Explain CRI to a noob . . .

Thank You.

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A number from 1 to 100 that tells you how well a light source will show color. The awful orange street lights that make everything sepia are about 17-19. Most LEDs are probably 50-80, and expensive specialty ones are in the high 90s.

'Color Rendering Index' is an attempt to quantify how well various light sources reproduce colors compared to a standard light source, usually sunlight.

It's one of several metrics for doing so.

Might I suggest the wiki for more info?
http://en.wikipedia.org/wiki/Color_rendering_index

Here's the physics for LED:

A white LED creates blue light, and has a phosphor coating to make yellow light when the blue light hits it. This mix of blue and yellows covers most of the spectrum.


That dip in the middle and the tailed ends create a problem for seeing greens and reds. By making the phosphor coating different (thicker? better? More magic?), the LED will have decreased output, and the expanded yellowish glow from the phosphor will fill in the greens and reds better. That's a higher CRI, which is better for seeing colors.

AnAppleSnail said:

Site Search, your new best friend.

A number from 1 to 100 that tells you how well a light source will show color. The awful orange street lights that make everything sepia are about 17-19. Most LEDs are probably 50-80, and expensive specialty ones are in the high 90s.

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Searched, found that link, you explained it better. Thanx.

Theres a great wiki page on the subject. The problem with CPF is that many (manufacturers included) confuse color temperature (CCT) with CRI... the two are completely different.

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

My layman's understanding (please correct me if I am wrong) is that ambient sunlight not only produces its own fundamental color temperature (~4300k), but it also has over/under tones (for lack of a better term) to that central color. It is these over/undertones that allows the human eye to render colors better with ambient sunlight than artificial lighting which is traditionally more mono-tonal, centered more closely around a fundamental color temperature.

Wow, the information provided in the links is a bit overwhelming .

All i know is that when i fire up my SunDrop XR-U with a CRIa of 96 and a CCT of 5800 the natural color of of the object being illuminated just seems to come alive.

Thanks for the info/links :thumbsup:.

kramer5150 said:

It is these over/undertones that allows the human eye to render colors better with ambient sunlight than artificial lighting which is traditionally more mono-tonal, centered more closely around a fundamental color temperature.

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My understanding is that, in order to see green (or red), you need green (or red) photos flying around. Otherwise you will see the right shade and a wrong color.

At 500 nm (green) there's a dip - LEDs are often weak in green light. And it trails off in red (the right side) - again, a weak point at red. Fewer red and green photos makes it harder to see these colors as colors - they'd be shades of less-red or less-green. The extreme case is using a red light to read a colored map - the worst thing ever, where every color and line will be a shade of black or red.


Everything is yellow! Argh! Notics that snow, pavement, yellow road lines, red, green, blue, silver, and black cars are all just different shades of the same color. The color of the green bus stop is barely discernible because of blue light from the sky. That's low CRI.

AnAppleSnail said:

That dip in the middle and the tailed ends create a problem for seeing greens and reds. By making the phosphor coating different (thicker? better? More magic?), the LED will have decreased output, and the expanded yellowish glow from the phosphor will fill in the greens and reds better. That's a higher CRI, which is better for seeing colors.

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Just to follow up, filling in greens and reds does not necessarily mean a higher CRI. It *could* lead to a higher CRI, but it _could_ also lead to a lower CRI or no effect at all.

Proof of point: Take Cree's LEDs, which are very popular here for flashlights. The cool white (5000K-10000K) has a CRI of 75.
The outdoor whites (4000K-5300K - more reds & greens) has a lower CRI of 70!!

However, do note that there ARE higher CRI LEDs which have more reds as well.

I'm sure things will make sense once you've read the wikipedia article. Basically CRI measures how accurate an LED renders colors compared to a black body radiator (like the sun, incandescent lamps, etc.) of the same color temperature / CCT. You should also be aware that there is debate on whether CRI is the best way to measure color rendering accuracy.

Just buy white tint flashlights!

richardcpf said:

Just buy white tint flashlights!

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Haha, I'd hope that we are The issue is that "White tint" refers to a whole range of "tints" which are still "white" (I.e. the sun, fluorescent bulbs, incandescent lights, LEDs could all be argued to be white, yet they all look different)

And we should remember here that tint is a separate discussion - completely different from CRI.

Lots of good info posted. And here's more:

"Typical phosphor-based white LEDs have color rendering index (CRI) values comparable to discharge lamps (fluorescent and HID lamps). Many people mistakenly believe that a high CRI means high color rendering properties. Actually, the CRI is merely an index of how similar a light source makes colors appear in comparison to a reference source such as incandescent. That's why an incandescent lamp has a CRI near 100. Recent studies show that mixed-color "white" LED systems with a CRI in the 20s can result in higher color preferences than systems with a CRI in the 90s. Recognizing the limitation of the current CRI rating, international standard-making groups are now developing new measurements to better characterize the color-rendering properties for all light sources, including LEDs."

Full article here: http://ewweb.com/greenbiz/electric_led_report/

This stuff still confuses me too, especially AFTER reading many articles. What I'd really like to see is comparisons of lights with the same color temps, but different CRI's compared and then lights of the same CRI, but different color temps.

Now if I'm not mistaken, Cree's cool and neutrals both have a CRI of 75, R2 "outdoor white" Crees have a CRI of 70 which I believe is a sacrifice they made for that color temperature at that flux bin and Cree's warms have a CRI of 80.