Light effects in diurnal and nocturnal species: A complex role of the spectral composition.

<p>Light is known to promote sleep in nocturnal species and alertness in day-active animals. Our hypothesis is that the opposite responses to natural polychromatic light may result from higher sensitivity of nocturnal species to green light, and diurnals to blue wavelengths, resulting in hypnogenic and alerting effects, respectively. This can be modeled as different blue and green weights on a balance, explaining either an alerting (higher sensitivity to blue) or sleep-promoting effect (greater sensitivity to green) of white light in diurnal and nocturnal species, respectively.</p

Summary of light parameters influencing sleep and alertness in humans.

<p>In humans, light exerts strong alerting effects that depend upon several parameters, such as dose (irradiance), duration, and the time of day of light exposure. This photic regulation of alertness also critically depends on the spectral composition of light, with blue light as a powerful alerting stimulus, contrary to green light, which might be less powerful to awaken a subject from sleep.</p