Most lights are IPV8 waterproof which means they can be dunked, but you wouldnt want to use em as a dive light.
They basically have a rubber O ring or two where the joints are, and a clickie that is rubber covered, thus making them waterproof.
I wouldnt go with drop-ins because that is an additional pain and or something to mess up.
Instead there are tons of CR123 and AA lights that will work very nicely for you.
Have you considered a keychain light? An itp A3 using 1xAAA is up to 80 lumens, 3 modes, and very very small. You always have it with you which is quite convenient!
A CR123 light will be brighter than an AA one due to its higher voltage. An RCR123 will be even brighter due to even higher voltage. Id go with an RCR123 protected if you go CR123 style.
Is this an occasional use light or one you expect to use often? Will you use it for a few minutes or a few hours? Is it a close up worklight/general purpose one, or a walking light, or are you wanting to see things hundreds of feet off? These questions will help us recommend the right type of light.
FYI, the brands to investigate are itp and Romisen. Both are decent quality at a low price point. Check out
www.shiningbeam.com and
www.goinggear.com for a pretty easy-to-browse place to compare and see various lights.
