I have heard that there may be undesirable optics when it comes to clear headlight covers:
Also in certain windshields, such as:
What says the clan? I'm particularly interested in the headlight cover thing, as I'm working on a car that will take a small-diameter headlight bucket, and I'd like to go with LED projector lights behind a Lexan cover.
The headlight in your picture has those lines because it works a little like a freznel lense to focus and direct the light. The bezel does have an effect but they've showed up on various OEM applications so it can't be that bad.
A quick google search tells me that LED headlight bulbs are already on the market. As long as the headlight bucket reflects correctly, the cover shouldn't cause a big problem. You can test them by shining the headlights against a dark wall and looking at the pattern. It should have a fairly obvious "cut" across the top of the pattern to keep from blinding oncoming drivers.
the covers you picture only have issues when they get pitted and worn.. then they refract light everywhere but where you want it to go. Europe, which has had better lighting optics for years, continued to allow the use of them much longer than the US did (I think 67 to guess by when VW stopped using them)
As for LED headlights.. I think only GE, Philips, and Sylvania make the ones worth owning.. and at upwards of $500 a pair, they are not cheap.
My 64 Corvair has a curved edge windshield like the car above. I have never noticed any distortion.
If you look at the angles, there actually less viewing angle through the glass then flat windshields (because you are looking at an angle anyway). The glass is perfectly uniform in the curves, so that does not cause issues.
Acrylic is cheap enough that it's worth experimenting with. I've certainly seen distortion in a windshield.
The Catfish kit car uses a pair of decent LED projectors with a shutter mechanism for high vs low - flipping on the "high" beams just puts more light into the trees. It also has plastic covers over the lights and I've not notice any trouble although it's a fairly flat piece where the light shines through. They're not the best headlights I've driven - my 7" GE LED lights pretty much take that crown - but they're sexy.
The upper light is the headlight, lower is the turn.
Refraction optics on complex curved surfaces are extremely delicate to try to predict or calculate. You end up needing to get so accurate with your measurements that it is almost impossible. Similar to airflow and aerodynamics, usually the easiest way to engineer is to 'guess and check'.
(from a physics major who did his senior project on measuring the thickness of layers deposited on glass via reflections and refractions of a laser - those were assumed FLAT surfaces, the light was single wavelength and point of origin, and the math was nuts)
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