This may muddy it even more but here goes.......
A light bulb without a shade lights up a room in candlepower, and the light from that bulb that shines through a hole in the wall that is a given diameter and distance from the bulb is measured in lumens.
Hope this helps. For a technical explanation you might try http://www.intl-light.com/handbook/ch07.html
Then it gets into lux and candela and flux......all of which I get really lost in. :?
I was looking at getting a light set up for a shotgun and I guess what I want to know is how much brighter is a tactical light than the Mag lite. I have a Mag lite but was wondering if the tactical lights are worth the money.
A tac light is way better for that than a Maglite. Pelican M6, Streamllight Scorpion and Surefire G series (composite body) are in the $25 to $45 range if you look hard enough. You can go up to several $100's if you want to.
There's more at issue than "how much light" in a tactical light. They are manufactured to higher standards and use different bulb technologies to make them more resiliant to the effects of recoil breaking the element and leaving you in the dark.
I use the Sure Fire 6P on my SU-16. I use a Mini Mag lite and the Streamlight Rechargeable (same size and dimensions as the Mini)on my Pistols. In the dark the Little guys work well and are less bulky than the 6P. The 6P works much much better for Tac situations. Buy the Sure Fire if you can.
I'm a big fan of the Surefire 6p myself. I carry a surefire and a streamlight when on duty. I use the streamlite for "standard" flashlight use. I use the Surefire for nightfire situations. The thumb button works better for me when firing at night.