I need to buy a landing light to mount in a fiberglass cowl. I have
been looking at Zenon HID's, halogens, etc., but the most powerful seems
to be a halogen Spotlight.

I am not sure what the current draw is but I would guess about 6 amps?
I will strip the batteries off of it and run straight from the planes
power supply.

What am I missing here? Beam shape? Heat? Power requirements? Weight?

I can buy these things at Walmart for about $60. When I was younger, I
used to use them for spotting and they sure light up everything : )

LG