Pilot lights and indicator lights are indicating lights for machines or instruments. Most indicators favor the use of LEDs or incandescent lamps.

Types of Lights

Pilot lights and indicator lights vary primarily by the type of lamp used.

• Incandescent lights emit light through a thin wire (filament) which becomes hot when electricity flows through it. It can operate on either AC or DC circuits; however, these devices are relatively inefficient, generate heat, and have shorter operating life spans than LED pilot lights.
• LED lights are semiconductor light sources that require DC to operate.  If a DC circuit is not available, an LED driver can be used to supply the appropriate DC voltage and current. They have the advantage of smaller size, longer lifetimes, and lower energy requirements than incandescent or fluorescent lights. Some LED lights can change color with the polarity of the current.
• Fluorescent lights utilize fluorescent bulbs which house electrodes at both ends of the tube and argon and mercury vapor throughout. A phosphor coating on the inside of the tube emits light through emission of ultraviolet light from excitation and stabilization of mercury atoms. Fluorescent bulbs tend to be more energy efficient and longer lasting than incandescent bulbs, but are less commonly used as indicators.
• Halogen lights utilize a tungsten filament, inert gas, and a small amount of a halogen to emit light. This combination allows for higher temperature filaments which can produce more light given the same energy (higher color temperature). This favors their use as daytime indicators and warning lights which require brighter light.

Product Specifications

Important specifications for pilot lights and indicator lights include electrical requirements such as voltage, size, and color. Based on the application, mounting style (panel, PC board) and terminal type (feed-through, wire leads, etc.) will also need to be considered.

To rate LEDs for use as pilot lights and indicator lights, manufacturers state the luminous intensity in candelas, which is a function of the viewing angle.

Applications

Pilot and indicator lights are used as malfunction lights in automatic equipment, voice mail lights for telephones, condition panels, and dashboard lights for vehicles. They can also be built into switches.