Lights are our friend in a self defense situation. An armed bad guy is going to shoot at a shadow or a light, it doesn't make any difference. The point is that YOU, as a responsible gun owner, MUST know your target and what's behind your target before pulling the trigger.
Is the target a threat or a mistaken identity (teenager, cop, whatever).
Is the target armed? If so, with what?
Does the target have a hostage?
What's behind the target?
What's in front of the target?
Another advantage is blinding a target. EVERYBODY reacts the same way when a bright light is pointed at their eyes; they either put their hands over their face, turn their head, or close their eyes for at least a second. That buys valuable time for the person behind the light to determine the correct course of action.
I have a light on the gun and a separate tactical light. I can determine when the light is on or off with a small motion of my finger.
If anything, it's foolish to try to defend yourself in the dark when you refuse to use a light.