“What is color? No object of itself alone has color. We know that even the most brightly colored object, if taken into total darkness, loses its color. Therefore, if an object is dependent upon light for color, color must be a property of light. And so it is.” Paul Outerbridge, Photographer 1896 – 1958
In the post, “Color Rendering I” I delved into the nature of color and light…as Paul Outerbridge says above, color is a property of light…the color that we see an object as “being”, is in essence, light…the wavelengths of light it reflects, as opposed to absorbs.
In this post, I am seeking to clarify CRI…what does that mean?
CRI, or the Color Rendering Index, is a scale that measures not color, not light, but ” the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source”.–http://en.wikipedia.org/wiki/Color_rendering_index
The ideal or natural light source being daylight, because “it (daylight) displays (1) a great variety of colours, (2) makes it easy to distinguish slight shades of colour, and (3) the colours of objects around us obviously look natural.” –P.J. Bouma
The International Commission on Illumination (which is usually abbreviated C.I.E. for its French name Commission Internationale de L’Eclairage), the international authority on color, color spaces, light, and illumination, has defined CRI as the “Effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant”.
Trying to explain CRI reminds me of trying to translate from one language to another, in a manner that makes the meaning of a phrase in one language, comprehensible in another. It isn’t enough just to translate the words…the whole meaning, context, and sense of the phrase must be understood.
The closer the red of your child’s red beach ball inside, under the light of say, your dining room chandelier, looks to the red the same ball appears to be outside, on the beach, under the sunlight, the higher the CRI is of that dining room chandelier illuminant. CRI measures the ability of a light source to reveal, render, depict or show color the way daylight would.
Put another way, the color rendering index describes the effect of a light source on how the color of an object appears to us. It is the measurement of how much an object’s color appearance shifts when illuminated by an artificial (other than daylight) light source compared to the color appearance of the same object when illuminated by a “reference” light source (daylight), of comparable color temperature.
Whoops! Color Temperature!?! Suffice it to say, right here, right now, the CRI of a light source can only be determined when it is being compared to a reference illuminant, (natural light/daylight), with the same, or comparable color temperature. The role of “Correlated Color Temperature“ in CRI will be discussed in a future post.
So…until then chew on the above…and I hope the light bulb goes on for you about what Color Rendering Index is.
May both your days, and nights be illuminated with light sources of the highest CRI!