Light pollution to be monitored
A network of monitors to measure the level of light across the city is being planned to provide reliable baseline data against which to measure future changes in light pollution, according to researchers at the University of Hong Kong's department of physics.
The move was announced as researchers reported a 500-times light difference between the brightest and darkest spots in Hong Kong, revealed by the first citywide light pollution survey and resulting map launched yesterday.
The results reinforced calls for laws to regulate light pollution in the city and prompted a plan to introduce automatic light monitors across the city to gauge levels of brightness.
Comprising between 15 and 30 stations, the network is expected to run for up to two years to collect the data.
Researcher So Chu-wing said the automatic stations could provide much more representative, continuous and accurate data to study light pollution, compared to statistics in his survey which were obtained from hand-held devices operated by volunteers at fixed times.
'The network will help us to scientifically explain more about to what extent the brightness level in a spot is affected by human activities and meteorological conditions,' he said.
Apart from human activities, weather conditions like the amount of cloud, the intensity of the moon as well as the level of air pollution on a particular day would also affect brightness.
According to the light map covering nearly 200 spots in the city, the brightest places were Tsuen Wan, Tuen Mun, Hung Hom, Wan Chai and Mong Kok.
The brightness level at these spots was measured at or above 13 magnitudes per square arcsecond which means fewer than seven stars in the sky were visible to human eyes at night.
In the darkest places, such as Sai Kung and south Lantau, the measurement was about 20 magnitudes which would allow viewing of up to 6,000 stars.
The survey also found that city light levels decreased after 11pm when buildings began to turn off lights. But the extent of the difference had yet to be ascertained.
The Friends of the Earth called for the quicker introduction of laws to regulate light pollution.
It said the power used on lighting increased by 20 per cent from 5.6 billion kilowatt hours in 1997 to 6.7 billion kWh in 2006, though the city's population had increased by only 6 per cent.
A spokesman for the Environment Bureau said it aimed to complete preparations for a proposed law to control external lighting on buildings by the year's end.
