DIFFERENT LIGHT SOURCES

THESE ARE THE FOUR MOST COMMON FORMS OF AUTOMOTIVE LIGHTING USED IN HEADLAMPS. THE FIGURES ARE FOR A SINGLE HEADLAMP CONSISTING OF A HIGH AND LOW BEAM.

HALOGEN

A bulb with glass envelope (similar to the household item) operating on the incandescent principle. Usually, a tungsten filament is employed in the glass housing filled with a mixture of an inert gas (like argon) and a small amount of a halogen (as listed on the periodic table, such as iodine or bromine). The “halogen cycle” redeposits the evaporated tungsten back on the filament, which prolongs its life and keeps the glass envelope clean. This results in the production of constant light throughout its operating life.

HID (XENON AND BI-XENON)

A high-intensity-discharge (HID) headlamp is also known as a xenon unit. It employs a similar type of technology as found in household tube lighting. There is no glowing filament (as in halogen lights). Instead, a high-voltage arc between two electrodes is used to excite the gas mixture in the glass tube. Interestingly, only a small percentage of xenon gas is used in the (mostly metal-halide) lamp to speed up the start-up process. The lamp needs to reach optimal operating temperature before constant light is produced. Bi-xenon refers to a single xenon headlamp with a moveable, internal shield to produce both high and dip beams from a single light source.

LED

The light-emitting diode (LED) produces light by electroluminescence, which is based on quantum theory. It involves semiconductors with electrons moving from a high-energy state to a lower level and releasing energy in the form of photons (light). Interestingly, the light produced is directional, thereby eliminating the need for a reflective element, which results in a smaller headlamp. Compared with halogen, little heat is dissipated, presenting a problem with temperature build-up on the LED chips, especially in high-power applications. To compensate, cooling measures or heat sinks must be implemented to prevent damage. LEDS are commonly used for daylight-running lamps because their lower power outputs mean no cooling measures are required.

LASER

No, lasers are not actually pointed at the road ahead in the fashion of a sci-fi ray gun or phaser. Rather, mirrors focus blue lasers onto a lens filled with yellow phosphorus. The reaction that follows produces intense white light reflected onto the road. Currently, laser lights (used mainly for high-beam applications) are employed in conjunction with one of the other lighting technologies (usually LED) to cater for lowbeam operation.