The Physics
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Power of Car Headlights

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Serway, Raymond A., Beichner, Robert J. Physics for Scientist and Engineers with Modern Physics. 5th Ed. Orlando: Saunders College Publishing, 2000: 895. "An automobile battery has an emf of 12.6 V and an internal resistance of 0.080 ohms. The headlights have a total resistance of 5.00 ohms (assumed constant). What is the potential difference across the headlight bulbs when they are the only load on the battery?" 30.76 W
Honda Motor Co. Civic 1999 Owners Manual. Detroit: Helm Incorporated, 1999: 265.
Headlights (HI/LO) 12V - 60/50 W (HB2)
50 W, 60 W
Job, Ann. Bright Headlights Big Future. MSN Auto, 2005. "Thus Corvette's HIDs use a power saving 42 watts for the low beam as opposed to a halogen's 55 watts." 42 W, 55 W
Klipstein, Don. Automotive Xenon Metal Halide HID Lamps. 1996-03. "D1 and D2 type lamps are 35 watt lamps… the ballast must deliver 35 watts to the lamp." 35 W
Kerr, Jim. Headlight Aiming. Canadian Driver Communications Inc., 2005. "There are wattage standards for each type of headlamp system, but typically, high beam headlamps should use no more than 70 watts and low beam no more than 60 watts of power." 60 W, 70 W

Headlights were never mounted on the first cars produced. In fact, they never existed until they were compelled to do so for obvious reasons and by 1885, "headlamps" were installed on cars and was powered by acetylene gas. Electric powered headlights were not introduced until 30 years later. The most common type of headlights now since the 80s are the halogen headlamps, which are also beginning to be replaced by the high intensity discharge, HID, lamps.

Halogen headlight bulbs are generally 55W on low beam. An average car, such as a Honda Civic, utilizes a 60/50 W halogen headlight bulbs, the power adjusted for the high and low beams respectively. On the road they usually have a yellow-orange tint to them.

Most luxury cars today, most made internationally, namely the BMW, Porsche and the Mercedes-Benz utilizes the high intensity discharge lamps. The HID covers the mercury vapor, metal halide, high-pressure sodium and xenon short-arc type lamps. Most distinguishable about these lights are their color, which are blue-white as opposed to the halogen lamps.

HID headlight systems generally utilize 35 W lamps. 35 W must be delivered constantly therefore requiring a ballast that helps in regulating the voltage and current going to the headlamps. Since HID headlamps emits light equivalent to what would be seen at several thousand Kelvin, it takes up time to build up enough pressure to reach its brightest intensity. The warm up time is for several minutes with an ignition voltage of around 20 kV. This is very impractical if used as a headlamp therefore this problem was solved by having constant power being delivered to the HID lamps, which would result in about only 2 seconds warm up time to reach over a third of its full intensity. After the warm up, smaller voltages are needed to keep them running.

Yat Man Tsui -- 2005