Definition
A method of controlling the brightness of aircraft instrument and panel lights by wiring fixed resistors in series with the lamps and using a multi-position selector switch to choose which resistor (or combination of resistors) is in the circuit. Each switch position routes current through a different resistance value, producing a different fixed level of brightness rather than a continuously variable one.
Plain English
A way to dim panel lights using a knob or switch that clicks between set brightness levels. Each click sends the electricity through a different resistor, and each resistor produces one specific brightness — bright, medium, dim, off — instead of a smooth slide from bright to dim.
Context Anchor
Seen in aircraft electrical system descriptions, instrument circuits, temperature indicating systems, lighting controls, and maintenance troubleshooting.
Derivation
Resistor comes from resist, meaning to oppose or hold back. That helps because a resistor does not make electricity; it opposes the flow of electricity. Selector comes from select, meaning to choose, and switch means a device that changes an electrical path.
Why Pilots Care
Knowing the lighting system uses stepped selector switches rather than a continuous dimmer explains why brightness changes in jumps. It also means a failed resistor in one position can leave that step dead while other positions still work — a useful clue when troubleshooting partial lighting failures at night.
Analogy
Like a three-speed fan switch: each position picks one fixed speed. There's no in-between — you get the speed the switch is wired for, and nothing else.
Intuition Check
Do not assume a resistor is a power source; it reduces or controls electrical flow. Do not assume a selector switch changes the equipment itself; it chooses which electrical path is connected.
Example Sentence 1
The panel lights on the older trainer use resistors and selector switches, so the pilot clicks through bright, medium, and dim rather than turning a smooth dimmer.
Example Sentence 2
Proper function of resistors and selector switches ensures reliable operation of radios and navigation equipment.