Can polarising filters sandwich in glass block light from all directions?

  • Level: Undergrad 
  • Thread starter Thread starter MIKEBROCK
  • Start date Start date
  • Tags Tags
    Windows
Join the discussion
Registration is free. Start your own thread to ask a follow-up.
Sign up Log in
8 replies · 12K views
MIKEBROCK
Messages
3
Reaction score
0
Would it be possible to use 2 sheets of glass as a window, within the 2 sheets of glass are 2 polarising filters, acting as blinds sandwiched in the glass, at 90degrees from each other. By remote the polarised lens can ascend or descend up and down the window blocking light at different levels. Letting no light come through the window, and only a bit of light through window or all light. Would this work from all directions outside the window?
 
Physics news on Phys.org

Discussion

I don't understand what "the polarizing lens" is supposed to be. If you have a circular window and there are two polarizing foils of which you can turn one, then you should be able to adjust the transmission between close to 45% and 0% because the first foil will cut out half of the light, and the window reflects about 4%. The incidence angle should not matter much, but you may see that you can suppress or enhance light that is reflected of clean surfaces like puddles since that tends to be polarized. With two 90 degree foils and a third one that you can turn in between for "magic transmission" at 45 degrees, you will be able to adjust the light intensity between under 3% and 0%
That is pretty dark.
Transmissions (maximum case):
window 96%
polarizer 50%
45 deg polarizer 25%
polarizer 25%
window 96%
 
MIKEBROCK said:
Would it be possible to use 2 sheets of glass as a window, within the 2 sheets of glass are 2 polarising filters, acting as blinds sandwiched in the glass, at 90degrees from each other. By remote the polarised lens can ascend or descend up and down the window blocking light at different levels. Letting no light come through the window, and only a bit of light through window or all light. Would this work from all directions outside the window?

Polarizers generally work at restricted angles of incidence, so the effect would only be partial. Kent State's Liquid Crystal Institute developed a similar device- the transmission was controlled by altering the retardance of a thin liquid crystal layer, and could be switched very rapidly:

http://www.lci.kent.edu/switch.html

IIRC, the technology has been adapted for welding glasses.
 
Last edited by a moderator:
thanks for the help, and sorry for the very late reply. So it would not be possible as an everyday window due to the variation in incidence angle? Seems to be a conflict in answers here, thank you anyway.
 
Again, I do not think that the incident angle matters much. Just get two pairs of 3D glasses and hold them over one another such that all light is blocked. (you might have to flip the direction) I do not think you get light through even at low angles. Liquid crystals are another matter, there the incidence angle matters much more as you see with TFT displays.
I think the polarization is the least of your problems. The way you describe it, you have the same effect just with an ND filter and much cheaper at that.
 
ok thankyou, good idea i will try that. Do ND filters block all light though?
 
ND Filters block all light evenly, they are basically shades.
 
0xDEADBEEF said:
Again, I do not think that the incident angle matters much. Just get two pairs of 3D glasses and hold them over one another such that all light is blocked. (you might have to flip the direction) I do not think you get light through even at low angles. Liquid crystals are another matter, there the incidence angle matters much more as you see with TFT displays.

Even with displays, it depends on the technology. Good LCD panels are pretty much angle-independent. Only the inexpensive (TN) panels have substantial changes with viewing angle.