City Lights

“Artificial light in the environment must be considered a chronic impairment of habitat...While lamp efficiency and consideration of SPD (spectral power distribution) are significant accomplishments, true night sky friendly lighting can still only be achieved by vigilant examination of how much light actually needs to be used and routine implementation of minimum levels required for security and recreation"  (“Seeing Blue”).

According to the Clinton Foundation, there are some 35 million municipal streetlights in the U.S.  Most of these are of the older "cobra head" variety with "drop lenses" that extend down below the fixture and project much of the light output horizontally - into the eyes of drivers and pedestrians - and even upward into the sky, where it does no good at all.  The International Dark-Sky Association estimates that 30 percent of the light from such fixtures, and the energy generated to produce it, is wasted in this way.  When one considers that there are at least several times as many private outdoor lighting sources - "security" lights, advertising billboards, and purely ornamental floodlights directed at signs, trees, and the sides of buildings - the true scope of this waste becomes clear.  In the battle against global warming, reduction of unnecessary outdoor lighting should be low-hanging fruit.  In addition to consuming electricity without providing any benefit, excessive and ill-designed outdoor lighting also negatively affects human health and the natural environment in a myriad of ways.

Some lights are far worse than others. Now that mercury vapor lights are being phased out because of their poor energy efficiency and high mercury content, the blue-white metal halide lamps are the most environmentally damaging type in common use. Metal halide lamps emit a substantial portion of their light as shorter wavelengths, including in the ultraviolet range, where it cannot be seen by people (and therefore provides no benefit) but can - as with light from any UV source -damage retinas and contribute to macular degeneration. According to a recent study published in the Journal of Environmental Management, blue light is also especially effective at altering circadian rhythms and suppressing melatonin production, leading to difficulty sleeping (among those exposed at night, for example, people living in houses illuminated by metal halide streetlights).  According to Professor Abraham Haim, head of the Center for Interdisciplinary Chronobiological Research at the University of Haifa and co-author of that study, "Short wavelengths should be eliminated from the nocturnal spectrum."  A low melatonin level, caused in part by exposure to metal halide or other blue-white light sources, has also been linked to a higher risk of breast and prostate cancer.

Street LightsStreetlights with full cut-off fixtures (flat lenses) project light downward at the street below, and not upward or to the sides, making them preferable to the more commonly used protruding “drop lenses” that spread the light out in a wide cone of illumination,  much of it directed laterally and into the sky. Most streetlights could also be far less bright (lower lumens) and still be adequate for safety, while consuming less electricity and reducing the associated carbon emissions. The goal should be better light, and less light. While the energy efficiency of new LED lights is promising, more work needs to be done to develop LED lighting with greatly reduced blue-spectrum emissions in order to decrease its most negative impacts on the night environment. We must wean ourselves off the idea that night must be as bright as day:  humans, animals, and astronomers all benefit from naturally dark nights.

More light does not mean more safety: intersections DO usually need to be lit (preferably with high or low-pressure sodium lamps in full cut-off fixtures), but on a straightaway, bright lights mostly serve to embolden drivers to increase speeds.  Bright white bulbs, especially those such as metal-halide that emit a large quantity of UV light, cause much greater glare for the same light output compared to sodium-vapor bulbs.  The eye instinctively reacts to the sudden onslaught of bright white and UV light by contracting the pupil to protect the retina.  Then, when the driver or biker passes back out from under the streetlight, they are temporarily blinded as their eyes struggle to readjust to more normal night-time conditions.  This effect leads to an increased risk of accidents in the areas that drivers pass through immediately after leaving the cone of illumination of a blue-white streetlight.

Dark streets and houses are often more safe than lit-up areas.  This counter-intuitive effect results from the fact that thieves and other criminals need light in order to "work" (consider also that a potential intruder using a flashlight to see in a dark area is quite conspicuous), and pedestrians blinded by the glare from overly bright or poorly shielded fixtures have difficulty spotting threats (you can see this in the photos at the two Illinois Coalition sites). Many cities around the world have dramatically reduced outdoor lighting and experienced a decline in crime and accidents.

In short, outdoor lighting is often poorly designed or overused, and consequently does not provide the benefits to safety that one might expect, while negatively impacting human health.

Then there's the devastating cost to nature of lighting up the habitats of wild animals throughout the night.  When one considers that most streetlights operate on photo sensors and so are on from dusk until dawn - perhaps an average of 12 hours each day in the northeast - it seems obvious that there must be some impact on wild animal species that evolved over millions of years in conditions of night-time darkness.  And this is indeed the case.  Like people, animals benefit from regular periods of darkness, and suffer in their absence.  This is especially true for nocturnal animals, for which feeding, mating, and other critical behaviors are strongly (and negatively) influenced by artificial night-time illumination.  Most of us are familiar with the attraction of nocturnal insects, particularly moths, to outdoor lights, but it is not widely understood just now negatively insect populations are impacted by artificial  lighting.  All the time and energy that insects expend circling endlessly about a lit bulb, which they may mistake for the moon, necessarily detracts from their ability to successfully find food or mates, while making them easy prey for predators such as spiders.  A 2003 German study suggested that each streetlight in that nation was responsible for the deaths of, on average, 150 insects each night.  Assuming a similar figure applies for each of the 35 million streetlights in the US, we might conclude that a staggering 5.25 billion insects die at streetlights on a typical American night!

Their detrimental effect on insect populations is one reason to eliminate unnecessary or ornamental outdoor lights, and use less bright (and better shielded) bulbs where possible, but it is also a reason to switch from blue-white lamps such as the mercury vapor and metal halide type, to yellower high or low-pressure sodium lamps.  This is because insects (and most other wild animals) are most sensitive to light at the bluer end of the spectrum, including UV light.  As a result, insects are more attracted to - and fatally ensnared by - blue-white lamps, relative to the yellower sodium-vapor type.  In a 2000 German study published in Natur und Landschaft (see Eisenbeis and Hassel, below) the number of nocturnal insects captured was 50 percent lower overall, and 75 percent lower for Lepidoptera (butterflies and moths) at sodium-vapor lamps, compared to the mercury-vapor type (which produces a white-blue light similar in spectrum to metal-halide lamps).  It is therefore reasonable to conclude that replacing a single mercury-vapor or metal-halide streetlight bulb with a high or low-pressure sodium bulb could easily save the lives of 10,000 or more insects each year.

Even if one does not particularly care for insects per se, these creatures are vital links in the food chain, providing sustenance for thousands of species of birds, bats, reptiles and amphibians (aquatic insect larvae are also an important component of fish diets), and pollinating countless millions of flowering trees and plants each year.  So avoiding light-induced deaths of insects would benefit - directly or indirectly - nearly every species of wild animal, and many wild (and domesticated) plant species as well.

In addition to their harmful effects on insects, bright and abundant outdoor lights intimidate salamanders and frogs, discouraging them from emerging from their daytime hiding places (in leaf litter, etc.) to feed or mate, and consequently reducing their populations as well.  But the most detrimental effect of all is on bird migrations. Birds, accustomed to navigating by the moon, become disoriented by lights that are directed upward (either intentionally, as with ornamental floodlights and sports stadiums, or unintentionally, in the form of poorly shielded outdoor fixtures and illuminated buildings with large windows).  Estimates for the number of birds killed each year in collisions with lighted structures range as high as 100 million in North America alone.  Certainly this is a powerful reason to properly shield outdoor lights so they do not illuminate the sky, and the same argument can be made for turning off indoor lights when nobody is around, as well as taking the simple step of drawing the blinds or curtains at night.

Night light blocks our view of the starry sky and makes astronomicalobservations difficult or impossible, which is why astronomers have spearheaded the fight against light pollution. (See

Cornell’s campus observatory was rendered nearly unusable by the addition of dozens of nearby blue-white parking lot lights, as well as innumerable fixtures that might charitably be called "ornamental". The use of low-pressure sodium lamps (favored by astronomers because they emit light on a very narrow range of wavelengths, and so can be easily filtered out by spectrometers), combined with flat lenses and sensible shielding directing light downward (see Fig. 1), and simply not installing superfluous floodlights and ornamental fixtures on and around buildings and parking lots, could greatly reduce sky glow. It would also save money and CO2 emissions (since low-pressure sodium lamps are literally twice as energy efficient, measured in lumens of light produced per watt of energy, as metal-halide bulbs).

People who think they prefer bright blue-white light often come to like less bright, yellower, and smaller lights. (We personally think that the yellowish sodium-vapor lights, which are also the most environmentally friendly, are softer and more attractive than the blue-white metal halide "glare bombs".)

Sodium bulbs are also more energy efficient, and contain less mercury than metal halide bulbs. While it may not be financially feasible for local governments to install entirely new fixtures at the present time, the replacement of blue-white mercury vapor and metal halide streetlights and outdoor building lights with high-pressure sodium bulbs would be an inexpensive way to make our towns and cities friendlier to wildlife, while saving money in the long run (due to the increased efficiency of sodium-vapor bulbs, relative to the other types).  Going forward, we should make sure that the environmental and human health effects of new outdoor lighting are adequately considered before new fixtures are installed!

The article was co-authored with Seth Bensel. 

(Photo 1 © NASA/DMSP)

(Photo 2  © Illinois Coalition for Responsible Outdoor Lighting)

(Photo HP © Farfromthepicture from Flickr)


William J. Clinton Foundation 

Israel Ministry of Foreign Affairs

Science Daily 

American Medical Assn. House of Delegates Resolution March 30, 2009

American Cancer Society

Audobon Magazine

General Electric Corporation

Memorial Sloan-Kettering Cancer Center 

See also:

"Sleeping with Lights on can Spur Cancer" 

“Our Vanishing Night”, National Geographic, November, 2008.

“The Dark Side of Light: A Transdisciplinary Research Agenda”, Ecology and Society 15(4):13.

“Research on the Effects of Light Pollution” 

“Green Light for Nocturnally Migrating Birds"

"Visibility, Environmental, and Astronomical Issues Associated with Blue-Rich White Outdoor Lighting" International Dark-Sky Assn. Information Sheet 125, August, 1997, 

IDA, “Seeing Blue” 

Carl Shaflik, “Environmental Effects of Roadway Lighting” “Blinded by the Light” British Astronomy Assn. Handbook.

Eisenbeis, G. and F. Hassel (2000) "[Attraction of nocturnal insects to street lights - a study of municipal lighting systems in a rural area of Rheinhessen (Germany)]" Natur und Landschaft 75(4):145-156.

Illinois Coalition for Responsible Outdoor Lighting:,,

The title of this presentation was borrowed from Simon and Garfunkel

(Opinions voiced by Global Minds do not necessarily reflect the opinions of The Global Journal.)