Color Rendering Index



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    Osman Bilger

    The perfect cri benchmark is the sun at 100. We perceive the sun as yellow as well, but the cri performance is due to the variety of wavelengths of the light it emits. High pressure sodium is also yellowish like incandecent but it only emits a single wavelength that "paints" everything as yellow. Incandescent is warmer light but the output in variety of wavelengths gives it the high cri. There are also high performance fluorescent lights that come close to 90 cri but in a cooler tone.

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    Theresa Bort (Edited )

    Thank you for your response, Osman. So it sounds like, since incandescent lights output such a variety of wavelengths, we're perceiving the true color of an object under incandescent lights, right? So when comparing the CRI graphs below, it's not the relative energy produced by a light that "paints" an object a certain color, but the sparsity of wavelengths?

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    Anna Oursler

    Thanks Theresa, you've helped me distinguish between CRI and color temperature (warm, cool, measured in degrees Kelvin), which I was conflating.

    I think this is getting a little too complicated for the ARE exam, but the link between the two seems to be the Correlated Color Temperature (CCT), which describes lights by temperature, that don't have equal radiation across all wavelengths in their spectrum (fluorescent above). This gives them less than perfect color rendering on the CRI chart.

    Lets stick to the knowledge that and incandescent light source can have an almost perfect CRI, alongside the sun!


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    Theresa Bort

    Aha! Thanks Anna, I did a little research on the CCT and this is the link I was missing. So to summarize: The CRI compares how objects appear under light sources to how they appear in daylight of the same color temperature, or the Correlated Color Temperature. This means the CRI doesn't affect color temperature, but rather accounts for it.

    So I was confusing myself by trying to combine CRI and color temperature. Despite incandescent lighting having a near perfect CRI, it will still give cool colors a warmer tone (e.g. making blues appear muddy) and render warm colors as warm colors.

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    James McKenna (Edited )

    Theresa, can you expand on your last comment regarding incandescent light still giving cool colors a warmer tone? If incandescent light has a CRI of near 100, would it render all colors 'perfectly' (including blues)? Do you have a section in MEEB or another reference I could refer to? 

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    Theresa Bort

    Hi James,

    Good question. If an incandescent light has a CRI of 100, it would make all colors appear exactly as they would under natural light that has the same color temperature of an incandescent light. Think of it this way: When the sun is in a clear sky at noon, it produces a cool light. Let's say this is comparable to the color of a cool white fluorescent light. But when the sun is setting, it produces a warm, golden color. This would be closer to the color temperature of an incandescent light. The setting sun would still be rendering blues as warmer than usual, but this effect is the comparison point (i.e. "perfection") for an incandescent light with the same color temperature.

    I hope this helps!

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