h a l f b a k e r yContrary to popular belief
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Existing one-way windows and mirrors have two major flaws.
They a) require a significant difference in light intensity on
either side of the window to be effective, and b) are not
really
one-way since they transmit the same amount of light in
both
directions.
My idea is simply a window
with a circular-polarising filter.
One surprising thing about circular polarisers is they do not
transmit reflected light (see diagram at the bottom of first
link). This effect is currently used for things such as testing
if
a filter is actually a circular polariser, and as an anti-
reflective
coating on touch screen devices; however as far as I know
this
effect has not been used as a privacy window.
The idea would require that *all* light entering the private
room is circularly-polarised. So all windows and lights
would be coated in the circularly-polarising filter material.
Obviously, all filters would all circularly polarised in the
same
chirality (i.e. clockwise or anti-clockwise)
This idea is predicated on my assumption that if an everyday
object is illuminated with circularly polarised light then it
will
simply reflect circularly polarised light (I know there are
some
things that change the polarisation light as it is reflected,
but
I am guessing this is exception rather than the rule).
EDIT: I've tested it out and my assumption was wrong! So
although this idea doesn't work I'll leave it the idea on HB
for entertainment value only.
circular polariser diagram
http://www.apioptic...lar-polarizers.html
[xaviergisz, Aug 19 2013]
You may have to wear one of these.
http://www.polyvore...size=l&tid=38263735
Mirror ball suit. [spidermother, Aug 20 2013]
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Annotation:
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So, if I understand the reflection business, the
point is that light which is circularly polarized one
way (say, left-handed) becomes oppositely-
handed (to right-handed) on reflection. So, if the
lightbulb in your room is covered by a left-handed
circularising filter, and the windows are likewise
left-handed, then the light shining from the bulb
and bouncing off objects in the room will, being
right-handed, not be able to get out of the
window. |
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What about light that undergoes two reflections
(eg, a ceiling light that bounces off the ceiling
before hitting an object in the room, then
bouncing off that and out the window)? |
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You have explained it better than I have. |
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Yes, the outside observer you would be able to see the
lights and secondary reflections clearly, but not
primary reflections. If a dark colour scheme was used in
the house then secondary reflections could be minimised. |
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Never knew that light could be circularly polarized. Or even circular waves. Mind considerably boggled, even as I look at the diagram. |
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I agree it is all a bit counter-intuitive. I was just
playing around with a camera circular polariser filter
and confirmed the mirror effect with my own eyes. |
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My expectation would be that light reflected from a mirror-like surface would not go through the polarizer, but when light reflects from a surface which has texture and depth (partial transparency), that the light would experience multiple reflections on the surface and would therefore be a mix of polarizations. That would work well for reducing glare which is generally light reflected from a mirror-like surface, but would do litle to prevent seeing most objects inside the room. |
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[xaviergisz] Did your experiments with your filter prove otherwise? |
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//Never knew that light could be circularly polarized.// |
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Indeed, that's how some modern 3D movie systems (such as
RealD) work. One eye is polarized one way and the other
eye the opposite way. The advantage to this system over
traditional horizontal/vertical polarization is that you can
view the screen from any angle or rotation and the 3D
effect is retained. |
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I suspect you might be right, scad mientist. |
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Since I only have one circular filter at the moment I haven't been able to properly test my assumption. However, I plan to go and buy another circular filter later today so I can do a proper experiment. I'll put one filter over a torch, look through the other filter, and shine the torch at objects in a dark room. Expect results in roughly 12 hours from now. |
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You may (or, equally, may not) be interested to
know that circular polarization is responsible for
speciation in the Knapweed Chafer, a type of
beetle found in much of Europe. |
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Knapweed Chafers have an iridescent greenish hue
which, due to the chirality of chitin (the main
component of their cuticles) is circularly
polarized. The same polymer is present in the
transparent cuticle over their eyes. |
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In the ancestral population, the reflected light
was clockwise (right-handed) polarized, and was
visible through the correspondingly polarising
cuticles over the beetles' eyes. However, very
recently (within the last couple of centuries,
according to analysis of genetic drift), a mutation
arose which inverts the polarization of the
cuticle, both over the body and over the eyes.
The result is a population of Knapweed Chafers
which look green only to others carrying the same
mutation. |
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As a consequence, there are now two populations
- to all intents and purposes two distinct species -
of knapweed chafers. The "lefties" only see the
green iridescence of other "lefties", and will mate
only with them. The "righties", equally, can only
see and mate with other "righties". |
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It might be expected that the minority "lefty"
population would have died out quickly for want
of mates, and that the "righties" would have won
out. However, this is not the case: "lefties" thrive
in areas where they occur, until a roughly 50:50
mix is obtained. It seems that when most of the
population has the same "handedness", a lot of
energy is wasted by fighting off rivals or unwanted
suitors. A minority population has fewer choices
for mates, and therefore wastes less energy in
choosing. |
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Wait a minute… I thought he was the Ninth Duke of
Uxmouthshireford—and a distant relative of yours? |
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Whether this pans out or not, I'm bunning it for the original thought and effort. |
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I just bought a filter (Hoya 46mm circular polarising filter - left) for $60 (yes, had I been patient I could have bought it online for half that). It is still a few hours until I can perform the experiment. |
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Well, the results are in and... it doesn't work ;( |
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I couldn't even get the (circularly polarised) torch light
reflecting off the mirror to be eliminated with my viewing
circular polariser, let alone reflection off any other surface
to be eliminated. |
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(Although I originally thought I had the experiment partially
working this was mistaken - I was using the ciruclar
polarisers the wrong way around which made them
essentially linear polarisers). |
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In summary, circular polarisation is confusing. |
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That is a shame, [xav], but keep thinking... |
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//Ninth Duke of Uxmouthshireford// No, though
you may be thinking of the Sixth Earl of West
Norfolk, who is a cousin and great-aunt. |
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OK folks, an update on the experiment. |
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It turns out that my circular polarisers were actually left and right polarised, whereas I had thought they were both left polarised. Oops. |
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I figured this out by buying some passive 3D glasses and viewing each polariser. Passive 3D glasses work by having one left circular polarised lens and one right circular polarised lens. |
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Lo and behold, light passing through one of my polarisers was obscured by left lens of the 3D glasses but not the right. Light passing through the other of my polarisers was obscured by the right lens of the 3D glasses but not the left. |
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Why didn't I notice this before? mostly because the effect is not as stark in reality as the theory leads one to believe. I can still see some light that passes through both the left circular polariser and then right circular polariser. Basically, I lacked something to compare with and thus made an incorrect inference. |
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I might try the experiment again (this time using two circular polarisers of the same chirality) but the quality of my polarisers is apparently not great. |
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Of course, you already have //two circular polarisers of the
same chirality// if you include the lenses in the 3D glasses.
Both chiralities, actually. |
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So I performed the experiment again using one lens
of the 3D glasses and one of my polarisers. |
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Two polarisers of the same chirality (one covering
the torch light,one covering my eye) had the
expected effect: The light from the torch was
attenuated in the mirror reflection when compared
with shining straight into my (circularly filter
covered) eye. There was no attenuation in reflection
of any other object. |
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The one puzzling thing about the experiment was
the colour of mirror-reflected torch light was
dependent upon the orientation of the circular filter
covering the torch. So as I turned the polariser, the
apparent colour of the torch light changed from blue
to red to
yellow to purple. (Note this same effect happened when a left-circular polariser covering the torch was shon into my right-circular polariser covered eye). |
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Although my original idea did not work, I have a variation that probably will: A one-way mirror with a circular polarising coating. |
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Start with a one-way mirror (i.e. half-silvered) that reflects 70% light and transmits 30%. If a circular polariser coats the 'private' side of the mirror, there is no reflection and only the transmitted (polarised) light can be seen. |
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On the 'public' side of the mirror both transmitted and reflected light can be seen. However, the reflected light will overwhelm the transmitted light, and consequently the private side will remain fairly private. |
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The advantage of this idea over a typical one-way mirror is not needing to keep the private side dark compared with the public side. |
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