Figure 6-14.Streetlight manufacturers literature.
footcandle values per 1,000 lamp lumens. Each
footcandle value must be multiplied by 50 to obtain the
correct footcandle value on the isofootcandle diagram.
Lighting efficiency is seriously impaired by
This ratio of actual lamp lumens divided by 1,000 is
blackened lamps, by lamp life, and by dirt on the
known as the lamp factor (LF). Note that the lamp
reflecting surfaces of the luminaire. Tocompensate
factor allows a curve to represent the distribution from
for the gradual loss of illumination, you must apply
more than one lamp wattage; for example, from 250-
a maintenance factor (MF) to the lighting
and 400-watt lamps.