Light pollution is defined as the excessive or misdirected use of artificial outdoor lighting, causing an alteration to the natural patterns of light and dark in the environment. This phenomenon is a rapidly accelerating environmental concern, with the brightness of the night sky increasing at a rate that far outpaces population growth. This unintended consequence wastes enormous amounts of energy, disrupts natural ecosystems, and compromises the health of both human and animal populations.
Primary Sources of Unwanted Illumination
The majority of light pollution originates from sources within urban and suburban environments. Public street lighting has historically been the largest contributor, illuminating roadways and sidewalks for safety and navigation. However, recent studies suggest that private and commercial light sources now account for a substantial and growing portion of the problem.
Illuminated commercial and advertising signage, including brightly lit billboards and the floodlighting of building facades, pours significant amounts of light into the atmosphere. Industrial facilities and sports complexes also use high-intensity lighting that often spills far beyond the intended boundaries. Residential outdoor lighting, such as security floodlights and light escaping through unshaded windows, collectively adds a pervasive layer of unwanted illumination.
Design Flaws and Mechanisms of Light Waste
Light becomes pollution due to failures in lighting design and application. A fundamental mechanism of light waste is the use of unshielded or poorly designed fixtures that allow light to project horizontally or upward into the night sky. In many common designs, 30% or more of the light generated is emitted above the horizontal plane, serving no useful purpose on the ground and contributing directly to skyglow.
Over-illumination is another mechanism, which is the use of more light intensity than is necessary for a specific task or area. This excessive brightness is often driven by a mistaken belief that more light equals more safety. This practice wastes energy and increases the total amount of light available to become pollution through reflection off surfaces like pavement, buildings, and ground cover.
The spectral composition of modern lighting also increases pollution, particularly the widespread adoption of high-color temperature Light Emitting Diodes (LEDs). These “white” LEDs are rich in blue light wavelengths, which scatter exponentially more easily in the atmosphere than longer, warmer wavelengths. This preferential scattering is governed by Rayleigh scattering, where light hitting particles is diffused throughout the sky. The increased scattering from blue-rich light intensifies skyglow and extends its reach over a much wider geographical area.
Categorizing the Forms of Light Pollution
Skyglow is the most visible manifestation, appearing as a diffuse, dome-like halo of light over populated areas. It is caused by artificial light scattering off dust particles and gas molecules in the atmosphere, obscuring the natural darkness of the night sky for millions of people.
Light trespass occurs when unwanted light falls onto a property where it is neither intended nor needed, such as a streetlight shining directly into a bedroom window. This form of pollution disrupts human sleep cycles and can interfere with the behavior of nocturnal animals trying to navigate or forage.
Glare is the third primary form, defined as excessive brightness that causes visual discomfort or reduces a person’s ability to see effectively. Glare can be categorized as discomfort glare, which is annoying but temporary, or disability glare, which is more severe and causes a reduction in visibility by scattering light within the eye itself. This blinding effect reduces contrast and can pose a safety hazard for drivers and pedestrians.