Capsule LED Bulbs

What a capsule bulb is

Capsule describes the shape, not the fitting. It is a small cylindrical lamp with two pins in the base instead of a screw or bayonet cap, which is why it fits where nothing larger will. American listings call the same thing a bi-pin bulb. Because the format is defined by its size rather than its base, capsules arrive with two different caps that are not interchangeable, and telling them apart is the whole job.

G9 or G4: measure the pin gap

Two flat pins nine millimetres apart is a G9, and it runs on mains voltage with nothing else needed. Two round pins four millimetres apart is a G4, and it runs at twelve volts through a transformer. That single measurement decides everything else, and it is the reason most capsule replacements go wrong: a G4 on mains fails immediately, and a G9 on a low-voltage circuit barely glows. Hold the old lamp against a ruler before ordering.

Where each one is used

G9 turns up wherever the light source needs to disappear into a decorative fitting: multi-arm chandeliers, glass wall lights, slim bathroom fittings and compact table lamps. G4 belongs to low-voltage accent work: under-cabinet strips, display cabinets, plinth lights and small picture fittings. If the fitting has a chunky black transformer somewhere in the circuit, it is almost certainly G4.

Replacing halogen with LED

Compare lumens rather than watts, because an LED capsule draws a fraction of the power for the same light. Around 200 lumens covers an old 25W halogen and roughly 400 lumens a 40W. On low-voltage circuits there is a second thing to check: older wire-wound transformers need a minimum load that a couple of LED capsules cannot reach, which shows up as flicker, buzz or a lamp that will not strike at all. An electronic driver rated for low LED loads solves it, and the lamp was never the fault.

Dimming, heat and enclosed fittings

A capsule dims only if its own driver is built for it, so look for the word dimmable rather than assuming, and pair it with a trailing edge dimmer. Heat matters more than it does with larger lamps because there is so little body to shed it: in a fully sealed shade the driver runs hot and life shortens, so choose a lamp rated for enclosed use when the glass closes completely.

Handling capsules without breaking them

Hold the body, never the glass, and let a lamp cool before removing it. Pins are fine and bend under very little force, and a bent pin will not seat again, so pull straight out rather than rocking or twisting. A dry cloth is all the cleaning any capsule needs, and nothing damp should reach the pins or the holder.

Choosing by cap

Once you know which pins your fitting takes, the cap pages carry the full range for each: G9 for mains-voltage fittings, G4 for twelve-volt ones. Both list warm and cool whites, clear and frosted glass, and dimmable options where the driver supports it.