Ok. I have been light painting for many years , the best way is to have a small flash to show the subject then light paint over it.
I have written a lesson on it , see my website tutorials, one of the great light painters was a guy called Aaron Jones he invented a fibre optic device called the hosemaster a fantastic machine for pros. with many acces.
The only problem was the price around 6000 us, when I had my first one. Broncolor also do a light brush that was in the past greatly inferior to the hosemaster.
Anyway it's difficult to explain so go to the light painting lesson on the site.
Regards
Phillip