Bright side of the night – 2.5.1

Physiological dimensions of light pollution

Consequences for human health

Artificial light is any ambient or external light from a source other than nature. In the scientific publication, „Light Pollution: a systematic review about the impacts of artificial light on human health“, authors show that artificial light at night influences a range of health conditions, including obesity, diabetes, depression, and heart attack. Apparently, as little as the exposure of 3 lx of artificial light before bedtime is enough to increase human blood pressure over night. The researchers conclude that the increase in exposure to artificial light triggers mainly sleep and mood disorders, with light from electronic devices and artificial night the mains source of pollution. Typical consequences from artificial light exposure include disturbances of the circadian- or biological – rhythm due to alterations in the levels of melatonin and cortisol and specific metabolites. These physiological changes can in turn lead to depression as well as to alterations in spermatogenesis, ocular structures, thermoregulation, and other cardiovascular conditions.

Too much light, too little sleep

Excessive artificial lighting at night is not just irritating—it directly influences the cycle and production of the sleep hormone melatonin, and thus, the circadian rhythm. This compromises sleep, quiet and rest, with far-reaching consequences for human health. The reason: artificial light at night in the short wavelength range below 490 nm can suppress the release of melatonin for more than one and a half hours. The short-wave radiation from the displays of smartphones, tablets and e-readers and also from computer screens are specifically detrimental. Night mode and blue light filter software provide a remedy.

Too much light can harm you?

With increasing age, it is normal that the cornea, lens and vitreous body of the eye cloud, causing more short-wave light scatter in the lens and thus more glare. However, excessive or improper consumption of artificial light can result in a premature loss of visual acuity. The constant exposure of the human eye for a period of 12 to 48 hours to short-wave light of low intensity (e.g. computer screen) has been linked to accelerated degeneration in eyesight, retinal damage and age-related macular degeneration. But also, permanent damage to the retina can occur within a few minutes, in case the eye is intensively dazzled by high levels of illuminance and short-wave radiation, e.g. from the sun or a projector.

The science of secure street illumination

More light does not always mean better vision. Artificial light can also introduce traffic risks, such as dazzle and distraction. Visual acuity decreases in the dark, colours are less distinguishable and sensitivity to glare increases. The human eye involuntarily focuses on the strongest light source and adapts to it. The time available for navigation and hazard detection is reduced. The eyes are strained and fatigue sets in. Advertising installations such as LED screens, flashing warning lights, streetlamps and oncoming headlights can all irritate and distract the driver, with possibly serious consequences.

Driving blind through glare

Strong contrasts between light and dark and high levels of luminance cause glare. While the human eye has an excellent ability to adapt to different levels of brightness, full adaptation from light to dark takes up to 30 minutes. In the case of a sudden change from light to dark, regular visual perception is not available in the first few seconds. One is virtually blind. Therefore, municipalities, road traffic regulators, and procurement offices are called to inquire carefully about possible glare from streetlamps. There are a number of rules and regulations in place in terms of road traffic, but they can vary from country to country. They define limit values and specify criteria to ensure that road users experience no significant problems deriving from the traffic infrastructure, including visual information carriers such as signs from roadside locations. The focus shall be on reduced light intensities, weak light-dark contrasts and warm white color temperatures. Which wavelength range and illuminance values are harmful?

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*City lights. Image by Pexels – Pixabay*.

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Images

Numerous images of the night sky can be downloaded on Pixabay.