Q & A: Prisms in various shapes

Can prisms come in different shapes?
- Kyle (age 89)
Jacksonville,FL,USA

Hi Kyle,

You bet! Prisms normally have a triangular cross-section and extend in the direction perpendicular to the plane of the triangle. But prisms can bend around in a curve, they can have four or more sides, and just about any shape will work. Some companies sell oddly shaped prisms for hanging in sunny windows to cast rainbow-colored light around a room. At some point it may become a matter of definition. One person's pretty piece of glass or plastic which splits light into many colors the way a prism does may not be called a "prism" by someone else, but does it really matter?

One undesirable consequence of the fact that many different kinds of shapes break light apart into many colors is the fact that the edge of a convex lens looks just like a prism, going around in a circle. In fact, most convex lenses, all by themselves will in fact split light into many colors (try a cheap magnifying glass someday -- you may see colored fringes around the images of objects you want to look at). More expenseive magnifiers will have a set of lenses made of different kinds of glass carefully arranged so that the distortion introduced by one lens is canceled out by another lens or lenses.

Tom

(published on 10/22/2007)