Building Design and Construction Handbook - Merritt - Ventech!

ELECTRICAL SYSTEMS 15.55
restaurant, warm-colored light would make food served appear more appetizing,
whereas cool-colored light would have the opposite effect.
Sources producing white light are generally used. Because of the spectral energy
distribution of the light, however, some colors predominate in the illumination. For
example, for daylight, north light is bluish, whereas direct sunlight at midday is
yellow-white; and light from an incandescent lamp is high in red, orange, and
yellow. The color composition of the light may be correlated with a color temperature.
For a specific purpose, a source with the appropriate color characteristics
should be chosen. Lamp manufacturers provide information on the color temperature
and color rendering index of their products.
Colored light, produced by colored light sources or by filtering of white light,
is sometimes used for decorative purposes. Colored light also may be used to affect
human moods or for other psychological purposes, as indicated in Art. 15.10.8.
Care must be taken in such applications to avoid objectionable reactions to the
colored light; for example, when it causes unpleasant changes in the appearance of
human skin or other familiar objects.
Perceived color of objects also is affected by the level of illumination (Art.
15.10.8). When brilliant color rendition is desired and high-intensity lighting is to
be used, the color saturation of the objects should be high; that is, colors should
be vivid. Also, a source that would enhance the colors of the objects should be
chosen.
See Art. 15.20, Bibliography.
15.13 QUANTITY OF LIGHT
As indicated in Art. 15.11, quantity and quality of light are actually inseparable in
contributing to good lighting, although they are treated separately, for convenience
of presentation, in this section. Illumination should meet the requirements of visual
tasks for safe, efficient performance, esthetic reasons, and the purpose of attracting
attention. Factors that affect visual performance of a task include:
Luminance, or brightness, of the task
Luminance relation between task and surroundings
Color rendering of the light
Size of details to be detected
Contrast of the details with their background
Duration and frequency of occurrence of the task
Speed and accuracy required in performance of the task
Age of workers
The influence of these factors on visibility is described in Art. 15.10.
Dim lighting is sometimes desirable for mood effects. For merchandising, however,
a pattern of brightness is depended on to capture the attention of potential
customers. For task lighting, sufficient lighting must be provided on the work area
if the task is to be executed without eyestrain and fatigue. Higher than the minimum
required level of illumination usually improves visibility but often with greater
energy consumption and increased life-cycle costs for both lighting and cooling the