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Polarized sunglasses reduced glare by blocking light polarised by reflection off a horizontal surface. Also, they block half the unpolarized light.
Already suggested on the halfbakery (link), manually adjustable sunglasses could have a second polarizing filter which could be rotated through up to
a quarter-turn, to optionally remove more of the unpolarized light.
Which is all very well, but why not make it more complicated with a view to expediting the marketing campaign?
I propose sunglasses which have two fixed outer polarizing filters at right-angles, and a number of adjustable filters in-between, to progressively persuade the light to change its polarization. These filters are ganged together with a slider to smoothly rotate over a range between 0 and some angle close to 90 degrees.
I know this sounds like it shouldn't work, but the universe is stranger than intuition expects.
It turns out a photon only 'remembers' its current polarization, and if you present it with a filter somewhere in-between 0 and 90 degrees it has to 'decide' whether to pass through the filter, or not - and if it does it acquires a new polarization.
QuickPolarizing Sun Glasses
QuickPolarizing_20Sun_20Glasses
Each 'lens' is made from two discs of polarizing filter; one is manually rotatable. [Loris, Nov 28 2022]
Bell's Theorem: The Quantum Venn Diagram Paradox
https://www.youtube...watch?v=zcqZHYo7ONs
The first 90 seconds of this youtube video has a good description of the surprising physics. [Loris, Nov 28 2022]
Malus's Law
https://en.wikipedi...nd_other_properties
What this idea exploits. [neutrinos_shadow, Nov 29 2022]
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If your inner lens, call it A0, and your outer lens is, A90.
And these are fixed. And your inner rotateable lenses are Bn, are you suggesting: |
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A0
- B15
- B30
- B45
- B60
- B75
A90
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Where there is some control over the distribution B15-B75? If A0 and A90 are fixed, normally would you not want an even distribution between them? If they are not even, then what would the effect be? |
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At first I found this idea to be quite appealing; even if you can just adjust one single lens; as viewing devices is difficult with polarized glasses, and being able to rotate polarities without rotating a device would be very convenient. But I don't know mechanically how what you discuss would work. |
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'Ganged together with a slider' to 'Rotate' but with fixed endpoints? |
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With solid wood lenses, these glasses would block 100% of harmful sunlight. |
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//If your inner lens, call it A0, and your outer lens is, A90. And these are fixed. And your inner rotateable lenses are Bn, are you suggesting:
A0 - B15 - B30 - B45 - B60 - B75 - A90// [formatting edited] |
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//Where there is some control over the distribution B15-B75? If A0 and A90 are fixed, normally would you not want an even distribution between them? If they are not even, then what would the effect be?// |
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An even distribution would give the maximal transmittance. The setup you describe would be the brightest setting for five intervening filters.
I'm sure there are other ways to do it, but the way I imagined it was to link the intervening filters to 'fan out' from one of the two outer filters.
The minimal setting would be something like:
A0 - B1 - B2 - B3 - B4 - B5 - A90 (which would be very dark indeed)
And an intermediate setting could be:
A0 - B10 - B20 - B30 - B40 - B50 - A90 |
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The settings of the intermediate filters 'telescope' smoothly between the dark and light settings. A low-tech mechanism for doing this would be to chain them together with elastic. The disadvantages of that are that it wouldn't go all the way down to zero (at least, not with direct chaining), you'd need a locking mechanism to hold position, and that it's obviously low-tech.
A more sophisticated mechanism would use gears. I think it would be cool if you could control them like an SLR camera lens. |
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How does this look in terms of light levels? As described in neutrino_shadow's link, transmittance is the square of the cosine of the difference in angle of the two filters. A 15 degree increment transmits about 93% of the light; 6 progressive rotations leaves 66%. The initial filter culls half the (unpolarised) input light, so the max transmittance would be 33%. |
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What about the 10 degree increment example? I make it 25% transmittance. |
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A0 - B5 - B10 - B15 - B20 - B25 - A90 -> 8.6% transmittance. |
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..
Here is a small PAK (pre-emptively answered questions): |
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Couldn't you just use two filters, with one rotating?
Yes. |
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Won't having multiple filters make the maximum brightness achievable lower?
Yes. But the whole point of sunglasses is to screen out excess light. Losing 77% of the light rather than 50% at the top end isn't really a concern. |
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Could you give it a linear scale?
Maybe not, at least not easily. But the eye's perception of light level isn't linear, so you probably don't want that anyway. |
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//Couldn't you just use two filters, with one rotating?//
What your idea achieves that 2 filters can't, it that both the initial filter & the final filter are always at a fixed orientation. So (for example) if you need to stop reflected glare, you always need the front one to be vertically aligned. If you have (in another use) say, a digital sensor behind it all that is sensitive to polarisation, the back one needs to always be in the correct orientation.
So it might be overly complicated, but I think there is a (small) use case group. Somewhat counter-intuitively, the more filters you have, the *higher* your max transmission (eg. 18 filters at 5° gives 87%).
Too bad it's not 2001, when I was doing some optics at university. This would be a fun idea to experiment with in the lab. |
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