On June 16 2009, the American Medical Association (AMA) voted unanimously to support efforts to control light pollution. Why has the AMA, a powerful and influential group, decided to support light-pollution legislation? They cite glare from bad lighting as a public-health hazard; the unnecessary energy waste; extra CO2 produced; and finally, the fact that all species (including humans) need darkness to survive and thrive.

Nearly every organism on Earth (with the exception of some abyssal sea creatures and species that have evolved to live permanently in caves) has wired into it the day-night cycle caused by our planet’s rotation. We tamper with this ancient programming at our peril.

At the Royal Institution in June 2015, Professor Russell Foster, Professor of Circadian Neuroscience and Head of the Department of Ophthalmology at Oxford University, gave a lecture entitled Light, Time and Health. Professor Foster is an authority on circadian, visual and behavioural neuroscience. We summarise his talk:

While early humans were not necessarily cave dwellers, modern humans certainly are: we live largely indoors, getting relatively little exposure to light during the day, while extending our active time with artificial light at night.
We cope with a very large range of illuminance: from starlight (0.0001 lux), if we can find anywhere dark enough to experience natural starlight, to full daylight (12,000 lux). Street lighting: typically 3 – 50 lux.

Professor Foster was involved in the recent discovery of a new type of non-image-forming photoreceptor cell in the eye: the photosensitive retinal ganglion cell (pRGC). The pRGCs regulate the circadian system. All life is governed by 24-hour circadian rhythms stimulated by the light-dark cycle. The circadian system controls vital biological functions within our bodies such as alertness, temperature regulation and production of the hormone melatonin.

Poor circadian regulation causes loss of attention, memory impairment, failure to process information, and reduced cognition and creativity. Compromised biological functions and melatonin suppression lead to immune system suppression, increased likelihood of cancer and cardio-vascular disease, diabetes, metabolic suppression and obesity. Mood instability, anxiety and increased risk of mental illness have also been linked. Natural strong blue light of 2000 lux reduces sleepiness and increases alertness. Sleep is disrupted by relatively high light levels.

Many new LED lights emit blue-rich light. The CfDS argues that the precautionary principle should apply: continued research is critical and we should choose our lighting types only when all negative effects have been identified.