Unlike both fluorescent and HID lamps, LEDs come to full brightness almost instantly when turned on. Because LEDs are mounted on a flat surface, they emit light hemispherically rather than spherically, thereby reducing wasted light. LEDs emit no Ultraviolet radiation (UV) which can be very hazardous to people, causing eye burns, as well as skin irritations. It is also especially damaging to materials such as clothing, artwork and artifacts. Because LEDs do not emit this, they are a safe alternative for both people and materials.