The cap has a built-in waterproof solar panel, battery pack and powerful, long-lasting LED light…The LightCap stands 8 ¼” tall and 3 ¾” wide and has a 32 oz capacity. With just a four-hour charge of sunshine the LightCap will stay bright for hours while the rechargeable Ni-Cad batteries will last for at least 300 cycles. Set it in the sun or hang it from a railing during the day and you’ll have light all night long!