Nature, International Journal of Science
Life on Earth evolved in day-and-night cycles. Plants and animals, including insects such as the fruit fly, have a biological clock that controls their circadian rhythms — as the 2017 winners of the Nobel Prize in Physiology or Medicine showed. Now, humans’ increasing reliance on artificial lighting is changing those rhythms.
For more than a century, incandescent light sources served us well. These bulbs were cheap to produce and dispose of, and easy to dim. Their spectrum is continuous and includes most of the colours of the rainbow, much like a sunset (see ‘Light-source spectra’). They had their problems. In the 1990s, some researchers blamed electric illumination for changing our sleeping patterns from the natural rhythm of two four-hour phases broken by an hour of wakefulness, to a single eight-hour phase each night. Incandescent lamps are energy hungry and policymakers worried about their contribution to global warming. In 2005, lighting consumed around one-fifth of the world’s energy.
In 2009, the European Commission began to withdraw incandescent lamps from the European market. Other countries followed, from Switzerland and Australia to Russia, the United States and China. Low-energy lamps — at first mainly compact fluorescent lamps (CFLs) and later light-emitting diodes (LEDs) — have been promoted as replacements. The health risks this policy poses to humans, animals and plants have yet to be thoroughly assessed.
As a lighting researcher and designer, I am convinced that the costs of this transition far outweigh the benefits for human health and the environment. Because the world’s urban population spends more time indoors under artificial lighting than in daylight, the health impacts are already evident. Around one billion people globally lack vitamin D or do not have enough. Seasonal affective disorder, a type of depression that can occur in winter when there is less natural daylight, is on the rise. Shift workers face increased risks of cancer, obesity and sleep problems.