The Shadow of Light at Night

by Dr Dennis Ang



Image credit: Photo by JF Martin on Unsplash


"Rows of lights to illuminate lines
Why don't they turn them off and let us see night "

- “Ohio” by Modest Mouse


Humans have lived in synchrony with natural light cycles. This entrainment is part of a cyclical process known as the circadian rhythm (Oatley & Goodwin, 1971). In simple terms, we react and respond to light and dark. Of particular interest, humans tend to wake and be productive when the sun is up, and stop what we are doing and go sleep when the sun sets.

Before the introduction of techniques to light up the night, the natural light cycle restricted what we could do at certain times of the day. While humans have exceptional day vision, in comparison, our ability to see at night, in low light, is relatively poor due to the lack of a layer of tissue in our eyes, that helps reflect visible light back to our retinas, known as the tapetum lucidum (Chijiiwa et al., 1990). Those who needed to be productive at night had to rely on natural light sources such as moon and starlight.

Artificial light has fundamentally changed the way we live. The introduction of candles, and oil lamps provided weak sources of light that extended the window of productive time we had in the light. However, these sources of light often did not last very long, or produced foul odours and smoke.

Gas lamps in the 19th century provided greater and more efficient illumination, and is credited for reducing crime rates while increasing literacy. Thomas Edison, and several other inventors, started experimenting with incandescent lamps and light bulbs to provide a more reliable, and economical indoor lighting. These early experiments were pivotal to the development of modern, ubiquitous lighting solutions.

However, not all changes brought about by artificial light are beneficial. In modern societies, the exposure to artificial light affects our internal body clocks. The artificial light from a multitude of sources such as street lamps, our laptops, and mobile devices affect our circadian rhythm. Research has shown that exposure to such light can suppress the natural production of melatonin, delaying sleet onset (Santhi et al., 2012).

Having access and control over artificial light also provides us with means of seeing what we are doing, and hence remaining productive. As such, we tend to stay up later at night. Despite staying up late, having to work or study in the morning means setting an alarm that jolts us awake in the morning despite our biological clock telling us we should still be sleeping. Artificial light disrupts our natural circadian rhythm.

Artificial light at night also affects ecosystems. Singapore is no exception to the effects of light pollution. In fact, there have been reports of turtle hatchlings at Changi confusing street lights with moonlight and as a result crawled inland instead of towards the sea (Tan, 2021). Without the help of rescuers, these hatchlings may not have survived for a variety of reasons including dehydration, predators, or accidents involving park goers.

The artificial light at night has no doubt been beneficial to humans, allowing a variety of activities to be carried out safely, and extending the time we get to be productive. Despite this, we must be mindful of the shadow cast by such light on us and the natural world. When was the last time you looked up at the night sky and got greeted by the twinkling of stars instead of murky reddish-purple clouds?

 NAF programme title:

 Incandescent - A City That Never Sleeps by NUS Dance Synergy featuring NUS Guitar Ensemble



Chijiiwa, T., Ishibashi, T., & Inomata, H. (1990). Histological study of choroidal melanocytes in animals with tapetum lucidum cellulosum. Graefe’s Archive for Clinical and Experimental Ophthalmology, 228(2), 161–168.

Oatley, K., & Goodwin, B. (1971). The explanation and investigation of biological rhythms. Biological Rhythms and Human Performance.(A 73-33154 16-04) London and New York, Academic Press, 1971, 1–38.

Santhi, N., Thorne, H. C., Van Der Veen, D. R., Johnsen, S., Mills, S. L., Hommes, V., Schlangen, L. J., Archer, S. N., & Dijk, D.-J. (2012). The spectral composition of evening light and individual differences in the suppression of melatonin and delay of sleep in humans. Journal of Pineal Research, 53(1), 47–59.

Tan, F. (2021, December 18). Turtle hatchlings at Changi confuse street light with moonlight, crawl towards park connector instead of the sea. Mothership.