Black Light Secret Message

UV light reveals hidden images that glow in the dark

Print this Experiment

Highlighters have a number of uses, from helping acknowledge important text to acting as brightly-colored markers in our favorite coloring book. Around Halloween, though, we’ve found an entirely different use for them. 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.


Experiment Videos

Here's What You'll Need

  • Black light
  • Glue
  • Highlighters pens
  • Scissors
  • Plastic cup
  • Pen
  • White paper

Let's Try It

  1. Use a pen to trace the circumference of a plastic cup on a piece of white printer paper.

  2. Use 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.

  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.

  7. Now that your cup and design are attached, push the black light’s bulb into the hole you poked in the bottom of the cup.  Turn the lights off and turn on the black light.

How Does It Work

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.  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!

Browse more experiments by concept: