Wouldn't it be awesome if your glasses could detect when it's bright outside and automatically darken? Well, the technology has been around for a while, but it'll set you back a few hundred bucks.
He used a photoelectric cell and a transistor to build a detector circuit that lets voltage flow through and turn the glasses dark. When the light is blocked, a 1K ohm resistor turns them instantly clear again.
If you want something a little more attention grabbing, try these Bionic Sunglasses by Ben Heck, which were actually the inspiration for Dean's LCD version.
His are a little more complicated—they use an ATtiny and servo motors that actually raise and lower the darker lenses based on light intensity. Check out the video to see how he made them.