Figure 6-22.Photoelectric cell control circuit.
that the street circuit can carry is 240 volts times 6.6
amperes or 1.584 kilowatts.
Figure 6-21 shows the maximum number of series
lamps in the various sizes that may be used for full-load
rating on a regulator. The average number of watts of
energy consumption for each size lamp may be
computed since the regulator ratings are based on their
output. In this manner, the load of a circuit consisting of
different size lamps may be computed.
Example: What size regulator would be required to
supply the following lamps?
251,000-lumen, 6.6-ampere, straight-series lamps
502,500-lumen, 6.6-ampere, straight-series lamps
106,000-lumen, 20-ampere lamps with isolating transformer
Solution: Figure 6-21 shows that the average
energy consumption of a 1,000-lumen, 6.6-ampere,
straight-series lamp with film cutout is 69 watts per
lamp. In a similar manner, the average energy
consumption of a 2,500-lumen lamp is 167 watts, and a
6,000-lumen, 20-ampere lamp with isolating
Figure 6-23.Cadmium-sulfide cell control circuit,
transformer is 405 watts. Totaling the combined load
shows the following:
25 x 69 = 1,725 watts
50 x 167 = 8,350 watts
10 x 405 = 4,050 watts
14,125 watts or 14.1 kilowatts
Therefore, a 15-kilowatt regulator would be
NOTE: The table makes allowances for line losses
in the average series street circuits.
Several methods are used to control the operation of
area lighting systems. For recreational lighting, only a
manual switch is required. On the other hand,
streetlights and security lights have more sophisticated
Lights normally are on during the hours of darkness
or when unusual weather conditions indicate the need
for artificial light. Although lights could be activated by
assigning an individual to operate the controls
manually, they are usually turned on and off by a
combination of controls.
Most control circuits that you will encounter in the
field use one of the following devices to control the
photoelectric cell (fig. 6-22),
cadmium-sulfide cell (fig. 6-23), time clock, pilot wire
relay (fig. 6-24), or cascading relays (fig. 6-25).