The author describes color rendering index as a percentage; it is not. It's 100 - [a calculation of average color error on 8 color samples]. Reporting the color error directly would probably be better; 90% and 95% would both be pretty good grades on most tests, but a rendering error of 10 sounds a lot worse than a rendering error of 5.
Being based on only 8 samples, CRI Ra doesn't tell the whole story. There are other standards like TLCI that use more samples, and six supplemental samples some sources report. R9 (strong red) and R12 (strong blue) are particularly relevant to modern lighting, as LED sources often struggle with them despite high CRI (Ra) ratings.
CRI is a comparison to blackbody radiation (like an incandescent bulb) or simulated daylight at the same correlated color temperature as the sample light source. An incandescent bulb and midday sunlight at the equator both have CRI of 100, but a CCT of 2700K and a CCT of 5700K will render colors very differently. White balance in a camera's settings or raw development software can make one look like the other.
CCT is roughly blue-yellow balance, but light sources can deviate from blackbody radiation on a red-green axis. This is most often expressed as "delta u v" or "Duv", as it refers to distance in the CIELUV color space[0]. Duv numbers are small, with differences of less than 0.001 being noticeable in a side by side comparison and more than +/- 0.006 falling outside the ANSI standard for white light. Positive numbers are green, and negative numbers are red/pink.
This is awesome. Are ordinary objects bright enough to register their spectra in it?
You might also enjoy this, a project to find real world things with all the cyans you can't display on a computer screen. https://moultano.wordpress.com/2026/06/19/where-to-find-the-... After doing this I was looking for some way to do spectrophotometry with a small enough amount of equipment that my wife would approve of, so that I can add more things to the list and confirm their color.
moultano
I sort of wonder is there a "true" way to represent color? Would a intensity over frequency curve do it?
I probably lack the terminology to express myself properly, but color ends up being a very human thing, with a huge focus on primary colors(the colors that match the frequency response of the human eye) This is fine, we are human after all, but then I always feel color theory dives off the deep end, with color wheels and complimentary colors and triplets, etc. why? there is nothing physically cyclic going on. It never makes any sense to me that patterns based on it being cyclic would be any better than just picking colors. Any way, silly rant aside, if we wanted to define an objective physical color format, how would it be done?
somat
White light discussion tends to focus around spectrums of perceptual/blackbody/the sun importance because... well, it's just the natural choice. Is there a name for a light source which has a constant emission intensity across a given range of wavelengths? Does such a thing have any practical purpose (beyond being interesting to think about) and do we actually make anything capable of producing such light output? I suppose one way might be to take some incandescent source and then stick a really well tuned filter in front to "level out" the normal curve, but that punts the problem to constructing such a well tuned filter.
zamadatix
CRI of lights is definitely a large factor in my purchasing these days. The muting, compressive response of some lights almost pains me at this point.
As this post's author noted white LEDs can be pretty solid. Bulbs that have a mix of white LEDs at various temperatures to be "bi-color" tend to be pretty solid as well. Its once you go towards RGB light bulbs that you tend to get a fairly iffy CRI.
This rules. Much like designing fireworks, I wish it were somehow more accessible to mess around with mixing our own phosphors.
I'd like to see this done for kit like ADJ / Eliminator / Chauvet, they do some wild near-UV shit to cause really cool/blown out color definitions.
monster_truck
Sun is white light. Wonder what that means. Brightest object in out awareness is modeled as clean white. Or is this the actual basic color.
deadlast2
> It's probably a good idea to buy a few samples of several different types and brands, test them all, and then decide which to buy in quantity for the home.
I'm looking forward to that. I own a bunch of Philips WhiteDial bulbs that are rated CRI90. It would be nice to test that and know how they really compare. No doubt there's a lot of dishonest CRI ratings out there.
tbirdny
Thanks for this comparison. Very interesting and surprising!
comments (9)
The author describes color rendering index as a percentage; it is not. It's 100 - [a calculation of average color error on 8 color samples]. Reporting the color error directly would probably be better; 90% and 95% would both be pretty good grades on most tests, but a rendering error of 10 sounds a lot worse than a rendering error of 5.
Being based on only 8 samples, CRI Ra doesn't tell the whole story. There are other standards like TLCI that use more samples, and six supplemental samples some sources report. R9 (strong red) and R12 (strong blue) are particularly relevant to modern lighting, as LED sources often struggle with them despite high CRI (Ra) ratings.
CRI is a comparison to blackbody radiation (like an incandescent bulb) or simulated daylight at the same correlated color temperature as the sample light source. An incandescent bulb and midday sunlight at the equator both have CRI of 100, but a CCT of 2700K and a CCT of 5700K will render colors very differently. White balance in a camera's settings or raw development software can make one look like the other.
CCT is roughly blue-yellow balance, but light sources can deviate from blackbody radiation on a red-green axis. This is most often expressed as "delta u v" or "Duv", as it refers to distance in the CIELUV color space[0]. Duv numbers are small, with differences of less than 0.001 being noticeable in a side by side comparison and more than +/- 0.006 falling outside the ANSI standard for white light. Positive numbers are green, and negative numbers are red/pink.
[0] https://en.wikipedia.org/wiki/CIELUV
Zak
You might also enjoy this, a project to find real world things with all the cyans you can't display on a computer screen. https://moultano.wordpress.com/2026/06/19/where-to-find-the-... After doing this I was looking for some way to do spectrophotometry with a small enough amount of equipment that my wife would approve of, so that I can add more things to the list and confirm their color.
moultano
I probably lack the terminology to express myself properly, but color ends up being a very human thing, with a huge focus on primary colors(the colors that match the frequency response of the human eye) This is fine, we are human after all, but then I always feel color theory dives off the deep end, with color wheels and complimentary colors and triplets, etc. why? there is nothing physically cyclic going on. It never makes any sense to me that patterns based on it being cyclic would be any better than just picking colors. Any way, silly rant aside, if we wanted to define an objective physical color format, how would it be done?
somat
zamadatix
As this post's author noted white LEDs can be pretty solid. Bulbs that have a mix of white LEDs at various temperatures to be "bi-color" tend to be pretty solid as well. Its once you go towards RGB light bulbs that you tend to get a fairly iffy CRI.
I've referenced https://optimizeyourbiology.com/light-bulb-database and https://optimizeyourbiology.com/smart-light-database before when looking at bulbs but if anyone has a better resource, absolutely please drop a reply.
miladyincontrol
I'd like to see this done for kit like ADJ / Eliminator / Chauvet, they do some wild near-UV shit to cause really cool/blown out color definitions.
monster_truck
deadlast2
I'm looking forward to that. I own a bunch of Philips WhiteDial bulbs that are rated CRI90. It would be nice to test that and know how they really compare. No doubt there's a lot of dishonest CRI ratings out there.
tbirdny
flimflamm