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By 'extremely blinding light', I mean light at least bright enough to blind somebody permanently, and at most bright enough to severely burn humans.
What material could be used to construct a helmet or some sort of eyewear in order to protect from extremely strong light? How would this equipment function? Would it be as simple as wearing a welder's helmet?
This depends a bit on the intensity and environment.
Welding arcs are bright enough to cause blistering in the eyes and to "sunburn" your skin; if you stared long enough you could blind yourself, but you'd have to be pretty ignorant to do so.
The better welding helmets are auto-darkening, and do this with a liquid crystal element similar to that used in a liquid crystal display like on some televisions/computer monitors. In either case, an electric field is used to change how transparent/opaque the crystal is, and thus how much light is absorbed vs transmitted. On a display, a driver controls this on a per-pixel basis to filter a backlight to create graphics. On the welding helmet, an optical sensor determines how intense the incoming light is and adjusts the opaqueness of the visor to compensate.
This isn't a perfect method, however. The energy of the light is still going somewhere, and with an opaque crystal layer the "somewhere" that it is is going is heat; strong enough light could damage the mechanism. Additionally, the electronics will have some limited operating temperature range, and may be susceptible to other forms of radiation. Astronaut helmets, for example, use a thin layer of gold to reflect the light, as opposed to absorbing it, which limits the amount of heat input and also doesn't fail if hit with (reasonable quantities of) other forms of radiation.
Even that kind of reflection wouldn't be enough, however, if you're talking about light from a high-powered laser, which would burn through that thin metallic layer. At those intensities, typically what is used to reflect light would be a dielectric mirror, which basically uses multiple layers of material that each reflect some amount of the light, and are stacked in thicknesses designed so that the wavelengths match up at each layer. This would be a bit difficult to use as protective covering, however, as the distance between layer boundaries changes with the angle at which the light comes in, and you'd also need to know the frequency in advance.
Do it in software, have a VR type display completely covering the eyes and use cameras or other sensors to feed the displays, with software (and hardware limitations) preventing dangerous levels of brightness to the users eyes.
The most typical blinding light pulse is the flash associated with nuclear explosions. During the 1950's, it was a common practice to paint bombers in an overall white "anti flash" paint scheme, in an effort to reflect much of the optical and thermal energy away from the airplane when a nuclear weapon detonated. The pilots inside would be wearing heavily tinted goggles as well.
Crews on warships also wore (and still wear) protective covering which serves much of the same function, although it is also fireproof, and designed to protect skin against the heat and flash burns of a shipboard fire, although it would have the secondary function of protecting a person who is on deck if a nuclear device goes off in the distance.
The issue here is that the amount of energy required to blind a person is going to be delivered in a large dose of radiation (arc welders can emit UV radiation due to the extremely high temperatures of the arc), and most other processes which could blind a person are usually accompanied by a large energy release which would burn the rest of the person as well. The only exception to this would be the deliberate blinding of a person using a laser. So for most purposes, an overall protective covering will be needed in addition to some sort of dark goggles or VR camera system.
Since light energy in all wavelengths will be arriving at the speed of light, no mechanical system would be able to close shutters fast enough to protect a person's vision. Either a deep tinting to absorb the incoming light will be needed, or some sort of reflective layer like the gold coating on astronauts visors or some sort of highly efficient mirror. A VR system would actually be more practical, since the lenses could be distributed over a wide area, allowing for graceful degradation if the light pulse burns out some cameras or damages some lenses. If you take the final picture as a starting point, imagine the visor is fully reflective, and the helmet and perhaps part of the uniform is covered in small lenses leading via fibre optic cables to a series of cameras that project the image on the inside of the visor.
No it would be a bit more complicated than a welders helmet. I'm assuming you want it to automatically defend from light. Welders helmets do not do that automatically. In fact, having your helmet pop down just before the light reaches your eyes is impossible because your closing mechanism would need to travel at near light speed.
The best way to solve this is just to put on an a helmet with a screen inside connected to a camera outside. If the camera detects light levels as too high it can just lower the brightness shown to you.
