Definition
A control device, typically a variable resistor (rheostat) or solid-state circuit, that adjusts the brightness of cockpit instrument lights, panel lights, or other aircraft lighting by varying the electrical current supplied to the bulbs.
Plain English
A knob or switch that lets the pilot make the cockpit lights brighter or darker.
Context Anchor
Seen on cockpit lighting controls, especially when adjusting panel or instrument lighting for night flying.
Derivation
From the verb 'dim' (to make less bright), with the suffix '-er' meaning 'a thing that does this.' So a dimmer is simply 'the thing that dims.'
Why Pilots Care
Adjusting cockpit light levels preserves night vision and reduces glare that can interfere with instrument scanning or outside visibility.
Intuition Check
A dimmer is not a main power control for the aircraft system. It controls light brightness, not whether the instrument or system itself is operating.
Example Sentence 1
After takeoff into the night sky, she rolled the panel dimmer back until the instruments glowed just enough to read.
Example Sentence 2
During preflight the instructor showed how to test the dimmer so the instruments would remain readable at night without being overly bright.