20 November 2014

LEDs and light pollution

Iris G writes:*

As the world demand for energy grows, research into more efficient and sustainable ways of using energy is booming. This is especially noticeably in the field of lighting, which is experiencing nothing short of a revolution. Just last month, it was announced that this years Nobel Prize in Physics has been awarded to three scientists for their work on light-emitting diodes, commonly known as LEDs. In the past decades industrial and domestic lighting transitioned from the traditional incandescent bulbs to CFLs and now moved on to LEDs, which are used for a variety of applications ranging from domestic lighting to cellphone screens to Christmas lights.

The improvement in energy-saving is significant: LEDs are much more efficient at generating visible light compared to an incandescent light bulb, their lifespan is over 40 years longer than that of a traditional bulb, and due to recent improvements in lighting technology LEDs have also become much cheaper. Many types of LEDs, however, also have one major downside: they can contribute severely to light pollution.

The phenomenon of light pollution has been recognized for some time and appears to be an almost inevitable consequence of development. It is virtually omnipresent in the urban areas of the United States and Western Europe, where it is estimated that around two-thirds of the population can no longer view the Milky Way with the naked eye [1]. In recent years it has become increasingly clear that light pollution can be very detrimental to the environment and human health, and many of its effects are not yet well understood. High levels of pollution are linked to weight and mood problems as well as breast cancer in humans, and generally impact the biorhythm and behavior of wildlife, especially nocturnal animals [2].

Although any light above pollution thresholds can have an effect on health and nature, the blue-white light (wavelengths below 500nm) emitted by LEDs may be especially detrimental. This type of lighting could cause two to five times as much light pollution if it replaced all of the current lighting, due to the greater scattering of blue light compared to green or red light (this is also why the sky is blue and no other color)[3]. Warmer hues of LEDs are being developed, but are currently not as effective and competitive as their blue light counterparts.

This is not to say that LEDs should not be used and celebrated - on the contrary. Rather, it should be recognized that while they are a major breakthrough in lighting, LEDs form only part of the solution to more efficient and sustainable lighting. Businesses and industries should still look critically at their use of lighting even when they implement LEDs, and shield their light emissions where possible. In urban areas, local municipalities should carefully consider where and in which way LEDs can be used efficiently without exposing citizens to detrimental effects from light pollution. Individuals could cut down significantly on their energy use by transitioning to LEDs in their home. Finally, it is important to remember that even when lighting becomes cheaper, it can't hurt to turn the light off every now and then.

Bottom line: LEDs are a great new money- and energy saving source of lighting, but we have to be careful about when and where to implement them as they are not without downsides.

* Please comment on these posts from my environmental economics students, to help them with unclear analysis, other perspectives, data sources, etc.

  1. Pierantonio Cinzano, Fabio Falchi, Christopher D. Elvidge. 2001 Monthly Notices of the Royal Astron. Society 328, 689–707
  2. Ron Chepesiuk. 2009. “Missing the Dark: Health Effects of Light Pollution.” Environmental Health Perspectives 117:1: A20-A27. Accessed at: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2627884/
  3. Fabio Falchi, Pierantonio Cinzano, Christopher D. Elvidge, David M. Keith, and Abraham Haim. 2011. “Limiting the impact of light pollution on human health, environment and stellar visibility.” Journal of Environmental Management 92: 2714-2722. doi:10.1016/j.jenvman.2011.06.029


  1. Iris, very interesting topic! I was curious though, is light pollution an inevitable consequence of LEDs, or are there also other factors that contribute to increased light pollution? I mean - you note how LEDs are more efficient at generating visible light than normal incandescent light bulbs. But how much does this change from light bulbs to LEDs explain of the increased light pollution?

  2. I've been involved with a handful of projects replacing city wide street lights with LED. I think your analysis is interesting. If you were to pursue it a little further you might find that there are other technological advantages to LEDs that could be used to reduce the light pollution. One is that typically the lumens at street level with LED fixtures are actually reduced somewhat relative to brand new traditional high pressure sodium or metal halide lamps. Also, LEDs are much easier to dim and are starting to come with built in dimming controls. For the most part these are used for tuning lumen levels and electricity pricing demand response, but you could make the argument that the dimming could be used to reduce lumen levels later at night to during lower street usage periods to reduce light pollution.

    Just some thoughts.


  3. Miika, thanks for your reaction! Yes, LEDs contribute to light pollution, but they are definitely not solely responsible for the increase in light pollution, which has been taking place for decades. Light pollution is a byproduct of industrialization and population growth (think big cities and 24h factories). In my blog, I tried to highlight that the characteristics of blue-white LEDs especially may be more harmful to health and the environment than other sources of lighting. However, warmer hues of LED are being developed and light pollution can also be mitigated by shielding lighting where possible, so light pollution is not inevitable.

  4. Jqkeller, thank you for your interesting response! I agree that LEDs are not necessarily detrimental, and their influence on light pollution depends largely on which type of LEDs are used and how they are implemented, so it is great to hear about projects that use LEDs in a sensible and effective way. The possibility of dimming LEDS is not something I've looked into so far, but it sounds very promising, and I'll certainly take it into account !

  5. One of the issues with LEDs is how easy they are to install, so I think we are likely to be getting them in lots of places where we've not had lights before, which may cause increased light pollution until people get to understand how the new uses contribute to light pollution.
    The other issue is likely to be that because they are so cheap to run, people will feel like they can use more of them, while still using less electricity than before, so there is likely to be more light and more light pollution,


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