Low light shooting along with dominant and non-dominant one hand shooting are skills we all need to develop or maintain. I will leave the "weapon-mounted vs handheld" discussion out of this. If you are in the weapon-mounted camp, make sure you have a handheld light available too. A 1000 lumen tactical light will fit in your pocket and can be had for less than $100.00. GET ONE and get some training. With the exception of a home invasion at night, you are unlikely to encounter a threat in total darkness. The bad guys have to be able to see. The dim light afforded by street lights, outside of businesses, etc. provide enough light to see while allowing predators to stand-off in the shadows. A hand held light is an invaluable tool that can temporarily blind your attacker and give you time to act. They are also legal to carry most anywhere and also serve as an impact weapon. Make sure the light can be activated from button on back (not the side of the light) and that there is a momentary on/off function.
Three points (in addition to those mentioned in the link below) to keep at top of mind when employing a handheld light: Use the center of the beam to blind and illuminate the assailant, be mindful of hand position and your muzzle, and a BIG point, turn off the light BEFORE you move.