To take photographs at night or in dark room, have your camera in the following settings:
Camera on a tripod or on a stable flat surface that does NOT move
Either use a shutter remote or shutter cord- if you don't have one, use the self timer so you don't move the camera. Note: if you are using the self timer, be sure that you are covering the bulb by using gaffer tape.
Mode: Shutter Priority
Shutter Speed: 15" seconds or longer
Aperture: low or f 5/6
Use the camera app "myLightPaint" or any other FREE light paint apps on your phone.
You can use glow sticks too, but they are sometimes aren't bright enough and can be costly.
Focus on the person first in the light (or flash a light on them to focus in on them) then turn the lights off.
Face your phone with the light painting app on towards the camera. If you are spelling something out, write it backwards.
To illuminate the model, use the flashlight on your phone to highlight them briefly.
You can also use colored gels to get different colors on your flashlight.
Experiment! For every good photo, there will be 29 bad ones.
Ultra cheesy youtube video on light painting.
Unusual techniques for light painting