In order to adequately time behaviour, endogenous clocks need to be synchronized to the cyclic environmental changes. Light is the most important Zeitgeber for circadian clocks. In D. melanogaster light is perceived by rhodopsins in the compound eyes, the ocelli and an extraretinal eyelet at the base of the posterior compound eye. In addition, the blue-light photopigment cryptochrome (CRY) is expressed in the eyes and in many clock neurons. Both, rhodopsins and CRY contribute to entrainment of the clock in different ways. Here we aim to clarify the individual functional roles of all photoreceptors in synchronizing the flies’ activity and in timing it optimally to natural light conditions. A special emphasis will be put on the synchronisation of the clock by spectral changes during twilight. In addition, we will investigate how insects living in habitats with different light intensity, spectral composition or light duration changed their photoreceptor composition and of what importance a newly discovered rhodopsin (Rh7) is in this adaptation.