It's incredibly easy to make a black light with your phone. Let's make one, and glow the fluorescent things in the dark with your blacklight.
Duration 15 Min
Difficulty 2/4

Material list

What is happening

It’s difficult to find a UV light source . But you can mimic the effect using a white light source, purple and blue filters.

Black light is technically ultra-violet (UV)light, more specifically, it is UV-A light, the long wavelength region of UV light. Generally, it is very expensive to make a bulb that emits UV light. But white light from a bulb contains a  very small portion of UV light. Using a purple and blue filter we can filter out that portion of UV light and make a super easy blacklight source.


Gather the materials

You will only need a few things to do this experiment that are readily available in your house.

Step 01

Rip off a small piece of tape

Step 02

Place the clear tape over the flash

Place the piece of tape over the camera light on the phone.

Step 03

Color with a purple pen

Color on top of the tape with a purple marker so that it covers the flash.

Step 03

Place another tape and color with blue pen

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

Step 05

Place another tape and color again with purple pen​

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

Step 07

You're done!

Your blacklight source is ready to use.

Step 09

Draw something on paper

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

Step 10

Lights out!

Grab your picture and turn off the lights. Then turn on the camera light of your phone and make your picture glow.

Step 10

More Science

 Many highlighters fluoresce or absorb and emit light, which makes them glow in the dark. But why? Light is a spectrum. The region of spectrum that we can see is called visible light. It ranges from red to violet light. However, there are other types of light, including infrared and ultraviolet  (or UV) light. UV light is what a blacklight bulb emits. More specifically, it is UV-A light, the long wavelength region of UV light.

The ink of the highlighter pen show a unusual glow becuse it converts some of the incident ultraviolet light that is invisible to humans into visible light.

White light is a combination of lights with different wavelengths. It contains a very small portion of UV-A light also. 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. It is enough to make the highlighter fluoresce because the wavelengths of purple and blue light are close enough to the UV spectrum.


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