How do I choose the right bulb fitting and brightness?
Reading lumens rather than watts, the colour temperature that suits each room, and identifying the fitting you actually have.
- Difficulty
- beginner
- Time
- 20 min
- Read
- 3 min
Short answer
Brightness is lumens, not watts — roughly 800 lumens replaces an old 60W bulb. Colour is measured in kelvin: around 2700K is warm and suits living rooms, 4000K is neutral for kitchens and workspaces. Take the old bulb with you to match the fitting.
Bulb buying used to be one number. It is now three, and the one most people still use — watts — is the one that no longer means anything about brightness.
Step by step
- Identify the fitting first.Bayonet caps are B22 for standard and B15 for small. Screw fittings are E27 standard and E14 small. Spotlights are usually GU10 with two pins, or MR16 for low voltage. Take the old bulb to the shop.
- Buy on lumens, not watts.Watts measure power consumed; lumens measure light produced. LEDs use a fraction of the power, so wattage tells you nothing useful about how bright a bulb is.
- Learn the rough equivalents.About 450 lumens for an old 40W, 800 for a 60W, 1100 for a 75W and 1600 for a 100W. Those four numbers cover almost every domestic decision.
- Work out how much light the room needs.A living room wants softer, layered light; a kitchen or bathroom wants considerably more. Several smaller sources usually beat one bright ceiling fitting.
- Choose the colour temperature deliberately.2700K is warm white and suits living rooms and bedrooms. 3000K is a softer neutral. 4000K is neutral and good for kitchens, bathrooms and workspaces. 6000K is daylight and looks clinical in a home.
- Keep colour temperature consistent per room.Mixing 2700K and 4000K in one room looks wrong in a way that is hard to identify but obvious. Match them within a space.
- Check the colour rendering index.CRI describes how accurately colours appear. Above 80 is fine for most rooms; above 90 matters where you judge colour — a kitchen, a bathroom mirror, a workspace.
- Check dimmability explicitly.Not all LEDs dim, and those that do need a compatible dimmer. A non-dimmable bulb on a dimmer flickers, buzzes and fails early.
- Check the beam angle for spotlights.A narrow 36-degree beam makes pools of light; a wide 110-degree beam gives even coverage. It matters more than brightness in a room with several downlights.
- Check the physical size.Some LED bulbs are longer or wider than the filament bulbs they replace, and will not fit inside a shade or a recessed fitting. Measure if the fitting is enclosed.
- Watch for enclosed-fitting ratings.LEDs are heat-sensitive at the base. A bulb not rated for enclosed fittings will fail early in a sealed shade, and many are not rated for it.
- Do not judge by price alone.Very cheap LEDs use poor drivers, flicker, render colour badly and fail early. The mid-range is where the value is.
Tips
- 800 lumens replaces an old 60W bulb. If you remember one number, that is it.
- 2700K living rooms, 4000K kitchens and bathrooms. Consistent within each room.
- Take the old bulb to the shop. Fitting codes are easy to get wrong from memory.
Common mistakes
- Buying by wattage — Watts measure power, not light. An LED at 8W can be brighter than another at 12W, so wattage tells you nothing about the result.
- Using a non-dimmable bulb on a dimmer — It flickers, buzzes and fails early. Dimmability is a specific specification, not a default.
If it doesn't work
New bulb much dimmer than expected
Cause: Bought on wattage rather than lumens — Fix: Check the lumen figure — around 800 for an old 60W equivalent.
Room feels cold and clinical
Cause: Colour temperature too high — Fix: Move to 2700K for living spaces. 6000K daylight bulbs rarely suit a home.
Bulbs failing quickly in a shade
Cause: Not rated for enclosed fittings — Fix: Buy bulbs specifically rated for enclosed use — heat at the base is what kills them.
Bulb does not fit the fitting
Cause: Wrong cap type — Fix: Match the code — B22, E27, GU10 and so on. Take the old bulb as a reference.