Is light pollution making us sick?

Image: Mike Knell via Flickr.

We all hate air pollution, right? It gets into our lungs, throats and noses, and makes cities from Beijing to Paris look like a badly ventilated bathroom after a long shower. 

But there's another pollutant that could also be making us ill: light.

A new study released by the Royal Society surveys research which seems to show that nighttime light can contribute to "breast and prostate cancers, obesity, diabetes and depression". These conditions become more prevalent as cities modernise and, as a result, electrify - but is light pollution really the explanation?

It's certainly unhealthy. All species develop something called a "circadian rhythm" based on 24-hour cycles of light and dark. Yet most humans now work indoors during the day, where light isn't usually bright enough to be registered by our bodies as daylight. And at night, light pollution from streetlights, cars, and all the other night-time activities in cities and towns, convince our bodies that it isn't night, either. We rarely experience what researchers call "true dark". 

According to the study's authors, this disruption of our daily cycles can affect our "Core body temperature, hormone regulation and release, and patterns of gene expression through the body".

Take Melatonin, a hormone which regulates our sleep patterns and also acts as an antioxidant. Our bodies produce it at night, but even low levels of light can suppress it - and reduced levels of melatonin have been linked to certain forms of cancer. 

Of course, while we're asleep, low levels of light don't penetrate to our retinas - so someone with light-blocking curtains and a solid eight or nine hours of sleep a night may well have developed a stable circadian cycle. But even waking up occasionally in a room permeated by light pollution, or turning on a bathroom light, can disrupt melatonin production. Here's a chart showing a normal melatonin production profile, versus the profile of a jetlagged subject who sleeps during the day:

Even with the lights off, the jetlagged person's body is registering the fact that it's not quite dark. 

As a result, the worst affected by disrupted circadian rhythms are actually shift workers: another study found that women who work night shifts have higher rates of breast cancer. And in 2007, the International Agency for Cancer Research declared that shiftwork may well be a carcinogen. Add enough floodlights and bright streetlights to our cities, though, and we might as well all be shift workers. 

Obviously, we should be cautious of blaming all our urban ills on a bit of night-time light. Indeed, the researchers note that findings linking light pollution and illness so far have been "promising" rather than final. But to be truly safe, it might be worth moving to Sark.


Everything you ever wanted to know about the Seoul Metro System but were too afraid to ask

Gwanghwamoon subway station on line 5 in Seoul, 2010. Image: Getty.

Seoul’s metro system carries 7m passengers a day across 1,000 miles of track. The system is as much a regional commuter railway as an urban subway system. Without technically leaving the network, one can travel from Asan over 50 miles to the south of central Seoul, all the way up to the North Korean border 20 miles north of the city.

Fares are incredibly low for a developed country. A basic fare of 1,250 won (about £1) will allow you to travel 10km; it’s only an extra 100 won (about 7p) to travel every additional 5km on most lines.

The trains are reasonably quick: maximum speeds of 62mph and average operating speeds of around 20mph make them comparable to London Underground. But the trains are much more spacious, air conditioned and have wi-fi access. Every station also has protective fences, between platform and track, to prevent suicides and accidents.

The network

The  service has a complex system of ownership and operation. The Seoul Metro Company (owned by Seoul City council) operates lines 5-8 on its own, but lines 1-4 are operated jointly with Korail, the state-owned national rail company. Meanwhile, Line 9 is operated jointly between Trans-Dev (a French company which operates many buses in northern England) and RATP (The Parisian version of TfL).

Then there’s Neotrans, owned by the Korean conglomerate Doosan, which owns and operates the driverless Sinbundang line. The Incheon city government, which borders Seoul to the west, owns and operates Incheon Line 1 and Line 2.

The Airport Express was originally built and owned by a corporation jointly owned by 11 large Korean firms, but is now mostly owned by Korail. The Uijeongbu light railway is currently being taken over by the Uijeongbu city council (that one’s north of Seoul) after the operating company went bankrupt. And the Everline people mover is operated by a joint venture owned by Bombardier and a variety of Korean companies.

Seoul’s subway map. Click to expand. Image: Wikimedia Commons.

The rest of the lines are operated by the national rail operator Korail. The fare structure is either identical or very similar for all of these lines. All buses and trains in the region are accessible with a T-money card, similar to London’s Oyster card. Fares are collected centrally and then distributed back to operators based on levels of usage.


The Korean government spends around £27bn on transport every year: that works out at 10 per cent more per person than the British government spends.  The Seoul subway’s annual loss of around £200m is covered by this budget.

The main reason the loss is much lower than TfL’s £458m is that, despite Seoul’s lower fares, it also has much lower maintenance costs. The oldest line, Line 1 is only 44 years old.

Higher levels of automation and lower crime rates also mean there are fewer staff. Workers pay is also lower: a newly qualified driver will be paid around £27,000 a year compared to £49,000 in London.

New infrastructure is paid for by central government. However, investment in the capital does not cause the same regional rivalries as it does in the UK for a variety of reasons. Firstly, investment is not so heavily concentrated in the capital. Five other cities have subways; the second city of Busan has an extensive five-line network.

What’s more, while investment is still skewed towards Seoul, it’s a much bigger city than London, and South Korea is physically a much smaller country than the UK (about the size of Scotland and Wales combined). Some 40 per cent of the national population lives on the Seoul network – and everyone else who lives on the mainland can be in Seoul within 3 hours.

Finally, politically the biggest divide in South Korea is between the south-west and the south-east (the recently ousted President Park Geun-Hye won just 11 per cent of the vote in the south west, while winning 69 per cent in the south-east). Seoul is seen as neutral territory.  


A driverless train on the Shinbundang Line. Image: Wikicommons.

The system is far from perfect. Seoul’s network is highly radial. It’s incredibly cheap and easy to travel from outer lying areas to the centre, and around the centre itself. But travelling from one of Seoul’s satellite cities to another by public transport is often difficult. A journey from central Goyang (population: 1m) to central Incheon (population: 3m) is around 30 minutes by car. By public transport, it takes around 2 hours. There is no real equivalent of the London Overground.

There is also a lack of fast commuter services. The four-track Seoul Line 1 offers express services to Incheon and Cheonan, and some commuter towns south of the city are covered by intercity services. But most large cities of hundreds of thousands of people within commuting distance (places comparable to Reading or Milton Keynes) are reliant on the subway network, and do not have a fast rail link that takes commuters directly to the city centre.

This is changing however with the construction of a system modelled on the Paris RER and London’s Crossrail. The GTX will operate at maximum speed of 110Mph. The first line (of three planned) is scheduled to open in 2023, and will extend from the new town of Ilsan on the North Korean border to the new town of Dongtan about 25km south of the city centre.

The system will stop much less regularly than Crossrail or the RER resulting in drastic cuts in journey times. For example, the time from llsan to Gangnam (of Gangnam Style fame) will be cut from around 1hr30 to just 17 minutes. When the three-line network is complete most of the major cities in the region will have a direct fast link to Seoul Station, the focal point of the GTX as well as the national rail network. A very good public transport network is going to get even better.