If you carry a gun an additional item that should go along with you every time you walk out the door is a white light of some kind. Everyone is well served by carrying a light as they prove enormously useful on a daily basis. For a gun carrier, however, the light serves a second and very important mission: it gives you the ability to positively identify potential threats when in the dark. While much ado is made about flashlight techniques for fighting, I propose that the most important ability provided by the light is to simply identify who is around you or approaching you while in darkness. This can prevent a negligent shooting from occurring, and it can also serve to dissuade a criminal actor.
If analyzing real violent encounters on video, of which I have watched many hundreds of, I have not seen a single instance where a civilian self-defender used a light with a firearm. Does that mean we should not bother carrying a light? Hardly. Not only does the light prove imminently useful for routine things, but again, as a safety measure, the light is a necessity.
In terms of what light to carry, I find most people are not willing to make the commitment to carrying a larger “tactical light.” I think a small but powerful EDC light can do most of what is needed. You can certainly identify people who are closer distances with a small but powerful light. Where the larger and brighter tactical light with tail cap activation comes in is in the ability to use the light as a supplementary weapon itself. A very bright light can immediately diminish the vision of a potential threat in the darkness, giving you a huge advantage. Even the more powerful keychain size EDC lights tend not to have the power or the focused beam to do this adequately. By carrying the larger tactical light you gain this ability.
I look at lights similar to the way I look at handguns: I have my preferred carry gun and my deep concealment gun. Likewise, I have my larger and preferred carry light and my deep concealment light. Obviously, a flashlight is allowed pretty much anywhere, but having a conspicuous flashlight clipped in your pocket while dressed formally at the ballet may look odd (yes, I have attended the ballet on occasion). Typically, when I carry my deep concealment gun I also carry my deep concealment light. My preferred small light at this time is the Streamlight Microstream USB light, which emits 250 lumens despite the tiny size.
Typically, when dressed casually and wearing my standard carry gun, I carry a Streamlight Protac light, currently it is the 2Lx version which puts out 500 lumens and uses Streamlight’s USB rechargeable batteries. This is a light that is bright enough to be used defensively, and the excellent tail cap design makes it perfect for using in conjunction with a handgun, should such a need arise.
I think you might find that needing at least two light options is necessary for your lifestyle, as it is for mine. The good news is that we live in a golden age of flashlights, so take your pick. We are now used to such bright lights made possible by modern LED technology that we don’t realize how bring even the very small lights can now be. I think the primary role of a light for the citizen is as a searching and identification device and the small keychain designs, which can now be found in very powerful varieties, can do this well. However, the designs that utilize a tail cap and provide a momentary on serve best for tactical use.