# problems encountered trying to make a DIY super high CRI array



## Anders Hoveland (Nov 26, 2014)

I have been experimenting with D.I.Y. multi-emitter arrays, trying to get white LED light with better spectrum.
However, what I have noticed is that it seems extremely difficult to get good skin tones and impossible to render correct yellow colors. 
When deep red LEDs are added in, they overpower skin tones, making them pink. When amber LEDs are added in to try to correct this, it results in yellows being rendered orange. The problem is they do not make a yellow LED. 

I have combined red and Philips lime, but skin tones and brown wood colors become too red.

Another problem is that when 495nm (greenish-)cyan is added, the overall color of the combined white light becomes a little too greenish, but at the same time green colors are rendered with poor saturation (they look a little washed out). (I am not using any green emitters because the cyan is already throwing off the color)

The fact is they do not make true yellow or true cyan LEDs, and this really messes up the color rendering when one tries to combine separate emitters to make white light.

The latest thing I found are yellowish-white LEDs (just cheap Chinese 3000-4000K with thicker phosphor). Only a small amount of blue gets through. These emit a pleasant quality of light, but the green color rendering of these is not the best (green colors look somewhat yellowish-green), and skin tones look dead and greyish, though surprisingly red colors do look red.

It seems like there is no combination of LEDs available that can be used to give a good spectrum of white. There are two real problems. The spectrum needs 490nm cyan-blue light to render beautiful [real] cyan and light blue colors, without the ugly unsaturated 495nm pale green wavelengths. And the spectrum needs more yellow wavelength, without too much of either of the yellowish-green or orange-yellow wavelengths on either side, which result in undesirable color shifts. 

If one wants to render colors, the color of emitters one would want are the basic colors: blue, green, yellow, orange, and red. But the fact is that the LEDs available are not always practically available in these basic colors. The "reds" might be orange-reds, the "yellow" might really be amber, the "green" might be mostly yellowish green if phosphor conversion is used. The "cyan" is likely to rather be slightly bluish green.

I have thought of using a deep red LED with a low color temperature white, but that would not work either. A typical white LED has too much orange wavelengths (to compensate for its lack of deep red when it comes to color coordinates). If deep red is added, that is going to result in a red-shift of any orange colors, or even orange-shift of yellow colors also. One cannot add in red without adding in yellow also, but they do not make a yellow LED!
So what if you combine a Luxeon lime with a low color temperature white, together with the deep red? I have tried that also, and it does not really solve the problem. The lime looks yellow, but actually the amount of real yellow wavelength is somewhat less than it appears. It peaks in the yellowish-green part of the spectrum. It only _looks_ yellow because there is a long trail of orange wavelengths too. So when I combine it to get wood colors looking just right, the yellow colors appear too orange.

And something else interesting I have discovered, if all the red wavelengths in your spectrum are all only _deep red_, even that will make yellow colors look orange. Because apparently yellow pigments do reflect some red wavelengths too, and if it is all pure red instead of orange-red like how it is supposed to be, there will be an imbalance. But you cannot just use amber wavelengths to counteract this, because yellow pigments are far more reflective of amber than red, so even if you used all amber and no red, that would still orange-shift yellow colors. You need orange-red wavelengths, that the yellow can reflect without being too red-shifted, but at the same time which the pigment does not reflect too much of it. The spectrum needs a high amount of yellow wavelengths, do not make the mistake of using too much green cyan and red/orange to get to the proper color coordinates.

Adding some 495nm can really make the white light appear more "natural", and helps get rid of the typical LED blue-tint at higher correlated color temperatures, but it also makes greens and even blues look a bit washed out. Definitely noticeable. 

I am very frustrated.

The reason I am probably going to have to resort to phosphor-conversion to get my red wavelengths is that is the only way to get those real yellow wavelengths, without too much yellow-green wavelengths. It is a less efficient strategy, but after doing much experimentation I think I see why there are no manufacturers using separate emitters to generate the deep red wavelengths for high CRI lighting. And blue-cyan wavelengths are very important, but if 495nm is the closest emitter available, the cost (in terms of throwing things off) is simply not worth it. What might be best is to simply get a standard 95 cri white LED and combine it with a 480-485nm cree blue.

Just my rambling thoughts. Might be useful to anyone experimenting with trying to combine multi-emitters for a better white spectrum.


----------



## SemiMan (Nov 28, 2014)

I don't waste my time with experimenting with real emitters. I can simulate all the work you have tried .... do it in an afternoon, and have far more accurate mixing and results.

The best sources have used 7+ separate emitters and the LRC lighting simulators uses 20. 

You can get almost any color you want, you just have to live with poor efficiency.

When you can get Xicato which is near perfect w.r.t. CRI, it makes little sense to try and mix unless you are looking for a specific lighting result ... which probably will not be high CRI.


----------



## WeLight (Nov 28, 2014)

We use a min of 15 to get to 97/98, but consider PC Amber, it has a broad coverage


----------



## Anders Hoveland (Nov 29, 2014)

Just placed an order for 10W(see note below) green phosphor-converted LEDs. Hopefully that should help with the spectrum.
I chose phosphor-converted because it should provide broader spectral coverage, including some into the yellow wavelengths, which are hard to fill with plain emitters.

The product states peak 420-425nm. I just looked on Intermatix's website (not sure if the phosphor they are using is exactly the same though) and spectral graph for their 425nm green phosphor shows substantial coverage in both the yellow and even into the *blue *! Even at 480nm, the amplitude is 40% of the peak at 425nm. I might not even need separate cyan emitters. 

green phosphor conversion efficiency is 70 lumens/W

note: will be running it with lower current power supply, so it will actually be using only 3.3W





WeLight said:


> consider PC Amber, it has a broad coverage


Unfortunately, the proportion of orange wavelengths to yellow wavelengths would be too high, and I am trying to get higher color temperature and deep red saturation, so probably aiming for a little less orange coverage than a normal black body spectrum. Though I do not want to throw off skin tones. Hoping that yellow+red can, with only a smaller amount of orange, can make skin tones look good (might be wrong here).

As I have already stated, I am using yellowish 3000-4000K phosphor-converted LEDs, which have yellow wavelengths, but have more orange than yellow.


I suppose what would really fit my project would be a custom phosphor-converted LED, around 4000K, but with a little extra green and yellow (not amber) phosphor to balance out the deep red wavelength emitter that will be added, and have a thick phosphor layer to only allow a smaller portion of the 460nm blue to get through (since I am supplementing it with longer wavelength blue).


----------



## Anders Hoveland (Nov 29, 2014)

(sorry to quote you in another place, but this topic seemed a better place for this question)


SemiMan said:


> Bridgelux has very high CRI as well and recently very large gamut lamps that eschew trying to mimic halogen and their hobbling and not necessarily relevant cri to provide a light that more effectively saturates a wider color range.


Could you elaborate on what portion of the spectrum is more important for achieving color saturation?
What wavelengths would one want to avoid?

I am a little afraid there might be some trade off. For example, using a deep red wavelength for red saturation seems to tend to result in unnatural skin tones.
And 440-460nm results in good blue saturation, but I do not want to use too much of these shorter blue wavelengths because it strains the eyes a little, more difficult to concentrate.

I really think yellow wavelengths specifically, rather than yellow-green or yellow-orange, are very important for yellow saturation. (perhaps that is just a truism)
What are your opinions about that?


----------



## Ken_McE (Nov 30, 2014)

If high CRI is your only concern, wouldn't you be better off with incandescent?


----------



## Anders Hoveland (Nov 30, 2014)

Ken_McE said:


> If high CRI is your only concern, wouldn't you be better off with incandescent?


Yes, but I think it would be cool to have higher color temperature.

I know there are specialized fluorescent tubes which have 98 CRI and violet-emitter white LEDs with 97-98 CRI.
Unfortunately, I have a skin sensitivity to several types of artificial lighting, and to a lesser extent the sun. 
So I am trying to obtain wonderful quality of light without the violet wavelengths that would cause me skin sensitivity.
That is the reason, if you really must ask.

Come to think of it, this is most likely the reason there are few others pursuing the multi-emitter concept.


----------



## SemiMan (Nov 30, 2014)

I have yet to hear of anyone or at least any study where a person has a higher sensitivity to artificial light versus sunlight. 0 sense in that. The level of short wavelengths in sunlight is orders of magnitudes higher than any violet led. Its not even close.

Of course you did claim it was a brother that had that sensitivity before not you so I don't know what to believe.


----------



## Anders Hoveland (Nov 30, 2014)

SemiMan said:


> I have yet to hear of anyone or at least any study where a person has a higher sensitivity to artificial light versus sunlight. 0 sense in that. The level of short wavelengths in sunlight is ... higher than any violet led.


I am well aware of this. However, my actual experience says otherwise. Not going to get into all the details here and derail the topic, but one possibility is that my sensitivity to violet at some definite wavelength range is greater than my sensitivity to UV. So while the sun obviously has a higher intensity of short wavelengths, it could be that fluorescent has a greater ratio of the specific wavelength causing me sensitivity. Bare exposed fluorescent tubes are the worst, metal halide is about equivalent to being out in direct sunlight at noon in the middle of a summer day.

As for my violet-emitter LED, it is difficult to really measure/compare _how_ sensitive I am to it, because it does not give off a large amount of light, but I _am_ sensitive.
Have not noticed any sensitivity problems with regular LED or incandescent.


----------



## SemiMan (Nov 30, 2014)

Ratios are meaningless. Total exposure is and in the case of the sun with 100x the levels that would ever be experienced with artificial light .... Well ....


----------



## Anders Hoveland (Dec 6, 2014)

Well, the green phosphor LEDs came, and I have looked at the light through a diffraction grating (a CD ) to get an idea of the spectral profile.
There does not appear to be any trace of a distinct shorter wavelength deep blue line, the phosphor is fairly thick so not surprising. So none of the original emitter wavelength is getting through. 

Although the light is very greenish, I can see a rainbow of colors in the spectrum. There is a decent amount of blue in the spectrum. It's broadwavelength and mostly light azure color blue, so I know it's all coming from the phosphor. It is difficult to be quantitative, but it appears that the blue emission is about 35% of the primary green emission. This is about what one would expect. Most of the blue seems to be about the same color as a 489nm wavelength, to give you some idea of what I am seeing.

The advantage is using the phosphor to obtain the long wavelength blue is that the ratio of ~494nm to ~489nm is about equal. When I was using a 490-495nm emitter to try to get the light blue, there was just too great a ratio of the ugly ~495nm murky green wavelength. Using an emitter, the slope of the emission curve is a lot steeper than if using phosphor. True, the phosphor is still creating a lot of green light, but this is more true green light, rather than greenish cyan, which is what I need anyway to get saturated green color rendering. A little complicated, but hopefully you who are reading this understand what I am trying to describe.

In daylight, the color of the phosphor over the LED is a lime-yellow, sort of greenish (more greenish than the phosphor on a Luxeon lime). The color of light is given off is yellowish-green, but not a completely saturated yellowish green. Despite the very greenish color, surprisingly the color rendering of objects in the room is fairly good, albeit with just a very greenish tint (forgive me for bringing this up, but one could draw a comparison to a sulfur plasma lamp here). Even reds look saturated, though that could mostly just be in part to the contrast with the greenish background, and while things may appear a deep colored red, they are noticeably less bright/illuminated than under regular lighting.

Very interesting.


----------



## Anders Hoveland (Dec 6, 2014)

I could be wrong on this, but one of the big reasons many people may find high color temperature LEDs so visually appealing is the fact that the phosphor being used is so green-shifted, it adds a little cyan and azure blue wavelength into the spectrum. This is not something I have ever read mentioned before, interesting theory. 

The phosphor used in the LEDs I have are probably the usual Ce:YAG, but more green-shifted than that used in a normal white LED. Probably the type of phosphor that would be used for a 10000K LED. But of course without all that blue.


----------



## SemiMan (Dec 7, 2014)

They find it visually appealing because it is more natural than 2700k. Sunlight it natural. 2700 is artificial and rarely experienced in nature except a few minutes a day and not black body. Fire is not 2700k.

Why 2700k? Because marketers and engineers many years ago decided that would be a good tradeoff between brightness, efficiency, bulb life and looks.


----------



## Anders Hoveland (Dec 7, 2014)

It would be interesting to do a little experiment and see whether people prefer high color temperatures when using an RGB LED array, with the blue emitter at 440nm. Is it more of the deep blue wavelength that people find aesthetically pleasing? Or is it rather the azure blue/cyan wavelength?

Even with fluorescents, higher color temperatures have more cyan-blue (the terbium phosphor used in the composition has a little cyan-blue line in addition to its green emission).


----------



## Anders Hoveland (Dec 10, 2014)

Update on results so far: 
Adding the green phosphor LED really improves the green color rendering, now it is excellent.
I have learned something else. Using 480nm for the blue makes the color rendering appear just a little washed out. But using 495nm cyan makes things appear more washed out. Using them both together makes things look very washed out. I am sure it gives turquoise colors the best saturation, but gives everything else somewhat of a washed out effect. 

495nm cyan and 490nm amber may enhance the spectrum in very small amounts, but they can easily overpower the spectrum, leading to color rendering problems. Neither of these is really a "primary color" so not surprising. They result in color shift taking away from saturation from the primary colors.

Not using short wavelength blue really makes the light feel "soft", it even feels softer than an incandescent, despite the white light being a much more bluish tint.
I even found 470nm blue to be a bit harsh.

590nm amber combined with red works great for skin tones. For some reason, the yellowish phosphor LEDs did not really pick up skin tones; even combined with red LED the skin tones just appeared pinkish (like they do with just red). However, a sacrifice had to be made, and too much amber could not be used, because it was throwing off yellow colors. I am not really sure what should be done in this area. Surely those "yellowish" phosphor LEDs have a good amount of orange wavelength light, but it just did not seem to be working. Perhaps the spectrum needs 620nm emitters.

I feel I have made a good compromise of combining different wavelengths to achieve decent yellows and acceptable skin tones. However, now the overall color of the light is a little green-tinted. It's more than just that, something about the light does not look right. The color rendering is okay, but there is just this feeling about the light, like it lacks any definition. I suspect it is because of the long wavelength blue, with the cyan added. The aura is almost comparable to a slightly greenish metal halide lamp. I probably should not have added cyan since I was not using a deep saturated blue wavelength.

Despite the unpleasant tinted cast, I would say CRI right now stands at about 92 (just a feeling). Fairly good, considering there is no blue saturation.
Before, when I was using 470-475nm emitters in the sky blue LEDs, along with luxeon lime, I was able to get about a 96 CRI, but with that setup skin and wood tones looked too reddish, and that was just a little harsh (though not quite as much as regular white LEDs).

I think the overall lesson is that using only a single wavelength LED for each color part of the spectrum is inadequate. To get a good spectrum, one needs both a long wavelength blue and short wavelength blue, both a deep wavelength red and an orange-red. One needs some sort of phosphor to generate yellow wavelengths, and there needs to be correct green wavelengths for green saturated rendering.


Latest Update: I added some 95cri 3000K white LEDs into the array, and am now getting excellent light. It really needed just some 460nm wavelength, gives it some definition and seems much less washed out. Skin tones are now looking excellent again. The greenish tint before is really getting balanced out (normally if you mix low color temperature white with high color temperature white it overall looks a bit magenta-tinted). This is now excellent light that I would be happy with in an office. Very comfortable reading light too.

Right now, I am using (3) 480-485nm blue, (2) green phosphor LEDs (each one is equivalent to 3-4 of the other LEDs), (1) amber 590nm, (2) 650-660nm red, (1) 495nm cyan, (4) yellowish phosphor LEDs, (5) high cri 3000K white LEDs.


----------



## SemiMan (Dec 10, 2014)

Your CRI feeling is likely way way way way way way off.


----------



## Anders Hoveland (Dec 12, 2014)

News: Osram is now making a multi-emitter chip with 95 CRI. It appears 3 of the emitters are phosphor based, while the fourth is a red emitter. It is tunable from 3700 to 5000K CCT.



> When it launches the new Osram Ostar Medical, Osram Opto Semiconductors will be introducing the first LED component with a high color-rendering index (CRI) of 95 and the possibility of adjusting the temperature of the color white. This makes it ideal for medical applications – for instance in operating rooms, where a precisely controlled chromaticity coordinate and high natural color rendering are crucial.
> The new Osram Ostar Medical comprises four different LED chips in the colors warm white, ultra white, verde [green] and amber. This permits customers to set the shade of white emitted by the LED according to their individual requirements within a color temperature range of between 3,700 and 5,000 Kelvin – and at a high overall CRI of 95. This combination of precise chromaticity coordinate control and excellent CRI is particularly important for lighting in the medical sector. When optimized for the red spectrum (Ra​R9), the CRI remains at around 95 so that red shades are particularly true-to-life – ideal for light systems in operating rooms.
> 
> With a footprint of just 5.9 mm x 4.8 mm and a housing height of 1.2 mm, the design of the Osram Ostar Medical is very compact. Indeed, it is only about one-quarter as high as the components ordinarily used. The product owes its compact design to the flat, antireflex-coated glass cover with which the LED is equipped instead of the usual lens



http://www.ledsmagazine.com/article...ri-led-for-medical-lighting-applications.html


I think a design that would have given even higher CRI would have been for them to use amber phosphor, then a deeper red wavelength for the red emitter, rather than the orange-red used in such multi-emitters as the Cree TrueWhite or Osram's earlier Brilliant Mix design.
This would give exceptional red saturated R9 color rendering without loss of efficiency.


----------



## Esko (Dec 14, 2014)

Anders Hoveland said:


> News: Osram is now making a multi-emitter chip with 95 CRI. It appears 3 of the emitters are phosphor based, while the fourth is a red emitter. It is tunable from 3700 to 5000K CCT.
> 
> My guess is that, since one of those emitters use amber phosphor, the red emitter they are using is probably a deeper red wavelength, rather than the orange-red used in such multi-emitters as the Cree TrueWhite or Osram's earlier Brilliant Mix design.
> This would give them exceptional red saturated R9 color rendering without loss of efficiency.



The text you quoted says: white, ultra white, green and amber. The whites are phosphor based and the red emitter is amber, not deep red. You can find the data sheet here:

http://www.osram-os.com/Graphics/XPic3/00128048_0.pdf/LE ACWUWV S2W - OSRAM OSTAR Meidcal.pdf


----------



## Ken_McE (Dec 19, 2014)

If I understand, you are trying for otherwise high CRI light that cuts off sharply down around 400 or so nm? If you are having trouble using additive means to produce this light, you might also consider subtractive means. Find a theatrical lighting supply house. Look for gels that will block deep blue/violet. Those people have all kinds of neat stuff.


----------



## Anders Hoveland (Dec 19, 2014)

*Re: 98 CRI from BLUE emitter*

I was looking at the spectral graph of Cree TrueWhite. As I have mentioned previously, I have a 92CRI TrueWhite lamp, 3500K, to compare the light quality and color rendering for myself. I realized that the problem with TrueWhite technology is they are using a yellow-green phosphor. They could do better if their phosphor had a wider spectrum coverage. I am sure they are just using a yellow-green phosphor for simplicity, and perhaps maximum efficiency, but the deep green and cyan color rendering could be improved if they were using a more green-shifted phosphor. Yet, they cannot just shift the phosphor more green without adding yellow phosphor as well. I tried experimented with this, and just using green phosphor with red LEDs gives orange-tinted rendering to colors which are actually yellow, in addition to making skin tones appear too pinkish. (yellow phosphor emits plenty of orange wavelengths as well)

So Cree TrueWhite is really using a rather "low CRI" approach with the phosphor they are using. Of course, the design is not aiming for high CRI, higher CRI is only an additional effect of their high efficiency approach. 

This would apply to the Osram Brilliant Mix concept as well, which uses a yellowish-greenish "EQ-white" phosphor-converted LED with a 615nm amber LED.


----------



## Anders Hoveland (Dec 20, 2014)

Ken_McE said:


> If I understand, you are trying for otherwise high CRI light that cuts off sharply down around 400 or so nm?


To be specific, I am trying for high CRI light that cuts down below around 475-480nm, but which has _some _450-465nm, but completely cuts off below that.

440-465nm short-wavelength blue is a little harsh on my eyes, difficult to focus on, but the spectrum needs_ some _of it, otherwise everything seems to lack "definition", and deep blue indigo colors completely loose color saturation. I just do not want a big spike in this area of the spectrum. The other part is I seem to have a sensitivity to violet wavelengths, I am not sure exactly which wavelengths specifically, but I want to try to keep [nearly] all the output above 440nm.


----------



## Anders Hoveland (Dec 23, 2014)

The yellow phosphor LEDs have arrived. The overall color of the light it gives off appears to be more of an amber than a yellow, but it is still more yellowish than a 590nm LED. There is plenty of true-yellow color wavelength when looking at the spectrum with a diffraction grating, so I am assuming the overall color of the light is just more amber-colored than its true yellow peak wavelength. These things happen when one is not dealing with a distinct wavelength. Also, unlike my green phosphor LED, some of the blue wavelength from the emitter is getting through in these yellow ones. It appears to be a fairly short wavelength line, maybe 440 or 450nm, looking at the color, compared to the line in other white LEDs. While noticeable in the diffraction grating, it's not a large amount, because the rendering on blue colored objects still appears dark, just barely discernibly blue-tinted, mostly washed-out with the amber-tinted light.

But there is an interesting effect here. Skin tones are brightly illuminated. Skin might appear a little more yellow-tinted than ideal, but it is not greyish dead rendering appearance under a standard white LED. The type of yellowish LEDs I had before were actually sold as "general green", which makes me suspect the phosphor in those was probably a little more green-shifted. These gave skin tones the typical dead greyish appearance. If one looks at a spectral reflectance graph of [Caucasian] human skin, it really starts absorbing below ~585nm. So what might not appear to be a big color shift could really make a difference for color rendering. And as I mentioned before, I cannot just use a 590nm (amber) LED because that will throw off yellow color rendering.
So it appears yellow-amber phosphor is the way to go, I think this will combine well with a red LED.

I am assuming a standard (low-CRI) white LED, if it is not below 3000K, uses a greenish-yellow centered emitting phosphor, rather than amber-yellow.
Trying to get a proper spectrum and color rendering from a multi-emitter LEDs seems to be as much an art as it is a science.


UPDATE: I have also ordered some Oslon SSL 150 emitters, 4000K, 90CRI min - 96CRI typical (according to datasheet)
I plan to combine these into the multi-emitter array. Basically these ultra-high CRI white LEDs give off nearly perfect light, so why not start from there? Then I can add a little more longer wavelength blue, and just a little 660nm to improve red saturation just a little more. But of course, it will still take a little yellow and green to balance out the overall color. 

I knew the spectrum would need a little shorter wavelength blue, just for proper blue color rendering, but if I am going to add in 450-455nm blue, might as well be in the form of high CRI white LED, is what I am thinking. So using high CRI white LEDs as my base, I can "tweak" the spectrum (in a multi-emitter array) to get it just perfect.


----------



## SemiMan (Dec 23, 2014)

Anders since you are enjoy this why don't you download the Osram color mixing tool and learn how to convert a graph into a spectrum and load it into the tool. You will be able to do the analysis in a 10th of the time, know the CRI and can let the tool optimize for you.

Trying to do this on the bench without proper tools is fruitless. Even with a spectrum analyzer it is not easy.


----------



## Anders Hoveland (Mar 25, 2015)

WeLight said:


> but consider PC Amber, it has a broad coverage


Yes, I think you are right on here. That is why I ordered some Osram Signal Series LCY CLBP ceramic yellow emitters, they looked like the most yellowish of the PC-amber emitters I could find, at least from the spectral graphs I saw on the datasheets.




WeLight said:


> We use a min of 15 to get to 97/98


That seems very interesting. Do you have any more information about this? Who were you referring to when you said "We" ?


----------



## Anders Hoveland (Apr 10, 2015)

I wanted to share a little tool I discovered. If you want to simulate how the spectral graph would look by combing different LEDs.

First, find a free online graphing calculator application. Type in the following equation:

y=150/e^(x/30-19.666)^2+200/e^(x/50-10.6)^2+100/e^(x/7-70.428)^2+100/e^(x/7-68.587)^2+100/e^(x/7-94.285)^2

Now graph it. You might have to zoom out and then focus in on the 400-700 region on the x-axis. This corresponds to wavelength (in nanometers).

So what do all these numbers mean? I will break it down. y=1/e^x^2 is basically the equation for a single sinusoidal wave.
Change the first number to increase amplitude of the function, making it taller. For example, 5/e^x^2
Want to stretch the function and make it wider? simply substitute out x with x divided by a constant, 1/e^(x/5)^2
Want to move the function to the left or right, such as to make it correspond to the wavelength value you want? If you want to move the function to the right (increasing wavelength), subtract that amount from x. 
For example 1/e^(x-500)^2
Now what about stretching the function _and_ shifting it to the right? For that you will have to subtract the wavelength value first, then divide by the constant you wish to stretch. (x-500)/5
You will likely have to manually distribute this out first, x/5-100, then substitute this value in for x, which in this example would be 1/e^(x/5-100)^2
Unfortunately many online graphing applications will not let you use parenthesis inside parenthesis. 
And lastly, to combine different functions together, simply add them. (you can simply cut and paste if you do not want to have to type out everything each time)

The above equation
y=150/e^(x/30-19.666)^2+200/e^(x/50-10.6)^2+100/e^(x/7-70.428)^2+100/e^(x/7-68.587)^2+100/e^(x/7-94.285)^2
basically simulates the combination of a 482nm blue LED, a 530nm centered green phosphor, a 590nm centered amber phosphor, a 493nm cyan LED, and a 660nm deep red LED. It is basically equivalent to a simulated spectral graph.


One of the interesting things I was able to see is that the wavelength distribution of one source is actually able to shift the peak wavelength of another source to some degree.
For example, y=150/e^(x/30-19.666)^2+200/e^(x/50-10.6)^2, which basically simulates a 530nm-centered LED phosphor and a 590nm-centered phosphor combined together. The peak of the phosphor hump is able to shift to 580nm (which is much more yellow).


One last tip, if you are having trouble conveniently copying and pasting the equations from this post, you might try clicking "reply with quote", and then copying from there.


----------



## idleprocess (Apr 14, 2015)

Anders Hoveland said:


> I wanted to share a little tool I discovered. If you want to simulate how the spectral graph would look by combing different LEDs.
> 
> First, find a free online graphing calculator application. Type in the following equation:


Why not build formulas for a more useful analysis tool, such as Excel?


----------



## SemiMan (Apr 14, 2015)

Or use Osram's color tool. I provided a link to Anders for it a while back.


----------



## Anders Hoveland (Apr 15, 2015)

SemiMan said:


> why don't you download the Osram color mixing tool and learn how to convert a graph into a spectrum and load it into the tool. You will be able to do the analysis in a 10th of the time, know the CRI and can let the tool optimize for you.


After playing around with that color tool, I was able to get a spectrum that the calculator characterized as 97 CRI at 3627K:

14 lumens 505nm verde
28 lumens 540nm green
25 lumens 605nm amber
10 lumens 650nm deep red
300 lumens 4000K white (85CRI)

And I got a 97 CRI, 4000K spectrum:

2.52 lumens 482nm blue
17 lumens 505nm verde
29 lumens 540nm green
15 lumens 605nm amber
9 lumens 650nm deep red
275 lumens 4000K white (85CRI)

After some more tweaking, I was able to get 98 CRI at 4000K:

32.9 lumens 505nm verde
14 lumens 540nm green
7.4 lumens 615nm amber
13.7 lumens 650nm deep red
460 lumens 4000K white (85CRI)

I do not think trying to achieve 98 CRI with this setup in real life would be practical though. It was very difficult to get it to 98 CRI, with the exact right color tint. Even a small change in exact wavelength value or mixing ratios throws the CRI back down to 96 or 97. I could get a higher R9 value if I used a 503nm verde wavelength instead of 505nm, used a little less deep red and a little more amber instead.

Using the following I can manage to get 98 CRI at 4023K, with an R9 value at 98 (but just barely)

504nm 28 lumens
540nm 14 lumens
615nm 5.6 lumens
655nm 12 lumens
4000K 460 lumens


----------



## Anders Hoveland (Apr 15, 2015)

Coltrin and researchers found that it is theoretically possible to synthesize a combined light source achieving 408 lm/W with a color rendering index in excess of 90 using four discrete wavelengths. The wavelengths are 463nm blue, 530nm green, 573nm yellow, and 614nm reddish-amber. Unfortunately they noted that there currently does not exist a 573nm yellow LED, or anything in close proximity, which could adequately satisfy the exact requirements for this particular wavelength.

_Limits on the maximum attainable efficiency for solid-state lighting
Michael E. Coltrin, Jeffrey Y. Tsao, Yoshi Ohno
Sandia National Laboratories, USA_


----------



## SemiMan (Apr 15, 2015)

Anders Hoveland said:


> The tool is a little frustrating because it does not offer the flexibility I would like. It only allows the addition of one specific LED wavelength within any given color range.



- Actually you can load in full spectrums and mix them arbitrarily


----------



## hakkikt (Aug 1, 2015)

*Oslon color tool*



SemiMan said:


> - Actually you can load in full spectrums and mix them arbitrarily



To get spectra from the datasheets I found this site to be quite useful
http://arohatgi.info/WebPlotDigitizer/app/

That Osram color tool you pointed out is really neat. After loading a few spectra from various datasheets I got some rather interesting results. For example the Nichia 219B 92CRI can be made to give 99CRI and 99R9 by adding 1.7% 475nm or 2.4% 482nm blue 4% 505nm verde and 0.1% 660nm red and the CRI was surprisingly tolerant of variation. Another nice one was the Oslon P5 93CRI with the Luxeon Lime and 4 other colors which gave a mix almost indistinguishable from sunlight at 4000k. It turns out Osram sells individually specified blue bins so you can get the 461 and 482 centered DWL bins needed to completely fill the phosphor gap.


----------



## Anders Hoveland (Aug 2, 2015)

*Re: Oslon color tool*



hakkikt said:


> It turns out Osram sells individually specified blue bins so you can get the 461 and 482 centered DWL bins needed to completely fill the phosphor gap.


Osram sells specified blue bins? Could you please supply a link to where one could buy these?
I was only aware of Cree selling specified blue wavelength bins. 

I really miss those old Philips Luxeon Bin 6 blue LEDs, but unfortunately these have long since been discontinued. At 485-490nm, the color was the closest to the blue side of cyan you have ever seen, despite LEDs putting out so few lumens back then. But this is a different story.


----------



## hakkikt (Aug 7, 2015)

*Re: Oslon color tool*



Anders Hoveland said:


> Osram sells specified blue bins? Could you please supply a link to where one could buy these?
> I was only aware of Cree selling specified blue wavelength bins.
> 
> I really miss those old Philips Luxeon Bin 6 blue LEDs, but unfortunately these have long since been discontinued. At 485-490nm, the color was the closest to the blue side of cyan you have ever seen, despite LEDs putting out so few lumens back then. But this is a different story.



Sorry, my mistake, I missed the fine print in the datasheet where they say you can't order a single wavelength bin. The main text said they will only ship one bin per packing unit. There goes that idea, only two of their bins are really useful and they pick a random one from four which means a 50% chance of getting something useless. I'd be OK with either bin 4 or bin 5 of the Rebel Blue but 5 would be easier to work with or the upper half of the Cree blue range. My goals are a little different from yours since I'm willing to accept more in the blue end, my main need is a reliable source between 475 and 485nm DWL with a preference for 480nm. That mixes very well with the 505nm from Osram or Lumileds to fill the hole between pump and phosphor.

Another idea I explored with that tool is the use of dichroic filters to reduce the blue output. I found that you only lose about 1lm/W by cutting 50% of the pump blue from a 4000k mix. This may be of interest to you although it seems to be hard to get dichroics cheaply unless you are willing to order entire production runs.


----------



## Anders Hoveland (Aug 7, 2015)

*Re: Oslon color tool*



hakkikt said:


> My goals are a little different from yours since I'm willing to accept more in the blue end, my main need is a reliable source between 475 and 485nm DWL with a preference for 480nm.


If I can make a recommendation, the Cree "Blue XP-E 470nm~485nm" emitters being sold on ebay appear to actually be a 475-480nm bin.



hakkikt said:


> That mixes very well with the 505nm from Osram or Lumileds to fill the hole between pump and phosphor.


Filling that gap in the spectrum may not be as desirable as you think, or at least you might want to be careful exactly_ how _you fill in that gap.
The 450-455nm pump wavelength was chosen for a very specific reason. If you start adding in something like 470nm it can start throwing off the R12 color rendering, and deep blues will not appear as saturated.

I have done much experimentation, and adding in some 480nm or 495nm can help make the light feel more 'natural' and visually more 'in-focus'. 470nm is still too short of a wavelength, and I can tell you this because I have some unusual chinese whitish-phosphor LEDs that use a 470nm pump, and although it feels better, the light still does not feel how I would like. Keep in mind this is _only_ using 470nm for the blue in the spectrum.

I have also experimented combining several cyan 490-495nm bin emitters with just a little 470nm blue, and the combined light (which is very greenish-cyan in overall color) _still_ does not feel as soft as the light from a 480-485nm bin emitter. That indicates to me that the optimal spot is really somewhere in between 475-490nm. It does not need to be all long-wavelength blue light. In my experiments, I have found that even just adding in a very small amount of normal 450nm LED light greatly improves the blue color rendering saturation, whereas if you only use all >470nm in the spectrum, the blues are going to look very dull.

My theory is that the most optimal spectrum will have the normal 450nm blue spike, but then it will also have a smaller 480-490nm azure blue spike. According to my theory, it is important that there be a narrow gap between the 450nm and the 480nm. This will allow the 450nm to more accurately render deeper blue color hues, without too much interference from the longer blue wavelengths. In other words, a gap in the spectrum is still important for color rendering (if we are not going to include shorter ≤440nm wavelengths), but we can_ narrow _this gap to allow the light to feel more natural. Lastly, we can then counter-balance this smaller 480-490nm azure blue spike with 505nm, so the teal colors will be well-rendered (and not too blue-shifted).

When we use a violet pump with blue LED phosphor we could avoid all these worries because the blue light generated from phosphor is so broad-spectrum, but I really do not feel all these shorter wavelengths are the most optimal for artificial lighting that people are going to be under all day, and I in particular have a sensitivity to them. If you want to look at it this way, blue phosphor is the "easy way" out, and it also comes with an inherent sacrifice in efficiency. White LED light that uses a blue phosphor does definitely feel very natural though, I can verify that.

[h=3][/h]


----------



## hakkikt (Aug 7, 2015)

*Re: Oslon color tool*



Anders Hoveland said:


> If I can make a recommendation, the Cree "Blue XP-E 470nm~485nm" emitters being sold on ebay appear to actually be a 475-480nm bin.


I bet they are, that's the upper half of the Cree XPEBL...05 order code, I doubt there are any 485nm emitters in the lot but there might be a few 470s if I've read the binning and labelling document correctly and Cree doesn't do single bin reels. After some more fiddling around I found that I can use nearly any LED in this order code and still stay at a CRI of 96-99 for my whole CCT range.



Anders Hoveland said:


> Filling that gap in the spectrum may not be as desirable as you think, or at least you might want to be careful exactly_ how _you fill in that gap.
> The 450-455nm pump wavelength was chosen for a very specific reason. If you start adding in something like 470nm it can start throwing off the R12 color rendering, and deep blues will not appear as saturated.


Indeed, this has been a subject of exploration for me, one of my goals is to not reduce any metric from the base Nichia 219B. So far my best 3 LED result that survives bin variation is 98-99CRI/98CQS with 99 R9 and 89-91 R12 at 4000-4100K using a Nichia 3500K as a base white, 478+-5 DWL center +503-5 DWL center. As I drop the color temperature on this to 3300K (need to add a deep red led to maintain CRI below 3700k) R12 drops to 83 which is still better than the native 76. Assuming decent mixing, above 3400K this is better in every way than the Oslon LCW-CRDP 97CRI although they only publish the 3200K spectrum which seems almost totally resistent to CRI improvement or CCT alteration. 

I'm hunting down spectra for the other 90+ CRI leds and not having much luck, Osram and Nichia are the only ones I can find who publish them. When I can buy an XHP35 90+ I'll get one and start looking for someone to run a spectrogram of it unless Cree breaks tradition and puts one in the datasheet. I eagerly await the release of the 219C-R90-E to see what performance improvements that brings and if they have changed the phosphor from the B model.



Anders Hoveland said:


> I have done much experimentation, and adding in some 480nm or 495nm can help make the light feel more 'natural' and visually more 'in-focus'. 470nm is still too short of a wavelength, and I can tell you this because I have some unusual chinese whitish-phosphor LEDs that use a 470nm pump, and although it feels better, the light still does not feel how I would like. Keep in mind this is _only_ using 470nm for the blue in the spectrum.
> 
> I have also experimented combining several cyan 490-495nm bin emitters with just a little 470nm blue, and the combined light (which is very greenish-cyan in overall color) _still_ does not feel as soft as the light from a 480-485nm bin emitter. That indicates to me that the optimal spot is really somewhere in between 475-490nm. It does not need to be all long-wavelength blue light. In my experiments, I have found that even just adding in a very small amount of normal 450nm LED light greatly improves the blue color rendering saturation, whereas if you only use all >470nm in the spectrum, the blues are going to look very dull.
> 
> My theory is that the most optimal spectrum will have the normal 450nm blue spike, but then it will also have a smaller 480-490nm azure blue spike. According to my theory, it is important that there be a narrow gap between the 450nm and the 480nm. This will allow the 450nm to more accurately render deeper blue color hues, without too much interference from the longer blue wavelengths. In other words, a gap in the spectrum is still important for color rendering (if we are not going to include shorter ≤440nm wavelengths), but we can_ narrow _this gap to allow the light to feel more natural. Lastly, we can then counter-balance this smaller 480-490nm azure blue spike with 505nm, so the teal colors will be well-rendered (and not too blue-shifted).



This is the approach that brings me the most success with the tool and I'm glad your experiments give this a positive visual and comfort check. I noticed both the CRI and CQS swatches lack a cyan patch so I created a couple of crude ones (broad and narrow centered between 485 and 490nm) that I use to validate and direct my search away from mechanistic local optima. It's easier to get higher CRI and gamut values by sacrificing this zone but like you I think it's a mistake. I'm undecided about including true violet, I'll only include it if I can see a clear benefit that outweighs the cost and damage potential. 



Anders Hoveland said:


> When we use a violet pump with blue LED phosphor we could avoid all these worries because the blue light generated from phosphor is so broad-spectrum, but I really do not feel all these shorter wavelengths are the most optimal for artificial lighting that people are going to be under all day, and I in particular have a sensitivity to them. If you want to look at it this way, blue phosphor is the "easy way" out, and it also comes with an inherent sacrifice in efficiency. White LED light that uses a blue phosphor does definitely feel very natural though, I can verify that.


The efficiency drop for violet pumped and availability have held me back, my mix is 92-96lm/W after accounting for system losses and the best I can see from Xicato and Soraa is 75lm/W but the real problem for me is I want to make a linear fixture which is a PITA with COB modules or prepackaged spot. A violet LED pumping just a blue phosphor along the lines of the lime and amber chips would be very interesting to me as an experimental device.


----------



## Anders Hoveland (Aug 7, 2015)

*Re: Oslon color tool*



hakkikt said:


> I'm undecided about including true violet, I'll only include it if I can see a clear benefit that outweighs the cost and damage potential.


Personally I do not believe adding 400-405nm would do virtually anything for CRI. It would be more the 420-440nm wavelengths that would make a difference for royal blue/indigo color rendering. What 400-405nm does do, however, is activate optical brighteners in white clothing and paper, causing them to appear a brighter whiter color. 

Though I think Philips found that even 430nm is a short enough wavelength to activate optical brighteners, they are supplementing with this wavelength in their CrispWhite technology LED lamps designed for retail.

It's not that 420nm is any more "blue" than 440nm, but the R-cone color receptors in the eye (the ones that see red) have some overlapping sensitivity at these short wavelengths, which is why violet appears "purple" colored (blue+red), if anyone was curious. For color rendering purposes, this is a very subtle effect and I do not think all but the most discerning eyes would be able to tell the difference between white LED light supplemented with 420nm emitters compared to those supplemented with 440nm emitters. I will mention here that I have some athletic pants that look a slightly brighter slightly purplish-colored hue under fluorescent light but just look like a very dark plain blue under the light from an LED lamp; under natural sunlight the color appears in the middle. 
I do not want anyone to have the wrong idea here however; In terms of trying to increase the CRI rating (even just from 97 to 98), using 420nm versus a 440nm emitter is going to make absolutely no difference.

I feel though that I might be getting a little off-topic here, because I was originally trying to focus the discussion on achieving super high CRI light (which also feels soft on the eyes) that _*does not *_contain shorter wavelengths.


----------



## PlantLEDGuy (Aug 7, 2015)

Philips is selling PAR38 lamps that use this trick to excite fabric whiteners- works great.


----------



## hakkikt (Aug 8, 2015)

*Re: Oslon color tool*



Anders Hoveland said:


> Personally I do not believe adding 400-405nm would do virtually anything for CRI. It would be more the 420-440nm wavelengths that would make a difference for royal blue/indigo color rendering. What 400-405nm does do, however, is activate optical brighteners in white clothing and paper, causing them to appear a brighter whiter color.
> 
> ...
> 
> I feel though that I might be getting a little off-topic here, because I was originally trying to focus the discussion on achieving super high CRI light (which also feels soft on the eyes) that _*does not *_contain shorter wavelengths.



I was thinking of a few mw of 415-425 DWL which provides violet to indigo. This increases R12 slightly but otherwise doesn't affect CRI and is good for fluorescence. 430nm is the key DWL for good R12.

Yes, lets not derail your topic. My main reason for posting here was to thank SemiMan for the link and offer a way to load spectra from datasheets. I'll post any other thoughts on this in your new topic where this discussion is more appropriate.


----------



## Anders Hoveland (Aug 9, 2015)

*Re: Oslon color tool*



hakkikt said:


> The efficiency drop for violet pumped and availability have held me back, [...] A violet LED pumping just a blue phosphor along the lines of the lime and amber chips would be very interesting to me as an experimental device.


I very much agree. If they could make a blue phosphor-converted LED, that would be very interesting.

In particular I was think along the lines of using a 430nm emitter with a cyan blue phosphor centered around 475-500nm, that only allows a negligible amount of 430nm to get through. This could then be used in a tricolor approach to make white light. There would be a regular 450nm using more typical LED phosphors, and then there could also be a red LED emitter to efficiently generate some deeper red wavelengths in the spectrum for a high R9a value. The three emitters could even be combined onto the same small chip. This would be more efficient, because it does not make sense to have to use the shorter violet/indigo wavelength to fluoresce greenish to orange LED phosphors. And if some of the 450nm directly from the emitter could contribute to the spectrum, that would help raise efficiency as well, even if there was a little spike in the spectrum.

The 450nm phosphor-converted LED would probably have to use a custom phosphor formulation though, to be optimally designed to coordinate with the other wavelengths. By itself, the color of light would probably be somewhat greenish-white, but it would have a broader spectral coverage than the single phosphor used in Osram's EQ-white emitters.


----------



## Anders Hoveland (Aug 10, 2015)

*Re: Oslon color tool*

Actually a phosphor-converted blue LED could be important for colored stage spotlights and nightclub lighting. 
I have noticed that all the other colored LED spotlights look just fine, but the light from the blue colored ones has a very different feel from the old blue spotlights that used incandescent bulbs with filters. The blue LEDs they are using now do not work so well for stage lighting, in my opinion; they work better for decorative background accent lighting, not as the main lighting. 

Generating the blue light through phosphors might help the light feel more 'natural', like the old filter lights, and perhaps help improve the color rendering appearance as well. Instead of the blues all appearing a monotone hue, it could bring out the subtle contrasts between cerulean blues and deeper indigos in costumes.


----------



## hakkikt (Aug 15, 2015)

*Re: Oslon color tool*

I don't know if you have seen this paper http://www.journalofsolidstatelighting.com/content/pdf/2196-1107-1-6.pdf but there are two known phosphors in the blue-cyan range, Sr0.25Ba0.75Si2O2N2 (orthorhombic) and BaSi2O2N2, both of which are too narrow to fill the gap on their own but it may be possible to combine them for good coverage. For the stage lighting application you mention this may serve quite well, for general white light the paper concludes that they are not useful due to the efficiency loss from pumping the longer wavelength phosphors from a UV source.


----------



## JoakimFlorence (Jul 2, 2016)

*Re: Oslon color tool*

I was playing around with the color calculator tool and noticed that, for lower color temperatures, it is important that the red emitter be a longer wavelength if we are trying to achieve maximum CRI. 635nm red seems to be the optimal wavelength to supplement a 4000K LED, but for 2700-3000K, 650nm red gives the best results. I am assuming that this is because a regular 2700K LED already has so much orange wavelength intensity in its spectrum, it really takes some deep red to compensate for this.

Unfortunately the color tool does not have any 3000K LED option to add into the spectrum so I had to improvise. 275 lumens of 2700K and 125 lumens of 4000K seems to be about equivalent to 3000K. By itself, just the 2700K and 4000K together give a CRI of 84.

Here is the combination I used:

2700K 275 lumens 
4000K 125 lumens
520nm 30 lumens
650nm 16 lumens

This resulted in a spectrum with the following properties:
2985K, 98 CRI, 99 R9 (red saturation), R12 still only 83


----------



## JoakimFlorence (Jul 2, 2016)

*Re: Oslon color tool*

This blog has an interesting discussion about the challenges of color tunable LED designs with multi-wavelength emitters:

http://agi32.com/blog/category/interior_lighting/


----------



## CuriousOne (Jul 5, 2016)

*Re: Oslon color tool*

Too bad I noticed this thread too late.

I've also tried to build such led array. But I have spectrophotometer, so I can control component intensity and wavelength with higher precision. No matter how much leds you gonna try, you will still have gaps and peaks, which will give you weird results. For example, one of my test systems consisted of 200 pcs of 5mm leds, with 12 different wavelengths. The intensity and spectral response was matched to 3000K halogen bulb as much as possible. It was quite good, but various items behaved strangely, under this light. For example, my orange-ish yellow Dewalt power tool was very bright orange, while normal, yellow lemon looked more like lime. After many many $$$ and hours spent, I came to conclusion, that Cree TrueWhite is so far the best available, and produces as much accurate color rendering as possible. Tests were finished in 2015, so I think, nothing new being introduced since then. I can try to dig and find my records, if someone interested.


----------



## JoakimFlorence (Jul 5, 2016)

4131K, 97 CRI, 99 R9 (red saturation), and perfect color balance
overall a very good spectrum

4000K 400 lumens
635 nm 15 lumens
520 nm 35 lumens
484 nm 6 lumens


4051K, 98 CRI, 99 R9 spectrum 
(spectrum shows low tolerance for any variation in the red, causes CRI to drop down to 97 )

4000K 460 lumens
648 nm 12.75 lumens (or 652 nm 12 lumens)
614 nm 8 lumens
520 nm 46 lumens
485 nm 4 lumens


----------



## NICHIRENSHU (Jul 6, 2016)

*Re: Oslon color tool*



CuriousOne said:


> Too bad I noticed this thread too late.
> 
> I've also tried to build such led array. But I have spectrophotometer, so I can control component intensity and wavelength with higher precision. No matter how much leds you gonna try, you will still have gaps and peaks, which will give you weird results. For example, one of my test systems consisted of 200 pcs of 5mm leds, with 12 different wavelengths. The intensity and spectral response was matched to 3000K halogen bulb as much as possible. It was quite good, but various items behaved strangely, under this light. For example, my orange-ish yellow Dewalt power tool was very bright orange, while normal, yellow lemon looked more like lime. After many many $$$ and hours spent, I came to conclusion, that Cree TrueWhite is so far the best available, and produces as much accurate color rendering as possible. Tests were finished in 2015, so I think, nothing new being introduced since then. I can try to dig and find my records, if someone interested.



Yes please this is interesting. So you are saying that there is no need to add different colors if our goal is only color rendering. Just Cree true white and there is no practical need for other leds.



JoakimFlorence said:


> 4131K, 97 CRI, 99 R9 (red saturation), and perfect color balance
> overall a very good spectrum
> 
> 4000K 400 lumens
> ...



Have you try this is in real or this is simulation?


----------



## CuriousOne (Jul 7, 2016)

*Re: Oslon color tool*

I'd like to say, that fighting for the perfect spectrum line is not a good idea, since we don't have all required wavelength sources, and gaps and peaks in existing ones render some objects weird. So if you look at Cree TrueWhite spectrum, it looks weird, but in real life, it produces most pleasant, and similar to halogen bulb illumination colors.


----------

