A G9 bulb is named after its base, the standardised connection that holds it in the fitting. It is a shape of connection, not a type of light. That distinction matters. The same G9 base is used by old halogen capsules and by the LED capsules sold to replace them, and the two behave differently once fitted.
Key Takeaways
- G9 describes the base, not the technology. Halogen and LED versions share the same base.
- LED G9 capsules are made to retrofit existing G9 halogen fittings.
- Wattage and brightness vary widely across G9 LEDs, so compare lumens rather than watts.
- Dimmable and non-dimmable G9 LEDs both exist, and a dimmable one still needs a compatible dimmer.
- Capsule dimensions differ between products, which matters in small or enclosed shades.
- Check the base marked on your old bulb before ordering anything.
The quick answer: A G9 bulb is a small capsule lamp with a compact base, used in wall lights, pendants and other compact decorative fittings. You can buy G9 bulbs as halogen or as LED, and LED versions are designed to fit the same holders. When replacing one, match the base first, then the brightness in lumens, then check the capsule will physically fit the shade.
What a G9 Bulb Actually Is
The G9 label is a base designation. It tells you how the bulb connects to the fitting and nothing else about what is inside it.
This is why the same shop can sell you a G9 halogen capsule and a G9 LED capsule for the same wall light. Integral LED, a UK lamp manufacturer, describes its G9 range as "designed to retrofit easily into existing G9 halogen bulb fittings". The base is the constant. The technology is the variable.
Capsule is the useful word here. G9 lamps are small, with the lamp body sitting directly on a compact base rather than on one of the larger bases used by standard household bulbs. That compactness is the point of the format, and it is why G9 turns up in fittings where a bigger bulb would be hard to hide.
Where G9 Bulbs Are Used
G9 bulbs are used in compact decorative fittings, including wall lights and pendants.
Integral LED lists its G9 capsules as "ideal for pendant fittings and accent lighting in domestic, hospitality and retail applications". Examples of fittings that use G9 bulbs include:
- Wall lights, particularly compact ones with glass shades.
- Small pendants and multi arm fittings where several little lamps sit behind glass.
- Decorative fittings where the lamp is partly visible and needs to stay discreet.
Lumination's own range includes fittings built around the format. The Franklite Cosmic wall light is a satin nickel bracket with a matt opal glass globe, and its product page states it is "compatible with G9 bulb (not included)" and "dimmable with compatible bulb and dimmer switch". That phrasing is worth noticing, because it puts two conditions on dimming rather than one.
G9 Bulb Sizes, Wattage and Brightness
There is no single G9 wattage, so check the figure on the bulb you are replacing.
Across Integral LED's published G9 range, the lamps run from 1.8W to 4.8W and from 180 lumens to 600 lumens, in 2700K and 4000K, with beam angles between 200 and 320 degrees. Lumination's own G9 LED range is listed at 3W and 4.5W in 3000K and 4000K.
So two bulbs that both say G9 on the box can differ by more than three times in light output. Wattage tells you what the bulb costs to run. Lumens tell you how bright it will look. If you want the same light as the lamp you are removing, the lumen figure is the one to match, and our guide to how many lumens you need covers how that maps to rooms.
Physical size varies too. Capsule length and diameter are not standardised across manufacturers in the way the base is. A replacement can therefore be electrically correct and still sit awkwardly in a small shade. Where a fitting encloses the lamp tightly, check the stated dimensions before ordering.
| What you are comparing | What it tells you | What it does not tell you |
|---|---|---|
| Base (G9) | Whether the bulb fits the holder | Brightness, colour, dimming or size |
| Wattage | Power drawn, so running cost | How bright the bulb will look |
| Lumens | Light output | Whether the beam suits the fitting |
| Kelvin | Colour of the light, warm or cool | Output or compatibility |
| Capsule dimensions | Whether it fits inside the shade | Anything electrical |
Replacing a G9 Halogen Bulb With an LED
The replacement itself is usually straightforward, because the base is unchanged. The decisions around it need a little care.
Match lumens, not watts. Comparing the wattage of an LED with the wattage of a halogen capsule tells you very little about brightness. Find the lumen figure for the lamp you are replacing where you can, and buy to that.
Check dimming properly. Dimmable and non dimmable G9 LEDs are both sold. Integral LED describes one of its dimmable capsules as "dimmable with compatible dimmers". The Franklite fitting above asks for both a compatible bulb and a compatible dimmer switch. The pairing matters, not just the bulb.
Check the capsule fits. Measure the space inside the shade if it is tight.
Check the colour temperature. If you are replacing one lamp in a multi lamp fitting, match the Kelvin value of the others or the difference will show.
If you are working through several different bulb types around the house, our LED bulb replacement guide covers the wider picture, and the running cost guide shows how to work out what any of them cost to run.
How to Identify the Bulb You Already Have
- Switch the light off and let the bulb cool before touching it.
- Look at the base and compare it directly with the replacement you are considering.
- Check for printing on the bulb body or its base, which often carries the base type and wattage.
- Check the fitting's own instructions or product page, which usually names the base it takes.
- Take the old bulb with you, or photograph the base, before buying a replacement.
Be careful with lamps that look similar. Integral LED's bulb range lists G9 alongside other bases including G4, GU10 and GX53, so a small capsule that resembles yours may use a different base entirely. These designations describe the base, which means a similar looking lamp is not necessarily interchangeable.
A Short Checklist Before You Order
- Confirm the base marked on the old bulb or in the fitting's instructions.
- Note the lumens you are replacing, not just the wattage.
- Decide whether you need a dimmable version, and check your dimmer.
- Check the capsule dimensions against the shade.
- Match the colour temperature to the rest of the fitting or room.
Frequently Asked Questions About G9 Bulbs
What does G9 mean on a light bulb?
G9 is a base designation. It identifies the connection that holds the bulb in the fitting, not the technology inside it. Manufacturers list it alongside other bases such as G4, GU10, E27 and B22. Because it describes only the base, a G9 bulb can be halogen or LED, and the two can look similar while behaving quite differently.
Can I put an LED bulb in a G9 fitting?
Yes, provided the bulb is sold as a G9. Integral LED describes its G9 range as designed to retrofit easily into existing G9 halogen bulb fittings. Check three things beyond the base: the brightness in lumens, whether you need a dimmable version, and whether the capsule physically fits inside the shade.
Are all G9 bulbs the same size?
No. The base is standardised, but capsule length and diameter vary between manufacturers, so a replacement can be electrically correct and still sit awkwardly in a tight or enclosed shade. Where the fitting encloses the lamp closely, check the stated dimensions before ordering rather than assuming the new one will match.
How bright is a G9 bulb?
It varies widely. Integral LED's published G9 range runs from 180 to 600 lumens at 1.8W to 4.8W, and Lumination's own G9 LED range is listed at 3W and 4.5W. That means two bulbs both labelled G9 can differ substantially in output, so compare the lumen figure rather than the wattage when you want to match an existing lamp.
Are G9 LED bulbs dimmable?
Some are and some are not, so check the specification for the individual bulb. A dimmable G9 LED also needs a compatible dimmer: Integral LED describes one of its dimmable capsules as dimmable with compatible dimmers, and the Franklite Cosmic wall light stocked at Lumination asks for a compatible bulb and a compatible dimmer switch.
What are G9 bulbs used for?
G9 bulbs are used in compact decorative fittings, including wall lights and pendants. Integral LED lists its G9 capsules as ideal for pendant fittings and accent lighting in domestic, hospitality and retail settings. Examples include wall lights with glass shades, small pendants and multi arm fittings, where the lamp needs to stay discreet behind or within the shade.
Choosing G9 Bulbs for Your Fittings
When choosing a G9 replacement, work through four checks. Confirm the base, match the lumens, check the dimming requirement against your dimmer, and make sure the capsule fits the shade.
Lumination stocks G9 LED bulbs in warm white and day white, including twin packs for multi lamp fittings. If you are unsure what your fitting takes, bring the old bulb into our Taunton (145 East Reach) or Wellington showroom and the team will identify the base for you. Delivery is free on UK orders over £75, and returns are accepted within 14 days.
