What Is Light Pollution?
Light pollution: Any adverse effect of artificial light including sky glow, glare, light trespass, light clutter, decreased visibility at night, and energy waste. Light pollution is not only a hindrance to astronomy, but it also has direct impacts on human and environmental health.
Click any of the links below to learn more about how light pollution affects
Why do we even use lighting? We are a diurnal species. This means that our eyes evolved to function best in daytime lighting conditions. While we can function at night with a little bit of light using the rod cells in our eyes, say from the moon, we do not function as well as other species that are truly nocturnal. So, outdoor lighting provides visibility for us to conduct day-like activities at night.
Correctly done, outdoor lighting is an attractive benefit for our communities. Because of our preferences for daytime light levels, and the very basic, primitive fear we feel for darkened places that could hide a predator (those that did not heed such feelings so long ago were, over time, eliminated from passing on offspring!), we very much like light. It gives us a feeling of safety and security, even if the feeling is sometimes inappropriate for a particular situation.
Light can be used to enhance a theme or goals of the community when highlighting something it is proud to display. But that one aspect is increasingly abused by so many that the displayed item just becomes hidden in the ever greater visual noise and clutter. As such, bad lighting is so pervasive and common now, that it is hard for people to recognize it when they see it (or are blinded by it!).
Nevertheless, there are still some basic concepts that everyone would probably agree about what good outdoor lighting provides.
Good Outdoor Lighting Should:
- Optimize visibility at night for what we want lit
- Minimize energy consumption
- Minimize impact on the environment
- Minimize glare
- Minimize light trespass
The second and third concepts everyone would naturally agree upon—no one wants our resources or money to be intentionally wasted, nor does anyone want to directly cause harm to the environment that we all depend on. The last two concepts are covered below.
See what’s lit, not the light. Believe it or not, it is that first concept, to
Optimize visibility at night for what we want lit that is often one of the hardest for people to realize, recognize, or understand. And yet it sounds so simple. It simply means this: we want to be able to see those things that are needed to be seen. Being blinded by the source of the light that provides the illumination is counterproductive to this end. Because the contrasting intensity of a light’s source is often so extreme compared to anything else that is to be lit up by that light, having to see the light’s source can actually impede our ability to see those things that we want or need to see. The Light pollution vs. Economics page shows an example of this concept.
It is an incredibly simple concept. However, more often than not, the only thing that can be seen is the light itself and not the area around it that needs to be illuminated. (Sunspots on the Sun have a similar problem—while they look dark to us, sunspots actually emit light. However, they are so overpowered by their surrounding, brighter photosphere surface regions that they look dark.) Decorative lighting in some kind of glassy-brassy housing fixture (or
luminaire) often makes no effort at all at hiding the source of the light and, as such, it fails in all of the above concepts. Yet how often does one see decorative lighting used in the front of homes or businesses? It is as if the sole point of the light is to just see the light itself and not particularly care that anything around it is properly illuminated.
The guiding principle to good lighting can be summed up in this concept:
the light source’s horizontal plane.
Once this simple guideline is understood, many of the problems caused by light pollution can be immediately dealt with and solved.
However, if that principle is not followed, then we encounter a variety of problems from light pollution. The immediate problems that poor lighting can cause are shown below. Other more long-term and damaging problems are listed on the other pages linked in the menu at the top of the page.
Identifying Light Pollution
Light pollution is light that is not being efficiently or completely utilized and is often pointed outwards or upwards and not downwards. Hence it is light that is often found to be rude or oppressive to the non-owners of the light. How so? Well, imagine spending an hour outside at night to enjoy the stars, when someone walks up to you and shines a flashlight in your face. The light hurts your eyes and temporarily blinds you. Such an action is clearly rude. Yet no one thinks that it is equally and permanently rude that a person installs an outward-pointing light on the side of a building to illuminate their grounds or parking lot or area around the building. Such people fail to consider just how far their security lights extend and bother other people. Such owners seem to think that if you wanted it to be dark, then you should go somewhere else. Yet the problem is that in today’s society there is nowhere else to go to avoid lights at night. The darkest region in America, the American desert, can still see the lights of Las Vegas from 250 miles away. Such owners have, in all probability, chosen to locate themselves to be close to where people live and work. I can guarantee that the other people, downlight from them, did not move to be near that offender’s light.