# Is there any relationship between light intensity and angle

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1. Mar 19, 2016

### ckyborg4

1. The problem statement, all variables and given/known data
I'm working on a project right now, which uses laser beams and part of the project requires me to find a mathematical model which relates angle of projection to the intensity of the light. Does anyone know of an equation(s) which relates the intensity and angle together?

2. Relevant equations

3. The attempt at a solution

2. Mar 19, 2016

### andrewkirk

There's a very simple relationship. Here's how to work it out.

Draw a beam of light with square cross-section of width $w$ hitting a surface at right angles. Label as $A$ the part of the surface illuminated by the light. Its area is $w^2$. Now, keeping the beam where it is, rotate the surface by angle $\theta$. Label as $B$ the the part of the surface that is now illuminated by the light. The area of $B$ will be a simple function of $w$ and $\theta$. Light has to be passing through $B$ at the same rate that it passes through $A$, so the ratio of the intensities must be the reciprocal of to the ratio of the areas. Use that to calculate the intensity when the light is at an angle to the surface.

3. Mar 19, 2016

### Simon Bridge

The intensity where? At the surface or someplace else?