Flashlights are technically a form of self-defense. However, I wouldn't reccomend you rely on it completely. A flashlight is a good backup plan. However, a flashlight cannot be a good mean of defending yourself from someone that could be stronger and faster than you. You should always have multiple means of self-defense such as martial arts/hand-to-hand combat, an attacking weapon, and perhaps a diversion/ runaway weapon(flashlight). Flashlights are pretty good at temporarly blinding, but if your attacker is determined enough, that definetely won't be enough.