The rule of thumb with weaponlights is that only SureFire is good enough. When it comes to handgun lights, Surefire X300U-A is possibly the best in its class. SureFire’s best-selling model can be mounted on practically any rail of a modern service handgun as well as shotguns and rifles equipped with a Picatinny rail. You can operate it with either hand and it delivers 1,000 lumens!
Even though SureFire X300U-A is primarily a handgun light, it is also perfectly suited for long guns. When you mount it directly on top of the gun, you can shoot from both sides. Furthermore, the light is always in line with the barrel and the sight. When mounted on the side of the gun, the light can still be blocked by the cover even though the barrel is already pointed at the target.
To be able to use a weapon light successfully, you need a pistol holster that is designed for your gun and weapon light combo. The best holsters on the market are made by U.S. Duty Gear.
You can find more information about the selection of weaponlights in this article.