This book offers comprehensive coverage of the most important areas in photoreceptors and light signalling. Photoreceptors enable most species to sense not only the presence of light but also the information, such as irradiance, colour or spectral distribution, direction and polarization of light. They are vital, therefore, in providing organisms with energy and information about their surroundings, such as day and night cycles. This book covers the range of photoreceptors that have been discovered to date and the broad range of methods used when researching how they operate, including: action