Throughout the electrified world, people turn lights on at dusk, and leave them on until dawn. In this post, we’ll look at the most obvious of these lights: those outdoors.

Bright Planet

The light bulb has come a long way since its dim beginnings in the 1800’s. We have become a planet whose glow can be seen from space, and where many places at night are as bright as day. Today, lighting consumes 25% of the world’s energy.i

Earth’s city lights

Earth’s city lights

This image of Earth’s city lights was created with data from the Defense Meteorological Satellite Program (DMSP) Operational Linescan System (OLS).ii

Why light? People have better vision during the day than the night. At night, our acuity may be reduced to 20/200 or less. We lose color vision. Our depth perception is degraded. With vision so limited at night, and serving as our most important sense during the day, it is no wonder that we worried about closet monsters and scary things under the bed when we were young. A fear of the dark is really a fear of possible or imaginary dangers that could be hidden in the dark.

Night lights can add to a feeling of safety. With a nightlight on the wall, we can see into the closet or under the bed, and be assured that nothing lurks. With outdoor security lighting, we can imagine that no monsters or muggers are lurking.

Lighting and Security

Security lights can make us less secure.

  • At an ATM, lighting makes it easier for a criminal to see and study an ATM patron. In addition, if the patron feels more secure, they might let down their guard, increasing the chance that a crime would succeed.
  • For an industrial wall, security lighting makes the job of a graffiti artist easier.
  • In the country, lighting makes it easier for a criminal to find the farmhouse, easier to see the obstacles and opportunities.
  • For some burglars, at least, lighting increases the thrill of crime.

Does lighting make us more secure from crime? It is hard to find any proof that this happens. Consider this evidence:

  • Day or Night: Violent crime rates are the same! The Bureau of Justice Statistics reports the distribution of violent crime by time of day for the US, using dataiii derived from the National Incident-Based Reporting System, 2007, administered by the FBI as part of the UCR Program. Assuming that “day” is 7 AM to 7 PM, we find that 49.5% of violent crime in the US occurs during the day, and 50.5% of crime occurs at night.
  • Lights added, crime rate doesn’t change. Shaftoe (1994) reports on a study in which brighter lighting was introduced to one neighborhood, and its crime rate compared with that of a control neighborhood, in which no lighting change was made. Marchant’s (2004) analysis of this study shows that crime was higher in the brightly lit neighborhood, and that adding brighter lights neither decreased nor increased the crime rate.
  • Turning off lights halved the number of thefts and burglary in Övertorneå, Sweden, after a rate dispute with the power company plunged the town into darkness. The town expected that thefts and burglary would go up, and was surprised to find it go down. The town also expected traffic accidents to increase, but they did not.iv
  • Adding all-night lighting increased the crime rate by 55%. A test in the U.K. added all-night lighting to selected control areas, and after a year compared crime patterns with control areas and the prior year. While residents reporting feeling safer with the all-night lights, crime statistics, though, showed a 55% increase in crime in the brightly-lit test areas as compared to the control areas and to the county as a whole! Graffiti increased as well with the brighter lighting. When the study was analyzed, the municipality decided against all-night lighting.

Just what lighting does to crime may depend on many factors. As Sherman et. al. conclude, “the limited research on lighting continues to use weak designs (typically without control areas) which fail to substantially reduce our uncertainty about the effect of lighting on crime. We may speculate that lighting is effective in some places, ineffective in others, and counter productive in still other circumstances. The problematic relationship between lighting and crime increases when one considers that offenders need lighting to detect potential targets and low-risk situations.” Good studies — done with proper experimental design and proper statistical analysis – are needed before trustworthy conclusions are drawn.

A feeling of safety is important, but it comes at a cost. There are drawbacks of leaving the lights on: the cost, the impact on birds and insects, and the impact on our night view.

The Cost of Lighting

Streetlights illuminate roadways, highways, or tunnels to improve visibility for drivers at night. Area lights illuminate outdoor sites such as parking lots and garages, outdoor landscapes, pedestrian walkways, and municipal and downtown common outdoor spaces Such lights were estimated to have consumed 178,300 megawatt hours (million watt-hours or MWh) of electricity in the US in 2007. Step, path, and porch lights consumed 22,000 MWh in the same period.v.

For most of us, such numbers are too large to comprehend. Consider that a wind turbine may generate 1-3 MW, an electric locomotive might use 5-6 MW, and the average US coal-fired power plant can produce 667 MWvi

Combined, we devoted 200,300,000,000 Watt-hours to outdoor lighting, and yet we don’t even know if this has increased our actual safety. What we do know, though, is that it was expensive.

Light Pollution

Damaged viewscapes occur whenever a bright light is added to an otherwise dark area. When a rural farmhouse adds a “security” light on a tall pole, the viewscape of the entire valley is compromised, the stars partly blocked out, and night vision impaired.

Skyglow is the lighting that comes leaking out of an urban sky, making it more difficult to see the stars. Places like Reno Nevada and Caribbean islands still deliver nights to remember, but if you live in more populated areas, closer to a city, you are likely to have nothing up there that you can actually see. Astronomers are not amused. Many telescopes are losing their value as skyglow paints over the night sky.

Lighting and Wildlife

Bird Migration. Hundreds of species of night-flying birds, including most songbirds and many shorebirds, use the constellations to guide them during their migrations. But in an urban area, skyglow makes the stars difficult to see, and building lights draw them, like a moth to a flame. The results can be disastrous.

On the night of October 7, 1954, for instance, 50,000 birds were killed when they followed the beam of a guide light at Warner Robins Air Force Base in Georgia – straight into the ground. The problem is particularly acute when the weather is bad. On a rainy, foggy Labor Day weekend in 1981, more than 10,000 birds collided with the floodlit smokestacks at Ontario’s Hydro Lennox Generating Station, near Kingston. And on January 22, 1998, between 5,000 and 10,000 Lapland longspurs crashed into radio transmission towers near Syracuse, Kansas.vii

Flying Insects. Few people seem to care about insects, but we should all care about their welfare – because of services they provide us directly, such as pollination, because they are the keystone of the food chain, and wildlife depends directly or indirectly on them, and because they are simply part of creation.

But lighting kills flying insects. Like birds, moths use the moon and stars to navigate, and like birds, they are confused by skyglow and drawn to streetlights, porch lights, and other artificial light sources. A moth that had planned a route in which the moon was on the right will circle a porch light, keeping that light on its right. Doing this all night exhausts the moth, depletes the energy she needs for developing eggs, deprives her of a chance of reaching a good nesting site, and increases her chance of being eaten by a toad, bat, or spider.

Turtles. Turtle hatchlings need to get from beach to water. Before humans, the brightest place on the horizon was the water, and so early species programming took advantage of this. Hatchlings head toward the light in order to head toward the water. Unfortunately today, this can take them away from the water and across streets, parking lots, and yards. The error usually leads to death from exhaustion, dehydration, predation, or passing cars.

Lights Out

More than 6,950 cities and towns in 152 countries and territories switched off their lights for an hour in Earth Hour 2012. The World Wildlife Fund and coordinates and promotes this. Other organizations work to get tall buildings to turn off night lighting. The Lights Out campaign runs in many US cities, such as Lights Out San Francisco, Lights Out DC, Lights Out Baltimore, Lights Out Toronto, and a number of other cities. See this map for locations.

But you don’t need a movement to do your part to solve this problem. Here are some ideas on how you can help:

  1. Turn your lights off! When you enter a room, turn on only what you need. Move reading lights closer to your book or newspaper, to extract more from each watt. Turn all lights off when you leave a room. Don’t turn any outdoor lighting on, except when guests are trying to find your front door.
  2. Use yellow bulbs in all outdoor lights. Insects aren’t attracted to them like they are to white light.
  3. Use fixtures that shield your lights. Ideally, your house should not be visible from the street on a dark night.


  • Bureau of Justice Statistics. Alcohol And Crime: Data From 2002 To 2008. Source: National Incident-Based Reporting System, 2007, administered by the FBI as part of the UCR Program.
  • Marchant, P.R. (2004). “A Demonstration that the claim that Brighter Lighting Reduces Crime is Unfounded” British Journal of Criminology 44, 441-447.
  • Shaftoe, H. (1994). “Easton/Ashley, Bristol: Lighting Improvements” in S. Osborn, ed., Housing Safe Communities: An Evaluation of Recent Initiatives, 72-7. London: Safe Neighbourhoods Unit.
  • Sherman, L.W., D. Gottfredson, D. MacKenzie, J. Eck, P. Reuter, S. Bushway. Preventing Crime: What Works, What Doesn’t, What’s Promising. National Institute of Justice, Office of Justice Programs, US Department of Justice. 1998.

 End Notes

iiImage from Visible Earth A catalog of NASA images and animations of our home planet. Credit: Data courtesy Marc Imhoff of NASA GSFC and Christopher Elvidge of NOAA NGDC. Image by Craig Mayhew and Robert Simmon, NASA GSFC.

ivCrime falls after streetlights cut out. The Local. Sweden’s News in English.

vEnergy Savings Estimates of Light Emitting Diodes in Niche Lighting Applications. Prepared for: Building Technologies Program Office of Energy Efficiency and Renewable Energy US Department of Energy. Prepared by:
Navigant Consulting Inc. 1801 K Street, NW Suite 500 Washington DC, 20006 Released: September 2008
Revised: October 2008

viSource: “Form EIA-860 Database, Annual Electric Generator Report,” US Department of Energy’s Energy Information Administration, 2005 data set. From:

viiJoe Bower. The Dark Side of Light. 2000.