Sunlight and artificial light are absorbed through the crystal and dial. Citizen uses special filters which allow a wide range of dial colors and styles. A solar cell beneath the dial converts any form of light into electrical energy to power the watch. With regular exposure to light, Eco-Drive continuously recharges itself for a lifetime of use. Eco-Drive's revolutionary lithium-ion rechargeable battery stores enough energy to power the watch for an astonishing six months (even in the dark.)