James Lowenthal

Light Pollution

Light pollution from downtown Northampton, Massachusetts
Light pollution from downtown Northampton, MA. All the sky glow and all the lights you can see here are a pure waste of energy and money, a menace to public health and safety and quality of life, and a benefit to no one.
Paradise Pond, Smith College, and Orion
Paradise Pond, Smith College, and Orion. Outdoor lighting at Smith is fairly well controlled against glare, resulting in a safe and beautiful campus at night.
Glare from streetlight on Village Hill, Northampton
Glare from poorly designed, overbright, too blue, unshielded streetlights on Village Hill, Northampton.

What is light pollution?

Light pollution is the artificial brightening of the naturally dark night sky due to excessive and poorly designed outdoor lighting.

Why is light pollution a problem?

  • Public health: Light pollution and excessive blue-rich light at night are associated with
    • Suppression of melatonin, an important hormone
    • Disruption of circadian rhythms, or natural sleep cycles
    • Elevated rates of diabetes, obesity, breast cancer, and prostate cancer

    Here is a report from the American Medical Association on the “Human and Environmental Effects of Light Emitting Diode Community Lighting".

  • Public safety
  • Streetlights and other outdoor lights that cast their light widely also cause glare -- unwanted light that shines directly in your eyes. This is dangerous for drivers, pedestrians, and bicyclists. Glare has particularly strong effects on the elderly. Glare is especially strong from LEDs, and especially blue-rich white LEDs. If the light is shining in your eyes, you can't see anything else!

    Lights that are poorly shielded against glare also tend to cause dark shadows that can easily hide intruders.

  • Wildlife
  • All animals -- insects, birds, and mammals including humans -- evolved with a 24-hour day-night cycle. Humans and other diurnal animals need complete darkness to sleep. The feeding, mating, and migration patterns of nocturnal animals can be seriously disrupted by light pollution; some species of birds, turtles, and fireflies are threatened with extinction due largely to light pollution.

  • Energy and climate change
  • Light pollution is pure waste. Billions of dollars per year are spent by US cities and states lighting up the sky, without even meaning to. Generating the electricity to power that light pollution produces millions of tons of CO2 per year, contributing significantly to the nation's total greenhouse gas emissions.

  • Historic preservation and quality of life
  • Historic cities and towns like Northampton, MA, founded in 1654, deserve well-designed outdoor lighting that enhances their beauty and charm -- not harsh, over-bright, unshielded, blue-rich white lights that make our downtowns feel like prison yards.

    And we need to see the stars! Most children growing up in the US today have never seen the Milky Way. There is growing concern about "nature deficit disorder," especially among city kids. The starry sky and the Milky Way are a priceless gift of nature that should be accessible to all.

Isn't light pollution a necessary evil to keep our cities safe from crime?

Absolutely not! Bad outdoor lighting -- too bright, too blue, and too spread out -- benefits no one, except maybe criminals who take advantage of dark shadows caused by glare. Decades of scientific research have failed to find a conclusive link between outdoor lighting and crime. Some very brightly-lit cities have terrible crime problems, while other cities with more subdued lighting have low crime rates. To make our cities safer, we don't need more light -- we need better light.

Lighting examples
Lights should go down only, not up or out sideways.
Floodlight Angles
Often, simply aiming floodlights down instead of sideways will improve the quality of light significantly, cut glare, and help your neighbors sleep better, while illuminating your own property better.

What can I do to prevent light pollution?

Follow these four rules of thumb of good outdoor lighting:

  1. The light should be fully shielded against glare, with no light escaping above the horizontal, and ideally no light above 80 degrees from vertical.
  2. The light should be only as bright as needed for safety, and no brighter.
  3. The light should not be too blue -- at most 3000K, and ideally a "warmer" color such as 2700K or even 1800K. 4000K is too blue.
  4. The light should be turned off when it's not needed. For streetlights, this could be after midnight. For parking lots, it could be an hour after the close of business.

Contact your mayor, city councilor, select board, or other elected officials to demand that your city's outdoor lights comply with all four of those rules!

Here's an outdoor lighting audit you can bring to your neighbors or businesses with problem lights (also available in MS Word).

Are there laws governing outdoor lighting?

Yes. For example, Northampton has an ordinance requiring all outdoor lights to be shielded against glare and light trespass, so that no light shines on neighboring properties.

Here is the Model Lighting Ordinance developed by the International Dark-Sky Association and the Illuminating Engineering Society. Bring this to your city's planners if you don't have a good dark-sky ordinance in place.

Good and bad outdoor lighting fixture designs
Good and bad outdoor lighting fixture designs. Read more here.