Studies by the Journal of the National Cancer Institute in England have shown night-shift workers are 60 percent more likely than those on day shifts to develop breast cancer and 35 percent more likely to have gastrointestinal cancer.

Israeli researchers have also found causal links between breast cancer and night-time illumination by overlaying satellite imagery of Earth taken at night onto cancer registries.

Sleeping in the dark is required for the body to produce melatonin, a hormone essential to regulate many of the body's regular functions. The hormone helps prevent tumors from forming and may also enhance the immune system.

Citing research by the International Agency for Research on Cancer and the Electric Power Research Institute, former Hong Kong University physiology professor Pang Shiu-fun said melatonin production dropped by half after 40 minutes' exposure to light from a regular bulb.

"Although the government has adopted the European standard for glare control, light scattering and wastage, this area has been chronically neglected and precious little has been done," Friends of the Earth director Edwin Lau Che-feng said.

Only nine out of an estimated 1,300 street lamps attached to residential buildings in the past 3 months have been retrofitted to minimize light pollution. Friends of the Earth wants such retrofitting before attention is turned to the city's roughly 130,000 street lamps.

According to government statistics, an average of just over 10 complaints of intrusive street lights are lodged annually, but Friends of the Earth environmental affairs manager Hahn Chu Hon-keung blamed that on obscure channels for complaints.

An elderly resident surnamed Au-Yeung said he only manages to get four hours of sleep a day at most.

Au said he has already experienced an accidental overdose of sleeping pills which he needs to sleep and would not have moved into his Wan Chai flat had he been informed of the night-time conditions.

Light pollution is also impacting on Hong Kong's marine life.

World Wide Fund for Nature's marine program head Guillermo Moreno said Green Turtles nesting in the city's shores can get disoriented, leaving their hatchlings at increased risk to predators.