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Creative Corner

Build Your Own Black Light Secret Message – Perfect for Trick or Treating!

We are always looking for new and fun science activities at the Steve Spangler Science Labs.This Halloween season we have really outdone ourselves with a new product line that includes Vampire Slime and Vampire Veins. We have also created this simple and easy craft that also teaches a lesson in the science of glow.

Some of the adults in the company may also sneak into Steve’s Playroom, turn off the lights and put together puppet shows with our black light projectors. I won’t tell if you won’t tell.

I’m also prepping to do this activity with 20 Brownie Girl Scouts this Tuesday. I can’t wait to see what they all come up with. I know it will be beyond anything that our Spangler lab rats have created the past few weeks.

This black light projector is perfect to take along Trick or Treating, not as a flash light, but as a fun way to say “Trick or Treat” or flash as you cross streets.

Let’s start with a lesson about Phosphorescence and Fluorescence.

Phosphorescence – Some materials glow after all the lights are turned off. This type of glow is called phosphorescence. “Glow in the dark” toys phosphoresce brightly in total darkness after being “charged” or excited by ordinary white or ultraviolet light. A phosphorescent material absorbs and slowly re-emits energy in the form of light. It will still glow after the lights are turned off. Remember those little stars you stuck to your roof as a kid? Those stars used a phosphorescent material to glow after you turned out the lights.

Fluorescence – Some glowing materials will only work in the presence of some form of radiation like ultraviolet light. These materials have a chemical property called fluorescence. Fluorescent materials absorb energy just like phosphorescent materials, but fluorescent materials re-emit their energy as light much quicker.  For example, fluorescent papers and poster boards glow in the daylight. They may seem to glow even brighter under black light (ultraviolet), but in either case, as soon as the light is removed, the glow stops. Fluorescent things do not glow in the dark all by themselves – they require some other form of energy such as ultraviolet light to “excite” them.


Glow Sticks
Glow sticks are yet another way that materials can glow in the dark. Glow sticks create their glow through a chemical reaction between different chemicals. The light that this chemical reaction produces is called chemiluminescence. Just like the other two types of materials, you can see chemiluminescent materials the best in the dark. It’s not a good idea to break open glow sticks to use the liquid inside. Most sticks contain a glass tube inside that shatters to mix the chemicals together. You don’t want to pour glass shards out for children to touch. The chemicals inside the glow stick aren’t incredibly toxic, but can cause eye and skin irritations and will stain.
Some highlighters use ink that contains dyes that are fluorescent. When you draw the designs with a highlighter, it probably looks like those designs will glow when you turn the lights off, but they don’t. The dyes in the highlighter ink require a black light to produce the special glow. Certain colors  and brands of highlighter do not fluoresce underneath the ultraviolet light. These highlighters do not contain fluorescent dyes.


  • Mini Black Light
  • Glue
  • Sharpie® highlighters (will fluoresce under a black light)
  • Scissors
  • Plastic cup
  • Pen
  • White paper


  1. Use a pen to trace the circumference of a plastic cup on a piece of white paper. Don’t use thick paper like card stock or construction paper. Just pull a piece of paper out of a printer… that’ll work perfectly!
  2. Use Sharpie highlighters to create brightly-colored designs within the circle you traced. Try using different colors when creating your design.
  3. Cut the traced circle out with a pair of scissors.
  4. Carefully poke a small hole in the bottom of the plastic cup using the scissors. Try to poke the hole as close to the center of the cup as possible.
  5. Apply a thin layer of glue around the edge of the circle. Make sure the glue is on the back side of the circle, away from your design, otherwise your design or message will be backwards. (Depending on what your design or message is, this could be a big deal!)
  6. Press the mouth of the cup onto the glue-covered edge of the paper circle. We recommend letting the glue dry before moving on to the next step, but hey… we aren’t here to slow you down. (Remember to clean up any glue that squeezed out and onto the table where you’re working. Happy parents make for happy scientists.)
  7. Now that your cup and design are attached, push the Mini Black Light’s bulb into the hole you poked in the bottom of the cup.
  8. Are you ready for this? Turn the lights off and turn on the Mini Black Light.
  9. Whoa! The ink from the highlighters glows in the ultraviolet light!

Susan Wells
Author: Susan Wells

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