Read the full guide on: https://learn.adafruit.com/3d-printed-electronic-sunglasses/overview
In this week's project, we’ll show you how to build pair of electronic sunglasses. These are really cool because you can actually control the dark tint from the glass.
Sandwiched in between two sheets of glass is a layer of liquid crystal material. When voltage is applied to the electrodes, it turns dark and filters out bright light. Depending on how much voltage is applied, you can control the tint or opaqueness of the glass.
This is a Liquid Crystal Light Valve (a.k.a a LCD Controllable Blackout Panel) and they’re mainly used in welding helmets because it can protecting your eyes from really bright sparks.