I've noticed that even with the auto-darkening, my eyes have to adjust to the light conditions...before, during the weld and after. Low light makes it really difficult.
You can get these lamps on Amazon for around $20. They really are bright enough to work in the dark.
Rechargeable batteries are great for something like this. You could make brackets to hold a standard flashlight to the helmet, some are lightweight so you may not even notice the added weight.