The Nature of Light and Its Interaction with Matter -- Principles and Nomenclature for the Quantification of Light -- Generation and Control of Light -- The Measurement of Light -- Light as a Tool for Biologists: Recent Developments -- Terrestrial Daylight -- Underwater Light -- Action Spectroscopy in Biology -- Spectral Tuning in Biology I: Pigments -- Spectral Tuning in Biology II: Structural Color -- Photoactive Proteins -- Molecules and Photochemical Reactions in Biological Light Perception and Regulation -- Photoreceptive Proteins and Their Evolution -- Signaling Crosstalk under the Control of Plant Photoreceptors -- The Diversity of Eye Optics -- The Evolution of Photosynthesis and Its Environmental Impact -- Photosynthetic Light Harvesting -- How Light Resets Circadian Clocks -- Photomorphogenesis and Photoperiodism in Plants -- The Light-Dependent Magnetic Compass -- Phototoxicity -- Ozone Depletion and the Effects of Ultraviolet Radiation -- Vitamin D: Photobiological and Ecological Aspects -- The Photobiology of Human Skin -- Light-Promoted Infection -- Bioluminescence -- Role of Ultraviolet Radiation in the Origin of Life -- Hints for Teaching Experiments and Demonstrations -- The Amateur Scientist's Spectrophotometer.