# Inverse Square Law - Calculating the solid angle

1. Apr 1, 2013

### CodyW

Hi Everyone,

For an individual inquiry and formal lab report task at school I have chosen to conduct an experiment to find out whether hot shoe mounted flash units follow the inverse square law and how the flash zoom is affected by the inverse square law.

My first question is that In order for me to find the solid angle I have to I have to find the area at a specific distance. Is there an easier way to go about calculating the solid angle other than using surface integrals?

My second question is that is there a way to calculate the luminous intensity from the power output of the flash (in watt seconds)?

Any help would be greatly appreciated. :)

Kind Regards,
Cody

2. Apr 1, 2013

### Staff: Mentor

Depends on the data you have. The area at a specific distance is sufficient to calculate the solid angle without integrals.
If you know the spectrum (and the efficiency, if the power is the input of your flash light).