LEDs watt weight to alternator HP

[notech]

I was going to install LEDs lights on turn signal, headlights, dash lights, etc..
LED (light emission diode) are consuming way less power than standard light bulbs which waste energy in heat. Replacing for a more efficient lights system should translate in less consumption watt, which consequently translates in less requirement from the alternator, which drains HP from the engine.
Curious to know how much?

By a conversion factor we should know that 747 watts = one horsepower. Regular automobile headlights typically run about 75 to 100 watts. So if you turn your headlights off, you save 200 watts, or less than a third of a horsepower.
The maximum theoretical efficiency of an alternator is 75% or typically 60%.

Therefore if you are taking the full load of 155 amps at 14 volts, that's 2170 Watts.

Allowing for the 75% max efficiency, you'll need to put 1627 watts of power in at the shaft to get 2170 watts of electricity out.

Taking into account the fact that the alternator is going to be far from perfect, plus drivebelt losses, I'd guesstimate 4000 watts maximum (4 kW) power from the engine to produce a full 155 amps at the alternator.

Using the conversion gives a figure of around 6 bhp to provide the full rated 155 amps.

By estimation for daily driving the engine will be giving up around 1-2 BHP to power the cars electrics.

But LEDs are cool..!