Light Intensity by Distance (Inverse Square)
Compute falloff using inverse square law for accurate lighting.
Intensity at the initial distance
Must be greater than zero
Distance at which you want to measure
Resulting intensity
25.00
cd
Intensity retention
25%
Of the initial intensity
4x
Distance factor
Inverse square law: I2 = I1 × (D1² / D2²).
What is the inverse square law?
The inverse square law describes how the intensity of a point light source falls as distance increases: if you double the distance, the intensity drops to a quarter. This calculator applies the formula I2 = I1 × (D1² / D2²) to estimate intensity in candelas at any distance, essential for realistic 3D lighting.
How to use this tool
- Enter the initial intensity in candelas of your light source.
- Set the initial distance at which that intensity is measured.
- Type the new distance and the result updates instantly with the percentage of light retained.
Typical use cases
- Estimate the light falloff of a spot or point light between two scene positions.
- Match lighting between shots with different camera to subject distances.
- Plan exposure levels on virtual sets with physical realism.
Frequently asked questions
Does the law apply to all Blender lights?
It applies strictly to point lights and spots with infinite distance. Area lights and globes follow other falloff curves, though the inverse square law remains a good initial approximation.
Why does intensity drop so fast?
Because the same amount of light spreads over a surface that grows with the square of the distance. At 2 meters you have a quarter, and at 3 meters a ninth of the initial intensity.