At 4:31 am on January 17, 1994, residents of Los Angeles were shaken by two things: the Northridge earthquake, and strange lights that appeared in the sky. Otherworldly and ethereal, these lights alarmed people enough to call their local emergency services to report a “giant silvery cloud” hovering above the city. Was it some kind of weather phenomenon? Particles in smoke? UFOs?
No, the mysterious lights were something far older, something forgotten: the Milky Way Galaxy, our home in the universe. In the city-wide blackout caused by the earthquake, it was visible for the first time in decades.
In major cities and small towns across the globe, light pollution veils the scenic beauty of the night sky. Here’s a look at that pollution and its causes and effects.
What Is Light Pollution?
Light pollution is defined as artificial light that is unwanted or unnecessary. These are the four main types of light pollution, along with some light pollution examples:
- Glare: Excessive brightness or unshielded lighting that causes visual discomfort or blindness. Think of a passing car with too-bright headlights that make you squint.
- Clutter: Grouped sources of bright light that are distracting, confusing, or excessive. Times Square is an oft-cited example.
- Light Trespass: Light extending into unwanted or unnecessary areas, like a street light illuminating a darkened bedroom.
- Sky Glow: Brightening of the night sky due to artificial light, usually from urban areas. This is what obscures the Milky Way over Los Angeles and many other cities around the world.
What Causes Light Pollution?
Light pollution is the result of inefficient artificial lighting. While electric lights are undoubtedly crucial aspects of our lives, society, and industry, they often go above and beyond their purpose—in a negative way. It’s estimated that about 50% of illumination from a typical light source is wasted by being directed upward at the sky. A further 10% emits horizontally, creating glare. That leaves only 40% of your average light source to illuminate its intended target.
When you multiply this excessive illumination with often over-abundant lighting, it’s easy to see how artificial light can glow with overpowering brightness.
Light Pollution Effects
A little extra light might seem relatively harmless on the surface, but light pollution has a variety of damaging impacts—especially when it comes to the effects of light pollution on the environment. Excessive artificial light is particularly harmful for nocturnal wildlife, and can cause disruptions in their circadian rhythms. Additionally, sky glow and clutter can be confusing for migratory animals like birds and sea turtles, who rely on the position of celestial bodies to orient themselves.
Light pollution affects human health by disrupting our own circadian rhythms and lowering melatonin levels. It also makes astronomers’ work more difficult, while preventing millions of people from seeing the beauty of the night sky without light pollution.
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