A G23 bulb is a 2-pin compact fluorescent lamp: a single glass tube bent into a narrow U, sitting on a plastic base whose two pins are 23 mm apart. The starter is built into that base, while the ballast stays inside the light fitting – which is why replacing one, or switching it to LED, is a little more involved than swapping a screw-in bulb.
In British homes the G23 turns up in bathroom shaver and mirror lights, slim wall lights, under-cabinet kitchen strips, cooker hoods, older desk lamps, outdoor bulkheads and some emergency lights. On the glass or the base you will usually see the wattage, a code such as PL-S or 2-pin, and a three-digit colour code. In 835, for example, the 8 means a colour rendering of Ra 80–89 and the 35 means 3500 K.
Be careful with lookalikes. A 2G7 lamp has exactly the same tube shape but four pins and runs on electronic gear; a G24d also has two pins and an internal starter, but a chunkier, keyed base and two pairs of tubes (four legs). Neither will go into a G23 holder.
Length goes up with wattage, so measure the lamp you are taking out, pins included, and check the clearance under the diffuser.
| Fluorescent G23 | Approximate length | Light output | Usual LED equivalent |
|---|---|---|---|
| 5 W | 105–108 mm | about 250 lm | hard to find at this length |
| 7 W | 135–138 mm | about 400 lm | 3.5–4 W, about 400 lm |
| 9 W | 165–168 mm | about 600 lm | 4–4.5 W, 450–550 lm |
| 11 W | 235–238 mm | about 900 lm | 6–6.5 W, 600–720 lm |
Two things stand out. LED versions are often slightly dimmer than the fluorescent they replace, so if you shave or do make-up under it, take the brighter option. And they are wider – around 32 mm against 27–30 mm for the glass tube – which matters in a tight shaver light.
Look on the LED's packaging for one of these markings:
Fittings with electronic (HF) gear are less common with this cap. There, an LED only makes sense if its maker explicitly lists electronic ballasts as compatible. Most G23 LEDs are also non-dimmable, which rarely matters: a 2-pin fluorescent with a starter in its base could not be dimmed either.
Emergency fittings deserve extra care. Their battery and inverter electronics may not get on with a retrofit LED, so have an electrician check before you change anything that has to work in a power cut.
For a mirror, a neutral or cool white around 4000 K shows skin tones honestly and makes shaving easier. Kitchen worktops benefit from the same. Warm white at 2700–3000 K is gentler in a bedroom wall light or a hallway. Outside, LED has one more advantage over the old lamp: it gives full brightness the moment you switch on, even on a frosty night when a fluorescent bulkhead can take minutes to warm up.
Many G23 LEDs throw light over about 120° rather than all the way round, so in a fitting with a reflector behind the lamp the spread can look a little different from before.
The same 2-pin cap is used for UV-C tubes in pond and aquarium clarifiers, blue UV-A tubes in fly killers and blacklight effects, and a few lamps for reptile tanks or gel-nail curing. They fit the same holder but do a completely different job. A UV-C tube also keeps glowing long after its germicidal output has faded, which is why pond keepers replace it every season. None of these should go into a household fitting, and a lighting LED won't do their work either.
Switch off, let the lamp cool, grip the base rather than the glass and pull straight out – a G23 doesn't twist or screw. Old compact fluorescents contain a small amount of mercury, so take them to a household waste recycling centre or a retailer's lamp collection point. If one breaks, open a window, sweep up the pieces and don't use a vacuum cleaner.
A 2-pin compact fluorescent, or an LED replacement for one, with pins 23 mm apart and the starter built into the base.
Usually yes, if the fitting has a magnetic ballast and the LED is marked EM. Mains-only LEDs and fittings with electronic gear need checking or rewiring first.
Typically 6–6.5 W. Compare lumens rather than watts: the old 11 W lamp gave around 900 lm.
A 4–4.5 W LED giving 450–550 lm, about 165 mm long.
Neither in general. Warm white suits relaxing spaces, cool white suits mirrors, kitchens and work areas where you need to see detail.
No. G24 has wider-spaced pins, a larger keyed base and more tubes, so the two are not interchangeable.
Other caps and lamp types are covered under light bulbs. If your fitting takes a long, straight tube instead, read up on T5 tubes.
