A motor vehicle's lighting system consists of lighting and signalling devices mounted or combined on the front, back, sides and, in some cases, the top of a motor vehicle. Each unit is equipped with bulbs. The demand contains many types of bulbs. Such bulbs come in different shapes and sizes. These also have different tension and wattage depending on the area these are mounted in. Mostly all lamps in cars can be easily replaced. In some situations, equipment is also not needed. The driver himself will immediately change bulbs such as a headlamp, tail lamp, reverse lamp, brake light, some interior lamps. A traditional lamp, an electric current heats up the tungsten filament to incandescence. Less popular are gas-filled bulbs where the glass bulb is filled with an inert gas such as argon under pressure. It allows the filament to function without collapsing at a higher temperature and thus creates a whiter light. Many cars are now using tungsten halogen bulbs for their headlights as they can produce better light. The light has a long life and will not blacken like other bulbs over a period of time. The capless bulb has a semi-tubular glass envelope with a flattened end that protects the terminal wires, which are bent over to form the two contacts. The power rating is up to 5W and these lamps are used for illumination of doors, sidelights and parking. Halogen bulbs are the oldest type of automotive bulb still commonly used today. Such lamps are packed with a halogen gas preventing the light to turn black. Such bulbs can be removed very quickly when damage is done, and can be replaced immediately. Xenon bulbs, also known as high-intensity discharge (HID) lamps, produce a brighter light than halogen bulbs, with much lower heat. The xenon bulbs emit a blue-white light that is very bright. Another new technology is the LED bulbs. Such bulbs are made of diodes that emit light.