turn signal

A turn signal is a flashing amber light mounted on the front and rear corners of a vehicle, used to communicate intended direction changes to other road users. The light flashes at a rate of 60 to 120 cycles per minute, typically 1 to 2 Hz, creating a distinctive rhythm that catches attention in daylight and darkness. Turn signals are mandatory on all road vehicles and are controlled by a stalk or button near the steering column that the driver operates manually.

The lamp assembly houses an incandescent or LED bulb behind a translucent amber lens. Modern vehicles increasingly use LEDs, which consume less power, last longer, and can be integrated into more compact housings than traditional 21-watt bulbs. The electrical circuit includes a flasher unit, traditionally a thermal or electromagnetic device that interrupts power to create the on-off cycle; modern vehicles use electronic flashers. The turn signal on one side of the vehicle flashes independently when activated, though both sides flash together during hazard warning activation.

Turn signals are wired in parallel on each side: front and rear bulbs light simultaneously when that direction is selected. The circuit includes a cancellation mechanism, either mechanical (self-cancelling after a turn completes) or electronic (driver-initiated). Bulb failure is detected by monitoring current draw; if a bulb burns out, the flasher rate increases noticeably, alerting the driver to replacement need. This failsafe has roots in older thermal flashers that increased cycling speed when load decreased.

Visibility standards vary by jurisdiction. In North America, turn signal lamps must produce 200 to 1000 candela depending on position and are regulated by FMVSS 108. European standards under ECE R6 specify similar output ranges. The amber colour is legally mandated in most regions to distinguish turn signals from white position lights and red brake lights, improving recognition of driver intent.

Failure modes include burnt-out bulbs, corrosion in connectors, relay malfunction, and wiring faults. In some vehicles, a faulty turn signal on one side causes both sides to flash together or creates an asymmetrical blink pattern. Drivers often fail to cancel turn signals after lane changes, a phenomenon sometimes called "directional amnesia." The turn signal is one of the simplest and most critical safety devices on a vehicle, yet its straightforward function masks a century of incremental standardization and electrical refinement.