Lighting Design Feature: Part 3 - Finding the Right Light

Think of lighting and color as mystical forces that can enhance and stimulate your non biological self or depress it. While certain colors elevate your personal, vital energy, others darken your spirit. Think of yourself as an alchemist capable of transmuting base colors to radiant, golden light. In color you have a magic wand that you can use in hundreds of ways every day to create more joyful moments where you feel you are living in pure light.

Matching colors, whether they be textile, paint, plastic, or ink requires a different technique than choosing colors for their appearance or harmony.

Measurements of Color Temperature

Warm, Cool, Daylight etc.

Yellowish white light, reminding people of a fireplace, is called "warm" while bluish white light is called "cool." These are based on associations with these colors. "Daylight" is supposed to mimic light coming in from a window. These are crude, but useful classifications. However, we can have differing degrees of "cool" and "warm": and therefore we need a quantitative measure, the Correlated Color Temperature, described below.

 

CCT in Kelvins

Correlated Color Temperature (measured in Kelvins)-or simply Color Temperature-is a scientific scale to describe how "warm" or how "cool" the light source is. It is based on the color of light emitted by an incandescent source. As a piece of metal (a theoretical Blackbody) is heated, it changes color from reddish to orange to yellowish to white to bluish-white. The color of light emitted by an incandescent object depends only on the temperature. We can use this scale to describe the color of a light source by its "Color Temperature."

When we say a lamp has a Color Temperature of 3000 Kelvins, it means a glowing metal at 3000 Kelvins would produce light of about the same color as the lamp. Instead, if the metal is heated to 4100 Kelvins, it will produce a much whiter light. Direct sunlight corresponds to about 5300 Kelvins while daylight, which has the blue from the sky mixed in, is typically 6000 Kelvins or above. A standard incandescent lamp has a filament at 2700 Kelvins, and therefore (by definition) a Color Temperature of 2700 Kelvins.

Color Rendering Index (CRI)

Color Rendering Index (maximum =100) is a measure of how closely the lamp renders colors of objects compared to a standard source. Implied is that the standard source is ideal, which may not always be true. Daylight is considered a standard but then so also is any "Blackbody," i.e. any incandescent object, no matter what its temperature. Based on this definition, daylight and all incandescent and halogen sources have CRI's of 100. For a warm lamp, CRI is a measure of how close to incandescent color it is; for a very cool lamp it is how close to daylight it is. Sources with very distorted colors will have low CRI. In general, the higher the CRI the more natural the appearance of the source and the richer colors appear. More information on CRI is provided in another section.

Color Selection

The choice of lamp color and space color(s) is the prerogative of the lighting consultant, the interior designer, and the owner. The decisions should be made jointly since the interaction of the light and colored objects will affect the success of the installation.

There are a number of common sense rules of thumb that can help make color selection easier:

• - All space colors (wall and floor covering, furniture, drapes, accents, etc.) should be chosen under the lamp color specified for the installation. Experience suggests that warm sources should be used at low lighting levels, cool sources at high levels. However, the choice may be influenced by space colors and by degree of luminaire brightness control.
• - Warm color schemes may appear overpoweringly warm is lighted with a warm source to relatively high levels - use a cooler source.
• - Cool color schemes may need warm sources, particularly at low lighting levels.
• - The color of a light source does not affect the visual performance of people doing black-on-white visual tasks. Vision and productivity studies, however, indicate that productivity may be affected by the color contrast and appearance of the visual environment and that color can contribute strongly to appearance.