Abstract

A prism placed on a well-illuminated horizontal piece of white paper can be viewed at different angles (Figure 1). When the viewing angle is high, one sees the transmitted light coming through the air-glass interface from the horizontal white paper. One can also see a weak reflection off the glass-air interface that superimposes the vertical object's image as well. If the vertical object is a black piece of paper this overlapping image can be made negligible in intensity. When the viewing angle is low, the light from the horizontal white paper cannot get to your eye, and only the reflected light from the vertical object is viewed. If this is a black screen then very little light is observed at that viewing angle. At the boundary between these two types of viewing, one observes an arc of color - a red arc that blends into a red-orange and bright yellow band before fading into pink and, finally, white. This attractive arc of color is reminiscent of a rainbow, and appears as a half-rainbow. When the white and black paper screens are exchanged, an arc of color is observed that is blue. The blue arc is not as high contrast as the red one and is bordered by a bright green arc that blends into a bluish white and, finally, white. This is the complimentary half-rainbow.

© 1990 Optical Society of America