Biological clock depends more on light’s color than its brightness

Science : Biologists have long known that the internal clocks of animals, including humans, adjust according to the available light. What role the different properties of light, such as color and brightness, play in governing a body’s circadian rhythms, however, has not been clear. Tim Brown of the University of Manchester in the UK and colleagues now say that the color of light may be more important than its intensity. They studied an area in the brains of mice called the suprachiasmatic nucleus (SCN). From the electrical signals emitted by the SCN, the researchers were able to watch how the mice reacted to an artificial sky in which the ambient light intensity was varied to mimic night and day, with and without color changes in the light. They found that when natural color changes were removed, the mice’s internal clocks became confused. The researchers suggest that one reason color vision evolved was so animals could continue to reset their internal clocks even when clouds reduced the brightness, but not the color, of light.