There are lots of offerings on eBay and elsewhere that would be a drop-in replacement for the old 222 bulb - it's a very common E10 (10mm Edison screw base) bulb. Most of them have the LED element in the same place as the filament was on the original incandescent bulb, so that's generally not an issue.
Assuming you pick one for the right voltage, the possible ones differ in three ways. They differ in color temperature - some will be quite yellow, like an old incandescent bulb, and some will be much closer to daylight, like those in most modern LED flashlights. Choose whatever is your taste. They also differ in brightness - the higher power ones will be hotter and brighter. I would probably pick a 0.5W one because the higher power ones produce a lot of heat and use up batteries faster. Any LED replacement is going to be much brighter than the original. The third way they differ is price. They're pretty much all made in China. You can get them a lot cheaper from Chinese eBay sellers than you can from Americam retailers. If you're willing to wait two or three weeks for delivery from a seller based in China, you can get them for 1/2 or 1/3 the cost of the same bulb sold locally.
