How to Turn Your iPhone Into a Black Light (UV Light)


  • iPhone with flashlight
  • Transparent tape
  • Blue marker (permanent recommended)
  • Purple marker (permanent recommended)
  • Highlighter (any color)
  • Piece of white paper (or another surface with fluorescent materials)


  • Prep the iPhone: Grab your iPhone and turn it with the flashlight lens that is next to the rear camera towards you.
  • Apply the Blue Filter: Take a small piece of transparent tape and stick it over the flashlight lens. Use a permanent blue marker to color completely over the taped area. Let it dry properly afterwards.
  • Double Down on Blue: Add another small piece of tape over the first blue layer. Repeat the coloring process with the blue marker to create a stronger blue filter.
  • Add the Purple Touch: For a more pronounced effect add a final layer of transparent tape. This time color over it with a permanent purple marker. Let it all dry completely.

Testing Your Make-Shift Blacklight

  • Dim the Lights: Head to a dark room or create a dimmed environment to see the effect properly.
  • Power Up the Flashlight: Open your iPhone’s Control Center and turn on the flashlight on full blast.
  • Shine on Fluorescent Materials: Point the iPhone’s flashlight beam at a white piece of paper or a surface containing fluorescent materials like certain inks or highlighters. You should see the highlighter’s color glowing under the makeshift blacklight.

Important Things

This method creates a colored filter not a true black light. True black lights emit ultraviolet (UV) light invisible to the human eye that excites certain materials and causing them to glow.

The effectiveness of this trick depends on the quality of the markers and the materials you’re trying to illuminate.

Be careful not to layer the tape or marker too thickly because it might block too much light.

This is a temporary modification. The tape and marker can be removed with some rubbing alcohol if needed.

More Examples of Objects That Can React

White fabrics: Many laundered white fabrics have brighteners added to make them look whiter and these react under the blacklight. Point your iPhone’s flashlight on a white t-shirt and see if it glows.

Tonic water: Tonic water contains quinine which fluoresces a faint blue under blacklight.

Some rocks and minerals: Certain minerals exhibit fluorescence under UV light so experiment with different rocks if you have a collection.

Banknotes: Many countries embed security features into their banknotes that only become visible under blacklight. That’s probably one of the coolest things you can see using the blacklight on your iPhone.

Pet Stains: Sometimes pet urine will leave fluorescent residues. If you find any glowing spots in your room and your cat or dog’s been living with you for a while you need to clean up ASAP.

Troubleshooting & Tips

Experiment with highlighter colors: Different highlighters contain different levels of fluorescent pigments. Yellow tends to be the most reactive but try pink and orange for other effects.

Check your room beforehand: Some household materials might already glow slightly under normal light conditions. Choose a properly darkened room for the best views.

Compare to a real UV light: If you can compare your DIY light side by side with a small UV flashlight to see the difference in how intensely materials react.

At the End of the Day it’s Not Perfect: This makeshift approach won’t replace a dedicated blacklight for scientific or professional use. This is just a fun DIY experiment instead of a precision tool.

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