Efficient
Lighting Strategies
Daylight is
unmatched for color rendering, and safety and productivity of
manual tasks. To supplement it efficiently, use electric light
with similar distribution. For even ambient light distribution,
introduce light high in a space with light-colored upper surfaces.
Locate fixtures just above work areas for task illumination.
Lighting levels
should respond to visual tasks. Efficient lighting power densities
(LPD) range from 0.75 to 1.5 W/sq.ft., though select areas with
task- and color-critical work may range from 2.0 to 2.5 W/sq.ft.
High-bay,
metal halide (MH) lamps supplement natural light efficiently.
Newer 360-watt lamps provide the same output as standard 400-
watt MH lamps. High-output 400-watt lamps can provide 10% more
lumens. Both have a 20,000- hour life.
Newer MH lamps
eliminate the color shift problems of older lamps. When color
quality is important, choose lamps with improved color stability,
or use high color rendering index (CRI) T8 or T5 fluorescents.
Metal halide
and high-pressure sodium (HPS) lamp output can be dimmed using
photo-cell controls and high/low ballasts, to respond to daylight.
Occupancy sensors can also switch high/low ballasts for areas
with intermittent occupancy, such as aisles.
Cautions
- Consider
power quality and lamp/ballast compatibility when using dimming
ballasts.
- Control
glare from direct sunlight.
- Requires
careful luminaire and sensor selection, placement and commissioning.
