High pressure sodium (HPS) lamps are the most efficient member of the HID
family where some degree of color rendition is important. Standard HPS lamps
produce a golden white light when they reach full brightness. Many recognize them
as the familiar golden light from street lights, one of their principal
applications. There are versions of the HPS lamp designed for indoor use with improved
color over standard HPS lamps, but the improvements come at the cost of
shorter lamp life and lower efficacy. These lamps are now a readily accepted light
source in industrial plants and also are being used in many commercial and
institutional applications.
HPS lamp sizes range from 35 to 1,000 watts. Ballasts designed specifically
for high pressure sodium lamps must be used. The figure shown here shows the
lamp shape for both a metal halide lamp and a high pressure sodium lamp.
Strengths:
Most efficient member of the HID light family, 7 times as efficient as
incandescent and over 2 times as efficient as mercury vapor.
Warm-up period is 3-4 minutes, which is somewhat less than that of a mercury
vapor or metal halide lamp.
Long lamp life -- 24,000 hours.
Excellent lumen maintenance.
Wide range of lamp types with wattages ranging from 35 to 1000 watts.
Most HPS lamps can operate in any position.
Weaknesses:
The light produced is a golden white color, which may not be appropriate for
certain applications.
Requires a ballast.
Once started can take from five to ten minutes to reach full light output.
They also require at least a one minute cool-down to re-strike.
End of life is characterized by on-off-on cycling, and continued operation can
damage the lamp ballast if not replaced quickly.
