The factors influencing flicker sensitivity are reviewed. Sensitivity is increasing because of improving lighting standards and personal peak sensitivity occurs for people approximately 20 years old. There is wide variability between people and the effect of flicker is related to the individual threshold. Office surveys reveal that significant numbers of people see flicker and that this feature is associated with the 'unsatisfactory' ratings of the lighting. Some headaches and eyestrain are related to seeing flicker. Light modulation from fluorescent lamps at 50 and 100 Hz has been measured and the growth in the 50 Hz component with time has been studied. The 50 Hz component is the one which is normally seen. The lamp characteristics show this 50 Hz modulation to remain at a low value for the first 7-8000 hours operation and thereafter to rise more rapidly with operation. Planned lamp replacement is now essential.

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