How do those windows, wich you can turn non transparant with a switch, work ?



In: Engineering

There’s a film of liquid crystal inside the window, specially constructed and treated so that the crystals inside respond to electric current. When there’s no current, the crystals go out of alignment, and their random orientation blocks light.

When you flip the switch on, a low-voltage electric current forces the crystals to align, letting light pass through.

[This website]( can tell you more.

It’s interesting – the ELI5 answer is “liquid crystal film between sheets of glass, electrically activated, lol”, but the ELI10(?) explanation has to do with polarized light and how liquid crystals twist light polarization when energized. The invention of LCD displays for things like calculators is an interesting story.

I’ve been waiting for LCD window shades for decades, and I think we’re getting close.

The window has two layers (A and C) which only allow passing of light with a specific property (other than color). In between the layers is an other layer (B) which can electrically change this property of light.
* Transparent window: light with property 1 passes layer A, passes Layer B unchanged and passes layer C.
* Non transparent window: light with property passes layer A, property 1 of the light gets changed by layer B to property 2, layer C blocks all light but the one with property 1.

It works by taking advantage of some physical and electrical effects.

Light waves swing when they radiate. If they have a extremely small grid in front of them only the waves can pass the grid, which swing in one direction. So all light waves passing the grid are now swinging in the same direction. (The grid is called polarizing filter and the light waves swinging in the same direction are called polarized light)

You can now add a second grid (polarizing filter) after the first one with the same orientation. The (polarized) light that passed the first grid will also pass the second one. so now you have a window you can look through (transparent).

Now you can place a thing between the grids that is called a liquid Cristal. This liquid Cristal can be electrically changed. Usually it has no effect, so you have your normal window. But wenn you apply electricity to the liquid Cristal, it has some effect on the Light. It changes it’s swing direction. Since it is between the two grids, the light now can’t pass the second grid.
No light passing means darkness. Voila, you have your mom transparent window which you can control through electricity.

🥏 Example:
Imagine light as Frisbees. Frisbees in all orientations flow through the window. You add a grid layer to the window. Now only the Frisbees with an specific orientation can pass the grid. Adding the same grid layer again to the window still allows the Frisbees with that orientation to pass. But if you add a twisting layer between the grid layers no Frisbees will pass the second grid.
The twisting layer can be activated electrically.

(Ehh, because of the effort it took me to write this crap, I’ll post it nonetheless.)