Purchase a powder brightener like Rit Laundry Treatment or Oxo-Brite.
Mix 1 cup of warm water with 1 tbsp. of powder brightener. Stir it until it dissolves. You can also use a cup of paint, ink or lacquer in any color.
Turn off the lights and look at the solution under a black-light.
Add more powder brightener to the mixture if you want a brighter hue.
Use a paintbrush to make a design on clothes or paper. Let it dry for an hour and look at it under the black-light to check the brightness.
Mix regular ink with glow powder according to the manual on the glow powder. Stir it with a wooden stick and wear gloves.
Turn off the lights and check the glow strength under a black-light. Add more glow powder to make it brighter.
Use a paintbrush to make a design on clothes or paper. Let it dry and then inspect it under the black-light.