Ok, it's only June 8th and temps in the mid 90's. This sucks. So yesterday I decided to try out the lights on my pitch black yard. Wow. It must have looked funny to any neighbors. If your lawn is grown enough so you can see the "strips", the lights work exceptionally well, and have literally no drain on the battery. If you have a lawn that doesn't have anything that might damage you mower if you run over it, try out the lights.
Even the blower on low is so quiet that I got my cleanup work done at 9:30 in the evening :)
On my small lot I'm not sure it really has much of an impact with regards to run time, but I wonder what the total impact is and whether it would make a significant difference to someone with a larger lot?
Regarding headlights, yes it's a nice option to have and they do work surprisingly well. I'd be interested in seeing a few "wall shots" that show how the headlights of the 20" and 21" mowers compare. You have to understand I'm a geek and have a thing for automotive lighting. People who upgrade their headlights do wall shots to demonstrate lighting output/improvement, like this:
Now if only I knew someone with both 20"'and 21" mowers and a camera who could point them at the same wall at the same distance at the same time in low light to compare them... ;-D
On a car, I don't like those new white light bulbs. They make it VERY hard to see in fog. The yellow penetrates better.
You asked the right question about the lights. I'll pull out both mowers and do a few pics to show the difference. My guess is that they are about identical.