Exploratorium Part I: Color from Light

Mylar light box at the Exploratorium's "Colored Shadows" exhibit

To study the caustics of different light sources, I created a box frame out of cardboard (let's say 6" deep), tape a transparency to one side, roll up a bunch of 6" by x" tubes from mylar, where x depends on different diameter tubes you want, place them all in the box, cover other end with tracing paper and *poof* you have an amazingly simple and fun tool to play with light and explore caustic networks.  From wikipedia: "In optics, a caustic or caustic network is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface. The caustic is a curve or surface to which each of the light rays is tangent, defining a boundary of an envelope of rays as a curve of concentrated light. Therefore, the caustics can be the patches of light or their bright edges. These shapes often have cusp singularities."

To study interference, fill a flat container with about an inch of water, place a piece of black construction paper into the water, use cheap, clear nail polish and drip a small drop onto the water.  It will quickly disperse into a thin film on the surface of the water.  Gently lift the black paper from the water, capturing this thin film on the surface and allow to dry.  Now think about what is going on to create the 'permanent oil slick' effect from interference.


The layer of nail polish you get by water-dispersing it first, is much thinner than if you tried to paint it onto the paper. Some of the light hitting the surface passes through the top surface of the nail polish layer and reflects off the bottom surface, while some of the light reflects off the top surface.  The light waves reflecting from these two surfaces overlap, adding or subtracting to each other depending on their phase.  The colors you see are the wavelengths left over when some colors are subtracted from the white light and it depends partly on the thickness of the layer of nail polish which varies over the surface of the paper.

hand shadow on homemade phosphor paper

simple cheap supplies: paper, glow in the dark paint,
leftover disposable camera

To study phosphorescence, you need to coat some sort of substrate (I used a thick cardstock) with several layers of glow-in-the-dark paint and allow to dry.  Then take apart a disposable camera so you can access the little gear wheel inside to advance the 'film' so that you can use the flash as your light source.  Have fun capturing your shadow play.