There are many illuminating options for working on equipment after dark. New flashlights with LED bulbs are far superior to old-fashioned incandescent bulbs in both brightness and longevity. Some folks prefer the traditional flashlight powered by D-cell batteries because they're cheap, but…nowadays, you get what you pay for when it comes to mobile lighting.
I carry a $60 penlight with an LED bulb, powered by two AA batteries, that is amazingly bright. A hands-free option are the small LED flashlights mounted on an elastic headband, the kind that 'coon hunters wear. I've got one and it works really, really well because I can point it's brightest area to compensate for my bifocal glasses. (Go ahead and laugh, all you young'uns…your time will come.) I use the light-on-a-headband when I know I'll be working in a dark area for a long time, otherwise it's handier to click on and off the pocket penlight.
For extended repairs after dark, the new battery-powered task lights with LED bulbs and computer-designed reflectors work great. They're pricey, in the $75 to $130 range, but are brighter than traditional battery-powered lights with incandescent bulbs and have run-times of up to 4 hours. Mine has a "rare metal" magnet to hold it in place, which is much better than trying to find someplace to hang the light so the light shines where you need it.
If it sounds like I've jumped on the LED bandwagon when it comes to lights, that would be a correct assumption. They're expensive, but once you've used one you'll never go back to traditional incandescent bulbs.