Coloured shadows

Abstract

The article reports an investigation of the relationship between knowledge of geometrical optics and the understanding of the phenomenon of coloured shadows. The research was conducted through interviews by asking adults with different expertise for the explanation of the experimental observation of a red and a green shadow on a yellow background and subsequently for the prediction of the phenomenon with three beams of light. The interviews were analysed in terms of a knowledge organized in networks of experience and theory. It is shown that the knowledge of geometrical optics facilitates the pinpointing of the colour problem while the experience with the mixing of paints may act as a barrier to understanding the mixing of light beams.