One thing that did the trick for me in pinch was to grab a sock and then dip it brake fluid. I then rubbed the hell out of that headlamp for a much improved immediate effect.
Please dont try this unless its a last resort. It's a trick I learned when your in college and cant afford the $20 for a kit as that was my weekly laundry budget money. An old shade tree mechanic told me to try it. It worked just fine, but you gotta rub the hell out that headlamp.
Worked though.