Name: FlashLight Helmet
It's rather self-explanatory, but made simple it would be a (yellow) Gold Helmet (as we don't use too much gold) + a torch, depending on if you want it to shine indefinitely or use battery
Personally I would like it to be a fairly low tech system as I usually stop mining myself once I have a Quarry from Builcraft.
Also I find it unforgivable to have nuclear reactor but be incapable of making light.
Depend of how accessible you want it to be
ps : on an unrelated note I liked needing 3x3x3 cube of water for nuclear reactor.