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Lumens Calculator: How Much Light Does a Room Need?
Work out the lumens a room needs from its size and use, with the LED power, the old incandescent wattage that matches it, and how many 800-lumen bulbs to buy, in metres or feet.
Lumens Calculator: How Much Light Does a Room Need?: The tool multiplies the floor area by a typical light level for the room, in lux: a 5 × 4 m living room at 150 lux needs about 3,000 lumens. Dividing by the bulb's efficiency, about 90 lumens per watt for LEDs, gives 33 W of LED light; the same light from old incandescent bulbs would take about 173 W. Runs 100% locally in your browser with zero server file uploads.
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Light on a surface is measured in lux, lumens per square metre. The room levels are typical recommendations for general lighting: about 100 to 150 lux for living rooms and bedrooms, and 300 to 500 for kitchens, bathrooms, and desks. Dark walls, high ceilings, and lampshades absorb light, so add 20 to 30% for those. LED boxes compare their lumens with old bulbs: 800 lumens is sold as a 60 W equivalent.
Bulb equivalents
LED boxes compare their lumens with old bulbs: about 450 lumens for a 40 W, 800 for a 60 W, 1,100 for a 75 W, and 1,600 for a 100 W bulb. Watts measure power use, not brightness, which is why lumens are the number to compare.
Running cost
To see what the light costs a year, enter the LED watts and hours of use in the electricity cost calculator.
How to use it
- Pick the room type and enter its length and width.
- Adjust the LED efficiency if your bulbs differ.
- Read the lumens, the LED watts, and the number of bulbs.
Privacy & limitations
Everything is calculated in your browser.
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Frequently asked questions
What is the difference between lumens and lux?
Lumens measure the light a bulb gives out; lux measure the light falling on a surface, one lumen per square metre.
Why does my room still feel dark?
Dark walls and floors, high ceilings, and shades absorb light; add 20 to 30%, or use several sources rather than one.
What colour temperature should I choose?
2,700 to 3,000 K looks warm and suits living rooms and bedrooms; 4,000 K is neutral for kitchens and workspaces.
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