I know there are differing opinions of weapon mounted lights, but I am a huge advocate of them and last night it was worth it's weight in gold. Here's the story in a nutshell:
Call came out of a subject with a knife who had just pulled it on the caller (victim) and ran north from the area. I came into the area and located the suspect. I exited my patrol car, and approached with my duty weapon at the low ready. Suspect starts screaming at me at about 25 yards away, raises his right hand over his head, and charges at me screaming "Do it, *expletive*!" I can see he has something in his right hand as I immediately raise my weapon. I turn on my weapon mounted light and take a couple of steps back as he closes within about 15 yards. When I turn on the light, the suspect stops just long enough for me to see that what he is holding is a black pencil with metallic writing on it. I used a quick burst of OC spray and he started running south. After a brief foot pursuit, I tackled him like an NFL lineman and the incident was over.
Other LEO's might read this and raise various questions. Based on the call, his actions, his distance, demeanor, language, etc - a different officer may have fired and been completely justified. I chose not to, and in the end it worked out just fine.
In this instance, my weapon mounted light saved the suspect's life. He reacted to the light by stopping, and in doing so it enabled me to identify what the object was in his hand. Turns out he is a psych patient off his meds who we were able to petition into the psych ward rather than the morgue.
Ironically, the pencil came from our police department and the metallic writing had our department name on it.