John Williamson wrote:

The efficiency savings for mobile use aren't worth bothering about
except for applications like battery powered cycle lights or torches, as
the power used by the lighting on a car is a small percentage of the
total power used to move it. At 30mph on a flat road, the absolute
maximum total lighting load on most cars, including headlamps and
foglamps, is less than 400 watts, as against ten kilowatts or more being
used to overcome rolling and air resistance.

If that 400W could be reduced to 100W there would be worthwhile fuel
savings.

Bill