Online Inverse Square Law Calculator

The Inverse Square Law

The inverse square law defines the relationship between the irradiance from a point source and distance. It states that the intensity per unit area varies in inverse proportion to the square of the distance. Distance is measured to the first luminating surface - the filament of a clear blulb, or the glass envelope of a frosted bub.

Example: You measure 10.0 lm/m² from a light bulb at 1.0 meter. What will the flux density be at half the distance?

Solution:
E₁=(d₁/d₂)²*E₂
E_{0.5 m}=(1.0/0.5)²*10.0 = 40 lm/m²

Please note the calculation is independent of units and only applies if the ligt source approximates a point source. Data may be entered into the calculator over the default values, either as a whole number (i.e. 20, 0.5, etc...) or in scientific notation (i.e. 2.00e⁺⁰¹, 5.00e-⁰¹, etc..). Enter the original measuement distance in the d1 box. Next enter the new distance in the d2 box (can be smaller or larger than d1). After that, enter the original measurement value taken at the original distance into the E1 box. Click the Calculate button to calculate what the measurement value will be at the new distance based on the Inverse Square Law. Click the Reset button to return the calculator to the default values. Click the Print button to print the results.