Polarized Light -- Idea for headlight safety

[sophiecentaur]

Xenon HID lamps for cars aren't a true xenon short-arc bulb, but they also aren't incandescent lamps or halogens. They're metal halide gas discharge lamps, with a bit of xenon to boost startup intensity.

I'm a bit confused by that. The Wiki article says that they take a warm up time of a few minutes. Mine are on instantly (or at least very bright at the start). Wiki says that automotive bulbs are metal halide gas discharge. I gave up looking because nearly all the hits are sites to sell you replacement bulbs.
Also, when I enter the Reg Number of my car, everyone claims that dip and main are the same type. They are not - one's blue and the other's hello halogen colour

 

[Sherwood Botsford]

You can put the same number of lumens on the road by jacking up the lamp power before it gets filtered. This takes a rule change in max wattage for headlamps. Given the difference between tungsten and LED efficiencies, it should probably be defined in terms of illumination anyway.

I think reflection from a non-metalic surfaces randomizes polarization.

So if random, it will be in effect rotated 45% -- half way -- So you would get back 1/sqrt(2) of the illumination -- a drop of about 30%

But the opposing headlights would be blocked close to completely. So the signal to noise ratio would be markedly improved. There would be some glow from forward scatter reflection of the opposing car's headlights, which would reveal the car's location even if headlight dimming were perfect, and would help you see the road.

 

[FactChecker]

I think reflection from a non-metalic surfaces randomizes polarization.

My experience is with the camera polarizing filter. There is a noticeable reduction of glare reflecting off of leaves, glass, water, etc. when the filter is turned correctly.

 

[sophiecentaur]

My experience is with the camera polarizing filter. There is a noticeable reduction of glare reflecting off of leaves, glass, water, etc. when the filter is turned correctly.

I would be very surprised if linear polarisation (as in camera filters) were used for this sort of project. Cancellation is very much affected by tilt when linear polarisation is used. That's the reason for using circular polarisation for stereo cinema and I think all the same advantages would apply for the headlight trick. However, it is all beginning to appear less and less attractive to me.
The problem with a system like the one being discussed requires everyone to be taking part and could not increase illumination above the present legal cut off angles. I think we would have to assume that the majority of vehicles would initially be using the standard dip arrangement. A more intelligent system, not involving polarisation at all, would allow the driver of a modified car to have better aimed headlamps, protecting any oncoming driver yet giving much better illumination of the parts of the road at higher angles and which are so hard to see at present. Since the early proposals for polarised systems, things have changed so much and the dynamically pointed and profiled beams are well within existing capabilities. The snag would be with regulations and specifications rather than the technogoly, I think.

 

[Klystron]

Why should I repeat work (testing degradation of polarization due to dirt/haze) when it’s already been done. Just consider the situation.

There are much more elegant solutions. Work has been done on DMD projection systems for headlights. Coupled with a camera system, the pixels corresponding to the head location of a driver in an oncoming vehicle can be dimmed or even shut off completely. This can also be done for pedestrians. No visible light = no glare.

More advanced implementations can project around falling snowflakes to improve visibility.

Google found this pdf. DMD (digital micro-mirror device) begins on page 2.
http://www.utc.ices.cmu.edu/utc/TNCCRKN-ECCV14.pdf

 

[FactChecker]

I would be very surprised if linear polarisation (as in camera filters) were used for this sort of project.

Yes. I was only responding to the hypothesis that only reflections from metal polarized a reflection. My experience from using linear filters refutes that.

 

[sophiecentaur]

It’s certainly easier to discuss linearly polarized light and to make predictions. CP is just another step. (Much easier - along with a lot of other EM wave questions- when applied to RF type wavelengths and bits of metal wire)

 

[Keith_McClary]

There is some research on polarized LEDs:

Here, we demonstrate light-emitting diodes presenting high-brightness polarized light emission by combining the polarization-preserving and directional extraction properties of embedded photonic-crystals applied to non-polar gallium nitride.

https://www.nature.com/articles/lsa201222

 

[sophiecentaur]

There is some research on polarized LEDs:

https://www.nature.com/articles/lsa201222

That is an interesting article but may not be too much related to a system that (imo, at least) would benefit more from circular polarisation than from linear.

 

[Eric Bretschneider]

I have been aware of that since the 1960s (wasn't around in the 1930s, sorry, I bow to your seniority )Nothing of the kind; how much have you experimented? Not much, to guess from your assertion...? Try it! Set up two polarisers at right angles and blow some dust or mist or smoke between them and see how much light gets through; THAT is what you call the whole system falling apart? Some people are very hard to please...

Scattering from airborne particles isn't the problem. It's scratches/defects and dirt on the external optical surface. You can clean and polish your optics weekly or perhaps monthly and have it work, but most people aren't going to bother.