Glowing Jell-O Physics

Jell-O — the jiggly dessert favored by kids everywhere — comes in a variety of flavors and bright, neon colors. Once the lights go off, however, typical Jell-O loses its characteristic colors.

But with a small change in the recipe, you can make this treat glow under a black light! Here's your guide to fluorescent Jell-O:

Fluorescent Jell-O

The tonic water Jell-O under normal light (top) and a UV light (bottom).

What You Need

  • Jell-O (flavor of choice)
  • Tonic water
  • A clear glass bowl or clear cups
  • A Black light

What to Do

1. Measure out one cup of cold tonic water. Microwave the tonic water for 45 seconds or until boiling.
2. Stir the boiling tonic water into the gelatin mix; stir for two minutes or until completely dissolved.
3. Stir in one cup of cold tonic water.
4. Refrigerate four hours or until firm.
5. Check out your psychedelic Jell-O under a black light!

What's Going On?

Ultra-violet light has a higher frequency and lower wavelength than the visible light you experience everyday. In normal light, fluorescent materials do not appear special; however, when put near an ultraviolet light, their atoms become “excited” and seem to glow. The energy of visible light is lower than that of UV light; therefore, visible light does not have enough energy to make fluorescent materials glow. We call this ‘glow’ fluorescence. Highlighters, for instance, have fluorescent properties that absorb the energy from UV light and re-emit it at lower energies. This produces light frequencies in the visible spectrum.

For the experiment, the tonic water added to the Jell-O mix contains quinine — a substance that has fluorescent properties. Consequently, the Jell-O glows under a blacklight.

Apply It!

What makes this Jell-O special? Will the Jell-O glow in the dark without an ultraviolet light? Why not? Does it matter what color the Jell-O is? Why or why not?

More Information

- Jamie Garrett