Gel polish contains photosensitive initiators that won't harden without the correct UV wavelength. Drying them with sunlight might take a lot of time, time that you do not have to spare. You ALWAYS have to use a UV light to make them dry properly. The professional UV lamp can cure all kinds of gel nail polishes in a faster and safer way. It comes with a set of timers for slow, moderate, and quick curing. It is powered by a set of LED's arranged in a 180-degree design for well-rounded curing.