Fluorescent lamps are high-efficiency lamps that use electrical discharge through low-pressure mercury vapor to produce ultraviolet (UV) energy, which is then transformed into visible light. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube, which makes up the structure of the lamp. The phosphors transform the UV to visible light. With fluorescent lamps, the wavelength of the emitted light is a function of the amount of energy that is released. As a rule, fluorescent lamps convert electricity to light with greater energy than incandescent lamps. They also work at cooler temperatures. Unlike incandescent lamps, fluorescent lamps cannot be connected directly to electric lines. Instead, fluorescent lamps require ballasts to stabilize the flow of current. Fluorescent ballast provides the starting voltage and limits the amount of current that can pass through the fluorescent lamp.