also there's actually less power draw as HID's are usually 35watts opposed to a traditional halogen bulb rated at 55 watts.
Most people don't realize that part... the better lamp technologies put out more output per watt, so an equivalent brightness uses less power. Halogen put out more light and a higher color temp... find some older cars floating around and they might have some non-halogen lamps still working... then one gets replaced by a halogen and it looks way brighter.
As far as I know, the best light output per watt is a low pressure sodium lamp, but produces a not-so-useful monochromatic golden color (like some LEDs are). What that means is that everything is either yellow or shades of gray (like holding a piece of notebook paper, the paper itself is yellow and the lines are gray)... Not a coincidence, but they also last the longest
They use it in Germany a lot, though, and near observatories cause it's easy to filter out the monochromatic light
BTW, almost all streetlights are HIDs (with some cities testing LEDs), the yellow ones are high pressure sodium and the ones with a greenish tint are mercury vapor with the white ones being metal halide (which are just mercury vapor with some halide salts that give off the colors missing to make a nearly white light... just like how all white LEDs are blue LEDs with a phosphorus coating).
I imagine car HIDs are metal halide due to the color.
