How to choose LED bulbs: lumens, colour and fittings explained

2 min read · 7 steps · Updated 3 October 2026

An LED bulb uses about 80 percent less electricity than the halogen bulb it replaces and lasts many times longer, so replacing the last old bulbs in a home pays for itself quickly. The confusing part is the packaging, which talks in lumens and kelvin instead of watts. Here is how to read it, following the UK's Energy Saving Trust.

Step by step

1. Read the fitting off the old bulb

   The code is printed on the base or the packaging. Common ones in Europe: E27 (large screw), E14 (small screw), GU10 (two pins with feet, spotlights), G9 and G4 (small pins), B22 (bayonet, common in the UK). The new bulb must have the same code.

   Done

2. Choose brightness in lumens

   Watts measure electricity used, lumens measure light. For a bulb as bright as an old incandescent: 15 W is about 140 lumens, 40 W about 470, 60 W about 800, 75 W about 1,050 and 100 W about 1,520. Most LED packs print the comparable wattage as well.

   Done

3. Choose the colour of the light

   The colour temperature is given in kelvin. 2,700 K is very warm white, like an old bulb, for living rooms and bedrooms. 3,000 K is warm white and suits most of the home. 4,000 K and above is cool white, bright and bluish, for kitchens, bathrooms and workrooms. Mixing colours in one room looks odd.

   Done

4. Check the colour quality

   The colour rendering index (CRI or Ra) says how natural colours look under the bulb. 80 or more is fine for the home. Cheap bulbs with a low CRI make food and faces look grey.

   Done

5. Check the dimmer

   Only bulbs marked dimmable work on a dimmer switch. Others flicker, buzz or fail early. Old dimmers made for halogen bulbs sometimes need replacing with an LED-compatible one.

   Done

6. Mind the shape and size

   LED versions of candle, globe and reflector bulbs exist. Check that the bulb fits in the shade or the enclosed fitting, and that an enclosed fitting is allowed, since LEDs dislike heat.

   Done

7. Fittings with built-in LEDs

   Some lamps and ceiling lights have LEDs that cannot be changed. When they fail, the whole fitting is replaced, and fitting a new ceiling light is a job for an electrician.

   Done

Good to know

The Energy Saving Trust puts the saving from replacing all halogen spotlights in a typical British home at about 45 pounds a year. Smart bulbs add remote control and colours but do not save more energy than ordinary LEDs.

Switching lights off when leaving a room still saves money, even with LEDs.

Dead LED bulbs are electronic waste. Take them to the recycling point or back to the shop, not into the household bin. Old halogen and incandescent bulbs can go in the normal bin; fluorescent tubes and energy-saving bulbs contain mercury and must be recycled.

More ways to cut the bill: how to lower your energy bill and how to draught-proof windows and doors.

In short: Match the fitting code, buy by lumens (470 for 40 W, 800 for 60 W, 1,520 for 100 W), warm white 2,700 to 3,000 K for living areas, cool white 4,000 K for kitchens, CRI 80 or more, dimmable only on dimmers.