I got the above from Roy recently and spurred on by Boxter's example
I thought I would take some measurements.
Different from his test, I am measuring the transmission through the material in question, not the reflection. Since I think we're trying to prevent laser light from reaching the plate (or headlight), and prevent reflected light off the plate from reaching the lidar unit, I think this is the right measure.
First I measured the laser shield by itself. This allowed ~23% of the light at 905 nm through. (If light had to pass through twice (to the plate and then back) this would be ~.23^2=5%. Since intensity falls off as the square of distance, I think this means that if this were the only reflective surface, you would have to be at 23% of the distance for the LEO to get the same return signal as your distance without protection.) Since there has been some question of which way out to mount the laser shield I tired it both ways and (not surprisingly IMO) it was the same. I also tried it at several angles around 10-15 degrees to simulate off-angle targetting and this had no effect on the transmission.
Then I tried the laser shield with one fairly heavy, I think, coat of Veil on the smooth side. This had a transmission of ~18%, or 3% after two passes. So I'm thinking it's probably not worth Veiling the laser shield.
All measurements had ~10% measurement error from trial to trial depending on exact placement of the laser shield.
The ultimate test would be if boxster could put a piece of a retroreflective license plate in his type of spec and try these tests on reflection.