Diffraction Grating - Rainbow Peepholes™

They are wonderful. I have been using them for decades, usually buying around 500 or so per year. I give them to kids, people who have helped me, as part of tips at restaurants and stores, to school kids who visited our science department at the university where I used to teach (before retirement), as part of children's messages at my church, and as Christmas gifts to kids, especially relatives. I almost always have some with me wherever I go. The vast majority of people to whom I give them seem to really like them.

I'm getting ready for an "open house" where we are talking about x-ray diffraction from a synchrotron source. These peepholes make the perfect analog for a "sample" when paired with an inexpensive puck LED light where I can easily change the color via a remote. I masked out a single LED with a piece of cardboard to simulate the source. Looking through the peephole and changing the color demonstrates some key features such as the shrinking of the square pattern as color goes from red to blue (although green is best given the spectral purity of the lights I have). The 4 fold symmetry of the peephole is an analog to crystal symmetry and tilting the peephole to 45 degrees or so away from the face shows the reciprocal relationship between spacing and spacing in the diffraction pattern since our eye is seeing an angular projection of the diffraction grating in one dimension. The single LED is the "x-ray source," the peephole is "the sample", and the eye is "the detector". An excellent teaching demo. In the pictures, I just put peephole in front of my cell phone camera and its very easy to capture the effect. The pictures show the bare LED puck and then the red and green colors.

We are a science communication company and this was a perfect little giveaway at a recent conference.

Our student go nuts over the light experiments with spectra.

I have used these for years to teach the wave nature of light and sometimes with additional equipment to help students understand spectra and how we use them in different science fields. And they are just Fun!