Buying a replacement bulb comes down to three things: the base that fits your light fitting, the colour of the light, and whether the glass is clear or frosted. Get the base right first, because a bulb with the wrong base won’t fit. The rest is about how you want the room to look.
Quickest way to check
Take the old bulb out and look at the base and the writing on the glass or base. Most bulbs have the base type (such as B22 or E14) and the wattage printed on them.
1. Which base (cap) do I need?
The base is the metal end that fits into your light fitting. UK homes mostly use bayonet bases that push in and twist, or screw bases that screw in. For these, the number is the width of the base in millimetres. Spotlights and small capsule bulbs use pins instead.
| Base | Also called | How to spot it | Where you’ll find it |
|---|---|---|---|
| B22 | BC, bayonet cap | Two small pins on the side, 22mm wide. Push in and twist. | Ceiling pendants, table and floor lamps. The most common UK base. |
| B15 | SBC, small bayonet cap | Two side pins like B22 but much narrower, 15mm wide. | Chandeliers, wall lights, small lamps. |
| E27 | ES, Edison screw | Screw thread, 27mm wide (about the width of a thumb). | Pendants, lamps and outdoor lights, especially modern or imported fittings. |
| E14 | SES, small Edison screw | Narrow screw thread, 14mm wide (about the width of a little finger). | Chandeliers, wall lights, cooker hoods, fridges and ovens. |
| GU10 | Spotlight | Two short pins with thick ends on the back. Push in and twist. | Downlights, kitchen and bathroom spotlights, track lights. |
| MR16 | GU5.3, low-voltage spotlight | Same size as a GU10 spotlight but with two thin, straight pins that push straight in. Usually 12V. | Older low-voltage downlights and display lights. Runs from a transformer, so an LED MR16 may need an LED-compatible driver. |
| G9 | Capsule | Small glass capsule with two looped pins that push straight in. Mains voltage (230V). | Chandeliers, wall lights, cooker hoods and small decorative fittings. |
| G4 | Low-voltage capsule | Very small capsule with two thin, straight pins 4mm apart. Usually 12V. | Cabinet and under-shelf lights, cooker hoods, and some chandeliers and desk lamps. |
2. Which shape?
| Shape | What it looks like | Best for |
|---|---|---|
| GLS | The classic pear-shaped household bulb. | Ceiling lights and lamps with a shade. |
| Candle | Slim and pointed like a candle flame. | Chandeliers and decorative wall lights. |
| Golf ball | Small and round. | Small shades, wall lights and lamps where a GLS is too big. |
| Spotlight (GU10) | Short and flat-fronted, with a beam. | Downlights and spotlights. |
| Vintage (ST64) | Tall teardrop with a visible filament. | Bare-bulb pendants where the bulb is on show. |
3. Which colour temperature?
Colour temperature is measured in kelvin (K). Lower numbers give a warmer, yellower light and higher numbers give a whiter, bluer light. Try to use the same colour throughout a room, or mixed bulbs will look odd next to each other.
Warm white
2700K to 3000K
A soft, cosy light, close to an old filament bulb. Choose this for living rooms, bedrooms, dining rooms and hallways.
Cool white
4000K
A clean, bright white light. Choose this for kitchens, bathrooms, utility rooms, garages and offices.
Daylight
5000K to 6500K
A crisp, slightly blue light like a bright day. Choose this for workshops, hobby and craft areas, and anywhere you need to see colours accurately.
4. Clear or frosted?
Clear
You can see the filament inside, and the light sparkles. Choose clear for chandeliers, crystal and glass fittings, open shades and bare-bulb pendants where the bulb is part of the look.
Frosted (opal)
The glass is milky, so the light spreads evenly with less glare. Choose frosted for shades where you can see the bulb from below, reading lamps, bathrooms and anywhere a bright point of light would dazzle.
5. How bright?
LED bulbs use far fewer watts than old bulbs, so we list each one with the old bulb it replaces, for example “7W (60W equivalent)”. Match the equivalent to the bulb you’re replacing. Brightness is measured in lumens (lm).
| Old bulb | LED bulb (about) | Brightness (about) |
|---|---|---|
| 25W | 2W | 250 lm |
| 40W | 4W | 470 lm |
| 60W | 7W to 8W | 806 lm |
| 75W | 8W to 10W | 1055 lm |
| 100W | 13W | 1521 lm |
| 50W GU10 spotlight | 3.5W to 5W | 350 to 450 lm |
On a dimmer switch? Choose a bulb marked dimmable. Older dimmer switches made for filament bulbs can make LEDs flicker or buzz, so the switch may need changing for an LED dimmer.
Still not sure?
Send us a picture and we’ll tell you which bulb you need
Take a photo of the old bulb, showing the base and any writing on it. A photo of the light fitting helps too. Send it to us and we’ll reply with the right bulb.
WhatsApp: 07710 680713
Email: jack@greenwoodlighting.co.uk
Phone: 01606 888006
Or bring the old bulb into our trade counter at 59 Mere Lane, Sandiway, Northwich CW8 2NR. We’re open Monday to Thursday 7:30am to 5pm and Friday 7:30am to 4:30pm.