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

1. The DIY UV LED Light Conversion Method

Warning: This method requires a small amount of technical expertise and extra care when working directly with the electrical components that we’ll tell you about.

1. Buy a UV LED: Buy a UV LED with a wavelength of 365-405 nanometers, which is the range for black light applications. You can find pretty cheap UV LEDs online.

2. Buy a resistor and power source: Buy a resistor with a value of 1 kΩ to 10 kΩ and a power source like a 9 volt battery or a USB power adapter.

3. Solder the components: Solder the UV LED to the resistor and power source.

4. Create a housing: Create a housing for the UV LED using a plastic or metal casing making sure that the LED is secure and has a cover.

5. Attach the housing to the iPhone: Attach the housing to the iPhone’s charging port using a USB connector or a custom adapter.

6. Use the black light: Hold the iPhone’s UV light close to the object you want to use the black light on.

2. The DIY Tape Method


  • 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.

3. The Black Light/UV Light App Method

1. Download a black light app: Search for *black light* or *UV light* in the App Store and download an app that produces a UV light effect. Some popular apps are *Black Light* by iDevStudio, *UV Light* by TapMedia and *Black Light Torch* by AppSoft.

2. Launch the app: Open the app you downloaded and grant it access to your screen brightness settings if it asks you to.

3. Adjust the settings: Change the app’s settings to optimize the UV light effect. Some apps give you the option to adjust the color temperature, brightness and duration of the light.

4. Use the black light: Hold the iPhone’s screen close to the object you want to illuminate. The app will produce a UV light effect that can help reveal fluorescent colors, detect counterfeit bills or create a unique lighting effect for parties. But don’t expect much, at the end of the day there’s only so much an app can do to your flashlight colors.

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 show fluorescence under UV light so you can experiment with different rocks if you have a collection.

Banknotes: Many countries have 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 and 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: These makeshift approaches 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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