http://www.1stdrive.com/speedcameras.html
Infra red is a slightly lower frequency than visable light, some of which is also reflected by the small reflective particles used in Photoblocker.
To test this use the infra red setting on you camcorder, I did.
And you tested it by holding the camera about 8 feet off the ground, pointing down at an angle of about 45 degrees whilst your car was travelling at 30+ mph?
For those small reflective particles to work, there would have to be many thousands more than you will get in the jollop and every particle will have to be aligned so as to reflect light back up to the camera - and you will need enough particles to cover each of the possible angles of reflection (from, say 35 to 70 degrees).