Coloured filters blocking short-wavelength light (“yellow” filters) have been shown to influence the circadian regulation of melatonin release, while blue filters blocking long-wavelength light have been used in the treatment of dyslexia, migraine and photosensitive epilepsy. We have been investigating the effects on sleep quality of wearing blue and yellow filters for 1 hour in the morning . Healthy volunteers wore blue filters for an hour after waking each day for 4 weeks followed by 4 weeks of yellow filter use, or vice versa. They completed a daily questionnaire to report the number of times they had woken during the night and marked visual analogue scales to indicate the quality of their previous night's sleep and their alertness on waking. During the period of blue filter use participants reported improved sleep quality (p=0.05), felt more alert when they woke (p=0.05) and tended to wake less frequently (p=0.08). In contrast, yellow filter use did not significantly influence any recorded attribute of sleep or alertness. These findings suggest that blue filter use increases retinohypothalamic drive and consolidates circadian entrainment. Thus blue filters may prove to be an inexpensive and effective means of improving sleep quality in a number of conditions.