Lighting Design Feature, Pt. 2 - Color Rendering with Light

A designer can only pick among the lamp colors that are available from the manufacturer, but they can modify the color with filters, etc.. To make this process easier for designers, lamp manufacturers provide information on lamp color to help with decisions on styles and applications.

Color Temperature

The Color Temperature of a light source defines its "whiteness", its yellowness or blueness - its warmth or coolness. The Color Rendering Index (CRI) was created to help indicate how colors appear under different light sources. It does not define how natural or unnatural the colors of objects will appear when lighted by the source. Two colors of lamps can have the same Color Temperature, but render colors very differently.

Shades of white light are measured in degrees Kelvin, where lower degrees indicate yellower light and higher degrees indicate whiter or bluish white light. Soft White (2700° Kelvin) is the warmest option that most closely approximates a standard incandescent bulb. It is most often used in areas like living rooms. Bright White (3500° - 4100° Kelvin) is a whiter light than soft white and is most often selected for kitchens and bathrooms or work spaces. Daylight (6000° - 6500° Kelvin) is recommended for reading areas or for use in craft rooms and is a more bluish white that most closely approximates an outdoor overcast sky.

Color Rendering Index

To help indicate how colors will appear under different light sources, a system was devised some years ago that mathematically compares how a light source shifts the location of eight specified pastel colors on a version of the C.I.E. color space as compared to the same colors lighted by a reference source of the same Color Temperature. If there is no change in appearance, the source in question is given a CRI of 100 by definition.

Technically, CRI's can only be compared for sources that have the same Color Temperatures. However, as a general rule "The Higher The Better"; light sources with high (80-100) CRI's tend to make people and things look better than light sources with lower CRI's.

Why use CRI if it has so many drawbacks? It's the only internationally agreed upon color rendering system provides some guidance. It will be used until the scientific community can develop a better system to describe what we really see. It is an indicator of the relative color rendering ability of a source and should only be used as such.