Types of LED bulbs: bases, shapes, watt-to-lumen equivalents and colour temperature

Short answer: When choosing an LED bulb, check four things: the base (E27, E14, GU10, G9, MR16/GU5.3), the shape (standard, candle, golf ball, reflector), the light output (lumens, not watts) and the colour temperature (Kelvin). An old 60 W incandescent bulb is replaced by an LED of about 800 lumens, typically 7–9 W. Warm white 2700–3000 K suits living rooms and bedrooms, neutral white 4000 K kitchens and work areas. On a dimmer circuit, only use bulbs marked dimmable.

Bulb bases: which socket does it fit?

The letter describes the type of connection, the number the diameter or pin spacing in millimetres.

• E27 (Edison screw): screw base, 27 mm. The most common base for ceiling lights, table lamps and pendants.
• E14 (small Edison screw): screw base, 14 mm. Candle bulbs, small wall lights, fridge and cooker hood lamps.
• GU10: a mains (230 V) spotlight bulb with two thick pins and a twist-and-lock fitting. Very common in recessed downlights.
• G9: a small 230 V capsule with two looped pins, used in decorative wall lights and pendants.
• MR16 (GU5.3 base): a 12 V spotlight bulb with two thin pins; it needs a transformer.
• G4: a very small 12 V capsule found in furniture and cabinet lights.

GU10 and MR16 look alike, but one runs on mains voltage and the other on 12 V. You cannot swap one for the other without changing the fitting.

Bulb shapes

• Standard (A60): the classic pear shape for general lighting.
• Candle (C35) and flame-tip candle: E14 or E27, for decorative fittings.
• Golf ball (P45) and globe (G95, G125): round bulbs for exposed fittings and wall lights.
• Reflector (R50, R63, PAR): directs the light in one direction, like a spotlight.
• Filament LED: clear glass that looks like an old incandescent bulb, popular in exposed pendants.

Spotlight bulbs also state a beam angle: 24–36° highlights a spot, 60° or more gives general light.

LED equivalents of old bulbs (lumen table)

With LEDs, brightness is compared in lumens, not watts. Approximate values:

• 25 W incandescent ≈ 250 lm ≈ 2–3 W LED
• 40 W incandescent ≈ 470 lm ≈ 4–5 W LED
• 60 W incandescent ≈ 800 lm ≈ 7–9 W LED
• 75 W incandescent ≈ 1,100 lm ≈ 10–12 W LED
• 100 W incandescent ≈ 1,500 lm ≈ 13–15 W LED

For halogen spots, roughly 35 W gives about 230–250 lm and 50 W about 350–400 lm; LED spot bulbs of 4–6 W replace them. LED wattage varies between brands, so always compare the lumen figure on the box. Our guide to lumens, watts and colour temperature explains this in detail.

Colour temperature: 2700 K, 3000 K, 4000 K, 6500 K

• 2700 K: the warmest, closest to an incandescent bulb. Bedrooms, living rooms, restaurants.
• 3000 K: warm white but a little crisper. Living areas and hallways.
• 4000 K: neutral white. Kitchens, desks, offices, shops.
• 6500 K: cool, bluish white (often sold as daylight). Storage, workshops, technical areas; it can feel harsh at home.

Avoid mixing colour temperatures in the same room for a calmer look.

CRI: does it show colours correctly?

The CRI (Ra) value shows how faithfully the light renders colours compared with daylight. At least 80 is recommended for homes, 90 or more for kitchens, dressing areas and bathroom mirrors. Cheap bulbs with low CRI make skin tones and food look dull.

Dimmable LED bulbs

Standard LED bulbs flicker, buzz or do not light at all on a dimmer. On a dimmer circuit:

1. Choose a bulb marked dimmable.
2. Make sure the dimmer is LED compatible; old incandescent dimmers often misbehave at low wattage.
3. Check the dimmer's minimum load; a few low-wattage LEDs may fall below it.

See our guide to dimmable LEDs and dimmers for details.

12 V MR16 bulbs and transformer compatibility

The most common problem when replacing MR16 halogens with LEDs is flicker. Older electronic halogen transformers need a minimum load (often 20–35 W); a 5 W LED does not reach it. The fix is to replace the halogen transformer with a 12 V constant-voltage LED driver, or to use a transformer the bulb manufacturer lists as compatible. Size the driver about 20% above the total LED load; our LED driver guide shows how.

Bulb or integrated LED fitting?

We do not sell individual LED bulbs. If you are planning a new ceiling or a renovation, fittings with the LED built in give longer life and more even light: downlights for suspended ceilings, LED panels for larger areas and track spotlights for adjustable light. With an integrated fitting, the LED and driver are designed together, so heat is managed better. Our guide to downlight sizes and spacing helps you work out the number of spots.

• → Lumens, watts and colour temperature
• → Dimmable LEDs and dimmers
• → How to choose an LED driver
• → Downlight sizes and spacing
• → Bathroom lighting zones
• → Downlights
• → LED panels