About the Lumens to Lux Calculator
This calculator converts between the main lighting units. Choose a conversion from the list, type the value and the second quantity it needs, such as the area of the room, the distance from the lamp, the beam angle or the bulb's efficacy, and the answer appears with the formula in words. It covers lumens to lux and back, candela to lux and back, candela to lumens and back through the beam angle, lux to foot-candles in both directions, and lumens to watts for LED and older bulbs. A short guide lists typical lux levels for rooms. The lux figures assume light spreading evenly over the area, and real rooms lose light to walls, fittings and dark corners. Beam conversions assume an even cone. The guide values are typical, not legal standards.
Updated October 2026
How to use the Lumens to Lux Calculator
- 1Choose what you want to convert from the list.
- 2Type the value you know, such as lumens or lux.
- 3Type the second quantity: area, distance, beam angle or efficacy.
- 4Read the result and the formula.
- 5Compare lux with the room guide to judge how bright the space is.
Lumens, lux, candela and watts
Lumens describe how much light a bulb produces in every direction. Candela describes how strong the light is in one direction, which is why spotlights are rated in candela. Lux is the light that arrives at a surface, and it falls with distance from the source.
Watts, on the other hand, measure the electricity a bulb uses, not its light. The link between them is the efficacy in lumens per watt, which is why an LED and an old bulb with the same lumens use very different watts.
How many lumens for each room
- Bedrooms: 100 to 300 lux for general light.
- Kitchens and desks: 300 to 500 lux.
- Reading and detailed hobby work: 500 to 750 lux.
- Workshops and detailed tasks: 750 lux and more.
- Multiply the lux you want by the area in square metres to get the lumens all your bulbs must give together.
Beam angle and spotlights
Spotlights and downlights concentrate light into a cone. A narrow beam has a high candela value for the same lumens, and a small area gets very bright. Converting between candela and lumens needs the full beam angle from the data sheet, usually between 10 and 120 degrees.
The calculation treats the beam as an even cone with no fade at the edges, so it is an estimate. Real fittings also lose light in the housing.
Bulb efficacy: incandescent, CFL and LED
Incandescent bulbs give about 14 lumens per watt, halogen about 20, compact fluorescents about 60 and LEDs about 100 or more. To pick a replacement, find the lumens of the old bulb and divide by the efficacy of the new type.
For the running cost of the bulb, see Electricity Cost Calculator, and to change other units use Unit Converter. Remember that lux depends on room size, so measure the floor with the Area Calculator, and change units with the Unit Converter if you need to.
Features
- Eight lighting conversions in one page
- Lumens, lux, candela, foot-candles and watts
- Bulb efficacy presets for incandescent, halogen, CFL and LED
- Formula shown in words
- Room lighting guide with typical lux levels
- Clear messages for zero areas, distances or angles
- Runs in your browser
Frequently asked questions
What is the difference between lumens and lux?
Lumens measure the total light a source gives out. Lux measures how much of that light lands on each square metre of a surface. The same 800 lumens gives 80 lux over 10 square metres and 800 lux over one square metre.
How do I convert lumens to lux?
Divide the lumens by the area in square metres that the light falls on. A 800 lumen bulb lighting 10 square metres gives about 80 lux. Choose the first option in the list, type 800 lumens and 10 for the area.
How many lumens do I need for a room?
Pick the lux you want from the guide, such as 300 for a kitchen, and multiply by the floor area in square metres. A 12 square metre kitchen needs about 3,600 lumens. Allow more if the walls are dark or the ceiling is high, because the lux figure ignores lost light.
How many watts is 800 lumens?
It depends on the bulb type. An LED at about 100 lumens per watt needs 8 W, a CFL at 60 needs about 13 W, and an old incandescent at 14 needs about 57 W. Use the last option in the list and choose a bulb type.
How do I convert candela to lumens?
Multiply the candela by the solid angle of the beam, which is 2π times one minus the cosine of half the beam angle. A 100 cd light with a 120 degree beam gives about 314 lumens, and with a full 360 degrees about 1,257 lumens.
What is a foot-candle?
A foot-candle is the illuminance of one lumen falling on one square foot, used mainly in the United States. One foot-candle equals 10.7639 lux, so 50 lux is about 4.65 foot-candles. The calculator shows both directions at once.