Solar Cheeta Glass

Often called "transition" or "transaction" glasses, these use photochromic technology to adapt to lighting. 
Function: They remain fully clear indoors and automatically darken into sunglasses when exposed to UV light outdoors.
Material: Originally made of glass using silver halide, most modern versions use plastic or polycarbonate with a specialized coating.
Limitations: They typically do not darken inside cars because windshields block the UV rays needed for activation.
Performance: Speed and darkness vary by brand; newer generations like Transitions GEN S can darken in seconds and clear up within two minutes