Also known as: Stop/tail light bulb, Stop/Tail Light Bulb, Combined Stop Tail Bulb, Bulb, stop/tail light
OEM & aftermarket brake & tail light bulb from top brands — compare prices, check fitment, order with free delivery
Browse brake & tail light bulb from trusted brands. Compare prices, check vehicle compatibility, and order with fast UK delivery.
The stop/tail light bulb (also listed as a stop-taillight bulb) performs two functions in one unit: it provides the low-level tail light glow when the headlights are on, and it brightens sharply to the stop-light intensity when the brake pedal is pressed. This dual function relies on a twin-filament design with two separate contact points in the base. A failed stop/taillight bulb eliminates rear visibility in the dark and removes the braking signal that warns following traffic — both are MOT failure items. Osram and Philips manufacture direct-fit twin-filament replacement bulbs in P21/5W (BAY15d) and 1157 base types for virtually every make on the road.
Because the bulb has two filaments, it can fail in three ways: the tail filament alone fails, the stop filament alone fails, or the entire bulb fails. Inspect the glass envelope carefully — a broken filament is usually visible.
On most vehicles the rear light cluster is accessible from inside the boot via a trim panel. The bulb holder twists out, and the twin-filament bulb pulls straight out of a push-fit or push-and-twist socket. The BAY15d base has offset pins to ensure correct orientation so that the filaments align with the correct circuits.
