LightCap™ 200, Red Bottle Cap Take the light with you! LightCap 200 turns any bottle with a 2" (51 mm) inside diameter opening into a solar lantern. The rugged waterproof cap contains a solar cell on the top with an internal battery and four white LEDs. The lights come on automatically in the dark. A built-in light sensor switches the cap off during daylight hours while the battery charges. You can also use the waterproof switch to turn the lights on and off.