How to Reduce Light Pollution?
The main cause of light pollution in Hong Kong is the excessive and improper use of artificial outdoor lightings. The ways to reduce the light pollution include reducing as many useless outdoor lighting as possible, modifying the existing lightings and redesigning them to become more dark-sky friendly, and choosing astronomical-friendly lighting sources.
Reduce Abuse of Outdoor Lightings
The rule of thumb is using lighting reasonably: do not set up unnecessary lighting and turn off lights which are not in use. We are not implying that you should live in the dark, rather just turn off the light when you leave a room can simply achieve the target. Turning off the neon signboards on the streets at midnight, reducing the hours of floodlight on golf courses, road lights in country parks and decorative lights on Tsing Ma Bridge are all possible ways being considered by government and organizations.
Turing off outdoor lightings at mid-night helps in reducing light pollution? If you have experience in star-grazing on Cheung Chau, you may noticed that by turning off the extensive lightings of the football court near Kwun Yam Beach, the strongest light pollution source among the island, at 11pm, many stars and even the Milky Way will emerge out immediately due to the dramatically reduction of light pollution. In 1996 during the brightened of comet Hyakutake, Ministry of the Environment of Government of Japan guided japanese to turn off the lights and so the night sky was 1.5 magnitude dimmer.
Modifying the Existing Lightings
Some of the outdoor lightings in Kong Hong, for example street lamps and lighting decorations on buildings' walls, have poor designs in term of dark-sky friendly. For street lamps, their main purpose is for security and guiding by illuminating the road. However their lampshades are poorly designed so that a portion of light energy is scattering up instead of down. Upward lighting is useless and wasteful, and also causes light pollution.
The better design of lampshades, like the so-called "Full-Cut-Off Lighting" or "Down Lighting", should focus the light energy to 0 to 65 degrees downward, meaning that minimum light is pointing upward and hence reduce light pollution.
Left: The design of Full-Cut-Off Lighting;Right: The design of non-Full-Cut-Off Lighting.
Most of the street lamps in Hong Kong hadn't blocked the light shining upward: from the picture we know that the tree above the lamp is illumined
Part of the street lamps in Hong Kong equipped with the properties of full-cut-off: pointed lamps show how the full-cut-off reduced the upward shine.
Design Lightings to Become more Dark-Sky Friendly