The original thread
is closed, so I started this one. Here's the original question:
ELVATO wrote:Anyone considered using this on headlights, windows and tail-lights to reduce the IR signature of the vehicle:
3M Crystalline Automotive Window Films 70
68% Visible Light Transmitted
50% Total Solar Energy Rejected
59% On Angle†
97% Infrared Rejected††
38% Solar Heat Reduction
9% Visible Light Reflection Int.
9% Visible Light Reflection Ext.
99.9% UV Rejected
23% Glare Reduction
Rejected means reflected, doesn't it? In which case, that would be bad.
Also, not sure I'd want my light output to be reduced by 32 percent.
Great minds thing alike... I recently started thinking along these lines. However, I sorta disagree with Elvato. Even if the tint reflects 100% of IR light, I don't feel it would be nearly as much a without the tint. The logic is this:
without the tint the laser light is entering the entire reflector housing which exploits the focal and culmination properties of the headlight as it was designed to do. This results in every square inch of the laser light entering the headlight being returned[/U]. This is why the headlights are targeted for the strongest return signal.
However, if one "rejects" the laser light from entering the headlight reflector housing then this culmination can not occur. I agree that one ideally would want a tint that could absorb 100% IR light. However, even if the Crystalline product reflects IR, I still believe it's worth using. Simply because most headlight lenses (outer plastic covers) are curved or angled to a degree, resulting in a large percentage of light rays bouncing in multiple directions. For example: try shining a flashlight at a chrome sphere verses a flat mirror of equal size. You'll note the sphere has a very small percentage of surface area perpendicular to the laser source. Of course the mirror would need to be angled perfectly back at you, but that's what the inside of a headlight is - a mirror. I'm not saying there isn't a return - just significantly less regarding the outside of a headlight assembly.
I would love to get my hands on a few sample pieces of IR rejection film to conduct these tests. If anyone has any local tint shop utilising these films, see if they will let you have any small scrap pieces - envelope sized and send them to me. I can mock up a controlled test to measure both transmission/rejection and reflectiveness of an IR source and post the finding here. Anyone willing to Help?