There are several light sources which have been used in electric street lights. The main types used since the 1940s in the United States have been Incandescent, Fluorescent, Low Pressure Sodium and High Intensity Discharge.

Incandescent lamps are among the first and least efficient light sources used in street lighting. Incandescent lighting was a popular option for street lighting until the 1950s, when other lamps proved to be more efficient and lower maintenance.

Fluorescent

Fluorescent lamps gained popularity for street lighting applications in the 1950s. The lamps were more efficient than their Incandescent counterparts, and required less maintenace. The lamps were primarily used in downtown areas and parking lots. They were good for any place requiring a lot of light over a large area. The popularity of these lamps was relatively short-lived, as more efficient, compact and lower-maintenance High Intensity Discharge lamp technology was advanced.

There are three main types of High Intensity Discharge (HID) lamps. HID lamps in general requre an external ballast to operate. These lamps usually take between 1 and 5 minutes to reach full brightness, and if there is a dip in electricity, these lamps will shut off. The lamps must cool sufficiently to restrike, which usually takes from 1 minute to 10 minutes. Street lights using these lamps have been labelled on the bottom of the fixture since the late 1970s. A number on the bottom multiplied by 10 yields the wattage rating of the fixture (e.g. "10" means 100 watts, "25" means 250 watts. The only exception is 1000 watt fixtures, which are labelled as "X1".) Mercury Vapor has a blue label, Metal Halide has a red label and both types of sodium lamps have yellow or gold labels.

Mercury Vapor was the first widely accepted HID lighting source. Clear mercury vapor lamps cast a blue-green light, which some say makes people look like "walking cadavers." Advances in technology have lead to color corrected mercury vapor lamps, which cast a relatively clean white light. This is done by coating the outer glass globe of the lamp with phosphors.

By the late 1950s, mercury lamps were very widely used around the US. The lamps were about as efficient as fluorescents, the fixtures were smaller, and lasted much longer. The lamps could also operate in extreme cold. One main difficulty with mercury lamps was "lumen depreciation." Lumen depreciation is a drop in light output of the lamp over time. In a lot of cases, a mercury lamp will burn for years past it's rated life, but it will burn much dimmer while using the same amount of wattage.