Definition of a Dimmer Switch in a Car

by Steve SmithUpdated August 06, 2023


A car dimmer switch is the switch inside the car that controls the brightness of the lighting. There are car dimmer switches inside the interior, overhead lights and inside the dashboard gauges. The speedometer, temperature, battery and oil gauges are often lit by lights controlled by the dimmer switch.

Dashboard Dimmer Function

When operated, the dimmer switch for the dashboard light increases of decreases the intensity of light behind the gauge dials. This light allows the driver to see the gauges in the dark. The dimmer reduces the brightness of the lights once the driver's eyes adjust to the dark. It allows the driver to more easily read the gauges in any light condition.

Interior Light Dimmer Switch Function

In interior lights, a dimmer switch reduces glare and eye strain, as the interior lighting affects the visibility through the car's glass. Bright interior lights cause glare on the inside of the windows, obstructing the driver's view. If a passenger must use the interior lights while the driver is operating the vehicle, the dimmer switch is one way to reduce the amount of glare on the windshield.

Older Car Dimmers

The older dimmer switch uses a resistor to decrease the charge flowing through the circuit to the light. When the dimmer is turned, resistance is increased. More heat is created and less current is passed through the circuit. This results in dimmer lighting since less current is reaching the light bulb.

Newer Car Dimmers

Newer dimming switches take a different approach. These dimmer switches turn the voltage off and on, rapidly thus decreasing the intensity of light. Since it is turned off and off, less energy is used, and the light appears dimmer. These dimmers are more energy-efficient.

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