Why you can't just match the watts
With old incandescent bulbs, wattage doubled as a brightness label — a 100W bulb was clearly brighter than a 40W one. But watts only ever measured energy use, not light. LEDs produce the same brightness for a fraction of the energy, so a 10-watt LED can be every bit as bright as an old 60-watt incandescent. That is why, when you shop for LEDs, you should compare lumens (brightness) rather than watts.
Old watts to lumens at a glance
| Old incandescent | Approx. lumens | Typical LED wattage |
|---|---|---|
| 25W | 250 lm | 3–4W |
| 40W | 450 lm | 4–6W |
| 60W | 800 lm | 8–12W |
| 75W | 1,100 lm | 10–14W |
| 100W | 1,600 lm | 14–18W |
These are approximate — efficiency varies between brands, so always check the lumens printed on the box.
How to use your result
The calculator gives you a small lumen range rather than a single number, because the ideal brightness depends a little on the room and your taste. If your old bulb felt too dim or too bright, tell us and we'll shift the range up or down accordingly. Once you have your lumen target, pick a colour temperature to suit the room and match your fitting.
Want the full recommendation — brightness, colour, fitting and finish in one go? Try the bulb finder. To understand the science, read what are lumens?