavelength difference between the two clusters produced a large difference in Ra. The rank order for the 6500 K series is the same for all four methods of evaluation._ "

I am not too sure if they have taken into account the human eye/brain behavior with different light levels - 
as shown in the Kruithof curve -
could this have any bearing on their 4000K results?

But best of all *-*
I have found a copy of the CIE TC 1-62 paper that is currently viewable on line using embedded FlashPlayer:

CIE 177 2007 - CIE TC 1-62 paper


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## Chauncey Gardner (May 5, 2010)

Interesting. 

Thanks for putting this up. 

I hate flourescent lights and find it hard to believe the CRI would be higher than even a warm white LED when compared.

I have returned a couple of suits after taking them out of the garment bag at home only to find out they were a substantially different color / shade than what they appeared to be in the store.

Just anecdotally it's no contest in what has the more accurate color rendering between the flourescents in my kitchen & warm white of an LF2XT & Quark mini aa (WW). Outside those two lights do a pretty good job of mimicking daylight against the trees & surrounding vegetation.

Flourescents make everthing look rather "flat" to my eye.

I'll check out the links.


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## HarryN (May 5, 2010)

Hi, it is a fascinating and complicated area, isn't it.

IMHO, the main challenge with the CRI indication is that it is based on a rather poor reference - the incan bulb. As a practical matter, this means the noon day sun is also has a relatively poor CRI rating, in spite of the tendency of our eyes to be designed for its light.

The whole area gets really interesting when you start putting in CCT preferences, which are somewhat genetically influenced. ( for instance, I prefer 5-6000 K, high spectral content light). Obtaining such an LED is nearly impossible, so I have to lower my goal to more like 4000K.

The MacBeth / Munsel system is not ideal, but not all that bad either. Certainly for LED general lighting and flashlights, it is a marginal issue. When it comes to viewing fine photographs, life can be dicey.

I saw a presentation on the possible influence of the MacBeth system, and it basically allowed a lot of discreet wavelengths to beat it, vs a nice continuous spectrum. Is that your interpretation?

BTW - if you don't like tube FL lights, there is a good chance that you are just buying the wrong tube. Buy the ones that are daylight, high CRI and it is entirely a different experience.


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## Curious_character (May 5, 2010)

Below 5000K, the CRI is based on comparison to a black body at the same color temperature. This means that a light with a good 2700K CRI, for example, would look and render colors quite differently than a light with good 4000K CRI. Above 5000K, a "phase" of daylight is used as the reference, so lights considered to have a color temperature in that range look different yet.

Even for a single color temperature, lights with a particular CRI can have an infinite number of spectral shapes and correspondingly different appearance and color rendering. Trying to reduce an entire spectrum to a single number inevitably results in losing a lot of information. It's a mistake to consider CRI an absolute measure of anything, when at best it's a crude grouping based on somewhat arbitrary criteria.

c_c


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## Chauncey Gardner (May 5, 2010)

HarryN said:


> Hi, it is a fascinating and complicated area, isn't it.
> 
> IMHO, the main challenge with the CRI indication is that it is based on a rather poor reference - the incan bulb. As a practical matter, this means the noon day sun is also has a relatively poor CRI rating, in spite of the tendency of our eyes to be designed for its light.
> 
> ...


 

I will take a look next time at what is available, maybe different tubes would be an improvement. 
I had planned on sticking in a skylight in the kitchen during a planned remodel, but even better rendering from higher CRI tubes would be an improvement.

I had assumed (incorrectly) the higher the CRI the closer to natural sunlight of a given source. 

Thanks for getting into a bit more detail, it was an "ah ha!" moment. 
I'll finish checking out the linked papers before commenting much further, but when it comes to well done photos I can see the same issues (complaints) that a serious foodie / cook would in his kitchen. 

Both cases you are less than pleased with the way colors are represented with what is before you & it is less than satisfying to a discerning eye when looking at subject matter you really enjoy.

Hopefully this isn't viewed as a minor "threadjacking"  by UnkownVT.


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## Yavox (May 5, 2010)

What is the highest CRI available LED at the moment, suitable for a flashlight which could produce 200 or more OTF lumens and who produces them? Are they more expensive than "normal" LEDs?


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## HarryN (May 5, 2010)

Yavox said:


> What is the highest CRI available LED at the moment, suitable for a flashlight which could produce 200 or more OTF lumens and who produces them? Are they more expensive than "normal" LEDs?



That is a surprisingly difficult question. From prior attempts at making flashlights, I use "rated lumens / 2" to get OTF lumens. Using that derating factor, that means we need to look for an LED package with something like 400 lumens, or 4 each x 100 lumens.

In the 4 each x 100 lumens, probably a high CRI Lumileds Rebel.

In the 1 x 400 lumens, perhaps LEDEngin neutral or warm tint.


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## HarryN (May 5, 2010)

Curious_character said:


> Below 5000K, the CRI is based on comparison to a black body at the same color temperature. This means that a light with a good 2700K CRI, for example, would look and render colors quite differently than a light with good 4000K CRI. Above 5000K, a "phase" of daylight is used as the reference, so lights considered to have a color temperature in that range look different yet.
> 
> Even for a single color temperature, lights with a particular CRI can have an infinite number of spectral shapes and correspondingly different appearance and color rendering. Trying to reduce an entire spectrum to a single number inevitably results in losing a lot of information. It's a mistake to consider CRI an absolute measure of anything, when at best it's a crude grouping based on somewhat arbitrary criteria.
> 
> c_c



CC - Thanks for that clarification. I will go back and look at those definitions again.

Harry


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## Archie Cruz (May 5, 2010)

Much of these new 'findings' and demand for a revamped metric for rating visually pleasing CRI/Colro Temp was pretty much confirmed by research done by the 'quack' Aten Imago, a former CPF member. 
Here's the original article Presented to the IEEE, LRI :twothumbs Fully digested by HarryN 
--
Theory & Method of LED Color Blending For Enhanced Nocturnal 
(Scotopic & Mesotopic) Subject Rendering

Authors:

Äten Imägo
Imägo Metrics - Bethesda, MD - USA

M.P.El-Darwish 
Geneva, Switzerland

Version 2.0
October 24, 2005


“Optimizing Human / Technology Interaction Performance”




Abstract

This document lays out the theoretical and research basis for the optimization of LED color blending for the purpose of better aligning the requirements of night adapted human vision (AKA Scotopic/Mesotopic Vision) with the artificial LED source illuminations prevalent in personal illumination devices such as flashlights, bicycle lights and personal reading lamps.

Keywords: Scotopic,Mesotopic,Photopic, Human Factors, Usability, Performance Optimization, Dichromasty, Night Adaptedness, Luxeon, LED, Flashlight, Reading Lamp, Vision, Amber, Straw, White


CONTENTS
EXECUTIVE SUMMARY 3
A BRIEF HISTORICAL OVERVIEW OF THE CASE 4
THEORETICAL BASIS 5
Illumination brightness and contrast as influencers 6
Conditions for optimized supplemental illumination 6
Shortcomings of current LED emitters 8
Methods for creating Amber/Straw/White light from combined beams 8
FUTURE OPTIONS 9
Design community barriers to blended LED theory 9
Current design solutions in development 10
REFERENCES 12



Executive summary
This document sets forth the theory and method associated with the blending the light of two or more high flux LEDs into a combined beam color that has a Color Rendering Index (CRI) as well as wavelength that is harmonized to the requirements of persons performing tasks in low or no ambient light conditions. The need for such a method is due to the lack of a suitable single emitter LED from the available manufactured stock. 
Who will benefit from combined color LED arrays?
o Individuals that have benefited from the wavelength of light produced by incandescent lights in the 3,000ºK to 4,000ºK range. 
o Individuals seeking variable combination beam colors
o Stakeholder communities that are developing large scale environmental lighting - using LEDs to replace incandescent lights.
o Manufacturers looking for ways to expand the markets for their products. 

Benefits
What benefits can be expected?
o Abandonment of incandescent bulbs
o Reduced cost of bulb replacement
o Elimination of color interaction issues resulting from the use of current LEDs
o Introduction of nuanced white combination arrays
o Increased sales opportunities
Productivity Enhancements
What benefit in productivity will result from this process?
o A competitive edge: Manufacturers, Distributors and Customers will flock to this solution, until a single optimum emitter bin color is introduced
o Enables end-users to experience the same advantages from an combined LED array that is currently available to users of incandescent bulbs
o This is a gap filling solution that will bridge a potentially long cycle in the High Flux design process


Improvements Realized in Actual Use
Improvements will be realized as a result of:
o Reduced eye-strain 
o Reduced user errors that can slow productivity down
o Increased speed of object identification as well as spatial navigation

The argument for an Amber/Straw/White VS Daylight LED source
A brief historical overview of the case
Taken from a layman's point of view and then underscored by empirical science, the argument for an Amber/Straw/White light for night-adapted illumination, versus a Daylight white is thus:
The current human visual sensory array of Retinal Rods & Cones evolved from a biologically adapted array that deliberately took advantage of the wavelength of light produced by flames. Flames such as those from camp fires, torches and later- oil lamps, candles and gas burning street lamps- invariably produced light that was Amber/Straw/White in wavelength.
This represents an adaptive evolution of the retinal sensory array to coincide with the available wavelength of light. The result is that our visual system became calibrated to optimize night vision to this wavelength-that in layman's terms we have called Amber/Straw/White.
The scientific deconstruction of this evolutionary trend leads to what we currently know about scotopic and mesotopic vision. What is known about scotopic vision is that Retinal cells called Rods are sensitive to very low levels of illumination and are responsible for our ability to see in dim light (scotopic vision). Rods contain a pigment with a maximum sensitivity at about 510 nm, in the green part of the spectrum. The rod pigment is often called visual purple since when it's extracted by chemists in sufficient quantities the pigment has a purple appearance. Scotopic vision is completely lacking in color; a single spectral sensitivity function is color-blind and thus scotopic vision is monochromatic.
The situation becomes more complex when nocturnal vision combines night adapted or scotopic vision, with full color or photopic vision. Mesotopic vision is the scientific term for a combination between photopic vision and scotopic vision in low but not quite dark lighting situations. 
For example: the combination of the higher total sensitivity of the rods in the eye for the blue range with the color perception through the cones results in a very strong appearance of blueish colors (eg. flowers) around dawn. 

The human eye uses pure scotopic vision in the range below 0.034 cd/m2,and pure photopic vision in the range above 3.4 cd/m2.
In the case of a general subject field that is a field of low contrast darkness that is then pierced by a smaller and localized region of illumination, the visual system works to resolve the brightness and color contrasts by combining the use of Rods and Cones. The resulting compromise illumination color that supports this effort is Amber/Straw/White - light near the 580nm region of the spectrum. This is the most productive supplementary illumination color space for both scotopic and mesotopic vision.
Caveat Emptor - Just as the anthropological record depicts divergent geographical trends in the evolution of human sensory perception, we do not contend that the generalized statements made about human scotopic, mesotopic or photopic vision are absolute or universal. The nomadic peoples of the arctic circle, for example, seem to have evolved an ability to perceive color nocturnal contrast differently from those living on at equatorial latitudes. 

Theoretical basis
The foregoing historical and scientific statements pertain to circumstances in which there is no ambient environmental light and the sole source of illumination is a highly localized one, such as might be generated by a flashlight, torch, candle or spotlight. The situation becomes more complex when one considers the following examples:
o Low level and general blueish illumination such as may be produced by the full moon on a clear night
o Low level and general Amber illumination such as might be produced by certain sodium vapor street light arrays
In such cases, the visual system resolves these 'casts' so that they are not perceived as casts at all. When a bright and localized beam is then projected onto a target subject that is surrounded by a diffuse base illumination color, the visual system is shocked and the newly introduced light appears to have a cast that is typically the spectral compliment of the prevailing light. As an example- the introduction of an otherwise neutral and spectrally pure white beam of light from a flashlight into a scene that is bathed is the amber hue of sodium vapor street lights (AKA 'Crime Lights') creates a discontinuity in signals sent by Rods & Cones to the brain- resulting in a perception that the Daylight beam is actually Blue in hue. This discontinuity is greater when the localized beam is smaller. Expressed differently- as the field of supplemental illumination widens and exposes more retinal cells (Cones) to its wavelength, so in turn will the resolution or 'leveling' be more in favor of this localized beam color. In practical terms this means that in a situation of a low level of general illumination plus a localized supplemental light- the supplemental light wavelength should match that of the general illumination. Interestingly, this statement holds true in broad daylight as well!
In cases where the general illumination is so low as to be negligible, then the sole and localized illumination source is optimally in the 580nm region of the spectrum.
Illumination brightness and contrast as influencers
Thus far we've only talked about the interactions of illumination source wavelengths in affecting perceived subject color and ease of night-adapted vision. Another part of the equation relates to the relative contrast and brightness of the scene and the target or 'focus' region within that scene.
I've already touched on the discontinuity that occurs when a bright light of a different wavelength is projected into the scene. I'd like to comment on the added effect of brightness on the visual system's interpretation of colors.
The prevalent thinking has been that the desirable torch or flashlight illumination is one that is closest to neutral daylight in color (approximately 5,400ºK) and brightness is as high as technically possible. Some manufacturers have gone so far as to insist that a bright narrow spotlight that is 5,400ºK in hue is the best solution to most personal illumination challenges. I beg to differ.
Introducing a highly localized (spot) beam of light into a scene bathed in darkness creates havoc for fully night-adapted vision. Choosing to make that beam Daylight balance by default, compounds the shock and reduces night adaptedness which results in increased perceived contrast between the spotlit target and the surrounding scene. This predicament not only makes effective object identification more difficult and less effective- it also 'bleaches' Rods and renders them null- making perception of details in the surrounding scene very difficult if not impossible. In summary, we can make the following statements with regard to localized light brightness, focus and color.

Conditions for optimized supplemental illumination
o In cases where effective perception of shape and form in the prevailing and surrounding darkness is important:
o Supplemental illumination level or brightness should only be just as bright as is necessary in order for the user to perceive sufficient detail in the subject for effective identification
o The transition from focus (spot) to corona, penumbra and then surrounding darkness- should be as gradual as possible
o If there is negligible or no ambient illumination, then a localized torch or flashlight beam color of Amber/Straw/White (580nm) is ideal
o If there is a predominant ambient color, then matching that color will mitigate against a chromatic discontinuity that will likely result in the perception of a cast
o The axis of illumination should be slightly off dead-center from the user's direct line of sight
o In cases where the ambient illumination is broad daylight and the subject is located in a pocket of darkness:
o The supplemental illumination level can be as bright as or slightly brighter than the ambient brightness level
o The transition from focus (spot) to corona, penumbra and then surrounding brightness- may be abrupt
o The supplemental illumination may be daylight or as close a match in color to that of the surrounding ambient scene
o In such cases, there is no advantage in using light that is the same as that used for night and indeed doing so would be counterproductive
o The axis of illumination should be slightly off dead-center from the users direct line of sight
o In cases where the subject area is a significant portion of the overall scene
o The supplemental illumination should cover as much of the target area as possible
o The light should be as diffuse as possible
o The axis of illumination should be slightly off dead-center from the users direct line of sight
o In cases where the entire scene is an enclosure such a small room, passageway or container with reflective walls and a high degree of subject color differentiation is important
o The supplemental illumination is more effective if it's a neutral white or slightly warm white in the 5,200ºK to 5,400ºK range with a Color Rendering Index (CRI) of between 90 and 100
o The transition from focus (spot) to corona, penumbra and then surrounding darkness- should be as gradual as possible
o The light should be as diffuse as possible
o The axis of illumination should be slightly off dead-center from the users direct line of sight
o The supplemental illumination level can be as bright as or slightly brighter than the ambient brightness level

Shortcomings of current LED emitters
Currently, LEDs are available in a wide range of colors. A narrow range of white LEDs have filled market needs for illumination that supplements or supplants the most neutral and highest color rendering Daylight. This is a boon to many industries that depend on repeatable, consistent and long-lived Daylight balanced artificial light.
Unfortunately, the need for an Amber/Straw/White LED has been neglected for lack of a scientific basis for such a need. In addition, research and development efforts have understandably been focused on serving the growing demand for large-scale end uses, rather than the smaller demands of the personal illumination markets.
The nearest to an ideal flashlight LED color for applications such as the outdoors markets, law enforcement, security and general consumer using such lights outdoors (as differentiated from high color differentiation applications), has existed in the form of an Amber Lumileds™ Luxeon™ emitter. A warmish white X bin LuxeonV emitter has also been a near proxy color. The Amber Lumileds™ Luxeon™ emitter is far too 'Orange' in cast to be useful for general applications. As a result, it is only through mixing of light from an Amber Lumileds™ Luxeon™ emitter with light from other White Lumileds™ Luxeon™ emitters that an output brightness and color optimized blended color can be achieved. This is the core of our theory. 
Methods for creating Amber/Straw/White light from combined beams
There are two approaches for creating the target Amber/Straw/White beam at 580nm from Luxeon LEDs
Approach 1 - Co-located flashlights
The most obvious approach, and one that I used in initial experiments, simply entailed binding together three or four identical flashlights- one using a Lumileds Amber Luxeon LED and the remainder containing White Luxeon LEDs of the same color or BIN and the same output. The axes of the resulting cluster of lights were adjusted so that all the beams would overlap- creating the single blended beam. 
Approach 2 - Co-located emitters
A more efficient and effective approach is to cluster either two, three or four white emitters around a single amber one and to then insert this array into a large flashlight. This latter method is currently popular in the design of products that seek to multiply the generated output from a fixed physical space inside a flashlight's head. Most typically, each emitter is contained in it's own reflector.

The benefits of using Approach 2 include:
o Ability to nuance the relative output between the Amber and White emitters
o Ability to create massive banks of light for large-scale applications
o Ability to replace one or more emitters to create special effects
o Smoother beam mixture
o Resultant beam is more akin to that from an incandescent bulb flashlight
Future Options

In the future, Lumileds may introduce an LED or series of LEDs that emit beam colors that are comparable to those currently produced by incandescent bulbs. In the interim, another evolutionary stage may involve the use of the new K2 series of Luxeon III emitters. 

This K2 series of emitters efficiently dissipates heat, a shortcoming of the prior generation of Luxeon III.

One advantage of this to the flashlight design engineer may include the ability to cluster a group of three, four and five emitters is very near proximity and in such a fashion that they may share one reflector. Though not necessarily envisioned for traditional flashlight designs, such arrays could be a boon to designers of illumination for other fixtures such as reading lamps, bicycle lights, camcorder lights, area lights and so forth. This would have the following advantages

o Individual emitter/reflector pairs would not require as precise an alignment to remaining emitter/reflector pairs
o A variable focus relationship between the cluster and single reflector could be established. 
Design community barriers to blended LED theory
The design community in any domain of industry is responsible for driving changes that ultimately benefit the user/consumer. Understandably, barriers to change exist within the flashlight community. The following is a list of possible design community barriers and how they may be overcome
o Cultural: The power of mass communication in disseminating information can result in 'mob mentality' or 'group-think', which can in turn result in sub optimal designs being adopted by masses of manufacturers. Once the concept of the LED as a light source for flashlights took hold, it was only a matter of time before cultural norms emerged that would set the stage for 'standards' of excellence in all aspects of LED use in flashlights. Changing the tone of these standards is critical to winning community adoption of a better design solution
o Technical: Design is often constrained by technical limitations. Before the advent of user-centered design that took human factors into considerations, nearly all efforts in the design of LED based flashlights have been concentrated on increasing brightness, achieving as neutral a white beam as possible and optimizing battery usage. By changing the attitude to beam colors to include Amber/Straw/White as an option; previous constraints cease to be an issue- paving the way for wider adoption of the blended beam solution
o Strategic: Manufacturers, while slow to making changes on a large scale- do notice design trends in the user community. Up-scaling adoption at the user level should drive changes up the value chain to the manufacturers- resulting in exponential changes across the entire flashlight landscape.

Current design solutions in development
Based solely on the 'prior art' trial experiments of imago Metrics's test of the multiple-lights with one being a Lumileds Luxeon III Amber, Andrew Wynn Rouse of Wynn Bright flashlights -with a mult-emitter light already in production immediately saw the possibility of replacing one of the four white emitters with an amber emitter which was furnished courtesy of Future Electronics - distribution partners for Lumileds, manufacturers of the Luxeon brand of LED emitters. 

The website containing the original pictures is here: http://rouse.com/RT4 (BAM+)

There are BAM+ beam shots here: http://rouse.com/beams
In the current design prototype, we did not have the physical space for a symmetrical array as is specified for the working prototype. Even so, the slight misalignment of the amber emitter in the array turned out not to be conspicuous in real-world use- though for aesthetic reasons we would like to continue development of a symmetrical array such as one amber surrounded by three white emitters (three points of an equilateral triangle) with a fourth, the amber emitter at the center.
One symmetrical design currently in alpha stage, is a flashlight using one amber emitter flanked by two white ones. This design is named the MiniMighty flashlight. 
The results of preliminary trials show that a high-power LED array can match the illumination quality of a medium/high power 'hotwire' incandescent lights, with all the advantages of using LEDs and none of the disadvantages associated with incandescent lights.
Prototypes in progress shall serve as proof of concept and as envisioned, will fill a gap currently unfilled by any solution other than filtration.
In addition, future trials will include the ability to variably nuance the relative output of amber versus white emitters, so as to affect a range of color temperatures from 4,000ºK to 3,200ºK in addition to permitting variable brightness levels. Such fixtures could have far ranging applications in interior architectural illuminations, where nuanced illumination hues can have a bearing on the intended mood of the interior design setting as well as in supporting effective task illumination.

References
Ware, C (2000) Information Visualization- Perception for Design 103-149.
Salvendy,G (1997) Handbook of Human Factors and Ergonomics (672,875-876,1737,1699,62-64,669,870,1735,862-863,176,872,59)
Morris,A (1950)Visual acuity at Scotopic Levels of Illumination
______________________________________________
© 2005 Imago Metrics LLC - All Rights Reserved

Finally folks are coming around to understanding that interactions of localized ( ie flashlight, display light, area light) illuminations with ambient illumination, context of use and level of light are the key drivers for determining ideal CRI and not blind engineering combined with manufacturing capacity.


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## UnknownVT (May 5, 2010)

Archie Cruz said:


> Much of these new 'findings' and demand for a revamped metric for rating visually pleasing CRI/Colro Temp was pretty much confirmed by research done by the 'quack' Aten Imago, a former CPF member.
> Here's the original article Presented to the IEEE, LRI :twothumbs Fully digested by HarryN



Yes, well, there is more than one mechanism at play here - 
first I do not claim to be any expert on this and have found/learnt some of this as I went along.

As mentioned CRI is very dependent on CCT (Correlated Color Temperature)
eg: it may surprise many to learn that an incandescent/tungsten bulb rates CRI=100 (perfect) by definition, yet anyone who has taken a photo under tungsten lighting with daylight white balance (or daylight slide film) will know immediately that that the light is very yellow/amber - and will have difficulties seeing yellow on white or distinguishing navy from black - so how can it possibly be CRI=100 perfect?

It is the way that CRI (color rendering index) is defined comparing to a reference black-body of the same color temperature - so an incandescent bulb is its own reference by the definition...... that's why it rates CRI=100.

Whereas a 2700K CFL (compact fluorescent spiral) may only rate CRI=82 on average - but may actually contain more blue component so that it may be a tiny bit easier to see the difference between navy and black - but its CRI rates lower - because it is not exactly like a true tungsten bulb..... how's that for circular logic?

A good white LED rates about CRI=70 and not much higher - and since there is a huge push to use LEDs for general lighting and a CRI=70 is very poor - 
one might suspect that the CIE (an accredited international body on illumination) proposal to use visual assessment for CRI of white LEDs might just be yielding a little to the pressure to use white LEDs for general lighting? 
eg: we might find that a white LED formerly rated at CRI=70 all of a sudden under the new CRI measurement guidelines rate in the 80's?
So has that white LED improved?
or just made more acceptable so that big corporations will start to use them to save energy...... 
don't get me wrong saving energy is obviously a very good thing - but will our eyes appreciate this?

Then there is this whole question of how our eyes/brain adapt to lighting levels - empirically our eyes follow the
Kruithof curve
that's why I questioned whether that experiment using the new CIE guidelines for CRI in the pdf VISUAL OBSERVATION OF COLOUR RENDERING (from some of the same authors who originated the CIE TC 1-62 paper)
may have missed the eyes' reaction to different levels of lighting.

Although noonday sunny daylight might be held as the ideal lighting - our eyes do not see that as "white" under all lighting levels - at lower lighting levels most people actually will persist in seeing 2700degK as "white" (please see the Kruithof curve for an explanation)

One should read this paper:

The Color of White

paper published by the WAAC - Western Association for Art Conservation -
specifically on illumination for displaying art/paintings -
their findings fit well in the Kruithof curve.


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## HarryN (May 5, 2010)

Archie Cruz said:


> Much of these new 'findings' and demand for a revamped metric for rating visually pleasing CRI/Colro Temp was pretty much confirmed by research done by the 'quack' Aten Imago, a former CPF member.
> Here's the original article Presented to the IEEE, LRI :twothumbs Fully digested by HarryN
> --
> Theory & Method of LED Color Blending For Enhanced Nocturnal
> ...



Hi Archie, thanks for including the info. 

Aten's presentation and book are more or less a rehash of what was well known and widely published in the 5 years prior. I don't fault him for that, as it happens commonly at many technical conferences. 

What I do credit him and Andrew for is taking the effort to really build a light to test the work with real life parts.

More or less, they pointed out the obvious - the phase diagram we all use to "trick our eyes into seeing a color using mixing" only tricks it some of the time. A house is not complete by just putting up the frame and exterior, and lighting is not complete by just throwing up 2 or 3 colors into a phase diagram.

The challenge that they faced then in actually using the technique still exists today - no one makes an LED in the desired wavelength that they qualitatively described as "straw" color. 

The reason is that most Red and amber leds are made using AlInGaP technology, which is great for red, and just barely works for amber. For blue and green, the common technology uses InGaN, which just barely works down to a yellow green. This means there is not a commercially viable way to make yellow directly.

The solution is now getting closer with the intro of Lumileds "amber" made from phos converted blue. This means that making "yellow" in a similar approach is no longer a technical problem, just a market size question.


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## blasterman (May 5, 2010)

> The present color rendering system gives a poor rating for white LEDs yet the color appearance of white LEDs is better than color rendering index would suggest.


 
I have two _really good_ opinions on this.

First, comparative CRI light sources like fluorescent tubes have horridly spikey spectrums. Cool White LEDs spike on blue, but are fairly smooth after that. Low CRI fluorescent tubes however have multiple spikes and valleys which tend to bother our eyes. Hence why cool-white LEDs (good ones in low CCT bins) appear to have better color rendition than their published CRI would indicate.

Next, the current CRI standard is near useless, as evidenced by the fact Philips is claiming it gets 98 CRI from a rather cheap fluorescent tube. If the sun is a 100 CRI.....whatever.

Regardless of how cool-white LEDs might be considered better than other mediocre CRI light sources, I still consider them totally inadequate for interior lighting.


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## jtr1962 (May 5, 2010)

UnknownVT said:


> Although noonday sunny daylight might be held as the ideal lighting - our eyes do not see that as "white" under all lighting levels - at lower lighting levels most people actually will persist in seeing 2700degK as "white" (please see the Kruithof curve for an explanation)


I've always had trouble wrapping my head around this because to me 2700K looks distinctly yellow and horrid regardless of lighting level. I could be in a room for hours but not acclimate enough so that 2700K appears white. I recently made a reading light so I can read in bed using 5 SSC high-CRI neutral whites. While the color rendering is great, to me the tint still looks more yellow than I'd like, and this is 4000K. Personally, I need to get to around 5000K before a light looks white to me, regardless of color level.



> A good white LED rates about CRI=70 and not much higher - and since there is a huge push to use LEDs for general lighting and a CRI=70 is very poor -
> one might suspect that the CIE (an accredited international body on illumination) proposal to use visual assessment for CRI of white LEDs might just be yielding a little to the pressure to use white LEDs for general lighting?
> eg: we might find that a white LED formerly rated at CRI=70 all of a sudden under the new CRI measurement guidelines rate in the 80's?


Not at all true that cool white LEDs only have a CRI of 70. One of the pdfs you linked to had a blue plus phosphor LED rated at 80. Actually, high 70s to 80 seems to be where most phosphor whites fall, provided the CCT is reasonable ( i.e. 5000K to 6500K ). The 8000K to 10000K ones are those which might have a CRI of 70, but no sane person would consider using them for general lighting. Subjectively, cool white LED always seems better than most fluorescent of similar CRI, likely because the spectrum is more or less continuous. This is telling me we need a new measurement of color quality simply because what our eyes are telling us is way different from what the CRI says. Right now I'm lighting my bedroom with some LED screw-base lamps I had received for testing. One was retrofitted with cool-white Rebels, another with Cree XP-Gs. The 6500K CCT seems just fine, and a lot more bearably than a 6500K CFL. Truth is, I probably wouldn't want much lower CCT using LEDs even though I lean towards 5000K fluorescents. The LEDs seem more natural than the CCT and CRI numbers might indicate.


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## McGizmo (May 6, 2010)

I am no expert on CRI and I can only hope not to make false or misleading comments regarding CRI. The following comments are what I have gleaned and believe to be true; corrections are welcome.

When a CRI number is given or stated it is a number for the CRIa which is an average of a dozen or so CRI indexes measured at specific spectral positions. It is also based on a specific CCT. In simple terms, CRI is used to evaluate how well an artificial light source renders colors compared to a black body source of light at the same CCT. An incandescent source is essentially the standard against which other sources are compared. 

I am in the camp of folks who believe that sunlight should be the standard against which other lights sources are measured and although direct sunlight may have a spectral distribution of a black body source of a specific CCT, indirect sunlight often does not.

I think there are specific spectral areas of output from the various artificial sources of light that can be identified as the problem areas. These would be the regions in the spectrum where a source either has excess or limited output, relative to the whole. If some single color rendering index number is to be used as a measure of a lights ability to render color in general then it might be more illuminating to base this average on the problem indexes and not dilute it by averaging in other indexes which are typically adequate. In other words, a white LED for instance might be measured in its ability to render blue and red and green (in the spectral bands where we see the peaks and troughs).

One white LED may have a CRI of 87 and another of 94. The immediate assumption is that the LED having a CRI of 94 is a better source for color rendition. Well what if the one having CRI of 94 has a CCT of 2200 and the one with CRI of 87 is at a CCT of 5000. What if the one with CRI of 87 has all of its index numbers being 87 where as the one with a CRI of 94 has some indexes at 99 and a couple in the low 80's? I personally would prefer the LED having the CRI of 87 in this example and this preference is based on presumed color rendering even though it doesn't score as high as the other LED. But it is a personal preference.

Color rendering can be a very significant aspect in artificial illumination and being somehow able to quantify a light sources ability to render color certainly has merit. I would think that if a standard is to be established then this standard should be as ideal as possible and widely accepted as a standard. I would also suspect that CCT should be integral and not set aside as a qualifier but perhaps I am wrong. Perhaps some measure of significant deviation from such a standard would tell us more than the present CRIa index. :shrug:

In fixed lighting, the subject of illumination and its reflective nature is just as important as the source of illumination and the source should be selected with this in mind. In portable illumination, the nature of the subject may or may not be known in advance and this can be significant if choices in the illumination device are available. To what ever extent a measure or index of color rendering can aid us in making the best choice for the illumination task at hand such a measure or index has merit.


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## blasterman (May 6, 2010)

> While the color rendering is great, to me the tint still looks more yellow than I'd like, and this is 4000K


 
Ditto on better cool white LEDs being superior than cheap 'daylight' CFLs. 

One thing I've noticed with commercial quality 4100k T8 tubes of good subjective color is they cheat a little and have just a smudge of pink in them. However, light sources that claim to be neutral and have a bit of yellow or green in them tend not to look as good, even though the CRI and even CCT might be identical. This is especially true of neutral white LEDs where even a slight variation to the yellow or green side causes complaints. 

I've noticed that my latest batches of Bridgelux LEDs aren't nearly as warm as prior ones, likely in an attempt to get efficiency up. However, the character is distinctly 'rosy' more than yellow, and this is certainly by intent given their focus on commercial use.


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## Yavox (May 6, 2010)

Has anyone tried to bulild a multi-LED flashlight that would give extactly the same spectrum as an incan? I mean putting a few high-CRI LEDs inside to act as a main light source and supplement them by a few auxilaty LEDs which could fill the gap in the spectrum (like a red LED) or make the spectral curve more smooth. This would probably require not only boosting the red frequencies but also absorbing some blues, but we could provide an optic to each led and paint some of the lens with a glass paint a bit, to filter out what is not needed.

With some luck, maybe even a quad P60 dropin would do the job? The main problem would probably be the driver, because if we would like to have 3 or 5 modes, those different colored LEDs should probably be powered in non-linear way (related to each other) in order to keep the spectral curve the same and only change the brightness, not the frequency distribution. 

I am not sure if I can describe this in english clear enough, but I hope it is more or less understandable what I mean


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## copperfox (May 6, 2010)

Built, no, but the idea has been presented: https://www.candlepowerforums.com/threads/268711


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## Greta (May 6, 2010)

Archie Cruz said:


> Much of these new 'findings' and demand for a revamped metric for rating visually pleasing CRI/Colro Temp was pretty much confirmed by research done by the 'quack' Aten Imago, a former CPF member.


 
Is that disassociative identity disorder kicking in again, Aten? Don't play people for fools here. You've been allowed to post and be part of this community again because you have refrained from your old assinine ways. I suggest you get yourself back under the radar... :ironic:


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## Curious_character (May 7, 2010)

I recently added onto my house, and lit it with Cree LR6C recessed lights. They consist of several white LEDs, a number of red ones, and I believe a few yellow ones as well to get a CRI of 90. (The LR6 is "warm white" 2700K and the LR6C is "bright white" 3500K -- both are 90 CRI.) The thing that sold me is that the light includes a color sensor and feedback system to keep the color constant by automatically adjusting the colored LEDs as necessary. Without this feedback system, the color would change with time as LEDs age at different rates. I like the color (and efficiency -- the light output of a 60 watt incandescent for about 10 watts), although when compared to CFL, the lights look a bit on the purplish side. In various other places in the house I have some cool white fluorescent tubes and warm and bright CFLs, and get some really interesting effects going from one environment to another, or looking from one lit area into another. For example, the cool white fluorescents look greenish when viewed from an area lit with the LED lights, and yellow walls in the LED lit area look peach colored when viewed from the fluorescent lit area. A new bathroom has the LED lights, and I still have CFL just outside. Looking from the bathroom, the floor seems to change color at the point where the incident light changes.

The problem is, of course, that all the spectra are different, even when light types have identical color temperature and CRI ratings. And that will inevitably lead to different color renditions and different light color appearances. All equal-temperature heated filaments have very nearly the same spectrum, so defining a spectrum required only the single number of color temperature. With the variety of spectral shapes we get from the various types of lights and phosphors, it's now much more complicated.

I had another thought that further illustrates a shortcoming of CRI as a defining parameter -- Do you have an incandescent light hooked to a dimmer? Turn the dimmer all the way up. The full brightness incandescent light has a CRI of 100. Now turn the dimmer down until the lights are reddish. What's the CRI now? Answer: 100. How about when they're turned down to make a dim, really red light? Still 100. So in what way is that really red light with a CRI of 100 better than an LED with CRI of 70? Which would you prefer to light things up with? Which do you think shows colors more accurately?

c_c


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## UnknownVT (May 7, 2010)

Curious_character said:


> and get some really interesting effects going from one environment to another, or looking from one lit area into another. For example, the cool white fluorescents look greenish when viewed from an area lit with the LED lights, and yellow walls in the LED lit area look peach colored when viewed from the fluorescent lit area. A new bathroom has the LED lights, and I still have CFL just outside. Looking from the bathroom, the floor seems to change color at the point where the incident light changes.
> 
> I had another thought that further illustrates a shortcoming of CRI as a defining parameter -- Do you have an incandescent light hooked to a dimmer? Turn the dimmer all the way up. The full brightness incandescent light has a CRI of 100. Now turn the dimmer down until the lights are reddish. What's the CRI now? Answer: 100. How about when they're turned down to make a dim, really red light? Still 100. So in what way is that really red light with a CRI of 100 better than an LED with CRI of 70? Which would you prefer to light things up with? Which do you think shows colors more accurately?



Interesting input. 
I think our eyes tend to be able to distinguish differences well - 
whereas without anything to compare to, 
I think our eyes/brain adapt to "accept" or optimize to that ambient lighting.

CRI is mostly misunderstood - and because it is quantitative - ie: there is a hard figure attach to it - many people just take it as some kind of gospel - ie: CRI=100 has to reproduce colors more accurately than CRI=82.

Of course without the corresponding CCT (color temperature) this is kind of meaningless. Just to cite the same example already given - 
an ordinary tungsten household bulb is rated CRI=100 by definition - yet most of us know that we have a really hard time being able to see yellow on white or distinguishing navy from black. 
Whereas even a cheapo daylight 6500K CFL with a CRI=82 does not have that problem.

However that says nothing about which is more pleasant to the eye -
at lower levels of illumination the daylight 6500K CFL would look too cool-blue and probably pretty unpleasant - whereas 2700K tungsten (or even CFL) actually looks quite nice - since our eyes/brain are conditioned through both physiology and evolution to see well under that color temperature.

So CRI is absolutely linked with the color temperature.

BUT even color temperature may be misunderstood - we almost always assume that color temperature is on the Planckian locus - ie: that of a radiating blackbody. BUT what happens when the light source falls off that locus?

Classic example is "white" light that's made up of just yellow and blue LEDs - its spectrum is obviously mainly the two peaks in yellow and blue - but to out eyes that light is "white" - it is only when we look at specific colors that we realize there is something amiss. This also applies to using RGB LEDs to make white - with spectrum of Red Green and Blue peaks - the light again does look "white" but specific colors may have some difficulties.

These may seem extreme examples but this is one area where CRI becomes very applicable - as "white" that is daylight has CRI=100, yellow/blue LEDs would have a very low CRI and similarly RGB LEDs would not have a good CRI either. (for real practical RGB application and some difficulties please see: LED Stage lighting )

This also shows that CRI is not any real indication of how pleasant a light source is to our eyes.

Our eyes/brain does adapt to different light levels - 
that is why I questioned the newer recommended visual assessment of CRI as used in
pdf VISUAL OBSERVATION OF COLOUR RENDERING
from Colour and Multimedia Laboratory of the University of Veszprém, Hungary 
(by some of the same authors of the CIE TC 1-62 paper that recommends the newer visual assessment for CRI or white LEDs)
They were surprised to find that the "cool white" lighting at 4000K did well - 
because of that I am not sure if they have taken into account the human eye/brain behavior that follows the Kruithof curve -
the illumination level and the surroundings are important - otherwise the results depending on human observation/comparison would vary wildly depending on the environment and surrounding ambient lighting - 
eg: experiment illuminated at 10,000lux, 1,000lux and 100lux would yield very different results -
also conducted during daylight hours in a natural daylight lit lab vs one held in the dark, or under tungsten lighting......
there are just too many variables, and I am not too sure if the eye/brain behavior has been rigorously taken into account, to have any new CRI measurements, based on human visual assessment, to be truly meaningful

I very strongly suggest please reading these two links:

The Color of White

and 

Kruithof curve


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## HarryN (May 7, 2010)

Less discussed, but equally important in our perception of which "white light" is most pleasing, are our genetics. 

If you compare a picture taken with traditional Kodak vs Fuji film, it jumps right out at you how virtually impossible it is to find one solution for everyone.


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## UnknownVT (May 7, 2010)

HarryN said:


> Less discussed, but equally important in our perception of which "white light" is most pleasing, are our genetics.



It's not just genetics but personal preference and where we come from and our "conditioning".

Not everyone will conform to the norm although the Kruithof curve is empirical - 
ie: can be confirmed and reproduced by experiment - 
individuals can have different results - eg: jtr1962 above from this thread.

This can make any visually based assessment of CRI kind of suspect -
eg: what happens if it's a panel of LED marketing people?
or people who may be color blind?

Where's the proposed standard for controls and controlled testing and even a mere mention of eye/brain adjustments to different lighting levels and environments?


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## Curious_character (May 7, 2010)

As UnknownVT and others have pointed out, a lot of the problem is due to the way our brain processes visual input. We internally declare any of a wide range of spectra to be "white" after being exposed to them for even a fairly short period. I first became aware of this a long time ago when we had chosen a very slightly off-white color to paint a room -- the paint mixer added just one glurp of green to a can of white. I was painting in a ceiling corner, where I was surrounded by the color. After some time, I stepped down, turned around -- and everything except the wall had a distinct pinkish hue. My brain had decided that the wall was "white", so everything else was pinkish. This is happening to me a lot now with the various lights in my house.

If you shine a white (say, hot incandescent) light through an object, say a thin piece of fabric, the object absorbs some wavelengths more than others, resulting in what we perceive as colored light. The spectrum that gets through probably has a bunch of lines of various wavelengths and intensities, and ranges of wavelengths where there isn't much being reflected. As it turns out, you can make a light consisting of just three spectral lines and, by adjusting only their amplitudes, have it look like exactly the same color as the complex spectrum from the filtered white light. The spectra are very, very different, yet they look just the same to us. This is, of course, the basis of color television, which produces nearly any color by combining just three. (As I recall from long ago, you can't quite imitate _*all*_ possible colors, but you can get very nearly all by careful choice of your three primary colors. It seems our eyes and brains can be fooled pretty easily.

The problem is that if you shine the two apparently identically colored lights on something of another color, you'll get different results. If, for example the three-color light is made of pure red, green, and blue, and the object reflects none of those exact wavelengths, it'll look black. The filtered light might contain some of the wavelengths the object reflects, so the object will be some color and not black. This happens with "white" lights, particularly so with fluorescents which tend to have spectra consisting of a number of discrete lines rather than a more continuous, filled-in spectrum. And that's why an RGB LED light might look white (or any other color we want by adjusting the three LED intensities) but won't render colors anything like a heated filament (black body) light.

c_c


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## kitelights (May 7, 2010)

I just made a comment in another thread about production LED headlamps not being suitable for surgery. 

I don't own any high CRI LED lights, but I do own some 'neutral' and 'warm' LED lights and none of them will show the distinction of redness on human tissue, such as a sore throat or an infection that I had on my shin.

They seem to do fine for me to distinguish colors in other applications, but not tissue. Can one of you gurus explain the reason to me, but so that I can understand it?

I seem to remember that Don put out a few specialty high CRI lights and Baby Doc was a tester who reported that the light worked well for him in medical applications. I had the impression that this was the springboard for the current demand for these higher rendering LEDs.


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## jtr1962 (May 7, 2010)

kitelights said:


> I just made a comment in another thread about production LED headlamps not being suitable for surgery.
> 
> I don't own any high CRI LED lights, but I do own some 'neutral' and 'warm' LED lights and none of them will show the distinction of redness on human tissue, such as a sore throat or an infection that I had on my shin.
> 
> ...


The reason has to do with the phosphors used. "Regular" neutral and warm non-high CRI LEDs simply have a higher ratio of phosphor to primary blue emitter output. This alters the color balance so that our eye perceives the light as warmer, but doesn't add much on the far red end. The relative size of the phosphor hump is higher, so there is a little more deep red there, but no much more than cool whites. Incidentally, triphosphor fluorescents use the same trick, simply altering the ratios among the red, green, and blue phosphors to achieve the desired color temperature. End result is that low color temperature triphosphor fluorescents are lacking in red relative to a blackbody emitter.

High-CRI LEDs are a different animal. They use an entirely different phosphor which has a lot more output in the deep red area ( at the expense of efficiency ). Although the light color on a white wall might appear the same as a non-high CRI LED of the same color temperature, the spectrum is much closer to that of a blackbody. When I shine one of my lights modded with a SSC high-CRI neutral white emitter outdoors in the backyard, it's like night and day compared to the cool whites. Indoors the difference isn't as great ( I still prefer cool-white indoors ) but outdoors among grass and trees the high-CRI light gives three dimensions to whatever you're lighting. That was the inspiration which led me to make a reading light using 5 of these high-CRI neutral white SSC LEDs ( my only complaint is I wish the color balance was closer to 5000K-5500K ). They should do just as well lighting human tissue. Also, from what I understand the Nichia 083 is slightly better than the SSC high-CRI, although it is a bit harder to obtain.


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## McGizmo (May 7, 2010)

Kitelights,
Consider this graphic representation of Nichia's regarding CRI:









Specifically consider R6 thru R10 and R12. R9 is probably the most significant when it comes to typical white LED's and to what extent is the CRI R9 effected by the CCT's offered in white LED's?

I would guess that R12 sucks for LED's compared to the incandescent "standard" established by incandescent (black body) for two reasons. Black body sources are not relatively strong in the low wave lengths and LED's are overly so. My gut tells me that indirect sunlight can not match the CRI-12 of an incandescent source; especially if there is plenty of blue sky above.


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## blasterman (May 7, 2010)

> If you compare a picture taken with traditional Kodak vs Fuji film,


 
Fuji dye coupling technology allows for a longer saturation ramp with a more density via more sloped integral resulting in more saturated colors without blocking. The sacrifice is density range. Kodak films are just the opposite in that they have very linear saturation ramps and high degrees of density, but poor saturation handling, aka color blocking. Take a picture of something very red or orange with a classic Kodak slide (or print) film and it will appear one solid shade of color. This is a big reason Velvia practically destroyed Kodak's entire slide division by itself. So, there is a measurable difference in Fuji emulsions -vs- Kodak, although Kodak has done much better to fix this problem (for those who still shoot film).

I actually ran into an interesting requirement that proved that cold-white, or simply older tech emitters weren't good enough to distinguish colors correctly. That application was building custom LED light-bars in a very busy night club where drinks are set and the LEDs are primary source of color. The problem is that because of the lack of decent red and amber cool white LEDs, or older Luxeons simply couldn't distinguish certain types of whiskeys or beers. They all looked the same in the window, and this really caused some issues. 

I experimented with half a dozen types of neutral and warm white emitters to fix the problem, and was about to resort to using high CRI Seouls when I stumbled on some older 1watt warm-white Cree P3s with that distinct 'rose' hue, and they do an amazing job on distinguishing drinks from each other. The difference is actually rather dramatic. I've not found this tint in newer Crees, but newer Bridgelux warm-whites are close.


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## Nil Einne (May 9, 2010)

UnknownVT said:


> It's not just genetics but personal preference and where we come from and our "conditioning".
> 
> Not everyone will conform to the norm although the Kruithof curve is empirical -
> ie: can be confirmed and reproduced by experiment -
> ...



Indeed differing preferences is one important thing that seems to be often missed. It always irks me when people say 'cool white' is 'unnatural' as I don't consider there's strong evidence for this. Obviously it's questionable whether incandescent light bulbs, or even camp fires etc can be considered 'natural'. The most 'natural' thing is very little light at night so the ideal colour temperatures of relatively bright lights at night doesn't seem something you can necessarily get from the patterns of the sun. (Of course I dislike many common uses of the word 'natural' anyway.) Perhaps we've been dealing with camp fires for long enough that we've evolved to prefer that sort of light, perhaps not, ultimately without good evidence it's still primarily theoretical. In any case, modern lighting is a lot brighter then that. 

The circadian rhythm issue is perhaps one of the few interesting things I've read whenever this 'natural' light idea comes up. However light which is good for your circadian rhythms (and that may very well be no artifical light source, i.e. just the sun during daylight hours and at night moon if present and stars) may not necessarily be light you prefer. The other thing which interests me is the rods & cones issue but it too appears to be primarily theoretically. 

And as for the anecdotal evidence and studies, and here I get to what I began with. Although I've never found a great ref (http://www.archlighting.com/industry-news.asp?sectionID=1341&articleID=460610 is one of the best I've found) I personally believe (and do have some personal knowledge here coming from Malaysia originally) it's generally accepted that colour temperature preferences in parts of Asia, what parts is one of the things that I've never really read studies of but I suspect most of SEA and East Asia at least, differs from that of much of the West. In particular cooler whites are usually preferred there. Most of the anecdotal evidence and studies are primarily coming from Western cultures (the museums ones I've seen mentioned have been in the west and while I haven't looked at the studies from what I've read it doesn't seem like it was possible for them to try and determine if there was specific difference in visitors from some places and in any case a visitor to a foreign visitors and in any case a tourist's preference may vary from an average person from those places anyway.) 

So the question becomes, why is this? While this could be genetic, getting back to my early points I don't think there's sufficient evidence that we can say any of the preferences are strongly genetic or innate. They could very well all be primarily cultural. In fact in some ways it reminds me of the way some people argue a female preference for pink is probably innate because it appears so widespread despite the fact we have some evidence it wasn't even always the case and pink may have actually been a masculine colour 80 years or so ago. 

While I admit I haven't really looked into the research available that well, it seems to me there is plenty of obvious areas of research here. I've already mentioned that it doesn't even seem to have been well studied how the colour temperature preference vary from country to country but another obvious study would be comparing people of different ancestoral groupings in the same country (since some argue there's a genetic component). 

P.S. Just for clarity, I have no problem with someone saying something seems unnatural to them. Obviously people are entilted to their individual preference. What I is the idea that cooler whites lights are in some ways inherently 'unnatural' or at least more so then warmer light ones.


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## McGizmo (May 9, 2010)

I think there is strong evidence for subjective and cultural preference in regards to color temperature and even color itself. In previous threads on these and related subjects it was mentioned that as we age, our eyes respond differently and even get yellowed. It was suggested that some of us older folks would be inclined to prefer a cooler CCT as we inherently warm the light as it is filtered through our eye's lenses. 

Another aspect of the subjectivity I think has substance is that of the terms of warm and cool light and how they relate to our present environment. In tropical and warm climates I find it no surprise that a cool CCT might be preferred and in the higher latitudes or in winter, a warmer CCT would have preference.

If you are freezing your heinie off and look in one direction and see a cool moon reflected off the snow and in another direction a warm fire reflecting off the snow, which will draw you to it?

On the other hand, if you are in sweltering in a humid tropic evening and see a cool moon reflecting off a lake or ocean and in another direction see a cooking fire's warm light, which would draw you near in hopes of perhaps some welcome relief?

In temperate zones where one is neither cold or hot, I suspect one would be most indifferent to the CCT of light. :shrug:

We have evolved to use ambient light in order to see and perceive. We have also used fire at night to see as well as cook (at anytime of day). We have learned and adapted with light as a significant part in our ability to perceive and function. There are likely inherrent biases and instinctual responses based on visual clues and perceptions and how they relate to light sources as well as time of day.

One thought I just had would be of primitive man, our ancestor, sound asleep under the stars. If all of a sudden his eyelids were bathed in a bright cool light this would be from a rising full moon and not likely to cause alarm or necessarily wake him. On the other hand, if all of a sudden his eyelids were bathed in a bright warm light, either day break has caught him by surprise or worse, a fire is present. In either case, it would make sense that this light would initiate a waking process.

The significance of color rendering is a function primarily of the need to identify and differentiate among objects and landscapes based on their color. In some cases this may be critical and others of no import. Our eyes have evolved based on natural light which is for the most part based on a full spectrum as represented by a black body source. It would be curious to know if primitive man shared the same visual spectrum as we do now or if perhaps he was more perceptive to say the IR end or even the near UV. I wonder if the proportion of rods and cones or their predominance has changed any over our history or if there are differences among genetic backgrounds. The need for glasses for instance does not seem to be consistent among contemporary races or perhaps that is a false perception on my part?!? Is there a "universal eyeball" that would make sense as a base and is there a universal, optimal, artificial light source? I kind of doubt it. :shrug: :thinking:

Regardless, we are no longer limited to only black body sources and to what ever extent they may fall short of an ideal, we may now be able to improve and enhance our visual perceptions.


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## blasterman (May 9, 2010)

> Obviously people are entilted to their individual preference


 
'Preference' is fine, provided were talking about light sources with similiar CRI indexes. 

What I have a problem with is people pulling the 'preference arguement' and then justifying cool-white emitters simply because they have a *technology fetish* with LEDs.

Low CRI, cool-white emitters might be better than cheap daylight CFLs, but they are still the 'fast food' of lighting technology. Basically, over-marketed, over-convenient, and just pimped on the public because they are in too much of a hurry to really stop and look at the difference.

The difference in color rendition and livability of Cree cool-white R2s -vs- drastically less efficient warm-white Bridgelux in my living room is *drastic*. I honestly don't care if the Crees are 2x as efficient. The color *sucks*, and is devoid of entire bands of spectrum our visual cortex spent millions of years evolving to see. This is the type of light thats good for the laundry room, or a porch light, or a college kid in his dorm spending 99% of his time on a computer.


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## jtr1962 (May 9, 2010)

Nil Einne said:


> Although I've never found a great ref (http://www.archlighting.com/industry-news.asp?sectionID=1341&articleID=460610 is one of the best I've found) I personally believe (and do have some personal knowledge here coming from Malaysia originally) it's generally accepted that colour temperature preferences in parts of Asia, what parts is one of the things that I've never really read studies of but I suspect most of SEA and East Asia at least, differs from that of much of the West.


I've said as much many times in response to the idea that "people prefer warm colors at home". Not true when you look at the world as a whole, and not even really dependent upon climate. Also, anecdotally when I go for walks I see more and more 5000K and up lighting compared to just a few years ago. Now that more people are using CFLs, they also realize they're not restricted to the 2700K of household incandescent. Many are choosing much cooler lighting as a result.



> So the question becomes, why is this? While this could be genetic, getting back to my early points I don't think there's sufficient evidence that we can say any of the preferences are strongly genetic or innate. They could very well all be primarily cultural.


I tend to agree. We haven't lived long enough under artificial light ( that includes fire ) for it to have shaped us genetically. Those kinds of changes take millions of years. Any preferences are largely to do with cultural expectations. If mainly genetics were involved, I would expect to see very little variation across countries in the type of preferred lighting. And yet that's not what we see. When you get huge general variations in preferences, such as 2700K-3500K in the suburban US, perhaps 4100K in US cities, 5000K in Japan, as high as 7500K in a few other places, this is telling me it's largely culturally-based. I doubt there's any significant differences due to race. NYC for example is a mix of races, and yet I don't see much variation in preferred lighting color based on neighborhoods. The increased use of hgiher CCT seems to be citywide, although it might be a little less prevalent in poorer neighborhoods where CFLs aren't as readily used due to higher initial cost.



> While I admit I haven't really looked into the research available that well, it seems to me there is plenty of obvious areas of research here. I've already mentioned that it doesn't even seem to have been well studied how the colour temperature preference vary from country to country but another obvious study would be comparing people of different ancestoral groupings in the same country (since some argue there's a genetic component).


Such studies would be interesting although I doubt we'll find a genetic component to lighting preferences. For example, I prefer anywhere 5000K and up, same as in many Asian countries, but I'm not Asian. I know some Asians who can't stand higher CCT lighting. Same thing with every other race or ethnic background. I think the best answer is lighting preference is largely influenced by culture, but even within a culture there are outliers ( like myself ).



> P.S. Just for clarity, I have no problem with someone saying something seems unnatural to them. Obviously people are entilted to their individual preference. What I is the idea that cooler whites lights are in some ways inherently 'unnatural' or at least more so then warmer light ones.


The interesting thing here is first time I saw a white LED, I felt it was more natural than any other artificial light source I had seen up until then. High-CRI, high CCT fluorescents weren't bad, but the LED just seemed better. This was before CPF and before I learned about spectral distribution. Now I know why the LED felt more natural. There's probably a good case to be made that a continuous spectrum will feel "right" more often than a discontinous one, even if the CRI numbers are the same. This is why we need a better measure of light quality than CRI.


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## UnknownVT (May 25, 2010)

I seemed to have missed this in the Wikipedia entry on CRI -

" _*New test color samples*
As discussed in (Schanda & Sándor 2005), (CIE 1999) recommends the use of a Macbeth (now X-Rite) color chart owing to the obsolescence of the original samples, of which only metameric matches remain.[13] In addition to the eight ColorChart samples, two skin tone samples are defined (TCS09* and TCS10*). Accordingly, the updated general CRI is averaged over ten samples, not eight as before. Nevertheless, (Hung 2002) has determined that the patches in (CIE 1995) give better correlations for any color difference than the Macbeth chart, whose samples are not equally distributed in a uniform color space._"


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## Canuke (Jun 1, 2010)

jtr1962 said:


> Such studies would be interesting although I doubt we'll find a genetic component to lighting preferences. For example, I prefer anywhere 5000K and up, same as in many Asian countries, but I'm not Asian. I know some Asians who can't stand higher CCT lighting. Same thing with every other race or ethnic background.



This would likely be correct. The lens of the eye has a yellowish cast, which filters out a little blue and UV, and this filtering tends to get stronger with age. There is a similar layer of yellow overlaying the fovea. Variations of the strength of these filters, due to age, genetics, nutrition etc. are likely the driving factor for color preferences.


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## Anders Hoveland (Sep 29, 2012)

This is an interesting article about CRI and LED light:
http://www.cinematography.com/index.php?showtopic=51884&st=20

Apparently regular white LED's are not suitable for illumination in the film industry because of their inferior color rendering.


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## RoGuE_StreaK (Sep 29, 2012)

We get it, you don't like LEDs. Why do you bother hanging out here then?


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## Anders Hoveland (Sep 29, 2012)

RoGuE_StreaK said:


> We get it, you don't like LEDs.


I am very enthusiastic about LED's. Did you not see my thread? http://www.candlepowerforums.com/vb/showthread.php?344630-My-100-Watt-LED-(pictures)

I am just more enthusiastic about building LED's for novelty than actually lighting my home with them. I am anxiously waiting for full spectrum white LED bulbs to become available. Only then I will start replacing more of my lighting with LED's. I have already experimented with several different types of LED bulbs but have mostly been unsatisfied with the quality of their light in many places.


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## AnAppleSnail (Sep 29, 2012)

Anyone still shooting film emulsions is kind of crotchety. Digital filming has done a lot, including full-reel color correction. I already correct for CCT and spectrum gaps with still photography.


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## blasterman (Sep 29, 2012)

> I am just more enthusiastic about building LED's for novelty than actually lighting my home with them



Then go off and do that then. 

The dedicated commercial fixtures we discuss in the fixed lighting forum such as the ones Cree makes do nothing less than surpass halide, fluorescent and incan light sources in terms of efficiency and especially color. You are basing conclusions on bad science and what's available at Walmart. Replace that crappy, 100watt contraption you made with a decent 4000k Bridgelux and you woulnd't be making these comments. 



> I already correct for CCT and spectrum gaps with still photography.



For fun, browse through the continuous lighting options at B&H or another supplier and you'll see an endless product stream of essentially _garbage_. Many of the lights are still based on 5mm cold-white LEDs...basically the same lights made for DJ and dance floors, but marketed towards video enthusiasts. So yeah....it's no wonder the cheaper lights tick off the guys in post because they can't get the color right. Digital cameras based on bayer sensors (which are like 99.99% of them) have an issue with red contrast in fine detail. When the digital camera is adjusted for color balance with light using cold white LEDs the lack of red starts causing all kind of issues. You also have the problem that dSLR video shooters think they're now Steven Spielberg when they are in fact shooting with 4:2:0 compression and throwing most of the color information away, so cheap light sources don't make the problem any better. Still, the myth is that a 5000-6000k light source with a CRI less than 70 is still better because it matches the "color of daylight".


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## bshanahan14rulz (Sep 30, 2012)

This post is old. The post Anders linked to is also, relatively speaking, old. Like B-man said, those lights they use don't use special LEDs or anything, so just because their crappy lights don't have good spectral content does not mean that you can generally say that LEDs do not have a good CRI. We now have high cri LEDs that aren't stuck in the warm white region, and maybe someone will be more concerned about making a good video light than about saving money and actually put these to good use.


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## Anders Hoveland (Oct 1, 2012)

bshanahan14rulz said:


> The post Anders linked to is also, relatively speaking, old. We now have high cri LEDs that aren't stuck in the warm white region,


That article specifically mentioned cyan frequency light, showing how that lady's dress appeared muted under LED illumination. Even the latest high CRI white LED's are still deficient in cyan frequency light, and, for example, the Phillips L-prize "enhanced spectrum" LED bulb and recessed lamps do absolutely nothing to solve this issue.


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## SemiMan (Oct 1, 2012)

The author of that post says that cyan is missing, but a relative comparison of LED spectrum and 3K tungsten spectrum shows similar cyan output. The peakiness on either side of the cyan is likely more of an issue. One of the problems is that the demosaicing of the camera is not tuned specifically to LED spectra. This can be done to greatly improve the color rendering under "traditional" LED light sources ... but that is more a discussion for consumer level devices like cell phones where this is done for LED flash. There is quite a bit of research that was done around this when LED flash came out for camera phones .... and why some of them looked really terrible at first beyond just being dark.

The latest high CRI LEDs, at least compared to incan, are not deficient on a relative basis, and their blue peak is greatly subdued. I would suggest looking at the 90+ CRI Luxeon Rebels, or the Xicato Artist Series modules. I would call them somewhat the state of the art in best spectrum at reasonable cost points. Sharp's 90+ CRI Zenigata has tons of cyan, but still has a somewhat significant blue peak. Interestingly enough, Sharp's have quite a smooth spectrum other than the blue peak which would indicate the blue peak could be filtered to have an overall smooth curve. I have not done this, but I looks possible on paper.

Semiman


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## idleprocess (Oct 2, 2012)

Anders Hoveland said:


> This is an interesting article about CRI and LED light:
> http://www.cinematography.com/index.php?showtopic=51884&st=20
> 
> Apparently regular white LED's are not suitable for illumination in the film industry because of their inferior color rendering.



Someone tell that to B&H, whose catalogs feature a wide variety of LED video lights.

That forum post focuses on how film reacts _(digital seems to be steadily grabbing market share and can do quite a bit of correction both before and after-the-fact)_, and also couples ancillary characteristics of _specific products_ - such as PFC - with the underlying light source technology, which is a bit odd in a fast-changing field.


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## SemiMan (Oct 3, 2012)

blasterman said:


> 'Preference' is fine, provided were talking about light sources with similiar CRI indexes.
> 
> What I have a problem with is people pulling the 'preference arguement' and then justifying cool-white emitters simply because they have a *technology fetish* with LEDs.
> 
> ...




In many situations, like you, I would prefer those Bridgelux LEDs. But not all, and perhaps that is the other variable for preference. It is application and environment dependent. If I was doing any tasks where fine visual acuity was important, I am going to go towards the cool whites as long as the CRI is not terrible. I would often feel that way about general daytime tasks as I need the blue in the cool LED to stimulate the circadian rhythm. My kitchen has high CRI cooler white 4000K. Its pleasant for me and others that occupy my kitchen at times. My shop and lab are lit with daylight high CRI .. yes fluorescents. Bedrooms are 2700K ... they are places to relax (except for the cool white reading light), and living room is 3000K ... mainly for relaxing but mixed. Bathrooms are mainly 3000K, but think I am going to change the ensuite on the master to 4000K. All the 2700 and 3000 in my house is 80-85 CRI CFLs and/or LEDs. 

I do outdoor commercial lighting and in those instances would take 65-70 CRI 5000K over 100CRI 3000K any day. 3000K at low lux levels suck when you are trying to accomplish something ... at least that is my opinion 

Semiman


There was a study a number of year ago that compared perceptions of 70-75CRI cool white against warm white. For that study, there was actually a preference for the cool white.

Not sure that latitude matters to color temp preference but I liked the theory. North America tends towards warmer whites at least for interior. Asia tends toward cooler whites. Europe somewhere in the middle .... all at the same latitude.


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## UnknownVT (Oct 3, 2012)

idleprocess said:


> Someone tell that to B&H, whose catalogs feature a wide variety of LED video lights.
> That forum post focuses on how film reacts _(digital seems to be steadily grabbing market share and can do quite a bit of correction both before and after-the-fact)_, and also couples ancillary characteristics of _specific products_ - such as PFC - with the underlying light source technology, which is a bit odd in a fast-changing field.


found this under Color Rendering Index on Wikipedia:


> *Film and video high-CRI LED lighting incompatibility*
> Problems have been encountered attempting to use otherwise high CRI LED lighting on film and video sets. The color spectra of LED lighting primary colors does not match the expected color wavelength bandpasses of film emulsions and digital sensors. As a result, color rendition can be completely unpredictable in optical prints, transfers to digital media from film (DI's), and video camera recordings. This phenomenon with respect to motion picture film has been documented in an LED lighting evaluation series of tests produced by the Academy of Motion Picture Arts and Sciences scientific staff.[30]​


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## SemiMan (Oct 3, 2012)

I would say that the color balancing issue is not unique to LED but applies to fluorescent as well for cameras. One of the big difference is the range of experience with fluorescent. I was involved in some early camera phone stuff with LEDs. For bayer filter sensors, properly rendering with LED required demosaicing algorithms that were specific to the spectrum of the LED. This could significantly improve color accuracy. As color of any object is dependent on the lighting used, really the goal is to accurately render colors under what the light is "supposed" to be, not necessarily what it actually is. High end cameras used to be mainly 3 sensors, one per color, but really high end stuff now is actually single sensor, so the whole color of the filter, demosaicing, etc. comes into play.

The bandpass filters on the sensors and/or emulsions does not need to match the light source though. What it needs to match is eye response such that what is rendered by the camera matches what the eye would perceive. If you achieve that, you can adjust the end result. Unfortunately depending on the medium, both in film and digital, that may not be the case. The RGB on RGB sensors generally does not match the eye response. That is if RGB is used. Complimentary colors are also used as they allow significantly more light to reach the sensor. This throws the whole eye match out the window.

Complex stuff, but not unique to LED specifically.


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## teddoman (Jan 14, 2013)

I'm a photography enthusiast, and first time poster, so please forgive any errors in advance. I must say this is an incredibly useful discussion. Obviously, the people in this forum know a ton about lighting. From the photography perspective, I'm just looking for continuous full spectrum lighting that give my photographs proper white balance and color rendition without unpredictable color spikes. However, after reading this thread, it feels like the folks in this forum haven't really come to a consensus on whether that is even possible with products on the market today.

If price is not a major issue (within reasonable limits), is there any continuous full spectrum lighting that can be bought today, and is definitively this type of lighting and not just falsely marketed as such? I just want to know that if I'm going to drop a few extra bucks to get the right lighting, that I'm not just fooling myself. I guess I don't want to rely on the manufacturer's marketing, since as has been discussed at length in this thread, CRI is not really an accurate measure, nor is "full spectrum" a regulated term so any manufacturer is free to use it and cannot be held accountable for it.

I have read that halogen lights are essentually continuous full spectrum lighting, but those generate heat and burn a lot of energy. Is there a more environmentally friendly alternative, if price is not a major issue?


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## Anders Hoveland (Jan 14, 2013)

teddoman said:


> From the photography perspective, I'm just looking for continuous full spectrum lighting


It is very rare, but there actually are two incandescent and fluorescent products that have spectral graphs that almost exactly match natural sunlight. _Truelite_ brand fluorescent tubes, and _SoLux_ brand halogen reflectors. 
However, you need to use some caution, virtually all the other products I have researched that claim to have "natural light" are exaggerated or deceptive.

For a simple solution, the best fullest spectrum of light can be obtained by using energy-saving halogen replacement bulbs, together with a small ammount of blueish white LED light.

There actually are two LED products that have high 92+ CRI at higher color temperatures but they are very expensive and have to be special ordered. These are the Richardson Company *MoleLED* series, and _*Selador Desire*_ series, the latter of which just consists of multiple different frequency chips in the same spotlight. The main reason LED spotlighting has not been more widespread in the film industry so far is that they have done a poor job at properly illuminating deep red and cyan (teal) colors.


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## neutralwhite (Jan 14, 2013)

adding to this topic, I never knew the CRI of the MCE 4000CCT LED is just 75CRI, and the Nichia 219 is like 93 HCRI.
so obviously, its best to go for the Nichia in this 4000 right?.

btw my pd32ue is also 75cri.


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## SemiMan (Jan 14, 2013)

teddoman said:


> I'm a photography enthusiast, and first time poster, so please forgive any errors in advance. I must say this is an incredibly useful discussion. Obviously, the people in this forum know a ton about lighting. From the photography perspective, I'm just looking for continuous full spectrum lighting that give my photographs proper white balance and color rendition without unpredictable color spikes. However, after reading this thread, it feels like the folks in this forum haven't really come to a consensus on whether that is even possible with products on the market today.
> 
> If price is not a major issue (within reasonable limits), is there any continuous full spectrum lighting that can be bought today, and is definitively this type of lighting and not just falsely marketed as such? I just want to know that if I'm going to drop a few extra bucks to get the right lighting, that I'm not just fooling myself. I guess I don't want to rely on the manufacturer's marketing, since as has been discussed at length in this thread, CRI is not really an accurate measure, nor is "full spectrum" a regulated term so any manufacturer is free to use it and cannot be held accountable for it.
> 
> I have read that halogen lights are essentually continuous full spectrum lighting, but those generate heat and burn a lot of energy. Is there a more environmentally friendly alternative, if price is not a major issue?




What are you lighting with continuous sources or is this just a model light? Most of the 3000K 90+ CRI lights will give you great colors and a little emphasis on the blue end may help at the capture end of things and can always be reduced later. Generally you need a strobe to stop motion even portraits and to get low ISO/ low noise. I am not on the latest CS edition from Adobe, but I think it can do custom mapping from light sources.

If you can find a light with Xicato Artist series LEDs of Bridgelux 90+ CRI units (can't remember the series) then that is as smooth as you will need.

Semiman


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## AnAppleSnail (Jan 14, 2013)

neutralwhite said:


> adding to this topic, I never knew the CRI of the MCE 4000CCT LED is just 75CRI, and the Nichia 219 is like 93 HCRI.so obviously, its best to go for the Nichia in this 4000 right?.btw my pd32ue is also 75cri.


It depends on the wavelengths you want to perceive. If you don't need reds, you won't miss the high CRI and will appreciate the bonus lumens.


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## Esko (Jan 14, 2013)

Anders Hoveland said:


> It is very rare, but there actually are two incandescent and fluorescent products that have spectral graphs that almost exactly match natural sunlight. _Truelite_ brand fluorescent tubes, and _SoLux_ brand halogen reflectors.
> However, you need to use some caution, virtually all the other products I have researched that claim to have "natural light" are exaggerated or deceptive.



There is a bunch of manufacturers that make so-called full spectrum fluorescent lights in daylight CCT and cri range of 95-98. For example, Phillips and Viva-Lite. I once saw a project where some amateur video photographers made a big videolight from some 10-15 full spectrum fluorescent tubes and a sheet of corrugated iron. It looked pretty nice. 



Anders Hoveland said:


> There actually are two LED products that have high 92+ CRI at higher color temperatures but they are very expensive and have to be special ordered. These are the Richardson Company *MoleLED* series, and _*Selador Desire*_ series, the latter of which just consists of multiple different frequency chips in the same spotlight. The main reason LED spotlighting has not been more widespread in the film industry so far is that they have done a poor job at properly illuminating deep red and cyan (teal) colors.



What is your source concerning MoleLED? The leds used in MoleLED seem to be rather ordinary blue leds with phosphors and the spectrum seems to be rather traditional, too. On the other hand, it seems to be somewhat close to the spectrum of high cri Nichia 219. I'd still pick Selador, it is more versatile and seems to cheaper, too.


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## teddoman (Jan 14, 2013)

Anders Hoveland said:


> It is very rare, but there actually are two incandescent and fluorescent products that have spectral graphs that almost exactly match natural sunlight. _Truelite_ brand fluorescent tubes, and _SoLux_ brand halogen reflectors.
> However, you need to use some caution, virtually all the other products I have researched that claim to have "natural light" are exaggerated or deceptive.


Thank you Anders. Today it requires so much knowledge to be an educated consumer. I can't imagine how regular consumers deal with an issue like this. Here I am posting in a forum for lighting enthusiasts, and I myself am coming from the photography perspective!

The Solux in particular seems to have some great testimonials from photographers and museums. It comes in different types though. Is there any reason from a photography perspective or from a human health perspective to use 3500 vs 4700 vs 6000? Would all of these be equally "full spectrum" Solux bulbs?



Anders Hoveland said:


> For a simple solution, the best fullest spectrum of light can be obtained by using energy-saving halogen replacement bulbs, together with a small ammount of blueish white LED light.


What is it about the halogen replacement bulbs that require a blueish white LED light? Are they insufficiently "full spectrum"?



SemiMan said:


> What are you lighting with continuous sources or is this just a model light? Most of the 3000K 90+ CRI lights will give you great colors and a little emphasis on the blue end may help at the capture end of things and can always be reduced later. Generally you need a strobe to stop motion even portraits and to get low ISO/ low noise. I am not on the latest CS edition from Adobe, but I think it can do custom mapping from light sources.
> 
> If you can find a light with Xicato Artist series LEDs of Bridgelux 90+ CRI units (can't remember the series) then that is as smooth as you will need.


Thank you. I don't know if you had a chance to read this entire thread but there are a bunch of people who know a lot more than me about lighting theory that are trying to debunk high CRI lighting as being falsely advertised as "full spectrum". So I'm less likely to rely just on a CRI number.

I am looking for bulb solutions for home photography. With the right lighting, I may not have to do all kinds of post processing adjustments that would otherwise be required.


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## AnAppleSnail (Jan 15, 2013)

The reason to add blue or red light is to cover a wide spectrum. For better or worse, CRI declares that the perfect ideal is a black body radiator. Never mind perceptual studies that show white-perception being nearly always off a black body curve (which of these lights is white? Mhmm.)

The trouble is, a black body radiator emits a bell-curve-like spectral power distribution. So one end will be weak, depending on the CCT you aim for. Most other light sources have a weak end, which can be propped up by added light at that wavelength. So halogens at low CCT need more blue photons. And so on. This is why I prefer to mix CCT for viewing lights. Of course, for photography it's easiest to match all CCT and bump saturation selectively as needed.


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## neutralwhite (Jan 15, 2013)

what would be the point then in say having an MCE LED at 4000k with a CRI being at 75, than just better using a Nichia 219 at like 93CRI?.
my PD32UE is 75cri, so what's so good about the old MCE anyway then if that too is 75CRI.

which would be better in a flashlight?. certainly the 219 right?.


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## Esko (Jan 15, 2013)

teddoman said:


> What is it about the halogen replacement bulbs that require a blueish white LED light? Are they insufficiently "full spectrum"?



The full spectrum is just biased towards the warm colors like in all warm white incandescent bulbs (even if the cri is ~100).

Of course, since the Solux bulbs (the higher CCT neutral ones) cost less than $10 each and the spectrum and the consistency will be better, there is no real reason to make a mixed light source.



teddoman said:


> Is there any reason from a photography perspective or from a human health perspective to use 3500 vs 4700 vs 6000? Would all of these be equally "full spectrum" Solux bulbs?



Full spectrum yes, but with different intensities in both warm and cool ends of the spectrums. For photography purposes? I'd choose the most balanced 4700K (there are Solux bulbs with more than three CTT choices available). Human health perspective? No reasons, unless you are going to use them in your ambient home lighting.


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## SemiMan (Jan 15, 2013)

Anders Hoveland said:


> It is very rare, but there actually are two incandescent and fluorescent products that have spectral graphs that almost exactly match natural sunlight. _Truelite_ brand fluorescent tubes, and _SoLux_ brand halogen reflectors.
> However, you need to use some caution, virtually all the other products I have researched that claim to have "natural light" are exaggerated or deceptive.
> 
> For a simple solution, the best fullest spectrum of light can be obtained by using energy-saving halogen replacement bulbs, together with a small ammount of blueish white LED light.
> ...




As has been pointed in the past Anders, Solux bulbs DO NOT match natural sunlight, they match the blackbody curve at 3000, 3500, and 4000K within the visible light spectrum AND sunlight when it is at these color temperatures which is for a short period of time in the morIning and evening DOES NOT match the blackbody curve. That said, as a continuous spectrum source for photography, that should be good. However, keep in mind for photography, as they go up in color temp, they go down in efficiency as they are using a filter to accomplish this.

Of course, generally for photography, except for taking pictures of small items, a continuous light is rarely used in the studio beyond a modelling light and you use strobes for the actual photos so I am not sure what you are trying to accomplish? Can you give us some more insight?

Teddoman, in terms of regular consumers, they would not be able to tell the difference unless told exactly what to look for between a 95CRI somewhat peaky spectrum and 95CRI smooth spectrum. Actually without reference colors even those that are quite experienced with lighting will not be able to readily tell the difference between incandescent and 85CRI LED ... or even a good CFL for that matter.

If you add "blueish white" LED to halogen, you will end up with a peaky spectrum ... just like you were trying to avoid.


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## Esko (Jan 15, 2013)

Esko said:


> Of course, since the Solux bulbs (the higher CCT neutral ones) cost less than $10 each and the spectrum and the consistency will be better, there is no real reason to make a mixed light source.





SemiMan said:


> However, keep in mind for photography, as they go up in color temp, they go down in efficiency as they are using a filter to accomplish this.



It looks like I didn't quite realize how much the efficiency drops. (link). Should have read the specs in more detail.

Mixing ordinary halogen bulbs with blue or cool white leds might have an advantage in reproducing reds (and blue) but one would still be lacking some output in cyan and deep blue range.



SemiMan said:


> Of course, generally for photography, except for taking pictures of small items, a continuous light is rarely used in the studio beyond a modelling light and you use strobes for the actual photos so I am not sure what you are trying to accomplish? Can you give us some more insight?
> 
> Teddoman, in terms of regular consumers, they would not be able to tell the difference unless told exactly what to look for between a 95CRI somewhat peaky spectrum and 95CRI smooth spectrum. Actually without reference colors even those that are quite experienced with lighting will not be able to readily tell the difference between incandescent and 85CRI LED ... or even a good CFL for that matter.



This is also true. Perhaps some extra information would be useful.


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## teddoman (Jan 15, 2013)

I reread this thread in full again. This is a lot of info to digest! I think I "got" a lot more on the second pass, particularly in studying the links on CCT, the Kruithof curve, and googling blackbody radiators. Thanks all for your patience. Now I have a few keeper points:
1. All objects emit light radiation and are natural blackbody radiators
2. CCT measures the radiation level of each blackbody radiator
3. Artificial light sources mimic natural blackbody radiators imperfectly. The spectrum of colors may not be smooth and follow the curve of a natural blackbody radiator. The colors graph often has big spikes.
4. The color spectrum of natural daylight, from some of the graphs I looked at, is not a straight line. It's a curve with a small peak in the center, and the entire curve is upward sloping, lower at the warm colors and higher at the cool colors.
5. Light emitted by natural blackbody radiator may not always be pleasing to the eye. For any CCT, the Kruithof curve shows that pleasing light colors are obtained only within a certain range of illuminance levels. But the Kruithof curve was found empirically and hence may vary from individual to individual.



Esko said:


> Human health perspective? No reasons, unless you are going to use them in your ambient home lighting.


Yes, this is EXACTLY my purpose, ambient home lighting. It's winter now, there was a post in this thread on seasonal affective disorder, my wife has at times had trouble sleeping, my 1 year old is not a great sleeper, and dealing with 2 kids has thrown my wife and I's sleep cycle rhythms off in the last few years too. So yes, whether it's proven or not, I would like to mimic natural light as much as possible, to capture any ancillary benefit regarding seasonal affective disorder and circadian rhythms. (Err on the side of health and good sleep.)



SemiMan said:


> As has been pointed in the past Anders, Solux bulbs DO NOT match natural sunlight, they match the blackbody curve at 3000, 3500, and 4000K within the visible light spectrum AND sunlight when it is at these color temperatures which is for a short period of time in the morIning and evening DOES NOT match the blackbody curve.


Thanks for this clarification. I think my summary at the top of this post are now consistent with what you are saying here.

So technically, to mimic real daylight, we would actually have to have a lighting solution that changes CCT throughout the day, peaking midday just like natural sunlight. Instead, what we actually have in our homes and offices is a solution at one fixed CCT, which the sun gives us just one or two times during a normal day. So we just have to choose, do we want it to always be a cloudy morning? Or do we always want it to be a sunny day in the shade? etc etc. From a human health perspective, I wonder which choice is better. This sort of reminds me of typical space shows/movies where the computer changes the time and it goes from looking out the window at nighttime to suddenly looking out the window at sunny daylight.



SemiMan said:


> Of course, generally for photography, except for taking pictures of small items, a continuous light is rarely used in the studio beyond a modelling light and you use strobes for the actual photos so I am not sure what you are trying to accomplish? Can you give us some more insight?


I am not talking about studio photography here, which is perhaps what you are thinking of. That is an entire model of photography that requires different lighting. Think candid photography of authentic moments, rather than formal portrait photography in a studio.

I am trying to achieve a home lighting situation where flash of any kind is not required for home photos of my kids in action. This gets into the aesthetics of photographs, but essentially if ambient lighting is sufficient, some photographers prefer to avoid flash. While sophisticated flash solutions can make the lighting seem more natural, I am trying to craft a solution where flash simply becomes unnecessary. Again, it's just my personal photography aesthetic inclination (but one I know a segment of photographers share).



SemiMan said:


> However, keep in mind for photography, as they go up in color temp, they go down in efficiency as they are using a filter to accomplish this.





Esko said:


> It looks like I didn't quite realize how much the efficiency drops. (link). Should have read the specs in more detail.


Ok, so the higher CCT Solux bulbs are basically filtering out a lot of the spectrum to achieve the blackbody curve at the higher CCT so you'd need more bulbs to get the same illuminance levels?

I assume the 4700 on Esko's chart looks so flat because it's a log chart, but that the shape of the 4700's color spectrum should be the same as the others.

Related to the efficiency issue is the Kruikof curve. If I am going to use a cooler CCT, the Kruikof curve requires higher illuminance (and energy usage) in order to achieve pleasing light colors (assuming the Kruikof curve is true). A warmer CCT allows more energy savings because pleasing colors can be achieved at lower illuminance.


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## neutralwhite (Jan 15, 2013)

thanks, nice post, so if you do suffer from SAD (seasonal affective disorder ), is the best room light say, a 4000k one, or a 5000k one?.
i thought 5000 would be daylight, to keep your moods happy. bright day, rather than sunset like.
thanks.


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## AnAppleSnail (Jan 15, 2013)

BRIGHT, first. Then good color rendering and decent CCT. I get along just fine with 4000K. Other people use pure blue light with regular home lighting.

Edit: how bright? I've seen behavioral studies get strong effects up to 2500 lux indoors.

Edit 2: 500-25000 lux. That's a wide range from office bright to 25000 lumen per square meter.


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## teddoman (Jan 15, 2013)

AnAppleSnail said:


> Edit: how bright? I've seen behavioral studies get strong effects up to 2500 lux indoors.


I think you meant "starting at" rather than "up to"...I think


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## neutralwhite (Jan 15, 2013)

so 5000k is better than 4000k re SAD?.



AnAppleSnail said:


> BRIGHT, first. Then good color rendering and decent CCT. I get along just fine with 4000K. Other people use pure blue light with regular home lighting.
> 
> Edit: how bright? I've seen behavioral studies get strong effects up to 2500 lux indoors.


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## Esko (Jan 15, 2013)

teddoman said:


> Yes, this is EXACTLY my purpose, ambient home lighting. It's winter now, there was a post in this thread on seasonal affective disorder, my wife has at times had trouble sleeping, my 1 year old is not a great sleeper, and dealing with 2 kids has thrown my wife and I's sleep cycle rhythms off in the last few years too. So yes, whether it's proven or not, I would like to mimic natural light as much as possible, to capture any ancillary benefit regarding seasonal affective disorder and circadian rhythms. (Err on the side of health and good sleep.)



Right. I guess this subject belongs more to the fixed lighting sub-forum but I might answer shortly here, too. I have been told that there are some offices in Japan that have this kind of CCT changing lighting. I don't have more information about those, though. There are also some led light bulbs and fixed lights with a possibility to change the CCT with remote control (namely Futlight which was sold by 4Sevens - I have a bulb in my evening light). The cri is poor but at least you can choose the CCT. 

My ambient lighting consists of full spectrum daylight ESLs (Viva-Lite 5500K ~97 cri bulbs). A few remarks:



If you buy them (or something similar, ESL or tubes), buy the biggest ones that fit your lights. You want them to be pretty bright (remember the Kruithoff curve). They are also less efficient than the standard cri fluorescent lights) 
They do have an effect on your wake/sleep cycle. My experience is that they tend to keep you pretty refreshed so if you have troubles in sleeping, you probably don't want to use them in the evening. On the other hand, if you use them in the morning and daytime and change to something else in the (late) evening (warm white, low illumination), it might be good for your circadian rhythm. 
SAD is treated with sun light / bright light lamps and I do have a pretty powerful one, too. A somewhat high CCT and lots of power have traditionally been the key features in treating SAD. However, compared to my ambient lighting, I think it is pretty much useless now. And yellow (the tubes are only 4000K ). I have had thoughts about changing those tubes to full spectrum 5500K, too. It might become a decent flood light for photography also.


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## neutralwhite (Jan 15, 2013)

thanks for that, good reply. I think though at 4000k, its a warm light enough not to make you that sad, really.
i thought warm, well, 4000k anyway, relaxes you, makes you happier...


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## AnAppleSnail (Jan 15, 2013)

teddoman said:


> I think you meant "starting at" rather than "up to"...I think



I did drop a zero, but most studies I found include 500 lux as the low end. Neutral white, it seems that brightness is more important than exact mid-range CCT.


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## SemiMan (Jan 15, 2013)

neutralwhite said:


> thanks, nice post, so if you do suffer from SAD (seasonal affective disorder ), is the best room light say, a 4000k one, or a 5000k one?.
> i thought 5000 would be daylight, to keep your moods happy. bright day, rather than sunset like.
> thanks.



In order to stimulate circadian rhythm which is somewhat related to SAD, you need lots of light under 520nm and preferably around 480nm. Halogen/Incandescent is obviously not a good source of light in these spectrums and Solux would be a bad solution as you would need a ton of power. Fluorescent and LED are your best choices and way way more efficient at providing these wavelengths.

Note for vitamin-D, you need UV.


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## teddoman (Jan 16, 2013)

SemiMan said:


> In order to stimulate circadian rhythm which is somewhat related to SAD, you need lots of light under 520nm and preferably around 480nm.





Esko said:


> It looks like I didn't quite realize how much the efficiency drops. (link). Should have read the specs in more detail.


I take back what I said about the efficiency chart being a log chart. I'm not so sure about that now (math was a long time ago and is a little hazy for me).

Looking more closely at the Solux efficiency chart, I'd say those 3 bulbs are totally different. 

The 4700 produces a relatively flat color spectrum with all wavelengths pretty equal.

The 4100 has a gap at 880 nm, which almost makes it look like the spikey graphs of CFLs.

The 3500 has a distribution very similar to that of natural light except that it peaks at 710 nm instead of sunlight's peak around 480-500 nm. So it's almost like the output is shifted over and emphasis is on the higher wavelengths.

The Solux "competitive analysis" graphs show a fairly flat curve, so they are probably for a bulb like the 4700 rather than the warmer ones. Which suggests to me the warmer Solux bulbs are not very similar to natural sunlight. Unless the shape of natural sunlight's color spectrum output graph changes throughout the day too. In which case when does natural sunlight have peak production at 710 nm?

Based on this wavelength color chart, the Solux 3500 would produce more red light than would normally be seen in natural sunlight. I forget how light works. Does that mean red objects will look redder to the eye than under natural sunlight?

ps is anyone here a moderator and can split this thread for me? We have such a good dialogue going on here. Want to keep it going. Thanks all


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## teddoman (Jan 16, 2013)

On second thought, please join me in this new thread in the photography forum to continue this great discussion so we can spare the LED folks.


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## UnknownVT (Jan 16, 2013)

teddoman said:


> On second thought, please join me in this new thread in the photography forum to continue this great discussion so we can spare the LED folks.



OK - sorry I haven't been monitoring ths thread - but I see that it has managed quite well with a life all of its own

As some may know I do a lot of photography and I have struggled with LED stage lighting
please see thread both 
here on CPF: LED Stage lighting
and elsewhere with quite substantial participation: Modern LED Stage Lighting & photography problems (




1 2 3 ... Last Page)

Although I consider myself quite critical of image quality (IQ) especially white balance -
I am by no means either an authority,
nor anywhere as near exacting as photographers who do catalogs and clothing/cloths.

I have found a pretty economical lighting solution for my indoor small object photography -
that is actually simple household CFL (Compact Fluorescent) light bulbs at 6500K or 5000K.

Please also see: CFL Color Temperatures

there are plenty of arguments against using these in that thread
and I am fully aware of the pretty spiky spectrum of these, and their CRI=82 on average
but I seem to do OK with these for the type of "non-critical" object photography -
portraiture might be a different matter - but most of my shots of people are on stage performing and I have to contend with LED stage lighting - 
but that is an entirely different story as the second thread I linked to will contest.

I use mostly 6500K CFL mainly because everything is supposed to have standardized on D65 -
and because I was seduced by this:


> The CIE positions D65 as the standard daylight illuminant: [D65] is intended to represent average daylight and has a correlated colour temperature of approximately 6500 K. CIE standard illuminant D65 should be used in all colorimetric calculations requiring representative daylight, unless there are specific reasons for using a different illuminant. Variations in the relative spectral power distribution of daylight are known to occur, particularly in the ultraviolet spectral region, as a function of season, time of day, and geographic location.
> —ISO 10526:1999/CIE S005/E-1998, CIE Standard Illuminants for Colorimetry


from Wikipedia on Illuminant D65

BUT I also know my dSLR is "daylight" balanced for 5200K
on AWB mostly is a wash if there are any color casts (slight blue) I normally just correct it by selecting a white or gray point with post processing.

I do occasionally use 5000K CFLs when I may want a warmer balance - 
but white/gray point in post processing is still the order of the day for me.

As I said portraiture may be a different story.

There are lots of "full spectrum" and high CRI "photo" CFL on the market - 
I cannot see how they can tame the spikiness which is characteristic of fluorescent lighting.

LEDs are also spiky, in their way - to some their graphs look less objectionable but they have not done so well in user based test either 
and most LED white lights are still not much better than CFL for CRI.

please also see: Ultimate Light Bulb Test: Incandescent v Compact Fluorescent v LED - Pop Mechanics

EDIT to ADD - found this under Color Rendering Index on Wikipedia:


> *Film and video high-CRI LED lighting incompatibility*
> Problems have been encountered attempting to use otherwise high CRI LED lighting on film and video sets. The color spectra of LED lighting primary colors does not match the expected color wavelength bandpasses of film emulsions and digital sensors. As a result, color rendition can be completely unpredictable in optical prints, transfers to digital media from film (DI's), and video camera recordings. This phenomenon with respect to motion picture film has been documented in an LED lighting evaluation series of tests produced by the Academy of Motion Picture Arts and Sciences scientific staff.[30]​



Using the link at Wikipedia take us to this page - Solid State Lighting Project
very interesting videos from the symposium.

It appears that solid state lighting ie: LEDs can cause lots of problems in film and video - 
even when they may appear to the eye as indistinguishable from normal lighting for the film industry.

There are lots of videos - this is a "summary" of sorts:

Summary

This is a good example with flesh tones and makeup -

Makeup Case


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## neutralwhite (Jan 16, 2013)

hi thanks. so would there be a noticeable difference with my PD32UE's 75CRI compared if I stuck a Nichia 219 90CRi in there ?.
thing is, is HCRI only available in warm white?, & is 75 a good rate of CRI ?.


thanks.


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## UnknownVT (Jan 17, 2013)

neutralwhite said:


> hi thanks. so would there be a noticeable difference with my PD32UE's 75CRI compared if I stuck a Nichia 219 90CRi in there ?.
> thing is, is HCRI only available in warm white?, & is 75 a good rate of CRI ?.


Don't want to be seen as ignoring you - but it is not clear who you are responding to.

You are really asking about changing the LED in your flashlight to a High CRI LED -
only in this most recent post did you indicate that the HCRI is a *warm* LED.

Earlier posts in this thread have talked about the dependency of CRI on the color temperature -
eg: Post #10 (link)


> As mentioned CRI is very dependent on CCT (Correlated Color Temperature)
> eg: it may surprise many to learn that an incandescent/tungsten bulb rates CRI=100 (perfect) by definition, yet anyone who has taken a photo under tungsten lighting with daylight white balance (or daylight slide film) will know immediately that that the light is very yellow/amber - and will have difficulties seeing yellow on white or distinguishing navy from black - so how can it possibly be CRI=100 perfect?
> 
> It is the way that CRI (color rendering index) is defined comparing to a reference black-body of the same color temperature - so an incandescent bulb is its own reference by the definition...... that's why it rates CRI=100.
> ...



CRI is very dependent on the CCT (Correlated Color temperature) - 
and are really only comparable at the same CCT -
ie: in isolation they are kind of meaningless.

I think you are asking "_would there be a noticeable difference_" between a *Warm* White LED with CRI=90 and a *Cool* White @ CRI=75?
as a simple answer - yes - 
because the warm white will be warm/yellow toned and the cool white will be cooler/daylight toned 
(notice: no mention of CRI)

BUT that's kind of like comparing apples and oranges.

For me it is more important to find the preferred color temperature
ie: cool white (closer to daylight) or warm white (closer to household tungsten lighting)
then find the highest CRI in that same color temperature range.

*EDIT to ADD*
Please take a look at this:

High CRI (Warm white) 4 Sevens Q-MiNi123 + Neutral White Comparison Review

Hope it helps to illustrate.


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## Anders Hoveland (Apr 5, 2013)

Currently the options for high CRI, high correlated color temperature LEDs are limited, because broad-spectrum phosphors have not been commercially developed yet for use in LEDs. This may eventually change with OLED electroluminescent technology. Basically, the operating principles are similar to LED, but it uses organic phosphors, and actually operates as a capacitor rather than a diode.

http://www.sciencedirect.com/science/article/pii/S0379677910000275

Electroluminscent technology (with non-organic phosphors) already exists, but currently has lower efficiencies (though higher than incandescent). Another potential idea would be to combine current electroluminscent panels with LED light sources, to fill in the missing parts of the spectrum. This could still offer an overall light source with good efficiency and high CRI.


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## SemiMan (Apr 5, 2013)

Anders Hoveland said:


> Currently the options for high CRI, high correlated color temperature LEDs are limited, because broad-spectrum phosphors have not been commercially developed yet for use in LEDs. This may eventually change with OLED electroluminescent technology. Basically, the operating principles are similar to LED, but it uses organic phosphors, and actually operates as a capacitor rather than a diode.
> 
> http://www.sciencedirect.com/science/article/pii/S0379677910000275
> 
> Electroluminscent technology (with non-organic phosphors) already exists, but currently has lower efficiencies (though higher than incandescent). Another potential idea would be to combine current electroluminscent panels with LED light sources, to fill in the missing parts of the spectrum. This could still offer an overall light source with good efficiency and high CRI.



Sorry, but you misunderstood this article you referenced.

An LED .... Light Emitting DIODE .... is not a capacitor it is a diode. It has capacitive properties, but that is secondary to the emission of light. I think you are confused as the term electroluminescence was more traditionally used in the AC excitation of phosphors. However, the term is general for the generation of light via the release of energy from an electron recombination. The emission of light mechanism is the same for an LED and and EL panel, the difference is the excitation method.

The paper you referenced is NOT phosphor based technology per se, they are organic LEDs that are stacked to achieve a wider spectrum. Organic LEDs generally have a wider emission bandwidth compared to standard semiconductor based LEDs which works well for illumination. By stacking a variety of materials with different emission patterns, you can achieve broadband illumination. If you look at the band-gap diagram, you can clearly see that they are both active layers, one is not a phosphor. Additionally, they show a spectrum graph of devices made with each material individually and then stacked to achieve white.

That said, OLEDs though are a much more complex topic as there are a variety of light producing mechanism more complex than simple electron/hole recombination and admittedly way beyond my limited knowledge. There is the concept of phosphorescence (electrophosphorescence: electrically excited, not optically excited) being applied to raise the quantum efficiency significantly beyond traditional OLEDs. This was responsible for the major leap in efficiency of OLED as a lighting source. If someone who really knows this stuff (beyond Wikipedia) would like to jump in, feel free! 

Semiman


p.s. The options for 90+ CRI LEDs are limited because the driving force for LED adoption and hence volume production up to this point has been reduced cost and higher efficiency with both being tightly related. For the majority of current applications and to drive volume sales, 80+ CRI is sufficient for indoors and 70ish is suitable for outdoor applications. 90+ CRI implementations either take a significant hit in terms of efficiency and hence total system cost and/or require more complex implementations (using RED LEDs) which again raises system cost. The loss of efficiency to achieve high CRI using phosphor technology can render a design difficult, i.e. 60 watt and greater replacement light bulb in standard A19 form factor, at least at a cost the customer is willing to pay.


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## Anders Hoveland (Apr 5, 2013)

I was referring to the so-called field-induced polymer electroluminescent (FIPEL) technology.
http://www.extremetech.com/extreme/...re-cheap-bright-shatterproof-and-flicker-free

Despite the fact that it operates as a capacitor and takes the form of an electroluminescent panel, the mechanism of light production is actually more closely related to OLED, which is how the researchers were able to achieve the higher efficiencies.


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## SemiMan (Apr 6, 2013)

Anders Hoveland said:


> I was referring to the so-called field-induced polymer electroluminescent (FIPEL) technology.
> http://www.extremetech.com/extreme/...re-cheap-bright-shatterproof-and-flicker-free
> 
> Despite the fact that it operates as a capacitor and takes the form of an electroluminescent panel, the mechanism of light production is actually more closely related to OLED, which is how the researchers were able to achieve the higher efficiencies.




If you were referring to FIPEL, then why did you post a link to something completely different? That does not make any sense at all. 

How is the mechanism closer to OLED than it is closer to a traditional EL? Curious minds want to know.

In addition, considering for FIPEL they claim they can tune it to any spectrum, why the heck would you need or want to mix it with LEDs to fill in the missing part of the spectrum ... since there wouldn't be any missing parts of the spectrum?

Semiman


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## Anders Hoveland (Apr 13, 2013)

UnknownVT said:


> CRI is very dependent on the CCT (Correlated Color temperature) -
> and are really only comparable at the same CCT -
> 
> For me it is more important to find the preferred color temperature
> ...


This really only applies if you are comparing different types of LEDs. When you are comparing an LED to another type of light source, CCT and CRI are not really adequate to describe the differences. There is a very noticeable differences between "daylight" color LED and natural sunlight, even if they are the same "correlated color temperature", the light is very different, in fact they are not even the same color! 

I just hope that people realize that "color temperature" is NOT really the color of the light, and CRI does not tell you everything about the quality of the light.
CCT and CRI are just vague indexes attempting to quantify these complex properties into simple numerical values.

It is theoretically possible to make two different light sources with the same CCT and CRI indexes, but which are completely different. Generally, however, for most light sources (with moderately evenly distributed spectrums) with the same CCT and CRI they will appear very similar. 

I just think CCT and CRI have been turned into something they were not meant to be used for, because of the recent coordinated public marketing campaign by the lighting industry. Again, I can't stress it enough, "color temperature" is necessarily the exact color, and CRI is not necessarily the exact quality of light.




SemiMan said:


> An LED .... Light Emitting DIODE .... is not a capacitor it is a diode.


I find it rather interesting how each type of lighting seems to correlate to a different type of electronic circuitry component. Incandescent bulbs are like resistors, LEDs are diodes, electroluminescent are capacitors, discharge lamps are like the equivalent of spark gaps, ESL is like an old vacuum tube rectifier.


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