DIY Blacklight: Use This Hack to Turn Any Smartphone Into a Blacklight

Share and decode secret messages with this DIY Blacklight hack!

Have you ever wanted to make something glow under a blacklight? Let us teach you one of our favorite hacks to make glowing highlighter messages and drawings at home with this DIY blacklight tutorial!

Recommended Age: 5+. Younger scientists will enjoy making and revealing their messages and drawings, but may need help putting together the DIY blacklight hack.

Materials you will need:

  • A phone with a camera light
  • Clear tape
  • A blue marker (a permanent marker, like a Sharpie, works best)
  • A purple marker (a permanent marker, like a Sharpie, works best)
  • White paper
  • A fluorescent highlighter (yellow works best)
Materials for DIY Blacklight



Rip off a small piece of tape (fold some of it over to make a tab for easy clean up later) and place the piece of tape over the camera light on the phone. Make sure you place the tape over the LIGHT, not the camera!

DIY Blacklight step 1


With the blue marker, color the portion of tape over the light. You don’t need to color in the entire piece of tape; you just want to make sure the area directly over the light is colored.

DIY Blacklight step 2


Place another piece of tape over the first. Color the area over the light blue again.

DIY Blacklight step 3


Place one more piece of tape on top of the others. This time, color the area over the light purple.

DIY Blacklight step 5


Draw a picture or message on white paper with your highlighter.

DIY Blacklight step 6


Grap your picture and turn off the lights or go somewhere dark. Then turn on the camera light on your phone and shine the light onto your picture.

DIY Blacklight end result

The Science Behind This Blacklight Hack:

Many highlighters fluoresce, or absorb then emit light, which makes them glow in the dark. But why?

  • Light is a spectrum. What we can see is called visible light. It ranges from red light to purple light. However, there are other types of light, including infrared and ultraviolet light (or UV) light. UV light is what a blacklight emits.
  • When you colored the tape with blue and purple markers, you created a filter that blocked out all colors of visible light except blue and purple. With the rest of the visible light spectrum blocked out, the resulting blue and purple light were enough to make the highlighter fluoresce because the wavelengths of purple and blue light are close enough to the UV spectrum, even though there is minimal UV light actually present.
  • Highlighters fluoresce under a normal blacklight because the ink absorbs ultraviolet light, which isn’t visible to the human eye, and remits it as visible light.
science of DIY blacklight

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