This chapter describes the physiological bases of the impact of light on non-image-forming functions before summarizing recent neuroimaging investigations that substantially increased the understanding of the brain mechanisms involved. In accordance with animal research, the neuroimaging results presented in the chapter are compatible with a scenario in which light would influence subcortical structures involved in arousal regulation before significantly affecting the cortical areas involved in the ongoing non-image-forming process. Several factors modulate the effects described in this scenario including light intensity, duration, and wavelength, and possibly task difficulty. The interaction between circadian and sleep homeostasis signals and PERIOD3 (PER3) genotype can amplify or diminish the non-image-forming impact of light on cognitive brain function. For tasks triggering emotional responses, effects within cortical areas specially devoted to decoding the emotional content of a particular type of stimulus appear to be quick and mediated through a network based on hypothalamus and amygdala interactions.