Circadian Light Visor. Male technician wears a Circadian Light visor designed to treat sleep disorders. Worn on the head, the portable visor emits a bright light (500-5000 lux) which shines on the eyes without the subject having to look directly at the lights. Light affects circadian rhythm, an internal biological clock that controls sleep-wake periods. In sleep disorders, this clock may be shifted and the subject may fall asleep too early or too late. By using bright light treatment of 2-3 hours for 2-3 evenings, sleeping disorders may be corrected for up to one month. Treatment is then repeated. The visor was made by Light Sciences Inc. in Braintree, Massachusetts, USA.