Our ancestors enjoyed a cleaner world. The water and air were cleaner, and when people went out at night, they could look at the stars above and ask questions about our place in the universe. Nowadays, in modern cities, we can barely see the stars at night because our view of them is not only obscured by the quality of the air, but by the quality of light as well. Not many people realize that the misuse or misdirection of light is a form of pollution. Quite simply, it is called light pollution.

Like other forms of environmental damage, light pollution is created by man and contaminates our surroundings. Like other forms of pollution, it also harms the environment. Just as our opportunities to enjoy rain forests are being taken away by human carelessness, so is our view of the stars at night. However, unlike other forms of environmental damage, the effects of light pollution can easily be reduced and even reversed.

The damage caused by light pollution comes from poorly designed outdoor lighting. Most cities in the world today use outdoor lighting that is not only far too bright, but also directed to places where it is not needed. This wasted light reflects off tiny particles of dust and moisture in the air, causing skyglow. Skyglow causes clouds to glow white, orange, or pink, and destroys our view of the nighttime sky.

The solution to light pollution is to use lower-wattage outdoor bulbs and full cutoff shielding. An electric lamp should send all its light down, not upward or sideways. Full cutoff means that no light rays from the lamp go above the horizon and that at least 90 percent of the light is blocked from going sideways.

Many cities in the world have made changes in the use of outdoor lighting. The result saves money and energy. It also restores our nighttime sky to the way it was when our ancestors gazed above.

我们的祖先享有比较干净的世界。那时的空气和水都比较干净，人们晚上外出时，可以看着天上的繁星，探讨我们在宇宙空间的位置的有关课题。如今，在现代化的都市中，我们晚上几乎难得一见天上的星星，由于空气和光线的质量，使星空的景像变得模糊不清。很多人不知道光线的滥用和乱射也是一种污染。简单地说，这就叫做“光污染”。

就像其它形式的环境破坏，光污染是由人类一手造成的，而且污染了人类自身的环境。和其它形式的污染一样，光污染也会对环境造成损害。晚上我们观赏星星美景和我们本就享有的欣赏雨林的机会，都因为人类的疏忽而被剥夺。然而，和其它形式的环境破坏不一样的是，光污染的影响是可以轻易被减轻，甚至被转变为好处的。

光污染造成的破坏，来自户外照明的设计不当。大多数城市现在所使用的户外照明，不仅远远超过所需的亮度，还照射到不需照明的区域。这些多余的照明，碰到空气中的微尘粒子和水分子后发生反射，就造成空中的“霞光”现象。“霞光”使云彩发出白色、桔色，或是粉红色的光，就破坏了我们的夜景。

解决光污染的方法就是使用低瓦数的户外灯泡与完全阻隔溢光的遮罩。电灯的光线应该向下照射，而不是向上或向旁边照射。“完全阻隔”是指电灯光线的照射不高出地平线，而且至少可以阻挡百分之九十的光线向旁边照射。

世界上许多城市改变了户外照明的使用方式，因而省下了金钱和能源。还使我们的夜空恢复到以前我们祖先所仰望凝视的模样。