# Why are warm tints better than cool tints for colour rendition?



## HighLumens (Mar 27, 2009)

Why? and why is a warm tint preferred for outdoors?


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## Owen (Mar 27, 2009)

Check out selfbuilt's new thread in the LED forum:
https://www.candlepowerforums.com/threads/227176
Whether you like them or not is up to you, but his comparison pics will help you see the difference.


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## GreyShark (Mar 27, 2009)

I don't recall of the specifics but in general terms it has to do with differences in the spectrum of light. What we're used to during the day is "full spectrum" light from the sun. At night we're starting from a position of effectively no light and we're relying on our flashlights to emit not just light but also as much of the full spectrum as is practical to approximate what we're used to. As I understand it the warmer end of the spectrum, from yellow to red, are the first to diminish as light output falls. For instance you'll notice things look a lot cooler or more blue in the dawn and dusk than in the middle of the day. A warm spectrum light adds more of that back in so what you're viewing looks more like what you'd be used to seeing during the day. This is why optics meant for use under dusky conditions are often made with a yellow filter.

While things do look prettier in a warm tinted light to me I'd also say that in practice it doesn't actually allow me to see any more or any faster than a cooler tint. The illuminated scene does appear more "live." Brighter does make a more noticeable difference to me. Many have said that warm tinted light cuts through fog and smoke better than cool tinted light but I haven't had an opportunity to really test this out yet. Your eyes may vary.


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## fixitman (Mar 27, 2009)

comparison pics don't always do neutral LEDs justice. I recently modded my Akoray 106 to a neutral white, and it makes a big difference in the woods near my house. As an example, a rabbit at 20 yards was almost unseeble with my cool white L2Dce, but with the neutral Akoray, it showed up clearly. The L2Dce is actually much brighter than the Akoray.
Some yellow/gold flowers showed up as very pale yellow with the L2D, but vibrant yellow/gold with the Akoray.
Tree trunks and blackberry bush stems all showed up as kind of greyish and hard to focus on with the L2D, but the Akoray showed them as various shades of brown and green, and much easier to see details. My dog, under the L2D shows up as kinda beige, but with the Akoray, she shows up much closer to her actual orangy brown. (as a irrelevent side note, my dog loves my flashlight addiction, since we go for alot of night walks!)

All this was noticed just last night, when I took a walk with my dog around the neighborhood, park, and woods.

My L2D used to be my favorite light, but now its my Neutral modded Akoray! I am a convert!
I am getting the Fenix TK 20 soon!

On the other hand, some prefer cooler lights, and some just put brightness over everything. whatever floats your boat!


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## BillyNoMates (Mar 27, 2009)

It never ceases to amaze me how super bright cool-white LEDs look so dark when you shine them on hedges/trees or brown mud. You get almost nothing coming back...

Neutral or (even better) warm white tints may not measure as bright when someone shines it into your eyes, but you get much more of it bouncing back of real world stuff, hence I find it is much better to see by.


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## Flashlight Aficionado (Mar 27, 2009)

I've been wondering about this myself. When I compare my LED to my incan, the led wins in brightness outside, after adjusting the level to equalize them indoors. But the incan shows more detail, while the LED makes appear muddy without depth. When purposely blinding myself, again equalized, the incan seems more disruptive to my nervous system. (I just noticed BillyNoMates has a different experience on that one) But the yellow is butt ugly when wall hunting.

I should probably go for a warm LED for my next light or mod. I just must resist the urge to white wall hunt. :sick2:


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## Yoda4561 (Mar 27, 2009)

If you look at the spectral output of a cool white vs warm white emitter (let's say Q5 WC vs Q2 5A) The 5A warm tint is putting out MUCH more light between the green and red of the spectrum. The WC puts out a good deal more blue and cyan light. Outdoors there's lots of greens and reds (green= grass, leaves, red= dirts, treebark, animals), and not a whole lot of blue to speak of. What you see in reality is whatever light gets reflected off of a surface, so given two 100 lumen lights in cool white and warm white, chances are the warm emitter will let you see more outdoors. Indoors the blue appears much brighter because the white surface of the walls reflects most of it back to you. Also like in the bunny example, because there's more green and red reflected from the environment around the rabbit, it increases contrast, making it easier to see. (Edit: or more red from the rabbit and less from the environment, I was thinking white rabbit when I real that the first time)

Fear not with white wall hunting. At night, unless your eyes are adapted to a cool white fluorecent the 5A led will have a pure but "gentle" white color. If you get used to the warm emitter's color a normal LED that used to look white is suddenly glaringly blue. Compared to noon daylight it will have a slight pinkish cast to it. Side by side with an incan it will be unmistakably white.


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## GarageBoy (Mar 27, 2009)

Odd thing is, a few years ago, we were getting ticked off at the yellowish greenish tint (akin to the "sickly yellow" incans) and here we are looking for lights to replicate the "sickly yellow"


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## flashfan (Mar 28, 2009)

I have very bad eyesight, and perhaps that's why LED lights work better for me regarding colors. 

The challenge: take three _pairs _of socks of the same size/style, but one pair black, one dark brown and one dark navy blue. Now mix up the six individual socks, and alternating between incandescent and LED lights, sort them back into matching pairs. What works better for you?


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## HighLumens (Mar 28, 2009)

thanks for the answers and for the link in the LED forum, it's great!



GreyShark said:


> ...as much of the full spectrum as is practical to approximate what we're used to.



So, if there were a LED covering all the spectrum it would seem purely white and would allow us see every colour perfectly, right? Is it possible to make this kind of led's? Can I add this dream to my dream list of the perfect flashlight (hundreds of lumens, powered by 1AAA battery, runtime of weeks ecc )?


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## Ilikeshinythings (Mar 29, 2009)

I too used to appreciate a nice cool bordering blue LED tint but after the Inova T2 came out with it's creamy white tint I came to appreciate it much more in outdoor activities. 

Warmer tints also tend to cut through fog better than cooler tints for the same reason that Incan lights are (were) usually better for cutting through fog than LEDs are (used to be).


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## SemiMan (Jan 14, 2010)

"Apparent" brightness has nothing to do with how many lumens are coming out the front of your flashlight, but has to do completely with how many are reflected off the scene and back at your eyes.

Natural environments has lots of red content. If your flashlight is not putting any out, then nothing is coming back at you ..... which means that the blue, green, etc. hitting that red is absorbed.

Neutral whites are a good trade-off between lumens and colors that appear in typical outdoor scenes both natural, i.e. trees, dirt, etc. and man made, i.e. what appears along a road. Neutral whites were initially developed for the automotive industry.

Semiman


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## kramer5150 (Jan 14, 2010)

For me it has more to do with the CRI, than the fundamental color tint. IMHO warm tint LEDs can't come close to incans in this one aspect.

http://en.wikipedia.org/wiki/Color_rendering_index


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## Vesper (Jan 14, 2010)

Millions of years of evolution. Your eyes are, after all, very used to that big warm incandescent in the sky.


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## stallion2 (Jan 14, 2010)

kramer5150 said:


> For me it has more to do with the CRI, than the fundamental color tint. IMHO warm tint LEDs can't come close to incans in this one aspect.
> 
> http://en.wikipedia.org/wiki/Color_rendering_index


 

dear God almighty...i thought i was the only one. i absolutely hate the excessively cool emitters of a few years back but i still prefer neutral or cool white tint (like many of the R2s) to warm tint, specifically 'LED' warm tint. 

judging an emitter to be 'warm' or 'cool' is obviously relative...i used to think my Olight M20 w/ the R2 had a somewhat cool tint until i received an order from DX for several low cost dropins and lights, virtually all w/ CREEs. the only 'warm' emitter i own (as most people here would classify as warm) is a Q4 5A pill from Dereelight. i was pretty disappointed. i still kick myself for not thinking of it beforehand, but warm emitters (just as neutral or cool ones) have a very narrow range of wavelengths being produced. this is in complete contrast to an incan. shining that warm emitter into the woods i can see why there would be a preference for warm tint but to me its not worth the loss of output. the glare that comes back to you off the leaves and trees still looks artificial. i probably won't pursue another warm emitter until somebody develops one that can produce light that covers a much greater range of wavelengths. 

in any case, if you want to see nature in its most undisturbed form, then go out when the sun is still up or go out at night and leave your light off. i realize thats kinda silly, i would want a light w/ me but if color rendition is paramont then there is nothing that can compete w/ incan...for now.


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## hoongern (Jan 14, 2010)

In the same way, I don't mind a cool tint which has 100CRI. Daylight when shrouded by clouds can be pretty cool. (For me personally, I love the 100CRI of my incans but can't stand their 3000-4000K color temperature, and I hate the low CRIs of slightly-warmer cool tints, but would prefer their 5500-6500K color temperature)

Ideally, I'd love a range of tints but all with 100CRI.


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## carbine15 (Jan 14, 2010)

Does anyone have that graph of the spectrum curve of cool white LEDs vs Warm high CRI tints? That'd be useful. i think the led museum has it but his site has always conflicted with my eyes and brain.

try this page.. it compares cool vs warm LED lights.


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## LEDninja (Jan 14, 2010)

From Spectrographic analyses, pg. 4 post #8 rehosted.
Unknown-type cool white LED.






The_LED_Museum did a spectrographic analyses of a neutral warm white Q2 5A bin for me a couple of years ago.
From Spectrographic analyses, pg. 3 post #154 rehosted.





Outdoors leaves and grass is green, tree trunks and mud trails are brown, very little blue.
The excess blue of cool white LEDs casts a haze over everything reducing clear colour rendition.

Indoors (and downtown concrete buildings) most walls are white or gray. The excess blue of cool white LEDs make the walls look whiter.

So warm white outdoors, cool white indoors unless your walls are wood paneled.


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## OceanView (Jan 14, 2010)

Thanks, LEDNinja, for those graphs. Very concrete representation of the difference. As can be seen from the graphs, neither cool nor warm LED's are necessarily "better" at rendering the full spectrum of colors _accurately_ since both are deficient in certain areas. 

For me, I just dislike cool tints because it bothers my eyes. Can't put my finger on exactly what bothers me, but could be the big blue spike in the spectrum. I suppose another option for me would be to just wear Eagle Eyes or BluBlocker sunglasses whenever I use cool LEDs!


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## DM51 (Jan 14, 2010)

OceanView said:


> I just dislike cool tints because it bothers my eyes. Can't put my finger on exactly what bothers me, but could be the big blue spike in the spectrum.


The spectrographs are very useful. You are right about the blue spike bothering some people - blue light tends to dazzle and glare, and the extra blue in the LED spectrum can give the impression of being brighter than it actually is. For other people, however, too much yellow/red can be annoying, which is why they prefer LEDs to Incans. It is very subjective.

Leaving aside these personal preferences, an object of a certain color will not show up properly unless it is illuminated by light of that same color. True white light contains all color wavelengths, so it will illuminate all objects. Most LEDs are weak in red, so objects that contain red are not properly illuminated and typically appear a rather dark muddy brown. That is why a purely blue light is useful for spotting blood traces - the blood is not illuminated and appears black. Equally, a red light will be no good at illuminating a blue object. 

It's just a question of what you like and what you need. Everyone is different.


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## Magic Matt (Jan 14, 2010)

Here is my opinion, based on what I know...

It's not really colour rendition so much as it is the way our eyes perceieve colours. If you use a cool white light, you can still get a perfect photograph with a camera, and your eyes will adjust to see very well in this light, but our eyes are more attuned to green than anything else, followed by red, and then blue. 

Our eyes are more sensitive to, and can distinguish far more shades, of green light than anything else. Any light source that has strong green light present will give you best rendition of shades. This is probably an affect of evolution, as most of our planet's foliage is green.

Many cool light sources are strong in the blue area of the spectrum, and far weaker in the green and red. Our eyes have to work a bit harder to adjust to the lack of light in the spectrum they are more attuned to compared to the bright light source in the area of the spectrum they are least able to cope with.

We have a much more evolved method of dealing with red light than with blue. Red is used a lot in nature to indicate danger, and we are more sensitive to it. As such, we can distinguish something that is 'not green' much more easily from a green background if it reflects red light than if it reflects blue light.

As an experiment, feel free to try walking around with a cyan light (mainly green and blue light) compared to a yellow light (mainly red and green light). The yellow is far more effective.

The presence of some blue light is helpful to distinguish things that may be white, cyan, or magenta or blue from things that are red, green or yellow... but with a yellow light source you're able to see very well.

Some people may also notice that blue lights (ie blue xmas lights) seem to 'swim' across their vision at night more than other colours. This is another side-effect of our mainly green-based vision system. The fact we are so green-biased is also why digital cameras use a bayer-matrix that collects twice as much information on the green spectrum than any other colour.

A light source that is truely a neutral white is no better or worse than one that is warm white, other than most people prefer warm looking colours. This is why so many photographers use "LBA" or "85" filters - they "warm up" photographic images. Try holding one in front of your neutral white flashlight and see - not as accurate, but a pleasing effect.

Also, almost every single computer monitor is configured to show far too much blue in the image. This tricks the eye into seeing the monitor as brighter, because our eyes tend to rely mostly on the amount of green light to judge the brightness of our environment. If you calibrate your monitor correctly, it will show far better colours, but also seem to drop in brightness.

This is also why we use red light for astronomy. Quite simply, when our eyes use green light to judge brightness, the red light can provide us with far more vision and you can look at a brighter red light source before our eyes would start to adjust than a green light would, thus preserving a lot of your night vision.


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## Outdoors Fanatic (Jan 14, 2010)

HighLumens said:


> Why? and why is a warm tint preferred for outdoors?


That's a myth. Warm tint is not the same thing as High CRI. For color rendering, you need a High CRI emitter, period. Tint does not matter.

A cool emitter with High CRI is much better at color rendering than a regular LED with warm tint. Tint (measured in K) is not CRI, this myth needs to die ASAP. Kelvin Degrees is not related to *C*olor *R*endering *I*ndex. Stop spreading this disgraceful fallacy!


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## Wiggle (Jan 14, 2010)

That's true, but CRI doesn't necessarily correlate to subjective effects of how humans see a particular scene (particularly outdoors). In my experience, outdoors shows more contrast and better depth under neutral Cree XR-E than cool XR-E despite the CRI being very close (75 vs 80 I think).


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## OceanView (Jan 14, 2010)

Outdoors Fanatic said:


> Stop spreading this disgraceful fallacy!


Well, in all fairness to the OP, his question may not necessarily be about the most accurate color recognition. Just why many prefer warmer tints for outdoors. I think the phrase "color rendition" can be understood in more than one way.

I do agree that green plants, tree trunks, and other outdoor objects are subjectively more agreeable to my eye using a neutral/warm LED versus a cool one. Green leaves and grass look unnaturally washed out to me using a cool LED.


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## Paul_in_Maryland (Jan 14, 2010)

As you can see from my now-5-year-old signature block, I'm biased toward incandescents. But last year, I made the switch to LEDs and never looked back. The Fenix TK20 made me a believer; when I walk with it, I could swear I'm using an incan. Since then, I've acquired two more warm LEDs: a Malkoff M30WF and a NailBender MC-E. I love 'em all. The only LED I own that's not warm is neutral white. It now stays indoors.


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## NoFair (Jan 15, 2010)

Outdoors Fanatic said:


> That's a myth. Warm tint is not the same thing as High CRI. For color rendering, you need a High CRI emitter, period. Tint does not matter.
> 
> A cool emitter with High CRI is much better at color rendering than a regular LED with warm tint. Tint (measured in K) is not CRI, this myth needs to die ASAP. Kelvin Degrees is not related to *C*olor *R*endering *I*ndex. Stop spreading this disgraceful fallacy!



I don't think my warm white renders colors a lot better, but they increase green-brown contrast which is valuable to me in the forest. A bit like wearing amber tinted sunglasses in on overcast days with flat light. 


Sverre


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## carbine15 (Jan 15, 2010)

Will someone post a HIGH CRI emitter vs WARM WHITE emitter Spectrographic analyses? That might prove useful here. 

I think my warm emitters render everything better except maybe blue shades where it is only slightly less. IMHO it's worth the loss of a tiny bit of output.


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## Magic Matt (Jan 15, 2010)

It doesn't help when what is technically 'neutral white' is way off in terms of what most people would consider to be a normal white - sunlight.

An emitter with the wavelength outputs closest to sunlight will give better perceived colour rendition compared to an emitter that has a tint coming from a narrower band of light emittance. I suspect a good deal of the CRI loss is because the warm tint LEDs have that sagging 460-510nm output (as on the graph posted earlier).


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## Analog (Jan 15, 2010)

Outdoors Fanatic said:


> A cool emitter with High CRI is much better at color rendering than a regular LED with warm tint. Tint (measured in K) is not CRI, this myth needs to die ASAP. Kelvin Degrees is not related to *C*olor *R*endering *I*ndex. Stop spreading this disgraceful fallacy!



This is the truth. 
I sometimes use the explanation that Kelvin is the color appearance of the light. CRI determines the colors that we see reflectected.


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## Magic Matt (Jan 15, 2010)

That's an interesting way to look at it... I've always regarded K as the indicator of the dominant wavelengths.


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## Analog (Jan 15, 2010)

Here are the definitions of CRI and K temp. as provided by General Electric.
*Color Rendering Index (CRI)*
An international system used to rate a lamp's ability to render object colors. The higher the CRI (based upon a 0-100 scale) the richer colors generally appear. CRI ratings of various lamps may be compared, but a numerical comparison is only valid if the lamps are close in color temperature. CRI differences among lamps are not usually significant (visible to the eye) unless the difference is more than 3-5 points.
*Color Temperature (Correlated Color Temperature - CCT)*
A number indicating the degree of "yellowness" or "blueness" of a white light source. Measured in kelvins, CCT represents the temperature an incandescent object (like a filament) must reach to mimic the color of the lamp. Yellowish-white ("warm") sources, like incandescent lamps, have lower color temperatures in the 2700K-3000K range; white and bluish-white ("cool") sources, such as cool white (4100K) and natural daylight (6000K), have higher color temperatures. The higher the color temperature the whiter, or bluer, the light will be.

http://www.gelighting.com/na/home_lighting/ask_us/pop_glossary.html#K


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## Magic Matt (Jan 15, 2010)

This is interesting....
http://www.effectiveconcepts.net/def.html
...looks like they've taken the GE definitions, but they have some spectral graphs for common light sources (no LEDs though, sorry)


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## divine (Jan 15, 2010)

I got a couple high CRI modded lights, and I did some comparing next to neutral, and it's a pretty big difference.

The blended together and indistinguishability of colors are still very much there with neutral white, but neutral white is much more comfortable to my eyes. The neutral white light only has slightly better CRI. I neutral makes more important colors more obvious like red, green and brown, but it isn't like daylight.


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## Benson (Jan 16, 2010)

Vesper said:


> Millions of years of evolution. Your eyes are, after all, very used to that big warm incandescent in the sky.


Warm? Not really. Direct sunlight is mostly in the >5000K region, and daylight (including the blue that got scattered _out_ of the beam) more like 6000K.


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## Mike V (Jan 16, 2010)

Professionally the colour of paints, dyes and pigments are judged under 6,500 degree Kelvin light i.e. D65 illumination.

The colour of printing and photographs are judged under 5,000 degree Kelvin light i.e. D50 illumination.

So people claiming that warm tints are better for colour rendition are misguided.

The error comes because often warmer LEDs have a better spectral response i.e. CRI.

It's a limitation of the current technology. 

It would be better for everyone if the spectral response of LEDs were better and the colour was around the 5,600 degree Kelvin mark.


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## Swedpat (Jan 16, 2010)

While warm tint is not the same thing as high CRI I wonder if warm LEDs usually hasn't better colour rendition than cool LEDs? When I compare my different flashlights this is the case. 
However, there is still one argument for warm tint undependent of CRI: it just feels more comfortable and relaxed for the eyes. In my opinion.

Regards, Patric


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## jblackwood (Jan 16, 2010)

I agree that we should stop saying warm tints render color better since that's a function of high CRI, but I've never heard of a high CRI light that wasn't warm. Conversely, I imagine that not all warm-tinted lights are high CRI.


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## stallion2 (Jan 16, 2010)

Benson said:


> Warm? Not really. Direct sunlight is mostly in the >5000K region, and daylight (including the blue that got scattered _out_ of the beam) more like 6000K.


 

yeah, but the only usable light, in terms of allowing us to see objects, is reflected sunlight off those objects, not direct sunlight itself. the glare that comes off most objects has a proportionally greater amount of red light than direct sunlight. shorter wavelength light, especially UV, is notorious for its ability to penetrate materials. our eyes have developed to use the sun's reflected light simply because its more useful.


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## Outdoors Fanatic (Jan 18, 2010)

Mike V said:


> Professionally the colour of paints, dyes and pigments are judged under 6,500 degree Kelvin light i.e. D65 illumination.
> 
> The colour of printing and photographs are judged under 5,000 degree Kelvin light i.e. D50 illumination.
> 
> ...


Excellent post! I agree 100%.

Cheers.


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## Outdoors Fanatic (Jan 18, 2010)

jblackwood said:


> I agree that we should stop saying warm tints render color better since that's a function of high CRI, *but I've never heard of a high CRI light that wasn't warm.* Conversely, I imagine that not all warm-tinted lights are high CRI.


 
Many High CRI LEDs are just "neutral". And most warm LEDs are not considered to be high CRI. 
And yes, not all warm-tinted lights are High CRI, but simply because not all man-made light sources are incandescent...


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## Analog (Jan 18, 2010)

Mike V said:


> Professionally the colour of paints, dyes and pigments are judged under 6,500 degree Kelvin light i.e. D65 illumination.



PPG, DuPont, BASF, Valspar, and Sherwin Williams all specify 4700K...D50
http://www.solux.net/cgi-bin/tlistore/infopages/dupont.html


[/QUOTE]The colour of printing and photographs are judged under 5,000 degree Kelvin light i.e. D50 illumination.[/QUOTE]

Nikon, Epson, and Eastman Kodak also prefer 4700K...D50
http://www.solux.net/cgi-bin/tlistore/infopages/color-proofing.html
http://www.solux.net/cgi-bin/tlistore/infopages/applications.html


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## Mike V (Jan 19, 2010)

D50 is 5,000 degrees (not 4,700).
Actually it's 5,003 if you want to be pedantic about it.

http://en.wikipedia.org/wiki/Standard_illuminant#Illuminant_series_D


There is no reason you couldn't judge paint under D50, but most places use D65.
I used to work at a place that sold the viewing booths and the flouro tubes.


I'd take what SoLux says with a grain of salt.
One because they can't even get the colour temp of D50 correct and two because they don't supply D65 lighting, so are pushing D50.

DuPont etc. make all sorts of stuff, so SoLux might be referring to domestic house paints or something where D50 would be more appropriate than D65.


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## tk40 (Feb 19, 2010)

Hi, speaking of CRI, does anyone know how good a Q3-5A might be at color rendition?


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## LEDninja (Feb 19, 2010)

tk40 said:


> Hi, speaking of CRI, does anyone know how good a Q3-5A might be at color rendition?


https://www.candlepowerforums.com/threads/201112
There is an outdoor beamshot of a Q2-5A compared to assorted other LEDs here.


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## hoongern (Feb 19, 2010)

tk40 said:


> Hi, speaking of CRI, does anyone know how good a Q3-5A might be at color rendition?



If you're just asking about CRI numbers, Cree rates their 5A bins at 75 CRI. Assuming you're talking about an XR-E or XP-E. http://www.cree.com/products/pdf/XLampXP-E.pdf

Quote from page 2 of the said PDF:


> Typical CRI for Cool White & Neutral White (3,700 K – 10,000 K CCT) is 75.
> Typical CRI for Outdoor White (4,000 K - 5,300 K CCT) is 70.
> Typical CRI for Warm White (2,600 K – 3,700 K CCT) is 80.



Hope that helps!


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## dymonite69 (Feb 21, 2010)

I think people are getting their reasoning a little reversed here.

Colour is just a psychovisual perception. Humans happen to register a very narrow part of the electromagnetic spectrum that we call 'visible light'. EM radiation doesn't have a 'colour' at all. Our brains turn it into signals that we call colour. Other creatures may not necessarily perceive anything in this range or see in another spectra.

Colour rendition or temperature arbitrarily uses the sun's illuminating spectrum as a reference point for what a colour 'ought' to look like. 

The reason why we use the sun as the reference:
a) it is a light source that anybody can reference to no matter where they live on this planet
b) it is as close to an ideal black body radiator i.e. its spectral radiance changes in a predictable way dependent only on the temperature of the source







Objects illuminated by any non-black body radiator will appear differently under that light compared to sunlight.

Incandescent and halogens are closest to sunlight in this regard.

LEDS, fluorescents and various discharge lamps are not.

How much these lights deviate from sunlight is somehow quantified by the CRI and CCT. Scientists like putting numbers on things. For everyone else we just say the colours look warm, cold or just odd.

As regard to what is 'acceptable' or 'pleasing' in colour is purely a psychological reaction to our conditioned visual experiences of nature under natural light.

Theoretically, if we were to take a baby and kept them inside under artificial light during their development then this will become their psychological reference point. Sunlight would then become 'unnatural'.


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## hoongern (Feb 21, 2010)

dymonite69 said:


> I think people are getting their reasoning a little reversed here.
> 
> Colour is just a psychovisual perception. Humans happen to register a very narrow part of the electromagnetic spectrum that we call 'visible light'. EM radiation doesn't have a 'colour' at all. Our brains turn it into signals that we call colour. Other creatures may not necessarily perceive anything in this range or see in another spectra.
> 
> ...



I'm not an expert on this area, but I'll give a couple of my thoughts:

1) Let's take a spectrum of light, and make a 'hole' at a certain wavelength, let's say, green. Now, if you had an object which reflected light at that wavelength (i.e., a green object) - it would just appear black. Thus, you have lost green color. Now, this to me is what makes high CRI - the ability to naturally illuminate all various colored objects at the same intensity across our eye's [visible] wavelength response. You can have a 3000K CCT high CRI source, and a 6000K CCT high CRI source.

2) You could take 3 monochromatic wavelengths (Red, Green, Blue - think of your monitor) and combine them in a way to create a "warm and pleasing" 3000K CCT source. This would have extremely low CRI. Thus, you can have 3000K CCT which have very low CRI, and 8000K CCT which has very low CRI. 

--- (Now, I always wonder, would a straight-line continuous spectrum across the visible wavelength provide the best accuracy with color? This ties in to your point about us just taking the sun's spectrum to be the CRI 'guide'...) ---

3) I believe that it is TINTs (CCT) that we are conditioned to psychologically, not CRIs. Take it from me, actually. I have weird preferences. I grew up with cold fluorescent lighting, so I like high (6000K+) CCTs. I find 3000K way too weird to look at. On the other hand, someone who grew up with 3000K incans would find 6000K CCT extremely odd. HOWEVER, here's my point - both people would still love the benefits of high CRI, and find high CRI natural. 

Which is why I either try to go for overdriven halogen Incans (100CRI, and as high a CCT as possible), or a cool-ish (5500-6000K-ish) as-high-as-possible CRI LED. (Which I don't have right now)

4) CRI is not necessarily the best of measures, btw. Some don't consider it to be the best of measurements. But it's still one reasonable way of measuring color accuracy.

Please discuss - I'm not pushing any "These are the facts" in this particular post - just trying to think this out  It's good to be able to hear what others think - I'm definitely still learning myself


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## Paul_in_Maryland (Feb 21, 2010)

hoongern said:


> I'm not an expert on this area, but I'll give a couple of my thoughts:


Hoongern, I like how you express yourself. You're both precise and colorful. I've read your post only once, but I'll remember it always. Truly food for thought.


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## dymonite69 (Feb 21, 2010)

hoongern said:


> what makes high CRI - the ability to naturally illuminate all various colored objects at the same intensity across our eye's [visible] wavelength response.
> 
> would a straight-line continuous spectrum across the visible wavelength provide the best accuracy with color?
> 
> people would still love the benefits of high CRI, and find high CRI natural.



With a black body radiator, radiance is not a straight line across all spectra (see the graph above). 

So our reference point is the sun's colour temperature with spectral radiance that obeys Plank's law of a black body radiator. The relative proportions of radiance for each wavelength is important.

Note that as the colour temperature decreases, the 'hump' in the spectra flattens. The proportions vary. This is a deviation from our reference source and so will be the perceived colour of the same object. 

The CRI is derived by trying to match the spectral distribution of the test source with the closest match for a black body radiator of a certain correlated colour temperature.

Not if the CRI is high but the correlated colour temperature is not similar to that of sunlight, then it will still won't necessarily be a good match


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## hoongern (Feb 21, 2010)

dymonite69 said:


> With a black body radiator, radiance is not a straight line across all spectra (see the graph above).
> 
> So our reference point is the sun's colour temperature with spectral radiance that obeys Plank's law of a black body radiator. The relative proportions of radiance for each wavelength is important.
> 
> ...



Agreed - the black body radiators are definitely not straight line spectrums. What I was wondering is how well a straight line spectrum would perform. I myself have not studied color/black body radiators/how CCT correlates/etc. much (or at least, quite some time ago!), so it's a bit of a question to myself. I don't know of any 'perfect straight line' spectrum emitters myself - I'd LOVE to see one!

I guess CRI was the wrong term for me to use. Of course, CRI relates to the sun's spectrum, and how close other sources get to it. I guess I'm searching more for what is considered to be 'perfect', i.e. something which equally lights up all wavelengths well. 

I myself don't know how the human eye reacts. I presume that most of our eyes are trained to accept the sun [or black body radiators] as natural (Thus a 100 CRI being good) - but is this something physical (wired into our eyes), or something we are conditioned to (psychological)?


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## dymonite69 (Feb 21, 2010)

Spectral sensitivity to certain wavelengths is hard wired (photoreceptors in the eye) and varies across animals. 

Emotional and psychic reaction to certain colours probably has a psychological component.


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## Benson (Feb 21, 2010)

dymonite69 said:


> Colour rendition or temperature arbitrarily uses the sun's illuminating spectrum as a reference point for what a colour 'ought' to look like.


Nope. CCT arbitrarily assumes the spectrum under test is intended to be "white", i.e. a black-body spectrum, and compares it to various blackbody spectra to match the nearest point on the BB locus. Sunlight is not used as a reference, both because it's not readily reproducible (varies with latitude, time-of-day, and atmospheric conditions), and because it's only a single point -- you need a full range of spectra to find the one _closest_ to the emission being tested.

Then, the CRI is not determined by comparing an emission to sunlight, or even to a BB of sunlight's CCT. It's compared to a BB at the _same CCT_.

Now, it could be argued that the "best"/"most normal"/whatever light would match sunlight in CCT and CRI, but I think most people would prefer a CRI of 100, supposing they could tell the difference. And it's a fact that people _don't_ generally prefer sunlight's CCT for all lighting -- it's called the Kruithof curve.


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## dymonite69 (Feb 21, 2010)

Sorry my explanation wasn't very good the first time.

1) Generate a set of spectral distribution curves of a black body radiator of different colour temperatures. See the above image I posted but this time for a whole range of colour temperatures

2) Determine the spectral distribution curve of the test light.

3) Find the curve from step 1 that 'matches' the best with step 2. The curve chosen in step 1 is the CCT

4) Compare the difference mathematically and generate a CRI

Thanks. I have not heard of the Kruithof curve. It adds another dimension, illumination.

I note that the pleasing white band is large within a certain illumination and colour temperature range. The sun operates in this area. If you deviate from it significantly then there are only limited combinations which provide a 'pleasing effect' e.g. the tungsten halide looks 'truest' in the 90+/-10 lux range.

The last thing is that 'white' is also perceptual. It is when the three wavelength specific cones of our eye are stimulated with equal intensity. An object appears white if it reflects light from a source in such a way as to produce this effect. This is dependent on the absorption spectra of the object and the radiant spectra of the light source. For reference purposes the spectral distribution is specified for a given CCT of a black body radiator - it approximates noon day sun. Colours of objects are then simulated under this light source. The colour 'white' is then defined by this method.

Changing the light source or its CCT or its illumination will cause what a scientist in a lab to call 'white' to no longer appear technically white. Humans aren't usually that discriminatory and just know if it is white enough.


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