Civil Engineering Reference
In-Depth Information
Fig. 14.2
Example of distribution diagram
Luminaire dirt depreciation is a major factor in maintaining good lighting levels
at low energy cost. Typical depreciation factor curves are illustrated in Fig.
14.1
and they are provided by manufacturers. A good maintenance program may yield
significant energy saving. In addition, other factors of depreciation such as room
surface and furniture dirt depreciation, and aging and discoloration of luminaire
shield materials, must be considered carefully in a lighting conservation program.
Luminaires must also avoid uncomfortably bright light (commonly called glare
effect) on the task surface. Generally, light emitted within a cone with a 90
angle
and with the axis along the vertical line from the luminaire to the floor does not
contribute to direct glare. Inside the same cone loss of contrast on the task surface
may occur; on the contrary, this effect is minimal outside the cone.
Shielding materials which direct light at particular angles can conveniently be
used; distribution such as batwing distribution like in Fig.
14.2
, where a high
percentage of light is emitted near 45
, allows a good compromise among different
requirements if the workstations are placed between rows of luminaires.
Lenses with polarizing materials and louvers (series of baffles generally
arranged in a geometric pattern) are also used.
14.3.6 Lighting Control
The best way to save energy in lighting is to ensure that lights are turned
on only when needed and are dimmed during periods when lower levels
of lighting are required.
