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Red light boosts alertness in afternoon, says research

Scientists at the Rensselaer Lighting Research Center in New York have discovered that red light boosts alertness without suppressing the sleep hormone melatonin.

The discovery could lead to workplace lighting featuring boosts in blue and red component of the spectral output to mitigate the well-known syndrome of the post-lunch dip in energy levels.

The team found that exposure to red light positively affects measures of alertness not only at night, but also during the day. Red light also seemed to be a ‘more potent stimulus’ for modulating brain activities associated with daytime alertness than blue light, although they did not find any significant differences in measures of alertness after exposure to red and blue lights.

‘This suggests that blue light, especially higher levels of blue light, could still increase alertness in the afternoon,’ said the report. ‘It appears that melatonin suppression is not needed for light to have an impact on objective measures of alertness.’

In most studies to date, the alerting effects of light have been linked to its ability to suppress melatonin. However, this shows that both short-wavelength (blue) and long-wavelength (red) lights increased measures of alertness but only short-wavelength light suppressed melatonin. Melatonin levels are typically lower during the daytime, and higher at night.

The study – titled ‘Alerting effects of short-wavelength (blue) and long-wavelength (red) lights in the afternoon’ by Mariana Figueiro and Levent Sahin – was published in Physiology & Behavior journal and funded by the US Office of Naval Research.