Prof. Dr. Shyam P Lohani

Planet earth has been bathed with light from the sun and is the primary source of energy. Sunlight warms us, produces weather patterns, helps plants produce oxygen and food from carbon dioxide and water, produces electricity and also assist our movement in the daytime. It was over two billion years ago that the cyanobacteria used sunlight in photosynthesis to make oxygen and carbohydrates from carbon dioxide and water. The process, thus, made the large quantities of oxygen in the atmosphere hence allowed life needing oxygen for survival to evolve. The plants use chlorophyll to achieve the same result today which keeps the atmosphere breathable and provides food energy for us and all other advanced forms of life (International Year of Light, IYL, 2015).
The importance of light is enormous in our life. It is almost not possible for a human to survive without light and at the same time excessive or overlighting has been associated with adverse effects on human health. In 2018, the Global LED Lighting Market is valued at USD 51.79 billion and is expected to reach USD 112.5 billion by 2024, with a CAGR of 13.75 per cent during the forecast period from 2019-2024. It has been estimated that the transition to energy-efficient LEDs will save USD 18 billion in electricity costs and avoid more than 160 million tons of carbon dioxide emission each year (Mordor Intelligence, 2019). The fastest-growing lighting market will be in the Latin America while the largest market will be the Asia Pacific in the projected period.

Cause
We are aware that humans cannot function well in the dark which led us to concentrate our efforts to brighten the night. The visible light and invisible radiations (UV and IR) are emitted by the sun and lamps. The wavelength of visible light determines its colour, from violet to red. The earth’s atmosphere blocks a lot of Ultra Violet and Infra-Red radiation emitted by the sun. The radiation and its wavelength, type of cell, the chromophore and the chemical reaction involved determine the effect of light on cells (European Union, 2017).
A little and healthy amount of light is good, whereas overlighting hurts our health. The exposure of light at night has been linked to obesity, depression, sleep disorders, cancers and so on. Glaring and exaggerated darkness are the two main issues of overlighting. The disability glare is the condition produced by bright points of light by poorly designed roadway lighting (Futurism, 2013). The condition can cause the light source into virtual invisibility and older drivers are more vulnerable as the increase in age results in the eye to lose its ability to adjust to changing levels of illumination. The exaggerated darkness is the condition when we cannot see anything behind the bright lights at night and people with nefarious intention still use this technique to temporarily blind people. Both the issues of overlighting are involved in road safety and road accidents.
The light pollution disrupts our circadian rhythms, interfere with melatonin levels thus causes sleeping disorders. The thermal and chemical effects, effects on the eye and the mood, sleep, and circadian rhythms are three main effects of light pollution. So, for a light source to cause burn it must be intense and example include lasers and high powered flash lamps which are not commonly used for illumination. Most of the lamps used for illumination are safe but some emit UV radiation. There are no studies on the possible effects of domestic artificial light on the human eye. However, there have been several studies about the hazards from specific artificial lights, mostly ophthalmic instruments, on human eyes.
The circadian clock, a 24-hour day/night cycle, affects physiologic processes in humans. The physiologic processes include many biological activities including brain wave patterns, hormone production, and cell regulation. The change or disruption of the circadian rhythms results in insomnia, depression, cardiovascular disease, and cancer. According to the American Medical Association, the light at night is recognised as a carcinogen and a health risk. The World Health Organisation (WHO) has also recognised shiftwork that causes disruption of circadian rhythms as a carcinogen and has been implicated for cancers of breast and colorectum.
Melatonin, a naturally occurring hormone, is released by darkness and inhibited by light and regulates our systemic activities. The decrease or elimination of light at night helps to maintain strict melatonin rhythm. The short-wavelength light, blue portion of the spectrum is the most potent for suppressing melatonin rhythm. The light used in the modern world and artificially extended daytime causes desynchronisation of internal rhythms leading to impairments of our ability to sleep and wake at appropriate times which leads to a decrease in cognition and motor skills (National Institute of Health, NIH). The NIH also believes humans function best when they sleep at night and function in the daytime. The conditions such as weight gain, stress, depression and the onset of diabetes are substantially reduced by a good night’s sleep.

Artificial light
Both the natural as well as artificial lights are necessary for optimal human activities. The artificial light at night prevents falls and injuries to elderly people. It has been recommended that to use 130 to 150 lumens per square foot of workspace. A 40-watt fluorescent bulb emits about 2,200 lumens and a 60-watt incandescent bulb gives 800 lumens. The Ministry of Urban Development has requirements for lights and ventilation in National Building Code, 2015. However, details of natural and artificial lighting requirements for residencies, different workplaces, and special purpose buildings should be promoted to the general public for safety, optimum human activities, and a healthy life.

(Prof. Lohani is the founder and academic Director of Nobel College and Hospital and can be reached at lohanis@gmail.com)