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The causal mechanism of light damage in the albino rat retina has been investigated. Male and female albino Wistar rats weighing 200–300 g and previously maintained in normal room lighting of approximately 15 hr light (0·85±0·05 × 10 −4 W cm −2 ) per 9 hr dark cycle were simultaneously exposed continuously to uniform fluorescent light flux of 3·01±0·5 × 10 −3 W cm −2 for a period of 6–18 hr. The animals were killed immediately after exposure and the retinas analysed for their contents of DNA, protein and lipids. There were significant losses of retinal DNA, protein, total lipid and polyunsaturated fatty acids, particularly docosahexaenoic acid. The losses were progressive with duration of exposure. There were also changes in phospholipid subclasses. These results could indicate altered photoreceptor-membrane viability secondary to continuous illumination. The ultimate effect would be the loss of photoreceptor cells with a concomitant loss of normal physiological function. Generally, gender was found to play no significant role, thus excluding possible endocrine interference. It is suggested that lipoperoxidative reactions could account for the observations made in this study. The danger of over-exposure to radiant flux in the tropics is inferred from these observations.