Effect of Voltage Variations.
—Voltage variation may be temporary, due to changing load in the circuit, or in constantly overloaded circuits the voltage may be constantly below normal. The change in electric pressure affects in a considerable degree the amount of light given by the lamp. As an example, a 5 per cent. drop from the normal voltage will cause a decrease of 31 per cent. in the amount of light given. This means that if a lamp is working on a circuit of 110 volts and the voltage from any cause were to drop to 104½ volts, the light would decrease 6.8, almost 7 candlepower. Drop in voltage may also be due to the resistance of wires that are too small for the service. Lamps attached to such a circuit will constantly burn dim.