G9 Bulbs

What a G9 capsule bulb actually is

G9 describes the cap, not the shape or the brightness. The two flat pins sit 9mm apart and push into a sprung holder rather than screwing or twisting in, which is what makes the format so compact. That small body is why designers reach for it: a G9 disappears inside a glass shade, a slim wall light or a multi-arm fitting where a screw-cap lamp would be visible. In the US the same lamp is sold as a bi-pin or G9 base bulb, and the pin spacing is identical.

G9 runs on mains voltage, and that matters

A G9 works directly on 240V, so there is no driver or transformer to find room for. This is the single most common mix-up when people replace a capsule: a G4 looks similar but runs at 12V and will fail immediately on mains, while a G9 fitted into a low-voltage circuit will barely glow. Count the pin gap before ordering: 9mm is G9, 4mm is G4.

Choosing a wattage and a colour

LED G9 capsules draw a small fraction of the halogen wattage they replace, so compare lumens rather than watts. As a rough guide, a lamp around 200 lumens stands in for an old 25W halogen and one near 400 lumens for a 40W. Warm white around 2700K keeps the yellow-tinted glow of the halogen you are replacing; 3000K reads slightly crisper; 4000K and above suits task and bathroom use where you want the light to feel clean rather than cosy.

Dimming depends on the driver, not the cap

A G9 capsule dims only if its internal driver is built for it, and even then it needs a trailing edge dimmer rated for LED loads. Fitting a standard capsule to a dimmer circuit causes the flicker and buzz people usually blame on the fitting. Check the lamp is described as dimmable and that the dimmer's minimum load is met, as several small LED capsules on one circuit often fall below it.

Enclosed fittings and heat

Capsules are small, which means their heat has nowhere to go. In a fully enclosed shade the driver runs hotter than it was designed for and life shortens noticeably, so look for a lamp rated for enclosed use if the glass seals completely. Fittings that vent at the top are far more forgiving.

Handling and care

Hold a capsule by its body rather than the glass, and let it cool before removing it: the pins grip tightly and the glass is thin. A dry microfibre cloth is enough to clear dust; nothing wet should reach the pins or the holder. If a lamp is stiff, pull straight rather than twisting, because the pins bend easily and a bent pin will not seat again.

Where G9 fittings turn up

Because the lamp is so small, G9 holders appear wherever the light source needs to be hidden: multi-arm chandeliers, glass wall lights, slim bathroom fittings, mirror lights and compact table lamps. If you are replacing a lamp in a decorative fitting and the old one had two pins you pushed in, this is almost certainly the cap you need.