Modular switch lamps provide a visual indicator of the condition of a switch on a board. They make it easy for workers to quickly assess whether or not a switch is on or off. They are usually mated to specific contact blocks for ease of installation.
Modular switch lamps are sometimes installed so that there are two or more lamps, which are lit depending upon the condition of the switch. In many cases, however, there is one lamp that is simply illuminated or turned off if the switch is in the on or off position, allowing for an easy visual assessment of the condition of any given switch.