# Intensity distribution of a LED light source

The light source: 190 high power LEDs in NIR. I have the datasheet of the LED.

I want to make a graph showing the spatial distribution, and to measure the intensity of the beam on the whole field of view.

Actually, I used to work with this light source without defining the exact distribution. According to the datasheet of the LED, I know that the radiant intensity is approx 500W/Sr.

Someone can suggest me a setup or a protocol to get the informations I want? Furthermore if someone heard about a powermeter that could help me.

-
BTW--Most shopping questions are off-topic. There are plenty of suppliers that can sell you photometers in a variety of bands if you have enough money. – dmckee Feb 21 '12 at 18:33

My first thought would be to ask the manufacturer (i.e. read all the data sheets and then call/email and ask to talk to someone technical).

If they can not or will not tell you or if you need to know the characteristics of an individual device then you'll have to build a jig and measure.

I'm not an expert at NIR, but I believe you can buy photo-resistors that work in that band. So rig a way to hold the diode and detector in a set of repeatable relative positions and go to town.

Of course, if you need an absolute (rather than relative) intensity profile you still have the matter of calibrating the photo-resistor to deal with. Experimental work is often like that.

-
NIR is a very convenient spectral region for just about anything you want to do, with only a few significant exceptions. Thor Labs, Newport, and CVI should have anything you can imagine. – Colin K Feb 22 '12 at 0:09

The easiest way to measure this experimentally is to place screens at various distances from the LED, take a picture of the spot with a digital camera and then analyze the intensity distribution using MATLAB. All it takes is one line of code. This is a poor man's way of doing things.

If you don't have MATLAB, use something else to do this. Usually, the spatial intensity distribution for the LED can be approximated by a Gaussian profile (TEM00 mode).

-
You're going to run into a mixed bag on using consumer digital cameras to image in the near-infrared. Some are sensitive in that range, some are not, and others are if you insure that you are using all glass lenses (no plastic). Some have a night-vision mode that selects only that range, but they are few and far between as there was a consumer outcry over some of their creepier uses. – dmckee Feb 21 '12 at 21:19
A handycam with a nightshot mode works very well up to 900nm. – Antillar Maximus Feb 21 '12 at 21:57

In regards to calculating the intensity distribution of LED light I have the following example. I have 4 LED lights attached to a apparatus with each LED located at the 4 corners of a square (5mm edge). I want to calculate the overall distribution of the light. After doing some research I strongly believe the gaussian beam model (http://en.wikipedia.org/wiki/Gaussian_beam) could be a good idea for modeling the distribution.

Instead of using one gaussian I will have to use 4 gaussians to model the overall intensity distribution. To calculate the unknown parameters of the model I have experimented with a white surface by capturing various images from different distances perpendicular to the surface. However my concern is where does the distance of the light source (LED lights) to the surface come into the formula? Because the distance affects the intensity distribution on the images. I would be so grateful if anyone could help or point to the right direction. Maybe my whole thinking is wrong.

-