Lesson Plan: Ultraviolet Light
I’m getting ready to do a summer camp all about light in astronomy. I’m particularly focused on doing some experiments with the kids showcasing “invisible” light, or the ways in which we can use light we can’t see to learn about the Universe.
One particular activity is pretty easy and uses inexpensive materials to explore ultraviolet light. Though it doesn’t directly use astronomy, you can use the Sun as a source of ultraviolet light for this experiment. It’s a twist on a common activity using UV-sensitive beads that can be bought pretty cheaply from science supply stores. It also teaches kids the concept of a blinded experimental test, very important to reducing the human factor in rigorous scientific studies.
This particular version of the activity, Invisible Light: Ultraviolet (pdf) was developed as part of an astronomy outreach club in Virginia called Dark Skies, Bright Kids. We had a whole day dedicated to exploring parts of the electromagnetic spectrum that can’t be seen by humans. This activity lets kids use special plastic beads which change color in the presence of ultraviolet light. This same material is used in all of those “magic color changing in the sun” chotchkies you can get in gift shops. (Spoiler: it’s not magic; it’s science.)
You need to prep beforehand, or, if you really want to do a double-blinded experiment, have someone else prep for you. Get several different SPF values of sunscreen and put them into bottles that are labelled with letters, numbers, symbols, or whatever won’t give away the contents. Now, you’re ready to take the activity to your kids!
Have them investigate what the UV beads do under regular indoor lights and under an ultraviolet light source, either artificial or the Sun. (Be sure to have tested the artificial light source beforehand and make sure that it works at the right wavelengths for your beads.) Then, introduce them to the randomly labelled bottles of sunscreen and ask them how they might determine which is the most protective. Depending on the age and level of your students, you can give them a little help or a lot in giving them hints or clues. I find it best to give them small plastic baggies to protect the beads from the sunscreen so you can use them again and again. As long as all the sunscreen coatings are done evenly, you should find after the reveal that the ones with higher and higher SPF ratings have the least change to beads colors at the end. But, as the SPF gets higher and higher, the differences become too small to tell.
When you’re done, if you are feeling especially crafty, help the kids make jewelry with their ultraviolet beads. There was one Mothers’ Day when a whole lot of women in one particular Virginia school district got UV-changing jewelry as a gift!