Difference Between HID and LED Headlights

Feb 13, 2014

Halogen lamps are commonly used in car headlights and consist of a filament and halogen gas. A current is passed through the filament making it extremely hot which emits light. The halogen gas is usually mixed with a small amount of bromine or iodine to prevent the filament from burning off. Halogen lamps tend to get much warmer in comparison to fluorescent or light emitting diodes. They consume more power and have a shorter lifespan.

Over the last decade, HID (High Intensity Discharge) and LED (Light-emitting Diode) lamps have become prevalent in new car models and available as an aftermarket headlight replacement product.

HID headlights

HID lamps produce light by means of an electric arc. Housed within a transparent or translucent fused quartz or alumina tube are two tungsten electrodes. The tube is filled with xenon gas, metal salts and a very high voltage is applied to the electrodes producing an arc. The arc heats and evaporates the metal salts creating plasma. Light is produced by the arc whose intensity is increased by the plasma which in turn reduces power consumption. HID lamps produce a more intense light than that of halogen lamps. HID lamps require a device known as a ballast which is a resistor or capacitor inserted into a circuit to regulate voltage supplied to the capsule if gas in the lamp.

LED headlights

LED lights consist of semiconducting material such as silicon doped with impurities to create a junction known as p-n. Doping is the intentional introduction of impurities in a pure semiconductor so it can regulate its electrical properties. A p-n junction is the boundary between two types of semiconductors known as p-type and n-type. When an electrical current is passed through a light-emitting diode, electrons recombine with holes within the device to release energy in the form of photons to produce light. This process is known as electroluminescence in which light is emitted by a material when an electric current is passed through it. LEDs last much longer than HID or halogen lamps and consume lesser power than the latter. LEDs also light up instantly unlike HID lights that have to warm up for about 15 - 25 seconds when switched on. HID lights, however, are brighter than LED lights.

History of HID and LED headlights in vehicles

The first car to introduce HID headlights was the BMW 7-series back in the early 1990's. Then, it was feared that the lights would be too intense and distract other drivers. Now, the technology has been accepted. HID headlights have shown to be safer than halogen lamps when driving at night creating a clearer view of the road. HID bulbs also last about 10 times longer than halogen lamps. Toyota's Prius 3rd generation was one of the first cars to offer LED headlights. Toyota chose this technology since LEDs consume far less energy than HID or halogen lamps as well as LEDs being more durable and lasting longer.

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