關於光污染 About light pollution
“Light Pollution” is a form of environmental degradation in which excessive artificial outdoor lighting, such as street lamps, neon signs, and illuminated signboards, affect the natural environment and the ecosystem. Light pollution not only rids us of the starry night sky, it also indicates a waste of electric energy and damages the natural and our living environment.
星空保育 Dark sky conservation
The wasteful light emitted directly upwards or reflected upwards from excessive and poorly-designed artificial light sources can be scattered to a wide area by the cloud, fog, and pollutants like suspended particulates in the atmosphere. A wide patch of the night sky is thus brightened, leading to a reduced number of stars visible due to a reduction of the light contrast in the sky.
The night sky is not only a common cultural heritage of all mankind but also an important part of our life. We are under a severe threat of the disappearing starry night, which is just another component of the environmental challenge the Earth faces. Dark sky conservation is the protection of our starry night sky and the preservation of our naturally dark sky, for the benefits of all humans, fauna and flora.
香港大學光污染研究 HKU light pollution research
HKU Department of Physics has been conducting light pollution research since 2003. The research team built the “Hong Kong Night Sky Brightness Monitoring Network” in May 2010. Since then, the network has monitored the light pollution conditions in different parts of Hong Kong and collected more than twenty million night sky brightness data. By analysing this world’s largest dataset, researchers found that the Hong Kong urban night sky to be 100 to 1,000 times brighter than the international dark sky standard between 8:30pm and 11:00pm. Even in remote locations such as the Wetland Park, the night sky there was above 100 times brighter than the standard. Hong Kong becomes one of the most light-polluted cities in the world.
The research team also found that the night sky dims progressively when public and commercial lightings are being turned off at night. For example, the urban sky showed sudden dimming near 11pm, 12am, and 1am every night, likely caused by the timing patterns of the nearby outdoor lighting. This no doubt proves that human lighting is the source of light pollution.
全球光污染監測 Global light pollution monitoring
近年，港大的光污染研究團隊將夜空光度監測技術推廣至外地，建立了「Globe at Night – Sky Brightness Monitoring Network」。這個全球性網絡目前有23個監測站，分布在亞洲、歐洲和非洲的9個國家或地區。研究項目的網站提供了監測站的資料和實時數據。
The HKU light pollution research team recently introduced our monitoring techniques internationally by establishing the “Globe at Night – Sky Brightness Monitoring Network project”. This global network currently has 23 stations operating in 9 countries/regions in Asia, Europe, and Africa. Details of the survey and the real-time data from around the world can be found in the project website.
Preliminary analysis of the data shows that there are large variations in night sky brightness worldwide: urban night skies are significantly brighter than night skies in pristine national parks. In general, in urban areas the night skies get progressively darker with time as the light usages by humans decrease over the night. The situation is similar to that observed in Hong Kong. On the other hand, rural stations show steady sky brightness throughout the night, reflecting low effect of human light usages.
如何減少光污染？智慧地使用照明 How to reduce light pollution? Use lighting wisely
減少使用不必要的室外照明 Reducing 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. Turning off the light when you leave a room can also help. From the perspective of the entire metropolis, turning off and dimming the neon signboards on the streets, floodlight on sport grounds, road lights in country parks and decorative lights on bridges are all possible ways to alleviate light pollution.
改裝現有的室外照明 Modifying existing lightings
A majority of the outdoor lighting currently installed are not dark-sky friendly, in which a significant portion of the emitted light is spread over a wide area and not concentrated in the targeted area. Upward-directed light is particularly useless and wasteful, and is a major culprit of light pollution. The improved “Full CutOff ” design limits the spreading of light and focuses the light downward, minimising light pollution.
選用有利天文觀測的光源 Choosing astronomical-friendly lighting sources
Unlike the high pressure sodium lamps and fluorescent lamps, low pressure sodium lamps are least affecting with regard to astronomical observations. It is because the emission spectrum of low pressure sodium lamps occupies a relatively small portion of the entire visible spectrum, and astronomers can easily filter out its contributions by applying filters.
香港夜空光度監測網絡 Hong Kong Night Sky Brightness Monitoring Network (NSN)
Globe at Night – Sky Brightness Monitoring Network (GaN-MN)
Globe at Night
Light Pollution Simulator