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UV Beads

In this activity, students use colour-changing, ultraviolet-sensitive beads to observe how sunscreen can block the harmful effects of the sun's rays.

One type of light radiating from the sun, called ultraviolet (UV) light, is visible to insects and birds, but not to humans. UV radiation helps us make vitamin D in our skin, but too much of it can cause radiation burns (sunburns) and skin cancer.

Unlike plants, humans don't needs photosynthesis to make our food and survive, but the sun is still very important for us. Among other things, humans need the sun to help our skin make vitamin D. Without vitamin D our bones cannot grow properly and they get soft and bend, causing the bone malformation called Rickets.

How can you tell if you have had enough UV radiation? Your skin will change colour when it is exposed to enough (or too much) UV radiation. Unfortunately, it can take a few hours for a tan, or burn, to show.

UV beads have special chemicals that change colour very quickly when UV light hits them. Sunscreen blocks some UV light so the beads change colour more slowly if they are covered with sunscreen.

Objectives

  • Observe the effect of ultraviolet radiation.

  • Explain the effect of sunscreen on UV light.

Materials

  • Per Class or Group:
    a sunny day! (indoor lighting won’t work, it lacks the UV light spectrum)
    UV-sensitive beads (available for purchase at TeacherSource)
    sunscreen
    pipe cleaners or string

Key Questions

  • Can you tell which beads have sunscreen on them?
  • How long can the beads with sunscreen stay in the sun before they change colour?

What To Do

  1. Divide the beads into two groups.
  2. Cover one group of beads with sunscreen.
  3. Take the beads outside into the sun.
  4. Watch what happens to the beads with sunscreen and the beads without.
  5. Make a UV–detecting bracelet or zipper-pull by stringing UV beads on a pipe cleaner.

Extensions

  • Experiment further by placing beads on a windowsill and test how fabric, window coverings, plain glass or cellophane may block UV light.
  • Experiment with the length of time it takes beads to change colour. Can you build a UV "clock"?
  • How does the brightness of the day/time of day/cloud cover effect the amount of time it takes beads to change colour?
  • Try sunscreens with different SPF. How does this effect the length of time before the beads change colour?