A tactical light is a flashlight used in conjunction with a firearm to aid low light target identification and allows the marksman to simultaneously aim and illuminate the target. Tactical lights can be handheld or mounted to the weapon with the light beam parallel to the bore. Tactical lights also serve a role as a method of non-lethal force, used to temporarily blind and disorient the target.

Handheld lights are generally restricted to use with handguns, as long guns require two hands to operate. While just about any handheld flashlight can serve in the role of tactical light with the proper technique, some features are more readily adapted to the role. Some manufacturers sell lights specifically designed for use as handheld tactical lights. Police training programs in shooting while holding a flashlight date back to at least the 1930s.

To use a handheld light as a tactical light, the handgun is held in one hand, and the light in the other. There are a variety of positions that can be used to allow the light and handgun to be held parallel and provide mutual support, or the light can be held off to the side of the body to present a false target to a potential assaiant. Since the weapon and light are not attached to each other, the light may be used to illuminate areas that may or may not contain a target, without pointing the weapon at the area. If a target is detected, the handgun can quickly be brought into line to cover the target.

A flashlight intended to be used in this way will have provisions for ease of use when used with a handgun. Some models will have a narrow body and a ring designed to fit through the fingers, allowing the light to be used in a tight two handed grip on a handgun, with the switch controlled by pulling back with the fingers on the ring. More traditional models can be used as well, but a push button switch mounted where it can easily be manipulated while in the firing position is best; this way the light can be turned off to minimize the ability of an assailant to locate the user, and turned on as needed to quickly locate and engage a target. Another useful feature is the ability to attach a lanyard to the light, allowing the light to be secured to the hand holding it; this allows the light to be dropped if the hand is needed (for a magazine change, for example) and quickly retrieved.

Weapon mounted lights offer hands-free use, leaving the operator free to use both hands to control the weapon. Weapon mounted lights are most commonly seen on rifles, shotguns, and submachine guns, but they are becoming more common on handguns as well. These lights are often much more expensive than the handheld lights, since they must be sufficiently robust to withstand the recoil of the firearm, and the dedicated mounting hardware also adds to the price. One downside of the weapon mounted light is that it is always aimed parallel to the bore, so illuminating an object means that it is also targeted. Because of this, weapon mounted lights may not be appropriate under some rules of engagement.

Weapon mounted lights used to be specific to particular models of firearm, and to some extent that is still true; for example, Surefire makes a dedicated light that replaces the forend of the Mossberg 500 shotgun. On the other hand, many modern firearms are incorporating Picatinny rail systems, allowing any appropriately sized Picatinny compatible system to be attached. Other mounting systems are simple clamps, designed to mount most cylindrical lights parallel to the barrel of most firearms.