When it is dark, they automatically light up creating a disk like light that appears to hover above your wheels, bring more color to your car/bike, bring more enjoyment to your drive. Features: No battery connection required - no need to connect to the vehicle battery. Waterproof - The valve has a light mouth small waterproof case. It lights up itself using high-quality metal gold-plated, inner zone button batteries. Easy to install: Simply screw it onto the tyre valve. Twist off your original valve cap and replace with this valve cap LED light. Installs on standard tyre air valve of cars.