# Homework Help: Help on IR light please

1. Feb 7, 2009

### mchi5cf2

I want to know the Power that comes out of an IR Illuminator. The manufacturer only gives that power is 12mW at 85m. It also gives a beam angle of 35 degrees.

A. I took the surface area of the sphere generated by the illumination. That is 4*pi*(r^2)
B. The fractional beam area is calculated using the beam angle given and is (35/180)*(35/180)

C.So the area of the beam is the multiplication of A by B=C

In order to calculate Power you then calculate the result in C by 12mW(given) and you get a power of approxmitale 41 W.

Do you think my methodology is right ?Do you seggest anything??

I really need to work this out as it is essential for my project

2. Feb 7, 2009

### LowlyPion

Re: Help on IR light please!!

Welcome to PF.

When you say that the intensity is 12 mw what is the area of the detection that is determining 12 mw of power? Would that be 12mw/m2?

Since an IR illuminator projects light in a directed way, it would seem that the 12 mw summed over the area of a circle of radius 85m*sin17° would determine the intensity of the light projected at the source.