I am trying to use an infrared LED and photodetector to make a crude obstruction sensor. The problem is that it has to work outside and the infrared radiation from the sun is causing false readings (non-blockage when there is a blockage.)

 

I had an idea of maybe using a polarized film to block out most of the sunlight. I've read that most reflected sunlight (off of the ground is my main problem I believe) is polarized horizontally. So I would install my film (right in front of the detector) so that it is vertically polarized.

 

Is my thinking correct or is it flawed? Any other ways to deal with the sun?

 

Thanks in advance for your help!

You might also be able to solve the problem optically by using a small lens to focus an image of the light source onto the sensor. That way the only light that the sensor would see would be coming from your light source.

I would first of all try placing a tube on the end of the detector to shield it.

To answer the original question, yes, reflected/scattered light is polarized to some extent, parallel to the plane of scattering as was suggested. But the degree of polarization depends on the angle of incidence, so simply adding a polarizing filter will have a varying effect over the course of a day.