How light intensity and colour impact nonvisual functions in humans:Effects of light on entrainment, sleep and pupil constriction

Besides visual perception, light has many more functions such as pupil constriction, synchronisation of our biological clocks with the day-night cycle and our sleep-wake cycle. One biological clock is not the same as the other, and in this thesis, a method is presented to characterise fundamental biological clock-properties on the level of the individual, with the use of ambulatory light reception measurements. The cells in our eyes that send information to our biological clocks, are the same cells that mediate pupil constriction. By studying how our pupil responds to changes in colour, it may be possible to directly conclude on how our biological clocks would respond to such changes. Our results suggest that red and cyan light have opposite effects on the pupil than blue and green light, which may thus also be true for our biological clocks. This provides an opportunity for the treatment of jet lag, or the minimisation of unhealthy effects of evening light. Although it is known that the biological clocks of mice are colour sensitive, this is not known for humans. In this thesis, I show that also for humans an integration of colour and intensity information may be evolutionary beneficial.: these two factors together provide a more accurate indication of time of day than both factors separately. Finally, I show with ambulatory light and EEG-measurements that humans who expose themselves to more light during the day have deeper and better sleep