Auto-Darkening welding helmet
These Auto Darkening Helmets are sometimes referred to as Auto Darkening Screens or Auto Darkening Masks.
The lens in an Auto-Darkening welding helmet is made up from a layer of liquid crystals sandwiched between two layers of glass.
These two layers incorporate an anode and a cathode which, with the help of a small battery, enable a voltage to be placed across the liquid crystal display (LCD).
When the whole unit is turned on, the crystals arrange themselves so that they all line up and are in straight lines allowing light to pass between them easily. .
When an arc is detected by the photo sensitive sensor in the head shield, the layers in the LCD rotate slightly and make it harder for the light to pass straight through.
The whole process is similar to how light can be shut out of a room using a Venitian Blind. When the slats are in the horizontal plane light is allowed into a room. Rotate the slats slightly and the room gets darker.
As with all my articles, I encourage you to do your own research into these subjects. These articles are my own point of view and are not intended to be advice in any way.