Optical Distance Law

Distance and geometric dilution of light

Optical distance law

The illumination intensity on a surface is inversely proportional to the square of its distance from the light source and can be expressed as

I = L / d2                  (1)


I = light intensity, illumination (lux, lumen/m2)

L = luminance of lamp (lumen)

d = distance from light source (m)


I1 d12 = I2 d22 = constant                   (2)

(2) can be modified to

I1 / I2 = d22 / d12                       (2b) 

Example - Illumination Intensity from a Lamp at distance

The illumination intensity from lamp with luminance 10000 lumens at distance 2 m can be calculated with (1) as

I1 = (10000 lumens) / (2 m)2

   = 2500 lux

The illumination intensity at distance 5 m can be calculated by modifying (2b) to 

  I2 = I1 d12 / d22 

     = (2500 lux) (2 m)2 / (5 m)2

     = 400 lux

Related Topics

  • Basics - The SI-system, unit converters, physical constants, drawing scales and more
  • Mathematics - Mathematical rules and laws - numbers, areas, volumes, exponents, trigonometric functions and more

Related Documents

Tag Search

Search the Engineering ToolBox

- "the most efficient way to navigate!"

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your SketchUp model with the Engineering ToolBox - SketchUp Extension/Plugin - enabled for use with the amazing, fun and free SketchUp Make and SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp from the Sketchup Extension Warehouse!

Translate the Engineering ToolBox!
About the Engineering ToolBox!