100 CRI - What's the deal?

[jkilo]

If this is not the appropriate place, feel free to relocate.

I am finding mysellf gravitating from LEDs, with their high efficiencies and "cool" factor, towards useful incans--the well driven ones.

I don't want to start another LED vs. Incan debate, that's irrelavent here, but it seems to me something is wrong with the whole CRI thing.

An LED's CRI is more or less fixed, regardless of drive level, based primarily on the phoshpors used.

But this claim that all Incans have a CRI of 100... You mean my half-dead mini-mag will render colors as accurately as an Aviator? Or even a Sundrop, with a High-CRI LED? Me thinks not.

What Incan lamp, at what drive-level, is being used to set the CRI of 100? Because we know that CCT and CRI are not directly related. And what happens if I overdrive that lamp? Does the CRI go over 100? Is the scale logarithmic?

I'm sure lots of others, like myself, are confused here.

Please discuss! :candle: (My apologies if this is posted elsewhere, but I couldn't find it.)

 

[moses]

Your question is faulty because of a faulty premise. I have not seen claims of incandescents having a CRI of 100.

Some are over 90 but never 100. And most are well below 90 if I understand correctly. So incans can have poorer rendition than high CRI LEDS.

Solux halogens are supposedly among the highest incan CRI and they use it in world class museums. We have that in our study and it is a beautiful light.

M

 

[Kestrel]

Your question is faulty because of a faulty premise. I have not seen claims of incandescents having a CRI of 100.

Running 'search' for:
'incandescent 100 cri by definition'
All 10 search returns on the first page basically claim that.
I am most definitely not an authority on the subject (it's not something I know much about), but I thought the statement above seemed kind of odd?

Edit: even searching for
'incandescent 100 cri'
basically returns almost-identical results, with many search returns claiming "... by definition"

 

[jkilo]

Agreed. They can't all be 100, if any are. And yet that's become quite common, here and elsewhere. It's practically cliché. What incandescent light source has the scale set at 100? The sun? I mean, one could design a light source to render colors almost garishly, perfectly flat output at every point on the spectrum, far better than the sun could do.

 

[herbicide]

CRI is apparently used with reference to "an ideal or natural light source"*, so I'd assume the sun, at noon, on a cloudless day would have a CRI of 100.

Also,

[...]note that CRI is not a good indicator for use in visual assessment, especially for sources below 5000 kelvin (K).

This would seem to preclude associating CRI with most incans, if the figures given by Lumensfactory (not a dig, they're just the first ones I could find data on) are any indication.



*warning - here be science

 

[Ragiska]

popular misconception by people. most incans doe NOT have a 100 CRI, or even 90, PLUS they don't have the right CCT to mimic sunlight. combined, many led's are better overall.

 

[Swedpat]

According to what I until now have read at this forum in this matter, all incans have a CRI of 100...
I find it fascinating (if) that the colour rendition seems to have (almost) nothing to do with the colour temperature of the light source(incans can't have bluish tint what I know). But I am not either an authority here...

 

[Phaserburn]

According to what I until now have read at this forum in this matter, all incans have a CRI of 100...
I find it fascinating (if) that the colour rendition seems to have (almost) nothing to do with the colour temperature of the light source(incans can't have bluish tint what I know). But I am not either an authority here...

This is correct. Incans have a CRI of 100, always. What is far more noticeable to quick observation is color temp, which also effects color perception of illuminated objects.

 

[AnAppleSnail]

The CRI describes "How close is the spectral output of this source to a blackbody radiator of the same color temperature." A blackbody radiator (a filament) is always going to be identical to a blackbody radiator of the same temperature - so CRI alone is, confusingly, no measure of actual color rendering. For good color rendition in an incandescent you need a sunlike color temperature - which a crummy mag on cheap batteries won't do.

 

[Swedpat]

This is correct. Incans have a CRI of 100, always. What is far more noticeable to quick observation is color temp, which also effects color perception of illuminated objects.

This is bit complex I guess. Am I getting this right that neither CRI or color temp can alone give a complete description of the perveived color rendition?

 

[kito109654]

You can get a pretty good understanding of CRI by just reading the Wikipedia article.

A couple of quotes from it:

"Note that the CRI by itself does not indicate what the color temperature of the reference light source is; therefore, it is customary to also cite the correlated color temperature (CCT)."

"The CRI is calculated by comparing the color rendering of the test source to that of a "perfect" source which is a black body radiator for sources with correlated color temperatures under 5000 K, and a phase of daylight otherwise"

_____

To me, that last quote is the part that says Incan has a CRI of 100 by definition...even though the CCT falls over the useful life of the battery. CRI has nothing to do with the color of the light (CCT) but everything to do with the completeness of the spectrum being emitted. Incans always emit the whole spectrum including those "beyond violet" or UV, and infrared.

 

[kito109654]

This is bit complex I guess. Am I getting this right that neither CRI or color temp can alone give a complete description of the perveived color rendition?

Indeed. Luckily, our eyes can do some amazing adjusting.

The CRI describes "How close is the spectral output of this source to a blackbody radiator of the same color temperature." A blackbody radiator (a filament) is always going to be identical to a blackbody radiator of the same temperature - so CRI alone is, confusingly, no measure of actual color rendering. For good color rendition in an incandescent you need a sunlike color temperature - which a crummy mag on cheap batteries won't do.

Actually, you are describing CCT, not CRI. Edit: woops, reading too fast. We're saying the same thing in different words.

 

[JCD]

Actually, you are describing CCT, not CRI.

No, he isn't.

For example, an LED with a CCT of 3700 K does not inherently have a spectral output resembling a black body radiator at 3700 K.

 

[kito109654]

No, he isn't.

For example, an LED with a CCT of 3700 K does not inherently have a spectral output resembling a black body radiator at 3700 K.

Right, yeah I get that, maybe I just read through what he said too quickly.

 

[computernut]

I found this article on CRI the easiest to understand:
http://www.edbergphoto.com/pages/Tip-fluorescents.html

 

[Colorblinded]

I found this article on CRI the easiest to understand:
http://www.edbergphoto.com/pages/Tip-fluorescents.html

You can get a pretty good understanding of CRI by just reading the Wikipedia article.

A couple of quotes from it:

"Note that the CRI by itself does not indicate what the color temperature of the reference light source is; therefore, it is customary to also cite the correlated color temperature (CCT)."

"The CRI is calculated by comparing the color rendering of the test source to that of a "perfect" source which is a black body radiator for sources with correlated color temperatures under 5000 K, and a phase of daylight otherwise"

_____

To me, that last quote is the part that says Incan has a CRI of 100 by definition...even though the CCT falls over the useful life of the battery. CRI has nothing to do with the color of the light (CCT) but everything to do with the completeness of the spectrum being emitted. Incans always emit the whole spectrum including those "beyond violet" or UV, and infrared.

Indeed. High CRI means it closely matches the blackbody emitter for that CCT. That doesn't mean it will render all colors ideally. A low temperature black body emitter won't do blues much justice which is why ideally I'd like to see high CRI LEDs in the 5000K range.

 

[mbw_151]

Here's a way to think about incandescent filaments. The "black body radiator" temperature changes as the current thru the filament changes. At for example at low current the filament is dull red. The CRI is 100 at a low CCT. As the current is increased the temperature of the filament increases resulting in a higher CCT, but still a CRI of 100.

When the topic of "color rendering" is discussed, the first question to ask is, "What is the reference?" Even the concept of "daylight" is complicated; what lattitude, time of day, time of year, clouds/humidity, dust, adjacent structures or landscape. Black body radiators in a furnace controlled to the appropriate temperature are accurate, but a little inconvenient for most applications. Deviations from this kind of standard are all approximations with some error.

 

[kito109654]

Indeed. High CRI means it closely matches the blackbody emitter for that CCT. That doesn't mean it will render all colors ideally. A low temperature black body emitter won't do blues much justice which is why ideally I'd like to see high CRI LEDs in the 5000K range.

High CRI means close to the full spectrum of light being emitted.

I'd like to think that rendering is only affected by CRI. CCT will cast a certain color over all colors but our eyes can adjust for the color cast quite well. We can basically choose a CCT that pleases us, whether for the color cast or for the output.

 

[AnAppleSnail]

High CRI means close to the full spectrum of light being emitted.

Not exactly. A uniform emitter - giving exactly the same amount of light over a broad range (Say, infrared to UV), would have a low CRI. And a blackbody emitter has most of its emissions at a central range (for the sun, green; even though it averages white, green's in the middle of the visible spectrum ROY G BIV) and tails off in either direction.

 

[fyrstormer]

CRI describes how close the apparent color of the light source being evaluated is to the range of black-body-radiator emission spectra.

CCT describes which point in that range of spectra is closest to the apparent color of the light source being evaluated.

All black-body-radiator emission spectra above ~2500 Kelvin are also 100% CRI, because they contain all visible wavelengths of light in some noticeable percentage. Below ~2500K, the blue component is absent or too dim for human eyes to detect.