Thread: HID headlights
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Old 03-14-2019, 01:26 PM   #16
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Join Date: Feb 2008
Location: Kansas, USA

Via another forum post...sniped...OEM lights have resistance wiring so light output is based upon some alternator voltage output.

These numbers are just calculations, not measurements so YMMV. They should be very close, though.

At 12V, a 55W light should use 4.58 amps. That means it has an effective resistance of 2.618Ω with the filament at operating temperature.

Using this resistance as a constant for the light bulb, we can calculate how much power the light will have when the voltage is reduced or increased. Formula is
P=((Vē)/R) so as you can see, the voltage component has an exponential effect on power.

14V - 74W - 134% of nominal power
13V - 64W - 116%
12V - 55W - 100% (Nominal Power rating)
11V - 46W - 84%
10V - 38W - 69%

As this shows, ANY voltage drop in the headlights wiring will dramatically reduce the power of the headlights. Tungsten Halogen bulbs will get dimmer and more yellow as the power is reduced.

Using #12AWG wire and heavy duty relays will allow a voltage drop of much less than 1V. This can bring the voltage up so that the power is in that 116 to 134% range - without any 'illegal' light bulbs, solid state voltage boost converters, or other nonsense.

The result is brilliant, piercing, white light that will really light up the countryside. The high beams will command respect from oncoming motorists who don't dim theirs and get a flash from yours.

Hence, clean up grounds/hots, or have dim lights with older vehicles.
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