Sodium lights work by using high temperatures to produce heat, which generates light. The color and vibrancy of the lights produced by sodium lamps varies depending on the pressure of the lamp (which is low or high) and the temperature reached by the internal chamber. At lower temperatures, sodium lights generally start as red bulbs and then turn to yellow and orange as they gain heat.
Low-pressure sodium lamps are frequently used in Europe for the purposes of outdoor lighting. These lights emit a vibrant lemon-colored yellow hue upon reaching their greatest internal temperatures. These lamps are made of sodium metal, which helps give lamps shape in their solid form. Sodium metal forms the backbone of the arc tube, which serves as a chamber to transmit sodium vapors that arise when low levels of heat are produced. As the air warms, the sodium vapor transforms into neon gas, which is red in appearance. As the gas heats, its red color transitions to orange and eventually reaches a yellow color at its hottest point. Some lights, particularly those with lower voltages, produce argon gas in addition to neon gases, which gives them a softer color and a gentler glow than their higher-voltage counterparts.