How to use the light intensity and illuminance calculator
Find illuminance at a distance from a point light source. Enter luminous intensity, distance in the fields above; the illuminance is computed instantly and plotted on the chart so you can see how the answer changes.
Formula
Variables
- I — Luminous intensity (cd)
- d — Distance (m)
Worked example
With luminous intensity = 100 cd, distance = 2 m, the calculator gives illuminance ≈ 25 lux.
Frequently asked questions
What is the formula for the light intensity and illuminance calculation?
Illuminance (lux) = I / (d × d). Here I is luminous intensity (cd), d is distance (m).
What inputs do I need for the light intensity and illuminance calculator?
You need luminous intensity in cd, distance in m. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use this calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.