Just a piece of advice, that I'm sure most firearms/weapon light instructors would agree with:
If you are going to use this light at all as a true "tactical light" in conjunction with a handgun, it should have the following 3 features:
1. Single mode - you do not want to be in the middle of a stressful life-or-death moment and accidentally go from 500 lumens down to 15 or to strobe, or S.O.S., etc. Every single time you press the tailcap, the light should come on in high. Most L.E.D. flashlights these days have 2, 3, even 10 levels of light output, including strobe and S.O.S. modes. These should be avoided if the light will ever be used with a firearm.
2. Press for on, release for off, twist for constant on tailcap - This probably isn't as essential as number 1, but it's what is usually recommended for a tactical light. You want the light on only when you press it. When you release the switch, the light should turn off. There are many "tactical" reasons for this (least of which is the audible click that you don't want when trying to be discreet in a dark and quiet situation). Some of the higher-end tactical lights also have a rubber ring around the body, so you can grip the light like a cigar and use the thumb joint to activate and deactivate the light while holding the handgun in your strong hand. "Clicky" switches are usually preferred for general use lights, but aren't recommended for tactical lights.
3. Shock-proof, rugged construction - This isn't as easy to shop for as number 1 and number 2, but price usually is a good indicator. If a light is advertised as tactical, has 5 levels, plus flashing modes, crenelated bezel, and claims 1,000 lumens but only costs $30-$40, it probably won't last as long or hold up to abuse as well as a $150-$300 light from Surefire, Elzetta, or Malkoff (those are the top 3 brands I would recommend for a serious tactical light that will take anything).
Good luck, and have a safe (and bright) trip.