About the Candela to Lux Calculator
Candela measures how intense a light is in one direction; lux measures how much light lands on a surface. The link between them is the distance: the further away the surface, the more the light spreads out. This calculator uses the inverse square law, lux = candela ÷ distance², to give the illuminance in lux and foot-candles. Enter the distance in metres or feet. It is ideal for torches, spotlights, stage lights and LED datasheets that quote candela.
Updated October 2026
How to use the Candela to Lux Calculator
- 1Enter the luminous intensity in candela.
- 2Enter the distance between the light and the surface.
- 3Choose metres or feet.
- 4Read the illuminance in lux.
- 5See the same light level in foot-candles below.
Candela, lumens and lux
Lumens count all the light a lamp gives out. Candela is how much of it goes in one particular direction, so a narrow beam has a high candela figure. Lux is lumens per square metre arriving at a surface. Converting candela to lux only needs the distance, because candela already describes the beam.
The inverse square law
For a small light shining straight at a surface, illuminance falls with the square of the distance. The formula assumes the surface faces the light; if it is tilted, multiply by the cosine of the angle between the beam and the surface's normal.
- lux = cd ÷ m²
- foot-candles = cd ÷ ft²
- 1 fc = 10.764 lx
Worked examples
A head torch rated at 5,000 cd puts 5,000 lux on something 1 m away and 200 lux at 5 m. A 20,000 cd spotlight at 10 m gives 200 lux, about the brightness of a well-lit living room. A bicycle light of 400 cd gives only 4 lux at 10 m, which is why road bike lights need tightly focused beams.
Going the other way
If you know the lux you want at a certain distance, multiply it by the distance squared to find the candela the light needs. To light a sign 4 m away to 300 lux you need a lamp of at least 4,800 cd aimed at it. Our Lux to Candela calculator does that sum, and the Candela to Lumens calculator turns the candela of a beam into total lumens.
Using it anywhere
Check a torch's throw on your phone in the shop or plan stage lighting on a laptop. The calculation happens instantly in the browser and nothing you enter is kept. Luminous intensity and illuminance are easy to mix up, so keep the distance in mind. Convert backwards with the Lux to Candela Calculator, turn candela into total light with the Candela to Lumens Calculator, and compare lighting levels with the Lumens to Lux Calculator.
Features
- Candela to lux and foot-candles
- Distance in metres or feet
- Uses the inverse square law
- Good for torches and spotlights
- Copy result
- Private and free
Frequently asked questions
How do I convert candela to lux?
Divide the candela by the distance squared in metres: lux = cd ÷ d². A 1,000 cd light 2 m away gives 1,000 ÷ 4 = 250 lux.
What does a torch's candela rating mean?
It is the peak beam intensity. Flashlight makers measure lux at a distance and multiply by the distance squared to get candela, so this calculator reverses that sum.
Why does lux fall so quickly with distance?
Light spreads over an area that grows with the square of the distance. Doubling the distance spreads the same light over four times the area, so lux drops to a quarter.
How do I convert to foot-candles?
1 foot-candle is 10.764 lux. The calculator shows both; if you work in feet, foot-candles = cd ÷ distance² in feet.
Does it work for floodlights and room lights?
The inverse square law is accurate when the distance is at least five times the size of the light. Close to a large panel or a room full of lamps it overestimates the fall-off.
How much lux do I need?
About 100 lux for corridors, 300 for kitchens, 500 for desks and reading, and 1,000 or more for detailed work.