Providing more diurnal light to people working indoors serves vitality and healthy entrainment of our internal clock via the non-image forming pathway. But we do not exactly know how much light people are exposed to in their office, nor do we know how much extra light they receive if we raise the overall illuminance. In this study, we tracked office workers’ personal exposure during two three-week field intervention studies, one in winter, one in late spring. Electric lighting provided, on average, either approximately 125 or 900 lux horizontally on the desk (40 lux vs. 300 lux vertically, at the eye), on top of daylight conditions. The aim of the study was to demonstrate the amount of variance in exposure of office employees in a modern office space. Detailed graphical visualizations are presented to illustrate personal exposure patterns. Data collected with a spectrometer at a reference desk clearly revealed the light intervention, despite variations in weather conditions and sun position. Yet the person-based data revealed large differences between - and within - participants in terms of light received at the eye, despite them working in the same office space. Moreover, whereas for some individuals the light intervention resulted in marked increases in exposure, light exposure patterns of others showed virtually no signs of the additional lighting. We discuss implications for research and practice.