Light pollution is not as simple as many people think. There are many types and sources of light pollution, including excess light created by human activity that disturbs natural darkness; insufficient light, such as when artificial illumination drowns out natural light, or when natural light is blocked altogether (such as by buildings) and needs to be replaced by artificial light; and changes to the non-visible light spectrum, such as radio-waves. The five most intrusive types of light pollution are:

1. Over-illumination

This type of light pollution is caused by misuse or neglect of light sources. Common examples of over-illumination are street lights that don’t have their schedules properly adjusted for daylight savings time, or interior lights that are left on when not in use (leaving a room without turning off the lights). Mistakes such as these can add up to enormous wastes of energy, raise utility costs, and disrupt the natural day/night cycle.

2. Light Trespass

This term refers to unwanted light shining onto someone’s property, such as a neon sign that shines into a residential area. Not only is this form of light pollution disturbing to those who are affected, it is actually considered to be a crime in some areas.

3. Light Clutter

This is a term used to describe an overly-dense placement of artificial light. The irresponsible placement of, for example, street lights or neon signs interferes with night vision and, if strong enough, could disturb the nocturnal systems of animals.

4. Glare

Glare is produced when ambient light reflects off a surface and disrupts vision. Everyone has experienced glare while driving when the sun reflects off a wet road, or off the windows of nearby buildings. Glare is obviously hazardous for motorists, but can also cause be sources of distraction or discomfort for people at home or at work.

5. Sky Glow

Looking at a big city at night from a distance, have you ever noticed a dome of light that covers it? That dome is created by artificial light, such as the light from homes, signs, street lights, and businesses, escaping into the atmosphere, where it is reflected back down and scattered out in all directions. Sky glow is obviously detrimental to the natural cycles of lightness and darkness for humans and animals that live within the city, but can also affect those that live outside the city limits. Sky glow can even make it more difficult for planes to navigate at night.