International Dark-Sky Association

3545 N. Stewart Ave., Tucson AZ 85716 U.S.A.



Economic Issues in Wasted and Inefficient Outdoor Lighting

IDA Information Sheet No. 26 (February 1990)

Let's consider the energy use of inefficient outdoor lighting fixtures. A very common fixture seen everywhere throughout the United States, in cities and in the country, the the so-called 175 watt dusk-to-dawn mercury vapor light. It is used for yard lighting, security lighting, even street lighting some places. It contains a photocell sensor switch to turn it on at dusk and off at dawn, hence the name commonly used for it. Quite a number of fixture manufacturers make such a unit, and many utility companies push its use for "security" or "safety" at night. We see ads proclaiming "Light Up the Night", all in the interests of security or safety or something. All this is in face of the fact that there is more crime in the daytime than at night, that there is more crime in well lit areas than in dark areas (compare the lighting of New York City to that in a typical rural midwestern area, for example, and the crime level in the same locations).

Due to all this advertising, we have all (most of us anyway) come to relate lighting at night (good or bad) with safety. The world runs on perception, not on reality. IDA believes that quality lighting can and does promote safety, security, and utility at night. We are definitely not opposed to quality lighting. We are definitely against poor lighting, lighting that causes glare, light trespass, urban sky glow, and that comprimises visibility rather than helping us see. Such poor lighting wastes light and energy and money.

Let's look at this 175 watt dusk-to-dawn mercury vapor light in some detail. It retails for $29.95 or even less. The system uses about 210 watts of overall energy when we consider the ballast and other items. Most security lights and street lights are switched on and off by a photocell, as part of the fixture. They burn approximately 4100 hours a year (4100 / 365 = 11.23 hr per night), and this value is nearly independent of the latitude of the location, as the seasonal effects average out over the year).

Multiply: 210 watts x 4100 hours = 860 kilowatt-hours (KWH) per year energy used. (One KWH is 1000 watt-hours.) At 8 cents per KWH (the national average electrical energy cost; some places are lower, many are higher, even twice that high), the average cost of operating such a lamp is about $69 per year. That is over twice what the fixture cost to purchase. In some places, it's over three time as much or more. The situation is a prime example of where those who look at the initial cost alone are killing themselves. We must take a longer term view.

Tucson (about 600,000 population) has over 20,000 such lights (They did anyway until a mass change-over to better lighting sources was accomplished. The local utility replaced the several thousand such mercury lights that they owned; think how many more are owned by private citizens.) So the annual operating cost of those mercury fixtures in Tucson alone was over 1.4 million dollars. The population of the United States is about 500 times that of Tucson. So the annual operating cost of that single type of fixture is over 700 million dollars. If all of these fixtures were replaced with quality 35 watt low pressure sodium fixtures (getting better lighting as well), the country would save over 500 million dollars per year.

Let us consider now the wasted light. At least 30 percent of the light coming out of the fixture is totally wasted (without even considering the energy inefficiency of the mercury lamps). It is light going up, to brighten the sky, and light coming out at nearly horizonal angles. Such light only causes glare and light trespass, doing nothing to light up the owner's property, only to offend neighbors like you. Some have estimated the wasted light at well over 30 percent. Have a close look at one What do you think?

Thirty percent of $700 million is about 200 million dollars. That is money totally wasted. The wasted light is doing nothing to provide security, safety, or utility at night. It is only burning coal (most of the power in the United States is produced by burning coal), producing additional air pollution and acid rain. We have enough of that already.

Consider now all the other bad lighting. Billboard lighting from below and other signs lit from below (in both cases, much of the light output is wasted, even if you like lit billboards; many people don't). Searchlights. Lighting up of buildings, with lighting fixtures that are not well controlled. Poor quality street lights, parking lots, and other area lighting. The many lights that burn all night whether they are used or not. How many lights do you see nightly that have too much glare or too much wasted light? Look around!

Let us conservatively assume that this added wasted light is five times the amount coming from the 175 watt mercury. Then the total wasted money being used to produce the totally wasted light is five times that of the mercury: over One Billion Dollars a year!

Let's look at the amount for coal or oil being wasted to produce the wasted light. It takes, on the average, 0.47 tons of coal (940 pounds) to produce 1000 KWH of electricity, so one ton off coal can produce 2100 KWH of electricity. I takes about 1.8 barrels (76 gallons of crude oil to produce 1000 KWH of electricity, so one barrel of crude oil can produce 556 KWH. The wasted light therefore equates to a waste of at least six million tons of coal (think of the added acid rain and air pollution!) or over 23 million barrels of oil (think of the added oil imports). These are non-negligible amounts, to say the least.

While the wasted energy and monet from any single person's poor fixture is not all that much (say about $5 to $10 a month, added to their utility bill), the overall amount is truly "astronomical" (mind boggling), and it is made up of the sum of all these individual contributions. The solution is for each individual to do better, to be aware of the issues, and to try to do better. We will save money and energy as a nation by doing better as individuals, at home and at business. We must.

All this wasted light and energy is doing nothing to promote safety, or a better life at night. In fact, it does the opposite. It costs us money and energy to have a trashy nighttime environment and to wipe out our dark skies. Bright skies. glare, and light trespass help no one. Glare never helps visibility, never. Light trespass usually offends neighbors. Glare and light trespass are also factors in many accidents at night, by blinding or confusing drivers or pedestrians. All this costs the nation far too much in money and pain. We shouldn't tolerate it. We must stop such waste. Now.

If we were letting our water sprinkler systems waste much off their water by scattering water everywhere, onto the street, through our neighbor's windows, and upward (evaporation), we'd not tolerate it. If together we wasted over a billion dollars a year this way, we'd declare a national disaster and begin conservation measures immediately. We must build awareness of the adverse effects of poor lighting and get on with the goal of using only quality lighting.

For more information about the issues, contact the International Dark-Sky Association. Other information sheets are available from IDA address the issues of energy savings (for example, the retrofit of all street lights in San Diego (Information Sheet #12) to LPS is saving the city there about 3 million dollars a year), the 175 watt mercury, the operational efficiencies of different kinds of lighting sources, and other quality lighting issues. Join the cause of better lighting, and energy savings. We all can win. The International Dark-Sky Association is a tax-exempt, member supported non-profit organization.

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A key source for information on outdoor night lighting is the International Dark-Sky Association (IDA).