What is light pollution?


    협력 및 번역 : Eric Vandernoot (Atlantic Observatory), Han Soul Lee (Florida Atlantic University Physics Department)


    What is light pollution?
    Light pollution is the use of excessive amounts of light from manmade sources in the outdoor environment. There are two ways that light pollution interferes with our ability to study the sky. As such, it becomes harder to:

    "See fainter objects" "Do spectroscopy"

    Figure 1.
    A map of the world, showing the extent of light pollution. The brighter a region is, the worse light pollution is for astronomical observations.
    Sky glow is the orange glow seen over towns and cities. It is caused by light being reflected of the ground or other sources and by being scattered off of molecules in the atmosphere. Naturally, the sky is never perfectly dark. The sunlight scattered by the dust in the solar system and excited oxygen atoms in the upper-atmosphere creates a natural sky glow. However, sky glow over time has been increasing due to an increase in heavily populated areas. A look at this map of Earth, showing the regions affected by light pollution.

  • In heavily populated areas, more inefficient, careless practices and poorly designed outdoor light fixtures increase the amount of sky glow through direct upward emission, wasted light falling into areas that do not need illumination, and over-illumination.

    The following pictures are some examples of sky glow and poor use of outdoor light fixtures.

    Figure 2.
    Imaged above is Henderson Athletic Field on Feb. 12, 2013 with lights so bright and poorly designed that it is setting the sky aglow.

    Figure 3.
    Imaged on the left is the same field with its light so bight that the full moon (the orange ball) on Sept. 13, 2011 is hardly noticable.

    This increase in sky glow is enough reduce the amount of stars we can see and makes it difficult to view dim objects in the sky. Sometimes, the sky glow is too bright to clearly see very dim objects like nebulas or galaxies.

    Figure 4.
    The constellation Orion, imaged at left from dark skies, and at right from the teeming metropolis of Orem, UT in February 2008

    For amateur and professional astronomers alike, this decrease number of visible stars affects observations. Light pollution has forced astronomers to either be content with fewer visible stars or move to areas with darker skies. Unfortunately, the new giant telescopes are being built in more remote areas such as in Chile, Arizona, Hawaii, and the Canary Islands.

    Spectroscopy is the most valuable tool an astronomer can have. It is used to find out a wide range of information on an object. By studying the spectrum of objects like galaxies, astronomers can determine the chemical composition and temperatures of the objects they observe. They can also determine how fast the object is moving by calculating the red shift of the lines. This becomes difficult to do because the spectrum of the outdoor light sources interferes with the spectra of an object.

    The type of light that is being emitted by a light source is very important to astronomers. Low-pressure sodium and high-pressure sodium lamps are preferred because they leave large parts of the spectrum relatively unpolluted, whereas broad-spectrum sources like broadband metal halide, white LED, and incandescent lamps do not. In addition, broad-spectrum sources emit shorter wavelengths that more strongly scatter in the atmosphere.

    Figure 5.
    Spectral power distributions of four different type lamps.
    A: Warm-white fluorescent tube (CCT = 3000 K)
    B:Cold-white fluorescent tube (CCT = 6500 K)
    C: High-pressure sodium (HPS) lamp used in outdoor public lighting D: Metal-halide lamp used for various outdoor lighting applications.

    Tips to Reduce Light Pollution

    01. Position lights so that they are pointed downwards where it is needed
    02. Use full cutoff light fixtures to better control
    03. Use motion-sensor lights

    Figure 6.
    The image, taken on Jan. 5, 2013, of the back driveway of Imagine Schools Chancellor Campus in Boynton Beach is an example of properly positioned lights with very little glare.
  • Light Pollution and Wasted Energy

  • Definition of Energy

    Although energy has many different forms, in general, it is the measurable quantity that matter or radiation has to provide action or the capacity to do physical work, whether it is mechanical or due physical work. Energy is measured in the SI unit of Joules. Electricity, which is made of moving electrons, has energy, but is typically measured in Watts. However, a watt is a unit for power, which is a measure of the rate of energy delivery or consumption.

    By equation

    Potential Energy=(Force x Distance)=[N x m]=[J](Joules)
    Energy consumption is measured by w x h(Hour), wh=3600[J]
    Also, keep in mind that kw=1000w

    Energy Efficiency

    As the law of 'Conservation of Energy' states, energy cannot be created or destroyed. It merely changes into different forms. In any system, the energy input is always more than the useful energy output. Although the 'lost' energy changes into many different forms, often times majority of the energy is converted into heat. Thus, the energy efficiency measures the quantity of useful output energy compared to the total input. By equation,

    Energy Efficency = Useful Power Output / Useful Power Output

    Higher the energy efficiency indicates more energy consumed for useful purpose, and less energy loss into heat.

  • Incandescent Bulb

    Most historic and traditional light bulb
    Common usage: very common and affordable bulb. It is often used in both public and private, especially in the house holds Has energy efficiency of 10%. It is the least effective source. 90% of the energy input is loss to heat

  • Fluorescent Lamp

    Started to replace incandescent bulb since the invention.
    Common usage: very common and affordable bulb. It is often used in both public and private, especially in the non-household building such as business , cooperation and schools.
    Has energy efficiency of 45%. It is more effective than incandescent bulb. 55% of the energy input is loss to heat

  • Light Emitting Diode (LED)

    Most recently discovered source
    Common usage: Very common and affordable, yet it is used most often for industrial purpose. It is commonly found in electronics and commercial.Unlike incandescent bulb and fluorescent lamp, it has very high efficiency. However the efficiency varies depends on the color.

  • Necessary vs. Unnecessary Light

    Security is the major purpose of the light use. Lights such as streetlights provide sights on the night road, allowing drivers to be alert . Although lights provide sights, excessive lightning could cause disturbance in sight in exchange of unnecessary economic loss.

    The light pollution could be reduced through the proper lamp design.

  • The Effects of Light Pollution on Birds

    Light pollution is a relatively recent problem for wildlife. Artificial lights can affect the natural behavior of many types of animals. Most animals evolved around a natural light cycle and being exposed to anthropogenic light can alter development, hormone regulation, and breeding cycles among other things

    The images above show light pollution worldwide, in the United States, and in an average neighborhood. The image of the neighborhood shows the night sky without light pollution during a blackout (left) and with light pollution (right).

  • Migration

    The map above depicts migratory routes used in North America. Light pollution can disorient migrating birds and interfere with their ability to orient themselves (

  • Migration

    Migrating birds can be disoriented and led astray by city lights at night. Light pollution is a worldwide phenomenon. It is estimated that 20% of the Earth's land is impacted by light pollution. Birds are often attracted to artificial lights on buildings and will fly into the buildings. These interactions often result in the birds becoming injured or dying. The above pictures show migratory birds, some that have been killed by interactions with buildings.

  • Morning Song and Breeding

    Artificial lights also impact when songbirds sing their morning songs and what time of year they begin breeding. Songbirds that live in areas that are affected by light pollution will begin singing their morning song before true night is over. The more artificial light in an area, the earlier the birds will start singing. The amount of light pollution in an area also impacts what time of year species of birds start breeding. Several studies have noted that birds that live in areas with light pollution begin breeding earlier in the season than those that live in areas with little to no light pollution

  • What can you do to help?

    1. Spread the word about light pollution and the negative impacts it has on birds and other wildlife.
    2. Turn off or dim outside lights and replace bulbs with more efficient types of light bulbs.
    3. Make sure outdoor light fixtures face downwards.
    4. For more information about light pollution visit: http://www.darksky.org/