When used effectively, the tactical flashlight is an excellent tool for self defense. It combines the power to blind an attacker with night adapted vision with the benefits of the palm stick. It's difficult to imagine how effective an extremely bright light can be, until you're shined with one in the dark. All you can see is light, as in the image to the left, and when the light goes off you see black while your eyes adjust to the change. But imagine what your attacker will experience, as immediately after losing his vision he gets kicked hard in the balls, hit in the solar plexus, or hammered in the face with what amounts to a thick, metal bolt. Not only is the flashlight a great self defense tool, but you can carry it everywhere, inculding where weapons of any kind are illegal to carry.
Using your flashlight as a deterrent should be your first option. It's always better to avoid physical contact when possible. If you maintain your distance and blind a potential attacker or attackers, that may well be enough for you to escape. If it's not, many combinations will work with a "flash and bash" strategy, including empty hand combinations where you substitute the light for hand strikes or elbows. Because most people instinctively bring their hands up to their face after being flashed, my preference is generally either to kick low, punch low, or grab or smack the lead hand down to strike the head with the light as an opening move. This palm stick defense also works well as an attack after a flash, and can be done to the face, throat, sternum, or solar plexus. Like everything else, in order to use it you need to train with it. So if you do choose to carry a flashlight for self defense you must put in the training time to be able to use it.
Another important point is that the light needs to be in your hand already. It's not going to do you any good in your pocket or purse. When carrying a light for self defense you should carry it in your hand when walking outdoors at night.
Below is an example of a combination I particularly like. The images have been brightened for the purpose of illustration.
All flashlights are definitely not made equal. For a flashlight to work as a self defense tool it needs to be:
A large flashlight isn't going to do you any good, because you'll never carry it with you. If a light requires you to twist the back to turn it on, or slide a button up on the shaft, it's not going to work for self defense. You need a light with a tactical thumb switch/button. And if your light isn't reliably and blindingly bright you'll be wasting your time with it. I've tried numerous lights, and my favorite two are the Surefire LX2 and the 6PX Tactical, pictured below:
Both of these lights are rated by Surefire at 200 lumens, and Surefire is not only known to under rate the brightness of their lights, but they also measure the brightness "out the front" rather than at the LED emitter. They're at least as bright, or brighter than any other easy to carry light. They're also made in the US with a lifetime warranty, and are extraordinarily solid lights. My preference is the LX2 due to the pocket clip (makes it a little easier to carry and access), slightly narrower size, and dual output levels (both being instantly accessible) allowing it to function as a self defense or general purpose light. The LX2 has a list price of $210 (you can find it for much less here) whereas the 6PX Tactical is listed at $115 (and sells for less here). The 6PX Tactical is an excellent self defense light with the same solid construction and blindingly bright output, but does not have the pocket clip and is just a little bit wider.
Note: Surefire also makes a self defense light called the LED Defender, but I'm not a fan of it due to the obvious weapon like design. In my opinion it's no better than the LX2 or 6PX Tactical, but you wouldn't be able to carry it where weapons are not allowed.
See more about using weapons for self defense.