Chapter 4:explores the interactions of light with structures, or strictly the interactions with the combination of the structure’s dimensions and the materials from which it is fabricated.In general terms we have the large compared to the wavelength, the comparable to and the small.The large includes light from the stars and, often contrived, structures such as lenses mirrors.But the detailed properties of these also depend on the comparable to – in minute imperfections and minute structural detail such as polishing.Even astronomical telescopes are tuned to the order of the wavelength of light!When we get to the tiny there are many strange effects exemplified in colloidal gold used in ancient glassware as permanent colouring.But are even these effects really that strange or unfamiliar?We all are aware that for example a piece of wire behaves very differently depending on it size (especially diameter) and its geometry – most familiar in the induction coil….The basic ideas are explored here with due recognition of how the very small wavelength and the very high frequency of a light wave can have profound impact on any interaction mechanisms.