The latest trend in automotive lighting is LED (Light Emitting Diode) lights. LED lights use an entirely different technology to produce visible light. Conventional incandescent bulbs and headlamps contain a tungsten filament inside a sealed glass bulb. Current flowing through the filament heats it up to around 4,000 degrees F causing it to glow brightly and give off light. This generates a lot of waste heat and is not very efficient at producing light. To prevent the filament from burning up, the air inside the bulb is evacuated and replaced with an inert gas such as argon. With halogen bulbs, the gas also contain traces of iodine or bromine. This allows the filament to burn brighter and produce more light and whiter light. Traces of xenon may also be added to the gas, or the bulb may be tinted with a special coating to give the light a more bluish cast like that of HID (High Intensity Discharge) headlights.
The problem with conventional incandescent bulbs and halogen headlights is that they use too much current for the light they produce and they give off a lot of waste heat. The bulbs also have a limited lifespan (around 1,000 hours or so), and the filament can break from vibration or being jolted.
HID headlights are about 2X as efficient as halogen headlights so they use much less current. But they do require a very high initial starting voltage (up to 25,000 volts!), which requires adding a special ballast and control electronics to the headlight circuitry. HID headlights do not contain a filament and use an electrical arc passing through a gas inside a high-temperature bulb to generate light. Because there is no filament to break or burn out, HID headlamps typically last 2X to 5X longer than ordinary headlamps. The downside is HID bulbs are expensive to replace.
LED lights are solid state diodes. They have no bulb or filament and contain no gasses. When current flows through the diode, it excites the material and generates light. LEDs are 4X more efficient than standard bulbs at converting current to light, and they produce much less heat than incandescent bulbs or HID headlamps. LEDs are also extremely long-lived (10,000 plus hours). But until recently, their light output has not been great enough for use in headlights.
