I was on a flight recently that had the dimmer style windows instead of the old style where you would just pull down a shade. I wondered how the glass could be made to go darker or lighter at the push of a button?

Comments

You must log in or register to comment.

_Connor t1_jdek7f7 wrote on March 23, 2023 at 8:48 PM

There's a film applied to the window that has a layer of liquid crystals sandwiched in-between two pieces of plastic.

When the film is turned 'off' the liquid crystals can do whatever they want which creates opaqueness in the window as they're all just scattered about.

When you turn it 'on' a current of electricity is run through the film which causes all the liquid crystals to snap into alignment and become clear.

It's called PDLC film.

imamydesk t1_jdfhecq wrote on March 24, 2023 at 12:33 AM

It is an electrochromic material, but it's not PDLC. For airplane windows you want to fail-safe to transparency, not opaqueness - so the power on state is the opaque, power off transparent. That way in an emergency if all windows lose power, emergency responders and passengers alike can look through the windows.

https://www.youtube.com/watch?v=U8OzpJPFiCE

TisIChenoir t1_jdezlbo wrote on March 23, 2023 at 10:29 PM

I've put some of those up on an office space we designed, years ago. Except it was included in the glass between two panes.

It's crazy expensive, and let me tell you, we didn't took any chances with the stuff.

Any-Growth8158 t1_jdeji98 wrote on March 23, 2023 at 8:43 PM

They're LCD screens without the reflective part. There is a polarization filter and the liquid crystal. When the polarizations are aligned it lets light through. You can control the polarization of the liquid crystal by applying a voltage. The greater the polarization mismatch the more of the light that is filtered and the darker the window.

It's the same idea to taking two polarizing filters and rotating them relative to each other. Instead of mechanically rotating one filter you adjust the molecules with an application of electricity to change the polarity.

[deleted] t1_jdftzwx wrote on March 24, 2023 at 2:06 AM

[removed]

CrimzonGryphon t1_jdmkrjk wrote on March 25, 2023 at 2:52 PM

This aint right, see my comment

Spork_Facepunch t1_jdejb6s wrote on March 23, 2023 at 8:42 PM

There are polarized particles in the glass that change orientation when they receive an electrical voltage through the edge of the panel. When the voltage changes, they reorient themselves and block some of the light.

CrimzonGryphon t1_jdf0rdl wrote on March 23, 2023 at 10:37 PM

I briefly read about this to learn more. From my brief understanding, the users talking about polarising filters are not quite right. U/connor is right.

PDLCs seem to be the predominate type in planes.

While in displays, LCs are used to control polarity of light, in PDLCs they are used to control the degree of light scattering (lower voltage = more scattering = more opaque)

manic47 t1_jdesnlq wrote on March 23, 2023 at 9:42 PM

It’s got a LCD film in it.
When energised the crystals in it align and it becomes opaque.

The mirrors in my car have the same film and will automatically darken at night to stop any chance of getting blinded by reflected headlights.