First, check out this diagram from
Flashlightreviews. Readings that I find important are lux and overall output. Lux is the amount of throw a light has. The more throw, or brighter hotspot, the higher your lux. Throw factors come from size/depth of reflector, type of reflector (Smooth/Orange Peel), and emitter brightness.
Each emitter spits out a specified (in a perfect world) amount of light when driven at certain levels of power. Say this emitter driven at this level has a 100 lumen rating. This emitter in a deep smooth reflector will have a bright hotspot (high lux) but less flood. The same emitter, driven at the same power levels, in a shorter OP (Orange Peel) reflector would have less throw but more flood. These 2 lights would produce the same lumen rating but the beams would look completely different.
The CPF member
Selfbuilt has some great reviews that discuss a flashlights lux rating, and he does a ceiling bounce test which is a way to decipher how much output a light has. A light beam that hits the ceiling with all hotspot and little flood would have a lower ceiling bounce figure than a light that produces more flood, or more output.
Lights that have a high lux rating and a high ceiling bounce test are those that have the highest lumen rating.
I have come to dislike actual lumen ratings. Some lights specify what their lumens are just based on the LEDs own specs. If this light drives this LED with this amount of power then this is what the lumen amount is. Lumen loss occurs with a bad lens (some light is blocked) or crappy reflector. Lights that have lumens tested OTF are the way to go. A light that has OTF lumen ratings are what you really get when that light is turned on. Not, "Oh the emitter is 300 lumens but the beam itself once projected is really 200 lumens."
Someone may more of a polished response for you, but now you have some basics. Enjoy. lovecpf