Abstract

Under natural circumstances,twilight is known to play an important role in behavioral and metabolic changes in mammals. Since experimental rooms are usually illuminated by on-off lighting system, an artificial twilight system was devised and its effect on feeding, drinking and motor activity was compared with those in on-off system. Following 10 days of on-off lighting (a 12:12 light-dark cycle), a twilight regimen was introduced. Illuminant intensity increased from 0 to 90 lumen during a 2 hr period of dawn and decreased reversely during same hour period of dusk. Three different types of twilight conditions were tested, i.e., (1) dawn: 0800-1000 hr and dusk: 1800-2000 hr, (2) dawn: 0600-0800 hr and dusk: 2000-2200 hr, (3) dawn: 0600-0800 hr and dusk: 1800-2000 hr. Total amount of 24-hr consumptions or activity was not influenced following the twilight conditions. Immediately after a period of dawn started, rats decreased food and water intake subsequent to their increase during the later periods of dark. During a dusk period, food and water intake increased markedly during twilight conditions in type 3. In type 1, however, such facilitated effects were not found.

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