Halogen bayonet base bulbs – P21W, PY21W, P21/5W, R5W

The bayonet base is a fastening system with two side lugs that lock with a quarter turn into the holder. It is recognized by its cylindrical metal base, with two small bumps (lugs) on the sides. The BA15S base (straight) equips P21W and R5W; the BAU15S (offset lugs) is reserved for orange PY21W to prevent cross-fitting; and the BAY15D (double contact) is used for bi-filament P21/5W. This system is more robust than the wedge and withstands vibrations better.

The P21W is a 21-watt clear-glass bulb, with a BA15S base (symmetrical pins). It is used for turn signals with orange optics, the reverse light and the rear fog light. The PY21W is identical in power, but has an orange-tinted glass and a BAU15S base with offset pins to prevent reversal. It is mandatory on vehicles with clear turn signal optics so that the light emitted is orange. The two bases are not physically interchangeable. AGM Vision offers both versions in stock.

The P21/5W bulb (BAY15D double-contact base) combines two filaments in a single bulb: a 21-watt filament for the brake light (braking) and a 5-watt filament for the rear position light. This design makes it possible to have two lighting functions in a single location, which is the standard on many European vehicle rear lights. The BAY15D base has lugs at different heights to ensure correct installation and prevent the filaments from being reversed.

The R5W and the P21W share the same BA15S base, but differ in power: 5 watts for the R5W and 21 watts for the P21W. The R5W is used for position lights, rear sidelights and license plate lighting, requiring low power. The P21W is fitted for functions requiring more brightness, such as turn signals, the reverse light and the rear fog light. Although they are physically interchangeable, installing a P21W in place of an R5W would overload the circuit and dazzle. Follow the original reference.

Yes, chrome bulbs (or Silver Vision) are coated with a metallic coating that gives a silver mirror appearance when the bulb is off, visually removing the orange tint in clear housings. When the bulb lights up, the heat from the filament makes the coating transparent and lets the orange light pass through normally. This process is particularly popular for PY21W turn signal bulbs in transparent housings. The ECE-approved versions sold by AGM Vision guarantee legal operation and passing the vehicle inspection.

The reverse light generally uses a P21W bulb with a BA15S base of 21 watts, producing a white light sufficient to illuminate the rear of the vehicle during maneuvers. On some older or compact vehicles, an R10W (10 watts) may be used. Check the original reference in the maintenance booklet or by removing the existing bulb. Replacement is simple: access the rear light, turn the bulb holder a quarter turn and replace the bulb. AGM Vision indicates vehicle compatibility on each product sheet.