Everyone's nerding out a ton here, with vocab that might not be totally understood to a new caver (hi hallaly! Lights tend to be something that gets us all excited given that we operate in a perfectly dark environment...so I'm going to join in the fun!).
I generally suggest one of three lights for new people:
(1) Black Diamond storm (entry level, great for everyday, 4 AAAs I think, 2013 edition sale for $34.96 now)
http://blackdiamondequipment.com/en/hea ... rm&start=1(2)Black Diamond Icon (better battery life, more options for brightness, 4 AAs; $79.95)
http://blackdiamondequipment.com/en/hea ... on&start=1(3) Princeton Tec Apex (really great light, runs on 4 AAs for a full day on the lower setting if you're using rechargeables...and use rechargeables because this light is well regulated...which means the light output stays constant for a very long time even as the batteries are being depleted; $89.95)
http://www.princetontec.com/apexBetter yet, get all three because you need backup lights. Some of the other suggestions on this list are of comparable price, but the things you want to look at are run time vs. brightness. Most light manufacturers report this on their webpages; look at other sites to buy though because sometimes you can find them cheaper.
When I was doing excavation and sherd survey in caves in Belize two years ago, I found my caving light (Lupine Pico X3) far too bright, even on the lower settings (i.e., 60 lumens), especially if I was doing any drawing. I went back to my "beginner" light (PT Apex) on low setting for any closeup work, and saved my bright, long-run-time light for moving from place to place in the cave. The comment about neck pain is legit--I had terrible neck pain for the first week I was excavating because I held my head a little to the side relative to my normal caving posture (allowed me to use my right hand to trowel and put my head to the left to get some contrast as I dug). So it's not a bad idea to consider a light with a waist-mounted battery pack, or something similar that keeps the weight off your head.
Other considerations:
-darkness of dirt you'll be excavating in (if you know). Some caves have really dark dirt, and this can feel like it sucks up your light. Do you know yet where you'll be working?
-how wet are the caves you're working in? If your light is ever going to be maybe dunked in water, that might change some of the recommendations.
-how remote will you be? If you're going to be away from electricity (or generators) for recharging lights for a few days, that can be a serious problem, and I would consider bringing a different light or finding a solar charger or something similar.
-are you going overseas? Make sure whatever light you get takes batteries that you can get in that country, if you won't be have electricity. For instance, anything other than AAAs and AAs can be really hard to find (thus why I try to find cameras that run on AAs)
That's all that sparked (har har) when I read your post. Good luck!