dennis@home wrote:
On 02/03/2016 15:24, Graham. wrote:
On Wed, 2 Mar 2016 07:01:15 -0800 (PST), Martin Bonner
wrote:

On Wednesday, 2 March 2016 15:50:34 UTC+1, The Natural Philosopher
wrote:
On 02/03/16 14:41, Graham. wrote:

Basically the idea is we all drive about using un-dipped headlights
with the lights, and windscreens polarized with a 90deg differential.

So this issue must have been considered time and time again, yet
always rejected for mainstream use. Why?

Oh dear. Does this mean you wouldn't see cars headlights coming
straight
at you?

No. Polarizers are not 100% efficient, so you would still see a bright
spot - but *most* of it would be blocked, so you wouldn't be blinded
either.

Two problems though:
- Polarizers cut out about half the light.
- That means the headlamps are only half as bright.
- It also means that the windscreen cuts out about half the
reflected
light.
- Net result: Your beam headlight needs to be 4x as bright!
(Actually, LEDs might be able to emit polarized light directly,
rather
than blocking light of the wrong polarization. Still have x2.)

- The killer problem though is legacy. If I am driving towards you
with
my new car with polarized headlamps, how do I know I don't need to
dip
my headlamps?

How much ND filtering is involved in a typical pimpmobile windscreen?



If its legal, not much.
They have to transmit 96% IIRC.

I thought it was nearer 70%, however it's some years since I
looked into this. One state in the US won't allow tinted front
windscreens at all if IRC. There is also the tilt factor of the
windscreen relative to the source which also comes into this. I had a
bad experience with a coated winscreen before Xmas where the in car
wireless RFID toll tag would only work on the LHS of the mirror, even
though the coating was supposedly not present all over. It was a pig to
remove the tag, even with a hair dryer and even then only 70% of the
glue transferred.