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, more stars than could be counted filled the night sky. That same view no longer exists there – light pollution has decreased the darkness of the night sky, even in such a sparsely populated location. 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 dark 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 hard to find genuinely 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 home. 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

Bert Kaufmann from Roermond, Netherlands, Chicago (2550963495), CC BY 2.0
Chicago skyline is showing skyglow from light pollution.
Photo Credit: Bert Kaufmann from Roermond, Netherlands, Chicago (2550963495)CC BY 2.0

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 affects us in various ways.


Excessively bright lights come from several sources – glare from the sun, from 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, 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

Light clutter refers to excessively grouped light sources. They can cause confusion and distract from obstacles, potentially leading to accidents.

Light Trespass

Light trespass is the result of poor control of outdoor lighting and occurs when unwanted light crosses property lines. A typical 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. Light trespass can lead to much frustration and agony.

Over Illumination

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


Skyglow is the diffuse illumination of the night sky and is a commonly noticed form of light pollution. It dramatically affects our ability to see the Milky Way. All the previously mentioned form 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. Diffuse skyglow is visible from considerable distances.

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

Blue-White LED Street Lighting

GiancarloGotta, 110213 LED vs Sodium vs Mercury, marked as public domain, more details on Wikimedia Commons
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 is in the foreground. Supposed superiority of “blue-white” lighting is at best questionable for common road applications.
Photo Credit: GiancarloGotta110213 LED vs. Sodium vs. Mercury, marked as public domain, more details on Wikimedia Commons

While LED street lights give the opportunity to save energy, they can also increase the amount of light scattering. Blue light scatters more in the atmosphere than yellow and orange light. As LED fixtures replace older light sources, skyglow is predicted to increase even if the total amount of light remains the same. Astronauts on the International Space Station have 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 reported to be 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 idea has not taken hold.

How Much Is Sky Glow There?

You can 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 required, 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.

Changes I’ve Made

I’ve made a few changes in my life to help reduce light pollution. Here are a few of them.

Using Motion Activated Outdoor Lights

I’ve reduced the amount of outdoor lighting around my house. When I bought my house, there was a 250 Watt mercury vapor light mounted outside one corner of my home’s second floor. It did a great job of illuminating half of the yard, but it was way too much light, and it was on from dusk to dusk.

I disconnected it and replaced it with a couple 240-degree motion-activated floodlights. These new light cover more of my yard, and I can point the light where I want it. And they only turn on when there is someone in the area. (Or something, like a raccoon, which we always run outside to see.) I like this as I save money by only having the lights on when I need them.

Changing Lighting Color Temperature

The color of the mercury vapor light is bluish. Blue light scatters more than other colors of light. Because of this scatter, cooler lights contribute more to skyglow more than warmer lights.

At the time I replaced the mercury vapor light, tungsten lights were my only bulb choice for my flood lights. I put tungsten halogen bulbs in as they were more energy efficient than standard tungsten lights. Both of these tungsten bulbs have less blue light than the original mercury bulb.

Recently I noticed the availability of LED outdoor floodlights. They come in several color temperatures – daylight, cool white, warm white. Warm white (3000K) lights have a less blue light in them than daylight (5000K) or cool white (4000K) lights. (The lower the “K” temperature, the warmer the light is.)

So I replaced my the two 90W tungsten halogen bulbs in each flood light fixture with 17W 3000K LED bulbs. The LED lights have a similar color temperature to the tungsten halogens, but they use much less power. That means I pay less to operate them!

We Can All Do Something to Help

Look around your home, and see where you have your outdoor lights. Check the type, the temperature, and where they aim. I bet you can make a few improvements. Doing this not only give you better lighting but can help reduce light pollution.

And possibly, this can save you some money. Maybe not enough to but that new f/1.4 astrophotography lens you’ve been wanting, but it all adds up!

Kirk Keyes