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 — 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.