The wide range of topics in this text are linked by the theme of the title. The subjects include the history of artificial lighting, eclipse cycles, glasses that go dark in sunlight, rainbows, the clock setting in the South Pole, zebra stripe patterns, lighthouses, colour perception, the harvest moon and how information and speech can be conveyed by light from the Sun or from a laser. It is not about the latest developments in optics, but attempts to encourage people to look at many familiar phenomena, such as the variations in the duration of twiglight through the year and the ability of human vision to misinterpret patterns of lines under certain conditions. The book describes the anatomical peculiarities of four-eyed fish and explains how the Jewish calendar contrives to follow both solar and lunar cycles. It presents the reasons why tortoiseshell cats are almost always female. Readers are informed where they can see 19th-century military equipment that could convey messages rapidly over vast differences.