Fluorescent lighting has been highlighted as a significant factor in eyestrain, headache, lethargy and other asthenopic (eye related) complaints by office personnel. These three symptoms rate amongst the most highly reported complaints attributed to the office environment. An interventional study was conducted in three data entry offices to assess the effect of fluorescent light flicker and modulation depth on the incidence and severity of common workplace symptoms, productivity and satisfaction with the work environment. Each of the three offices had three lighting regimes installed for a four week period in a crossover design with an initial four week baseline period. The three lighting treatments were selected to represent commonly available lighting conditions and included triphosphor fluorescent tubes with high frequency electronic ballasts and low frequency magnetic ballasts and halophosphate fluorescent tubes with low frequency magnetic ballasts. The study provided evidence to suggest that eyestrain and lethargy symptoms were considered to be more severe in the low frequency halophosphate lighting treatment. There was also a higher incidence of lethargy symptoms in the low frequency halophosphate lighting treatment. In addition, significant relationships were present between perceived decreased productivity (due to the work environment) and increased symptom severity in the low frequency halophosphate lighting treatment. The low frequency and high frequency triphosphor lighting treatments did not differ significantly. No significant relationships were shown between actual or perceived productivity and lighting treatments. There was no evidence to suggest that participants were able to perceive flicker from any of the lighting treatment installations on a consistent basis. When participants perceived flicker it was not considered to be disturbing or annoying. The actual productivity of participants was related to eyestrain and lethargy symptoms in one of the offices studied. The effect size was small to medium, explaining between 2-5% of the variability of the data. Actual productivity was not related to any other measures. Office personnel perceived that their productivity (due to the work environment) and work satisfaction was strongly affected by the eyestrain, headache and lethargy symptoms experienced. These results did not show that flicker frequency or modulation depth affected the severity of eyestrain, lethargy and headache symptoms, the satisfaction of the occupants or their perceived or actual productivity. These findings support previous research that has suggested that differences in task performance may be limited to difficult visual tasks with minimal cognitive or motor components. Further, these results suggest that the effect of low frequency flicker on asthenopic symptoms may also be small and easily overwhelmed by other workplace factors. The breadth of this study was ambitious and featured limitations (such as small sample sizes) that may have impacted on the results found in some analyses. This study may not have been sensitive enough to detect small differences in the health, productivity and satisfaction of office personnel due to fluorescent light flicker. The pattern of responses examined alongside research in this field suggested that differences in the spectral distribution of the tubes may be a culpable factor. A small colour component in the work task and an equally small luminance difference between lighting treatments may have contributed to this finding. However, given that there is limited support for this outcome in the literature, and the previous findings in research examining fluorescent light flicker, these results should be considered as exploratory. Taken together, the research findings present a compelling argument for additional field research. This study provides a foundation that will enable future studies to further quantify the relationships between health, productivity and qualitative aspects of lighting in the work environment.