Collection: BAY15D bulbs

The P21/5W bulb: stop and tail light in one bulb

The P21/5W is a dual-intensity bulb with a BAY15D base. It contains two filaments in the same glass:

• 5W in normal operation — permanently lit as a rear position light, with the tail lights.
• 21W during braking — lights up in addition to the 5W to form the stop light.

This dual system allows combining tail light and stop light in a single light point — a common solution on compact rear lights of small cars and city cars (Peugeot 107/108, Citroën C1, Toyota Aygo, Renault Twingo).

P21/5W or P21W: how to avoid mistakes?

Number 1 confusion in car signaling:

• P21W — 1 filament (21W), BA15S base with 1 centered pin. Single function (stop OR turn signal OR reverse).
• P21/5W — 2 filaments (21W + 5W), BAY15D base with 2 asymmetrical pins (different heights). Combines tail light and stop light.

The BAY15D base has its pins at different heights to prevent incorrect mounting — if one pin fits and the other doesn't, you have the wrong bulb.

To identify: look at the base — 2 pins at different heights = P21/5W (BAY15D); 1 single centered pin = P21W (BA15S).

Switching to LED P21/5W: what you need to know

Dual-intensity P21/5W LEDs reproduce the two brightness levels (5W tail light + 21W stop light). Important precaution: the LED must imperatively reproduce the dual intensity — some generic LEDs only have a single brightness, which makes the brake light identical to the tail light (dangerous and illegal — drivers behind do not perceive the braking).

Canbus version recommended for post-2010 vehicles to avoid dashboard errors and hyperflashing effect.