Light Pollution

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Light pollution is excessive and inappropriate artificial lighting at night. It is the brightening of the night sky over populated areas. There are four types of light pollution:

Light trespass is when light falls where it is not intended—for example, intense light entering the bedroom window, causing sleep deprivation.
Light clutter is excessive groupings of lights. It is common on roads where the street lighting is not well designed. The clusters may cause distraction and confusion.
Over-illumination is excessive and unnecessary lighting. It is a complete waste of energy and money and is common in urban areas. Office blocks, shops, street lighting, and residential regions left lit at night are the chief culprits.
Glare can be blinding, disorienting, disabling, and discomforting. Being blinded by vehicle lights is an example, which ruins dark adaptation and may even cause an accident. On a lesser scale, glare can become annoying and irritating.

Everyone gets some joy from looking up into a clear dark sky. Today, in the built-up sprawling urban districts of developed countries, residents can no longer see the night sky's awesome beauty from their homes. In some areas light pollution is so much out of control that even the first magnitude stars cannot be seen.

Look below at the alarming map of Europe at night:

Light pollution - Western Europe

Note the high levels of light pollution around the cities of Moscow and St. Petersburg compared to London - which is highly light-polluted. Between the Russian capital and Poland, there are dark sky sites - those are from areas in black. Western Europe is badly light-polluted. However, there are good dark sky sites for amateur astronomers in the Brecon Beacons of Wales, in Galloway, Scotland, the Island of Sark in the English Channel, and the Exmoor National Park.

Artificial lighting shining where it is not needed is the chief cause of light pollution. People are afraid of the dark, so local authorities put streetlights every 30 feet or so apart along roads. The combined lighting BRIGHTENS the night sky. 

If light pollution becomes too bad, there will be no point in looking up at the night sky, never mind experiencing the wonders of space through a telescope. However, with LED technology being introduced to road lighting, light pollution levels away from town and city centers are declining.

Light from poorly directed light fixtures always shines up into the night sky where molecules of air, moisture, and aerosols scatter it, causing the night sky to take on the all too familiar amber appearance called "sky-glow":

Urban astronomers must use light pollution filters to capture celestial objects with a camera. Many people who express an interest in astronomy never buy a telescope because of sky-glow and inappropriate and obtrusive lighting from uncaring neighbors. It is not only astronomers who have to put up with light pollution. Intrusive light shining into properties, like streetlights and "insecurity" lights shining into bedrooms, directly impacts life quality.

We have to sleep at night, and anything that disturbs that ought to be dealt with appropriately; otherwise, our health suffers. Bad and unnecessary lighting, therefore, is a health hazard.

Light pollution affects all creatures. Nocturnal animals are badly affected by artificial lighting. Do you think that moths, owls, badgers, and other night things are not affected by wasteful light? They certainly are.

Calculations show that high-powered lights produce MORE carbon dioxide over a year than a diesel vehicle does over a journey of 300 miles.

Download the PDF here from the UK Institute of Light Engineers for guidance on how to reduce unnecessary lighting. is a website detailing the levels of light pollution everywhere on the planet. Zoom in on the location from which you intend on observing the night sky, and note the light pollution levels. It will be an eye-opener.

Choose the Hybrid 'basemap' and then adjust the transparency slider to 100% to get the best effect:

The levels of light pollution across the planet are quite alarming. The southern hemisphere is better for astronomers, as shown in the light pollution map of Australasia:

Light Pollution and Astronomy

How to Deal with Annoying Lighting from Neighbors

If you experience annoying lighting effects from your neighbors while observing, there is an easy way to get them to turn off or redirect the annoyance. This method works 99% of the time. Your neighbors will not be into astronomy and will have probably never looked through a telescope. So, when you call on them, politely ask them to switch off the offending light and then invite them to have a look through your telescope.

The better your equipment, the more successful this method of persuasion will usually be. Most neighbors will readily come over to 'have a look.' We are all still like kids in a way and love novelties.

Explain to them what dark adaptation is (once you get to understand that effect on night vision in Lesson 3 of this module) and let them see a familiar celestial object, such as the Moon or a bright planet like Mars, Saturn, or Jupiter. As soon as they realize the harmful effect their lighting has on your observing, they will usually deal with the offending rays. The ignorant become knowledgeable. Introducing neighbors to the night sky sometimes gets them interested, and they may get involved. They might even get the bug and buy a telescope.

This technique is far better than complaining and winging and whining to the local authority, which will only cause strife and bad feelings between you and your neighbors. Few people like to be told off. Negotiation, tact, diplomacy, and thoughtfulness work every time. Wars do not.

LED Lighting

The conversion of sodium and mercury vapor lamps to Light Emitting Diodes (LEDs) favored by local governments and state authorities seems to reduce sky glow in the suburbs. However, LED lighting has its drawbacks for astronomers. Pictured above are the types of shades used on street lighting. Most are not of the kind on the right, which is a shame.

Because LEDs are cheaper than other forms of lighting, more get used, so there will probably be an increase in light pollution. Also, white LEDs emit light at all wavelengths, so it is now more difficult for astronomers to filter unwanted light. In the past, when sodium or mercury vapor lamps were common, specific filters were used to remove those unwanted wavelengths. Today, amber lighting LEDs are used almost exclusively in the world's designated dark sky places, which benefits astronomers who go there with portable instruments and are equipped with filters for those lights. Unfortunately, cheap white LEDs in urban areas are here to stay.

Sky-Glow: The Curse of Astronomers

As seen from towns and cities, the night sky is nothing like that from dark sky sites. Sky-glow slashes the contrast between celestial objects against the background sky, making it more difficult to make out the faint ones. This is one reason why professional observatories are perched on mountain tops.

Keen astronomers use narrow-band filters, which only permit specific wavelengths of light to pass through. However, most use broadband light pollution filters, which work by filtering out multiple wavelengths. Ultimately though, filters will NEVER replicate the conditions under truly dark skies.

Light pollution filters reduce the brightness of celestial objects, so they limit the useful magnification. By blocking the light of specific wavelengths, filters alter objects' color, hence why astronomers often witness a greenish cast in their images. Filters do not make celestial objects appear any brighter. They block ALL light at particular wavelengths. So, they tend to dim the view. However, in the process, the background sky is usually darkened more than the target, hence the so-called boost in contrast.

Light pollution filters might make a particular celestial object easier to make out, but not brighter. They work best on emission nebulae. Therefore, they are more or less useless on galaxies and stars, hence why no filter will ever match a truly dark sky's effectiveness. So now you know.

Many skywatchers in urban areas experience unwanted light entering their telescopes, which bounces off non-optical surfaces and reaches the eyepiece. The intrusive light causes a glow across the field of view, harming contrast and ruining dark adaptation. So, they need to attach a light shield to their instruments or even flock the telescope tube and accessories with a non-reflective, light-absorbing material to reduce the reflections. Some go to the extent of putting a cloth over their heads while observing!

You are now aware of the sky-glow menace caused by urban lighting. Only you can determine whether it is worth bothering to get into amateur astronomy and buying a telescope. If you are lucky enough to have access to a dark sky area, then go ahead. However, all is NOT lost - as you will discover in lesson 2 of this module.

A listing of the world's dark sky sites is on the website.

Watch Out for these LED Streetlights

The Good: the flat-lens cobra luminaire is a full-cutoff fixture. It effectively reduces light pollution because the light is directed below the horizontal, which means that hardly any light goes outwards and upwards into the night sky.

The Bad: the drop-lens cobra luminaire (very common) allows light to escape sideways and upwards. If you see these fixtures in your neighborhood, politely inform your local government authority about the harm caused by this poorly designed light and request that the flat-lens cobra luminaire replaces it.

How To Combat Sky-Glow

As urbanization spreads, the night sky gradually gets wiped out by light pollution. Here is how Fort Collins in Colorado State became a beautiful dark sky area. It can be done with the right attitude.

Does Street Lighting Reduce Crime?

Hardly. It is all a myth. There is NO evidence that street lighting deters criminal activity. Okay, it makes some people FEEL safer, but increased safety from criminals has never been proven. It is also costly to taxpayers.

Look at this.

Where it is pitch-black dark, do people honestly believe that low-life criminals will bother to target those areas? The truth is that scumbags are SCARED of the dark, as are most people – apart from us astronomers, of course ...

International Dark Sky Association Lighting Guidelines

This article is worth a read.

Health Effects of Light Pollution

This article shows the link of light pollution to human health.


You are now aware of the harmful effects on astronomy caused by artificial lighting. In reality, there is no need for excessive nighttime lighting. It is really up to people who understand the harm that light pollution causes to inform the uninformed, especially the ignorant in local authorities.



DISTINCTION: 90-100%   GRADE 2: 75-89%   GRADE 3: 60-74%   GRADE 4: 40-59%

FAIL: 0-39%

Although these lessons are free, they require putting together and hosting on our web servers. So, any donations via PayPal to help this using the link below will be much appreciated.

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