Writing in JACS recently, chemists at Yale University have reported details of the active site in the pigment molecule melanopsin. Melanopsin is present in the eye, but is not involved in vision. Instead it responds to light that enters the eye and reaches neurones (ganglions) deep within the retina. The pigment absorbs blue light, which hints at why there are so many current concerns about the effects of ubiquitous electric lighting and computer and mobile device screens that are always in our field of view. Absorption in this wavelength stimulates the pigment and sends a neuronal signal to the suprachiasmatic nuclei. This is a small region of the brain known to be at the heart of regulating the circadian rhythms of our neurones and hormones and matching them to the natural cycle of the 24-hour day.