How Hong Kong's urban light pollution creates 'mini jet lag'

Astronomer Dr Jason Pun Chun-shing of the University of Hong Kong's department of physics has been studying light pollution for nearly a decade. He says people often ask him if he is crazy. Hong Kong is supposed to be bright, they say. Why are you even talking about light being some kind of pollution?

The is famous for its nightscape: neon signs advertising market stalls, pawn shops and restaurants; illuminated skyscrapers; swanky malls that stay open and stay lit well into the night. "When I walk at night around some of these commercial centres, it is so bright you almost want to wear your sunglasses," Pun says.

In our collective imaginations, cities are meant to be bright. But as studies begin to show that too much light can be detrimental to health, and fewer of us are able to see the stars when we look up, are cities getting too bright for our own good?

Hong Kong isn't alone in celebrating light. Paris is still known as the City of Light; the English resort of Blackpool relies for tourism on its annual illuminations, when more than a million bulbs light a distance of 10km.

This celebration of artificial lighting is perhaps unsurprising, given how recently electric streetlights became the norm. It is easy to forget that being bathed in light is a relatively modern phenomenon. Although electric street lights first began appearing in European capitals in the mid-1800s, widespread street lighting did not become common until well into the 20th century.

In the years since, our cities have come to be lit in the extreme. Where once lighting was a luxury, now, a clear view of the night sky is what is become rare. With these metropolitan centres continuing to expand, things are going to continue to get worse n the night sky is going to continue to get brighter and our chances of seeing the stars anywhere other than in remote rural areas is going to get slimmer. That is why Pun decided