By Emmanuel Sauvage · Updated
Technical guide
Bulb bases: B22, E26, E27, GU10…
The base (cap) is the part that goes into the fitting. The letter gives the type (E = Edison screw, B = bayonet, G = pins), the number the diameter or pin spacing in millimetres.
Reference table
| Base | Type | Size | Where you find it |
|---|---|---|---|
| B22 (BC) | Bayonet, 2 lugs, push and twist | 22 mm | UK: the most common ceiling pendant and lamp base |
| B15 (SBC) | Small bayonet | 15 mm | UK: small lamps, cooker hoods |
| E27 (ES) | Edison screw | 27 mm | UK and Europe: lamps, newer pendants |
| E14 (SES) | Small Edison screw | 14 mm | UK/Europe: candle bulbs, bedside lamps |
| E26 (medium) | Edison screw | 26 mm | US: standard household base |
| E12 (candelabra) | Edison screw | 12 mm | US: chandeliers, night lights |
| E17 (intermediate) | Edison screw | 17 mm | US: appliance and some ceiling fans |
| GU10 | 2 pins with feet, push and twist | 10 mm pin spacing | Mains-voltage spots (230 V UK, 120 V US versions) |
| GU5.3 (MR16) | 2 thin straight pins | 5.3 mm | 12 V low-voltage spots, need a transformer |
| G9 | 2 looped pins | 9 mm | Small designer fittings, mains voltage |
E26 vs E27: can you swap them?
Mechanically an E26 bulb fits an E27 socket and vice versa (1 mm difference). Electrically, the bulb's driver must match the mains: a US 120 V bulb on UK 230 V will fail, a 230 V bulb on 120 V will be dim or not start. Many LED bulbs are sold as "100–240 V"; only those are safe to swap. Never force one into the other without checking the voltage marking.
B22 or E27 in the UK?
Most UK ceiling roses with pendant lampholders are B22. If your fitting is B22 and you want a bulb only available in E27, use a fitting-rated B22-to-E27 adapter only if the lampshade clearance allows the extra length, or better, change the lampholder.
Bulbs for each base
UK · B22
Philips Ultra Efficient LED A60 B22, 2700K, clear
Listed as a 60 W-equivalent B22 bayonet bulb in warm white (2700K), rated up to 50,000 hours. Philips' Ultra Efficient range is its high-efficacy line for the new A–G energy label.
Check price on Amazon UKUK · GU10 230 V
Philips LED Classic GU10 4.6W, 4000K (6-pack)
Listing: 50 W equivalent, 390 lm, CRI 80, 220–240 V, non-dimmable, energy class F.
Check price on Amazon UKUS · E26 120 V
Philips Ultra Definition LED A19, 8W, 2700K (8-pack)
Listing: 60 W equivalent, 800 lm, E26 base, dimmable, flicker-free. Listed as CRI 95.
Check price on Amazon USUS · GU10 120 V
Philips 465054 LED GU10 6W, 3000K, dimmable (3-pack)
Listing: 400 lm, 35° flood, 50 W equivalent, dimmable. A 120 V GU10: do not use it on 230 V UK circuits (and vice versa).
Check price on Amazon USProduct data below is taken from the manufacturer's listing on Amazon, checked on 22 October 2026. Prices change: check the current price before buying. As an Amazon Associate I earn from qualifying purchases.