Lumens ↔ Lux Calculator
Move between total light output and the brightness that actually lands on your floor — the two figures every lighting spec juggles.
Result
This assumes light is spread evenly across the floor. Real fittings, mounting height, and wall colour mean working areas often get less than this ideal figure.
Output versus illuminance
A bulb is sold by its lumens — the total light it pours out. But what your eyes care about is illuminance: how much of that light reaches the page, the worktop, or the floor. Because the same lumens can be spread over a small pool or a whole room, output alone never tells you whether a space will feel bright.
The bridge is area. Spread a fixed number of lumens over more square metres and the lux falls in proportion; concentrate it over less and the lux rises. That single relationship — lux = lumens ÷ area — is what lets you turn a shopping figure into a real-world brightness, or work backwards from the brightness you want to the output you need to buy.
Frequently Asked Questions
What is the difference between lumens and lux?
Lumens measure the total amount of visible light a source emits in every direction — its raw output. Lux measure how much of that light actually falls on a surface, counted per square metre. One lux is one lumen spread over one square metre. A bright bulb (many lumens) can still give a dim room (few lux) if that light is spread over a large area.
How do I convert lumens to lux?
Divide the lumens by the lit area in square metres: lux = lumens ÷ area. For example, an 8,000-lumen fitting over a 20 m² room gives 8000 ÷ 20 = 400 lux on average across the floor.
How do I convert lux to lumens?
Multiply the target lux by the area: lumens = lux × area. If you want 300 lux across a 12 m² kitchen you need 300 × 12 = 3,600 lumens of total output, which you then split across your bulbs or fittings.
Why is the real lux lower than this calculator says?
This gives an ideal average assuming every lumen reaches the floor evenly. In practice, light is lost inside the fitting, absorbed by walls and ceilings, and falls off with mounting height, so the working plane usually sees less. Treat the result as a starting estimate and add headroom for important task areas.
What lux level should a room have?
As rough guidance, living rooms and bedrooms want around 100–150 lux of general light, kitchens and bathrooms about 300 lux, and a desk or workshop 500 lux or more. Task spots add local light on top of the ambient level.
Educational estimate assuming light spread evenly across the area. For code-compliant workplace or safety lighting, follow a proper lighting design and the relevant standard.