CRI versus Color Temperature: Explained

The jargon in the lighting world can often get mixed up. Color rending index (CRI) and color temperature are one of the most to be confused with each other. This post is going to clarify what the different between CRI and Color Temperature is so we can end this confusion. Here is a short explanation why the CRI is more important to focus on before deciding for a color temperature. The color rendering index is the most important feature in certain applications as it determines the appearance of objects, faces and spaces. If this aspect is not relevant, the CRI can be as low as 60 or even 40.

What is Color Rendering Index?

The color rendering index (CRI) is a numeric evaluation of the light color accuracy with the reference of daylight (numbered 100). Sunlight and its broad spectrum will enable a person with normal vision to see 68 different colors in a color chart, but if the chart is illuminated by a light source of one wavelength only, each color from the color chart will appear as a different brightness of that one color. Some activities, such as walking or operating a vehicle, do not require the accurate perception of surface colors while others such as product selections in shops benefit from better color rendering features. Look at the application of the lighting installation. If the visual tasks are easy to perform the CRI doesn’t need to be high. In areas like offices, handcraft manufacturing and surgery, the requirements for visibility, contrast, visual guidance as well as face recognition need to be provided by a lighting system with a good CRI of >80 or even >90. How much is the light color affecting the space?

What is Color Temperature?

The term color temperature describes the temperature of objects by which they emit light, modeled through the "black body radiator". When increasing the temperature of a "black body", it starts to emit visible light in a continuous spectrum. The filament of a 60W incandescent lamp heats up to about 3000°F, as a result the lamp emits light with a color temperature of 3000K. Many of our artificial light sources do not create light by heating up a material until it glows like an incandescent lamps. Instead of creating a continuous spectrum, they generate an assortment of color emission lines. A black body color temperature cannot be directly given to this non-blackbody type of emission, generated by high intensity discharge and fluorescent lamps for example.

What is Correlated Color Temperature?

For those light sources, a correlated color temperature (CCT) is indicated, based on the black body color temperature. A cool white fluorescent lamp has a CCT of about 5000K. The lamps light spectrum is different from a black body one but has the same temperature. The light color influences the atmosphere in a space. The more cozy the ambiance the warmer the light color (lower color temperature) should be and the more dynamic the scene the cooler the light source (higher color temperature). The CRI is the most important factor to watch when choosing light sources. How good is the light source representing faces, colors and contrasts? The easier the visual task and perception the lower the CRI can be. The color temperature needs to be watched second, it is supporting the space’s atmosphere.

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