Let there be darkness

FITNESS

The Brihadaranyaka Upanishad says Tamaso ma jyotirgamaya, or "Lead me from darkness to light,"and Friedrich Engels in his The Condition of the Working Class in England says, in effect, "Lead us from our dark cellars into the light and air of day." This column will now tell you the opposite: leave behind the light and head for the dark.

This may sound counterintuitive, because we are always told that our homes and offices should be brightly lit. Our mothers ordered us not to read in the dark, and not to watch TV in dim rooms. Now, instead, scientists at the pioneering Lighting Research Center at the Rensselaer Polytechnic Institute in New York state are telling us that humans need not merely lots of light, but the right amount of light for the right length of time at the right time of day.

The reason is the circadian system, the human biological rhythms that repeat every 24 hours and are synchronised to the solar day. Thanks to Thomas Edison and others, we can turn night into day (or into Times Square). Researchers at Rensselaer discovered that the retinas of our eyes are the principal regulators of circadian rhythms. As daylight declines, the retinas trigger higher production of nocturnal melatonin, a hormone. Conversely, during the day, melatonin levels are kept low.

Too much light outside the natural cycle throws the rhythms off, and reduces nighttime melatonin levels. Melatonin has a variety of roles within the body, one of which is inhibiting cancer cell growth, so disruption in the melatonin cycle has been linked to increased risk of breast cancer "" apart from poor sleep quality, impaired alertness, immune deficiencies and seasonal affective disorder (SAD), a depression which afflicts many people in far northern countries subject to long, dark winters. (Spare a thought for nurses and call-centre workers on night shift.)

On the positive side, knowledge of how light affects the circadian systems can be used to mitigate the symptoms of Alzheimer's disease among older people, along with SAD, jet lag and sleep deprivation. This knowledge can also guide architects and designers in lighting indoor and outdoor spaces to optimise our work and well-being.

Technology has utterly changed the conditions under which we live. But we are animals, and our biological nature evolves much more slowly. We have to find a way to keep technology in step, or continue to pay a price.