Reveal invisible secret messages and drawings under a black light with a spooky homemade Halloween projector.

These handheld projectors are perfect for puppet shows, lighting up while trick or treating, flashing messages in the dark to your friends, haunted houses and more. Take them outside for fun after dark. Decorate a piece of paper, draw your message or picture with a fluorescent highlighter, glue it to a cup, add a black light and you are ready to take on the night.

With the Black Light Secret Message experiment, you’ll see that certain highlighters aren’t just brightly-colored – they’re actually fluorescent and glow underneath a black light! The secret messages and floating images you’ll create with this experiment are sure to create screams of joy and shrieks of excitement. Some even break open highlighters and squeeze out the ink to make glowing potions. On Friday, we will share the Science Behind some of our favorite glowing recipes.

Materials

  • Mini Black Light
  • Glue
  • Sharpie® highlighters
  • Scissors
  • Plastic cup
  • Pen
  • White paper

Instructions

  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!

NOTE: You may have found that certain colors of highlighter do not fluoresce underneath the ultraviolet light. These highlighters do not contain fluorescent dyes, but you can get creative with them. Try using them in unison with the fluorescent highlighters to make incredible creations!

The Science Behind This Activity

When it comes to glow in the dark, it’s important to know the difference between the two common types of glow,fluorescence and phosphorescence.

Fluorescence – This type of glow occurs when some form of radiation, such as light, causes an object to glow. 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.
Phosphorescence – Phosphorescence is just like fluorescence, except that the glow continues even after the light used to excite it is removed. “Glow in the dark” toys phosphoresce brightly in total darkness after being “charged” or excited by ordinary white or ultraviolet light.
Some highlighters use ink that contains dyes that are fluorescent. When you draw the designs on the circle, 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.
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  1. […] Invisible Secret Messsage that Glows in the Dark Use fluorescent ink highlighters to draw a message on a piece of paper. Glue the paper to the rim of a plastic cup, insert a small black light into the back. BAM! In the light, all you see is the paper. In the dark, flash the black light to reveal a secret message. […]

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