433N
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- Joined
- 20 Jun 2017
- Messages
- 752
I'm still thinking about the physics of this. Curved glass per se won't produce multiple images, it might distort a little but even that should be minimal if the glass surfaces are parallel. I've had a large number of vehicles (all road, alas!) with slightly curved laminated glass windscreens which were optically good. My guess is that the numerous laminae in the laminated glass are not as laminated as they should be and the extra reflective surfaces inside the screen are the problem and no one even thought this could happen. If I am correct a simple replacement of the correct quality should be enough. Leaving only the bolts and the software albeit after a long make, test and manufacture in bulk process.
I think from what has been said, the glass is quite thick. The incident light from the signal is partially transmitted and partially reflected at each surface. The light goes through one air/glass boundary at the outer surface of the window and then meets a glass/air boundary on the inner side of the glass. Part of the light is transmitted into the cab but part will be reflected back through the glass. It then hits the glass / air boundary at the outer part of the window where, again, it will be partially transmitted and partially reflected. The reflected part will pass back through the glass to the inner side of the window where again it will be partially transmitted. Given the thickness of the glass, refraction and reflection angles, the path of this reflected-reflected-transmitted light might be quite different to the transmitted light entering the cab, thus leading to two images. Of course, this happens in the day as well but the reflected-reflected-transmitted light is so weak that your eye will probably not pick it up. When driving at night, your eye becomes naturally more sensitive to light, hence more of an issue.
I don't know if that makes sense to anyone, but I can well understand this to be possible (but I have worked with optical components for a long time). It is possible that anti-reflection coating of the inside surface of the glass may cut this but the curvature might make it difficult.
More pertinently, I think the question has become as to what is politically acceptable. Suppose there is a quick fix, but then an incident occurs somewhere down the line that can be remotely tied to this problem ; can you imagine. The problem is so well-documented now that I think it will need a major revision and really do think that they should get in alternative traction PDQ.