For decades we chose light bulbs by watts — a 60W globe, a 100W globe. But watts measure how much energy a bulb uses, not how much light it gives out. With LED, that old habit breaks down: an LED can be as bright as an old 100W globe while using under 15W. Here's what to look at instead.
Lumens = brightness
Lumens (lm) are the real measure of light output. The higher the number, the brighter the light. As a rough guide for replacing old globes:
- 40W old globe ≈ 450 lumens
- 60W old globe ≈ 800 lumens
- 75W old globe ≈ 1,100 lumens
- 100W old globe ≈ 1,600 lumens
So if a box says "60W equivalent," what you actually want to see is around 800 lumens.
How much light does a room need?
It depends on the job the light is doing:
- Mood / accent: 100–400 lm
- Bedside & table lamps: 400–800 lm
- Task light (desks, kitchen benches): 800–1,500 lm
- Main room light: 1,500–3,000+ lm depending on room size
Watts still matter — for your power bill
Watts now tell you running cost, not brightness. Two LEDs might both give 800 lumens, but the one drawing fewer watts is more efficient. Look for a high lumens-per-watt figure — it's free money over the life of the bulb.
Don't forget colour temperature
Brightness is only half the story; the colour of the light sets the mood. Measured in kelvin (K): warm white (2700–3000K) for living rooms and bedrooms, neutral white (3500–4000K) for kitchens and bathrooms, and cool white (5000–6500K) for garages and task work. Prefer to keep your options open? Colour-changing and smart bulbs let you dial the temperature to suit the moment.
Quick checklist before you buy
- Check the lumens for brightness (not the watts)
- Check the kelvin for warm vs cool
- Check the fitting — E27, B22, E14 or GU10
- Want to dim it? Make sure it says dimmable
Ready to choose? Browse Light Bulbs & Globes, or read our full Lighting Buying Guide for the bigger picture.