What exactly are optical switches?

[loli bomb]

Just asking 

[the_fascist]

I believe it uses infrared to detect how far the key has actually moved.  So, lasers.

[Kevadu]

There are basically two varieties.  One has a horizontal infrared beam that some part of the slider will block the path of when the switch is depressed.  This operate basically like any other mechanical switch except they're possibly more reliable due to not relying on physical contacts.

The type fires the beam up from the PCB to the bottom of the switch which bounces the light back and basically acts like a small rangefinder.  These are interesting because the actuation point is actually arbitrary and can potentially be adjusted to be wherever you want it.  Or they can even be used as an 'analog' switch where you can assign different functions to a key based on how far you depress it.

The optical switches on the market so far are mostly linear (particularly the second variety since tactility isn't necessarily going to make sense if it's not correlated with actuation...) and targeted at the gaming market.  While the tech is interesting it doesn't necessarily change a whole lot for typists.  Of course switch longevity is always nice.

[tp4tissue]

Don't cross the Beams.. ~~~!!!!

[Findecanor]

There are clicky Flaretech switches and there may be other types in the future... but we have yet to see it.
The clicky Flaretech has very low tactility though - feels like a Cherry MX Brown, but with click sound.
The linear Flaretech feels almost precisely like Cherry MX Red.

There are "waterproof" (more like splash-proof) keyboards with Flaretech switches but they don't have analogue sensing.

Don't cross the Beams.. ~~~!!!!

You mean "streams"?