As a child, I remember seeing the Milky Way when visiting my grandparents in rural Klickitat County, Washington. It dominated the night sky in the summer, stretching from the north, up overhead, and on the southern horizon. To a child, the night sky was filled with more stars than could be counted. That same view no longer exists there – light pollution has decreased the night sky’s darkness, even in sparsely populated locations. But it doesn’t need to be this way – we can control light pollution.

We’re Turning Night into Day

Since the dawn of man, humans have feared the unknown that darkness brings to the night. Modern technology has allowed us to surrounded ourselves with light 24 hours a day. This ability to tame the darkness of night is one of the many benefits of the time in which we live.

But we have paid the price for it – it is actually hard to find truly dark skies. Only 100 years ago, nearly everyone on this planet could go outside of their home and look up and see a night sky filled with thousands of stars. Today, most people can see only the Moon, a few bright planets, and just a handful of stars from their homes. And they have never experienced seeing our own larger home in the Universe – the Milky Way Galaxy. The ubiquitous use of artificial lighting has not only impaired our view of the night sky, but it inadvertently affects our environment, health, safety, and even energy consumption.

Types of Light Pollution

Chicago skyline showing skyglow from light pollution. By Bert Kaufmann from Roermond, Netherlands (Chicago) [CC BY 2.0 ], via Wikimedia Commons

We’ve all heard of the effects of environmental pollution on our land, water, and air. The inappropriate, misdirected, or excessive use of artificial lighting is termed “light pollution.” It affects our environment, wildlife, and even people.

There are several types of light pollution:

  • Glare – an excessive brightness that causes visual discomfort
  • Light Clutter – bright, confusing, or excessively grouped light sources
  • Light Trespass – light falling where it is not intended or not needed
  • Over-Illumination – the excessive use of light
  • Skyglow – the brightening if the night sky over inhabited areas

Each of these types of light pollution affect us in various ways.


Excessively bright lights come from several sources – glare from the sun, oncoming headlights, or unshielded bright lights. The effects of glare can be long lasting or even permanent, such as from staring into the sun too long, or temporary, as with the headlights from oncoming traffic. Effects from glare increase with age, as light, scatters more in older eyes than younger ones. Safety is an issue when glare affects the vision of drivers or pedestrians and can lead to accidents.

Light Clutter

Excessively grouped light sources are referred to as light clutter. They can cause confusion and distract from obstacles, potentially leading to accidents.

Light Trespass

Light trespass results from poor control of outdoor lighting and occurs when unwanted light crosses property lines. A common example is when light from street lighting enters a bedroom window and illuminates the room. This light can disrupt sleep patterns and lead to health problems. This can lead to much frustration and agony.

Over Illumination

Over-Illumination is simply the use of more light than is needed for a specific task or activity. This leads to wasted energy and can contribute to glare, light clutter, and light trespass. Over-illumination can be as simple as lighting an unoccupied area.


Skyglow is the diffuse illumination of the night sky and is a commonly noticed form of light pollution. Skyglow greatly affects our ability to see the Milky Way. All the previously mentioned forms of light pollution can contribute to skyglow. Light propagating into the atmosphere from these sources, either directly or after reflection, partially scatter back to the ground. This produces a diffuse glow that can be seen from large distances.

Research has indicated that about half of skyglow is light reflected from the ground and half from direct upward emissions when viewed from nearby. Studies have indicated about 10% – 15% of light is bounced upward. Simply blocking upward light can remove one half of the skyglow when viewed from nearby and by a much greater factor when viewed at a distance.

Blue-White LED Street Lighting

Crossroad in Alessandria, Italy. Road lights with mercury lamps are in the background, LED street lights are in the middle, while high pressure sodium lamp are in the foreground. Supposed superiority of “blue-while” lighting is at best questionable for common road applications. By GiancarloGotta [Public domain], via Wikimedia Commons

While LED street lights allow saving energy, they can also increase the amount of light scattering. Blue light scatters in the atmosphere more than yellow and orange light. It is expected that sky glow will increase as older light sources are replaced with LED fixtures, even if the total amount of light remains the same. Astronauts on the International Space Station have already seen the amount of light increase as LED lights have replaced older lights. (Source: Business Insider) Light trespass and glare from these LED lights are also more disturbing than older sodium vapor lights. (Source: NY Times

There is a solution to this – LED street lighting could be designed to use the same yellow color used by sodium vapor lights. But at this point, this isn’t an idea that’s taken hold.

How Much Sky Glow Is There?

You can actually measure the skyglow at your location. Sky & Telescope magazine has instructions on how you can measure skyglow. You’ll need a digital camera, tripod, and software that allows you to measure the brightness of individual pixels. A fancy camera isn’t needed, just the ability to take reasonable long exposures using a set of predefined exposure settings.

What can we do?

Like other forms of pollution, there are steps we can do to prevent it. Awareness is the first step, and there are several things that nearly everyone can do to decrease light pollution. The International Dark Sky Association lists 12 suggestions – here are the first four:

  1. Inspect the lighting around your home.
  2. Use dark sky friendly lighting at your home and business.
  3. Talk to friends, family, and neighbors.
  4. Spread the word online.

Visit the IDA to see their remaining suggestions about what more about what you can do.