# Red or red-orange for increasing CRI?



## lolzertank (Jul 12, 2009)

Is it better to use red or red-orange LEDs to increase the CRI of a cluster of neutral white LEDs? I will be using Rebels, which are 100 lumen at 350ma whites, 50 lumen at 350ma red-orange and 30 lumen at 350ma reds. They will all be driven at 700ma. Also, what proportion of red/red-orange to white should I use?

Thanks!


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## jtr1962 (Jul 12, 2009)

White LEDs are most deficient in deep reds, so red will best fill in this deficient part of the spectrum. As for the amount, you have to experiment a bit but offhand I'd say one red to 4 or 5 whites (assuming all are driven at the same current). Because the addition of red might make the light slightly pink, a small amount of cyan will offset that (and also compensate for the other area where whites are lacking-the valley in the ~500 nm region).


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## lolzertank (Jul 13, 2009)

Thanks! From your advice, I think I'll put 9 white, 2 red and 1 cyan in my cluster.


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## jeffosborne (Jul 13, 2009)

Hey lolzertank, you have my attention! I am preparing to make a photography flood light with 9 neutral white Rebels, too! The 100-lumen parts I got recently from Future Elec. are, unfortunately, the coolest bin code they offer, so I will use the 90-lumen parts, which are a little warmer. I also have my cyan and red Rebels ready to go, 2 and 1, as you mentioned.

I plan to make a tripod-mountable enclosure built around a penium-4 heatsink and fan, and a home-made driver to drive 3 LEDs in series x4, and use a 12 volt power supply or 10.8 volt lithium battery pack. I will be trying various diffusers to complete the light.

Do you have heatsink and driver in mind?

Cheers,
Jeff O.


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## lolzertank (Jul 13, 2009)

I'm going to be using it in a Mag on 2x18650, so I'm just going to use a bunch of AMC7135s and Download's Multi-sink. I wanted to do a triple MC-E/P7, but the P7 only comes in cool white and the MC-E is less efficient than the Rebels for neutral white. At first, I was going to use 12 neutral Rebels, until I thought that since I'm using so many emitters anyways, I could go for some color mixing. 

Sorry to hear that you lost the Luxeon lottery. Did you at least get something on the black body line?


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## HarryN (Jul 13, 2009)

Hi, if you are going to this much bother, perhaps there is a more simplistic approach- just use single color LEDs and mix them in the first place.

I am a big believer in 6 color mixing, nominally 
450/460nm - strongly blue
488nm - kind of a torquoise / ghost like color
505nm - traffic green
525nm - amber
620nm - approx red / orange
650nm - fairly deep red

488 can be tough to get, so often, people just double up at 505 to get enough green into the light. The other challenge is that red and r/o rebels cannot handle the same current as the others, so you either need to double these up in parallel, or use Lux IIIs.

If you put these into two strings of similar Vf, then a 12 volts source and resistor would work, or a buck puck.


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## lolzertank (Jul 13, 2009)

Hm... doesn't that configuration kind of kill efficiency thanks to the relatively low efficiency of green?


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## JohnR66 (Jul 13, 2009)

Cree uses a mixture of red and yellow LEDs in their lighting fixture to obtain a claimed CRI of 90 or more. Of course It depends on the color temp of the main white LED used too.
http://www.creeledlighting.com/lr24.htm


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## HarryN (Jul 13, 2009)

lolzertank said:


> Hm... doesn't that configuration kind of kill efficiency thanks to the relatively low efficiency of green?



With LED lighting, it is always a trade off between good coverage of the spectrum and lumens ratings. LEDs are the most energy efficient (relative to an incan) in single color applications, such as a stop light.

CRI is a rating of how the spectral output of a source is relative to a fairly warm color temp incan bulb. (incan bulb = 100, everything else is worse) When you start getting closer to simulating the very broad spectral output of an incan bulb, the incan starts looking more efficient relative to LEDs than we like to imagine. A good example is the Lumileds Lux I warm white - it is virtually an exact spectral copy of the visible light of an incan, and its efficiency is very low.

In photography, the historic "white color standard" was the sun, so a color temperature of around 5,000 K. The CRI of the sun is actually lower than an incan bulb too IIRC, but most people dont' notice.

With digital cameras, the sensors are often have relatively narrow sensitivity to specific RGB colors, although some also have a cyan signal. This means that for digital photo use, you could potentially get away with a really mediocre RGB setup.

Yes, with RGB, you often have to double up the green. 

Lumileds made countless presentations for years at seminars trying to get them to see the advantage of RGB and other multi color LED mixing vs. white, both from an efficiency and lifetime perspective. Pretty much no one listened, so they put a lot of effort into white, just like everyone else. You will notice that most LED backlit TVs are RGB, not back lit with white. There are reasons for that - the TV makers understand the point.


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## lolzertank (Jul 13, 2009)

No, what I was trying to say was that green LEDs just don't produce very many photons. New blue LEDs convert 40% of their energy into photons, but green LEDs are stuck at about 10%. Even if phosphors are only 50% efficient, it's still more efficient to produce green through blue + phosphor. The narrower band of a true green LED obviously doesn't matter to me since I'm trying to get white light. Amber is similar in this respect as well, which is probably why Lumileds made the phosphor converted amber that stomps old amber LEDs despite needing phosphors on top of a blue die. 

If green LEDs were as efficient as blue, then I would certainly go with your solution. But until the 250 lumen at 350ma green LEDs come out, I don't think RGB will be a efficient solution.


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## HarryN (Jul 14, 2009)

LEDs specs are always on the move, esp. in the green area. Because of the nature of how LEDs are made, actually some equipment is more suitable for making green LEDs than others. Lumileds "just happens" to own that kind of equipment.

I double checked the spec for rebels, and interesting, if you compare the lumens at 700ma for neutral white, green, cyan, and amber, the posted lumens numbers are all within 10%. This makes at least the RG portion of RGB quite viable. 

http://www.philipslumileds.com/products/luxeon/luxeonrebel

I think the amber rebels from blue converted phos have more to do with the exceptional difficulty of making good AlInGaP based amber, then a fundamental problem making good InGaN based green. It also allowed PL to have similar electrical, mechanical, and optical specs for nearly all of the rebels now.

PL is so strong technologically in AlInGaP red that normally I would not expect them to make the red and red/orange from blue + phos, but stranger things can happen. IF they do it, it will have more to do with making the rebel line "all similar" than a real improvement in efficiency, IMHO.


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## lolzertank (Jul 14, 2009)

Here's what 2xTrinity said about green's weakness in RGB lighting. I just realized I'm trying to say pretty much the same thing, just minus the physics.  Using 6 colors will have this problem too, since the proportion of green to other colors will have to remain the same.

I realize that your solution will probably have higher CRI than mixing neutral white, cyan and red LEDs, but in a flashlight with limited battery power, efficiency is still pretty important and I don't want to throw all of it away for CRI. Something better than 70 is good enough for me. I'll make a Mag623 if I ever get tired of LEDs.


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## lolzertank (Jul 24, 2009)

Ok, so I built the Mag. Wow, colors outside look awesome. Trees actually look like what they look like in daylight. I'm coming from nasty WC tint Crees and dim/orange 6D Mags. There's a LOT of cyan, I even had to put some "transparent" tape over the optic to diffuse it a little. The neutral white LEDs were SM tint. I tried covering the cyan and red which dulled up the color quite a bit.


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## jtr1962 (Jul 27, 2009)

You mentioned earlier that you used 9 white, 2 red, and 1 cyan. How is the white balance? And are you driving all the emitters at the same current?

I think I might make a desk light or reading light based on a similar combination of white, red, and cyan. I've already played around with red, green, blue, and amber rebels to get a variable CCT light source. I use dip switches to set the CCT in 9 steps from 1900K to 9300K. Color rendering is fantastic compared to white emitters, but of course efficiency isn't too great.


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## jeffosborne (Jul 27, 2009)

Hey lolzertank, we would love to see a photo of your modified light. Also, beam shots are good!

Thanks,

Jeff O.


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## lolzertank (Jul 27, 2009)

The red is being driven slightly lower than the rest, around 500ma. The rest of the emitters are at 700ma. There's a lot of cyan, much more than is needed. Also, the triple optics aren't perfectly aligned into one hotspot causing one corner to be very green. You probably won't have that problem if you aren't using narrow optics like me. Covering the optic of the cyan with some tape to diffuse it solved both problems pretty well. Still a bit cyan on the edges though, not a big deal to me. I'm not really a white wall hunter.


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## Gryloc (Jul 27, 2009)

Just out of curiosity, how much does the increase in CRI affect efficiency so much when adding red or cyan emitters into the mix? Lumens are lumens, so when you have so many lumens in white, then you add more colored light, the total output does increase.

Lets say we have a cluster of 6 emitters using the best that the Rebel line offers. This is assuming that the colors mix to provide a slightly warmer white than with the bare cool white emitters alone. I have not had a chance to mix the colors in the below example, so I am not sure if the ratios will work out okay to get a balanced neutral or warm colored light.

```
In series at 350mA:
4 White     100lm    3.15V    1.103W    90.66lm/W
1 Cyan       70lm    3.15V    1.103W    63.46lm/W
1 Red        40lm    2.90V    1.015W    39.41lm/W
--------------------------------------------------
6 Total     510lm   18.65V    6.530W    78.10lm/W

In series at 700mA:
4 White     180lm    3.40V    2.380W    75.63lm/W
1 Cyan      130lm    3.40V    2.380W    54.62lm/W
1 Red        85lm    3.60V    2.520W    33.73lm/W
--------------------------------------------------
6 Total     935lm    20.6V    14.42W    64.84lm/W
```
Sure, efficiency takes a direct hit, but in these cases, the resultant efficiency does not seem that bad for a small improvement in color rendering. Even Lumiled's new CCT/CRI binned Rebels with higher CRIs have efficiencies in this range at only 350mA. I am not sure of the efficiencies of the high CRI Seoul emitters out there.

My quad TFFC K2 0200 Mag produces 900 lumens (4 * 1.125 * 200lm @1.2A) and consumes 16.32W (4 * 3.4V * 1.2A). My lumen figure is based off of Lumiled's datasheets, and the forward voltage of my K2 emitters are based on actual measurements. These relatively modern, and slightly warmer tinted cool white emitters are operating at 55.15lm/W to produce what appears to be a splendidly bright beam. Even though 0200 binned TFFC K2s are not that amazing in terms of performance to many here (I know there are better performing parts out there), in my case, they do perform very nicely. However, the efficiency is still far below that of the 6 above Rebels operating at lower current.

Can you guys please produce a simple chart showing known good ratios of lumens of each color required to get a few known CCT whites using white, red, and cyan, or maybe other colors? That would be extremely useful and helpful in future projects! From a ratio of required lumens of each color, we can determine the proper currents from each of our emitters to get a white color on that is close to blackbody line. Thanks!

-Tony


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## LEDAdd1ct (Jul 27, 2009)

Beamshot?


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## lolzertank (Jul 27, 2009)

The camera won't be able to show the CRI increase very well thanks to only having RGB filters on the sensor. Not to mention white balance totally messing everything up and the necessity for a calibrated screen to accurately show colors.  I also don't have anything good to compare it to. Well, unless you want to see this ~1900 lumen monster against a 10 lumen Fenix E01 and its angry blue/purple tint. Now I wish I didn't lose that Cree XR-E DIY kit with all it's WC tint glori/ugliness... 

The beam is extremely floody though, about 40 degrees from edge to edge. There's spill, but it's really not that useful since the hotspot is so wide. It doesn't actually look THAT bright until you think how wide the beam is. It has about the same throw as a TK10 after all.

The Fedex truck delivered the LEDs to me the day before Lumileds decided to put the high CRI Rebels on their website.  My sig became real, just with CRI instead of flux.

Gryloc, your mixes have way too much cyan. 1/4 of the amount would be enough, or else your light will start looking like a traffic light. That should help efficiency a little. You could also use the neutral white emitters which would give a lot more red and green.

I think the neutral white high CRI P4s are 72 lumens at 350ma. They have a higher Vf than the Rebels too, 3.25V at 350ma. That's 68 lumens/W. The high CRI Nichia 083 is 60 lumens at 300ma and its Vf is 3.3V, which makes it just about 61 lumens/W.


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## blasterman (Jul 27, 2009)

> Color rendering is fantastic compared to white emitters, but of course efficiency isn't too great.


 
Yeah...efficiency takes a hit. I was going to try an experiment building a mixed light bar along the same route with the goal to achieve +90 CRI. However, common sense keeps intervening and begs the question why not use high CRI Seouls to begin with.

I've also noted I can't break my addiction to mixing neutral white and warm white emitters for fixed lighting because I swear CRI is better with the emitters combined. 

Also looks like Cree is mixing amber and neutral white emitters with their +90CRI ceiling fixtures.

One approach I've taken to this is looking at the spectral graphs for high CRI emitters like the high CRI Seoul and typical neutral/warm-white emitters. You can kind of get an idea of what colors are missing looking at the difference in the graphs.


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## lolzertank (Jul 27, 2009)

The main reason I tried this instead of the Seouls is that 12 Seouls and optics don't fit in a Mag head. 

Here's some pics of the light...

Just a 3C Mag.






Lots of LEDs...





14 LED little brother joins in.


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## blasterman (Jul 27, 2009)

Oh yeah....in regards to taking pictures:

Years ago I used to have to make custom film profiles for digital imaging, and an easy target to shoot and see a LOT of color variation is a big box of Crayola crayons.

If you can, shoot RAW and white balance off the grey crayon. The different between CRI should be obvious then.


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## JoakimFlorence (Oct 5, 2022)

lolzertank said:


> Is it better to use red or red-orange LEDs to increase the CRI of a cluster of neutral white LEDs?
> 
> Thanks!


I can answer this question, since this is a subject I looked into in great detail.

Actually you could use a wide range of different possible wavelengths. Any of them would increase CRI, especially in the red area, and whether you go with a longer (red) or shorter (red-orange) wavelength has its own unique advantages and disadvantages.

The first thing that needs to be said is that if you simply add red to white, you are not going to have white color light. You are going to have pink-tinted light. The human eye is very sensitive to small color tints and color shifts.
But let's ignore that part for a moment and get to answering your question.

You can use a wavelength as short as 615nm, or as long as 660nm. Actually it depends somewhat on the CRI of the white LED to begin with. If you are using a very low 70 CRI white, and the color temperature is somewhat high >4000K, then something like 615nm is going to give a greater CRI and efficiency benefit than it would in other situations.

The human eye is much less sensitive to longer wavelengths, so the amount of red light added is going to be significantly (several times) greater at 660nm than it would be at 615nm.

I have played around with this and found that 650nm still gives excellent red color saturation, and is almost twice as efficient as 660nm, due to the rapid drop-off of human wavelength sensitivity. In fact the only reason to choose 660nm is if you are trying to go for an unnatural saturation of red.

635nm is also an excellent compromise, and gives pretty good color rendering overall, although is probably not going to bring you above 94 or 95 CRI.

Something else I have noticed that is very important - if most all of the red wavelength light is coming from the red LED, then if you use a wavelength that is too long, it is going to make skin tones look unnatural. Skin tones will not be as brightly illuminated (meaning they can still appear a little dead grey) and will also acquire an unnatural pinkish tinge, rather than a healthy orange glow.

You see, the problem is that you cannot up the amount of 660nm light to a level that will properly illuminate skin tones without it overdoing the red saturation on other red colors and throwing off the color rendering balance. The ideal red-orange for a healthy-glowing skin tone is about 520nm.
When you have a "high CRI" white LED of about 91 CRI, then the spectrum will be high in 620nm orange-red light, and so it will illuminate warmer orange-red colors well, giving their appearance balance, warmth, and life. But the deep red colors will still not be rendered the most properly and will acquire a more orange tinted red than they should.

If you are using an 87 CRI white LED, then 650nm is an appropriate choice to go with it. Especially at higher color temperatures at 4000K or above. At a lower color temperature (say 3000K) or if using a lower CRI (say 80 CRI) white LED, you may want to go with 640-645nm red, or perhaps even a mix of 620 and 650nm LEDs.

So it depends on several factors. The CRI of white LED that you are using, the desired final color temperature range, and the desired CRI level that you need to obtain.

I think "neutral white" is usually 4000K (sometimes 4000-4500) so in that situation I think 535nm is probably the wavelength of red you would want to use. To more specifically answer your question. It should be able to take your 80-85 CRI and bring it up to the equivalent of maybe around 93 or 94.

The amount of red you will want to add is really not that great. Maybe in the range of 7 to 11 percent of the total light.


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## alpg88 (Oct 21, 2022)

This thread was created in 2009, when MCEs and p7s ruled, Hi CRI leds did not exist back then, now, there are 95+ cri leds. no need to mess with color leds to increase it.


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## JoakimFlorence (Oct 24, 2022)

alpg88 said:


> This thread was created in 2009, when MCEs and p7s ruled, Hi CRI leds did not exist back then, now, there are 95+ cri leds. no need to mess with color leds to increase it.


For the hobbyist, yes, that is correct (or very much mostly correct). However it's still interesting from an engineering point of view. It could theoretically be used to increase power efficiency levels a little bit, or even (arguably) very subtly increase certain desirable properties of the light and its characteristics.

I think the main reason there are virtually no commercial LED makers that use a multi-wavelength emitter design is the added manufacturing complexity and expense. (Ideally one would want to integrate the different emitters on the same chip) Then the difficulty of trying to figure out exactly how to combine different wavelengths and in which ratios, something that it not well understood, or an area that is not understood by many people due to it being more complicated. And lastly there was a well-recognised industry issue of the output of red LEDs dropping over time as they warmed up, leading to color tint imbalances of the resulting white light. This required added electronic mechanisms to regulate and adjust the ratios. I'm sure there are probably some creative ideas for passive strategies to address this, but they might not always work perfectly in all situations. The human eye is very sensitive to subtle color tint shifts off from white.

I've looked into the ratios, and basically a multi-emitter design involves somewhere around maybe 82 to 88 percent "white" (phosphor) light, and then tiny amounts of other wavelengths (1,2,3,4, or sometimes even 5 other wavelengths). For a designer, that might not appear very practical, to have to be adding numerous little additional emitters when they do not contribute much light output. It would greatly increase the manufacturing expense for what most people would see as minimal gains.

Furthermore, if the main objective is only to increase color rendering as much possible and efficiency is a secondary concern, then the overall gains in efficiency are going to be very minimal. Most are not going to want to go to the trouble if the gains in efficiency are only 4 or 5 percent higher than all-phosphor approach.
(In that case, only tiny amount of additional 650nm red wavelength light would be added, with most of the red light still originating from the phosphor)
I think most schemes to add a separate red emitter are not going to be based only just where maximum possible CRI is the primary concern, therefore. Typically what we've seen so far is that the primary objective was obtaining significant increases in efficiency, with some added CRI (and improved red color rendering) being seen as an added bonus.

Thoughts on Cree TrueWhite technology (July 29, 2016)


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## HarryN (Oct 24, 2022)

In LED strip lighting, there actually is quite an increase in the use of strips that have 4 colors - RGBW.

The controls that run them are pretty inexpensive and can create some neat effects.

A number of companies offer them - example superbrightleds and ledsupply.

The controls range from simple PWM via knobs to DMX and more.


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## JoakimFlorence (Oct 25, 2022)

HarryN said:


> In LED strip lighting, there actually is quite an increase in the use of strips that have 4 colors - RGBW.


There is a post that mentioned in another 7 year old thread that RGB (white) LEDs have a CRI of only 67-81, but that RGBA can achieve a CRI up to 92.
Theoretical limit for the efficacy of red, green, blue and white LEDs

I still really don't think RGBA is the best way to achieve good light quality. Despite seemingly decent CRI number it still could have some significant color rending issues.

The reason that extra amber emitter boosts up the RGB's CRI so much is that reddish-oranges (620 to maybe 590 nm) is very important for proper rendering and lively illumination of skin tones and warm colors, and with only one red wavelength it's difficult to do that while simultaneously making red colors appear a deep pure red.

And furthermore, in the absence of any phosphor white emitter, a 570 nm amber helps compensate for the green light when trying to more properly render those orangish-yellow, yellow, and yellow-green colors.

The reason an RGB is never going to attain satisfactory coloring rending like a fluorescent tube is that the green wavelength in fluorescent phosphor is a yellow-green wavelength, whereas the G in RGB is going to be a deeper green. This is for two reasons, first because yellow-green LEDs have much lower efficiencies than green LEDs, and second because the primary intended use of an RGB LED is not just to produce white light, sometimes it will be expected to produce color light and the colors are not going to look very well if the only green in the palette is a yellow-green.
But that part is probably beyond the scope of this discussion since we are focusing on red-orange wavelengths.

I have tried adding 650 nm red LED light to low CRI white LED light, and while it does improve the feel and appearance somewhat, interestingly it still does not render skin tones or warm wood colors the most bright or lively. This is because the eye has a diminishing sensitivity to longer deeper red wavelengths, and if one were to use enough 650 nm light to accomplish the goal, the proportion of red color added to the light would be too great. It's much easier to balance out reddish-orange light to make white light, or orange-yellow light, than it is to try do the same with pure red light. The other problem is that 650 nm light is still "too red", and when that is the primary source of light within the red to orange range, it makes skin tones appear too pink, in a way that does not look the most flattering or attractive. However, use 615 to 590 nm (red-orange) light and then skin tones appear like a healthy tanned attractive bronzed color.

It's fine to add 635 nm red to a white LED when the resulting desired color temperature of the light will be higher than 3650K. That results in an acceptable balance. But when the desired color temperature is lower, like 3000K or especially 2700K, then it becomes more important to use a longer red wavelength like 650 nm. And I would recommend using a white LED that is not too much higher than the desired color temperature. For example, if the light you want is 3000K, use a 3500K or 4000K white LED, do not use 5000K and then try to make that work.

This is for a standard 84-86 CRI white LED emitter. If using a lower CRI white LED, I suspect it's going to be more important to add in or choose a shorter wavelength red light. The thing is, a standard 84-86 CRI does have enough combined orange and red-orange light in its spectrum to balance out with added red light from a red emitter. But then if you move into 70 CRI territory there is going to be a serious deficit of light in the red-orange area, and there will not be enough orange light by itself to balance out added pure red light. You actually do not want most of your total red light in that spectrum to be all red.
But sure, if you're willing to use both 650 (red) and 615 nm (red-orange) emitters, then I'm sure you could use a 70 CRI white emitter.

70 CRI white +615nm+650nm is not going to have any advantage in light quality over 85 CRI white + 650nm , but would have an even higher energy efficiency, especially at lower color temperatures, 2700 and 3000K.
85 CRI white +650nm is I think going to give you that excellent saturated deep red color (R9) rendering you can only get from those rare 98 CRI LEDs (using blue emitters; I am NOT referring to those that use violet chip), but without that big loss in efficiency -- a 98 CRI LED is going to be about 27 percent less efficient than a 90 CRI LED, mainly because for an LED phosphor to produce a distribution that is centered at 650nm it has to also produce a lot of even longer wavelength light that is not visible to the eye.


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## JoakimFlorence (Oct 25, 2022)

I said that 615 nm isn't necessary for 85 CRI white. That isn't entirely true. If the desired light is 2700K then just a little bit of added 615 nm will be helpful (although not very much needs to be added).
The rule is that the exact qualities of the red light become more important at low color temperatures. And the other rule is that the lower the color temperature, the more important it is for CRI to have a longer wavelength of red light be present.

However, if you are going to use a 90 CRI white emitter, then you could dispense with any need for having to add additional orange-red (615 nm) light. At that point it would no longer be necessary.


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## JustAnOldFashionedLEDGuy (Oct 26, 2022)

13 year old thread .... Maybe some research on reading thread dates instead of LEDs


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