Shedding light on inefficiency

Even if lightbulbs consume less electricity, we may not achieve energy savings or reductions in greenhouse gas emissions. The reason is simple: when light becomes cheaper, many users will increase illumination, and some previously unlit areas may become lit. In a recently published article in the journal “Energy & Environmental Science”, scientists from the Leibniz-Institute of Freshwater Ecology and Inland Fisheries in Berlin (IGB) and the Museum am Schölerberg in Osnabrück, Germany have presented three policy recommendations, which they say could greatly reduce energy consumption and light pollution – without leaving cities in the dark.

The United Nations has designated 2015 to be an International Year of Light and Light-Based Technologies to celebrate the importance of light for human society. The energy efficiency of lamps has continuously improved over many centuries, raising living standards across the globe. However, despite these increases in efficiency, the total energy required for lighting has continued to increase. In the recently published paper, the scientists note that lighting now accounts for an estimated 19% of all electrical energy use worldwide, and argue that changes in lighting strategies could therefore have a large influence on energy consumption, carbon footprint, and environmental effects associated with light and power generation.

Doubled efficiency, but fourfold consumption

In recent years, the most visible policy response to excessive energy use for lighting has been restricting sales of new lamps to “energy efficient” models with higher luminous efficiency. The scientists claim that such policy-driven improvements in efficiency are unlikely to reduce energy use and CO2 emission, because cities might instead use more light.

This is an example of a “rebound effect”, a case where higher efficiency due to technological innovation actually leads to greater consumption rather than reduced energy use. The scientists point to the case of the UK between the years 1950 and 2000 as an example: even though lamps became twice as efficient at producing light, per capita electricity consumption for lighting in the UK increased fourfold.

Three steps to sustainable illumination

The study authors made three recommendations to make nighttime outdoor area lighting more sustainable. Their first recommendation is a transition to need-based lighting, where lighting is only provided where and when it is needed. Franz Hölker of the IGB explains, “the idea is that by directing light more carefully, visibility could actually be improved while saving energy and money. In suburban and rural locations with very little activity after midnight, modern lamps could also be dimmed to 10% of their normal power until morning traffic begins.” In the future, motion sensors could be used to run lamps at full power only during periods with activity.

The second recommendation is for policymakers like the European Commission that specify minimum requirements for street lighting. The scientists say they should also stipulate conservative maximum illuminances, because in many cases in the US and Europe, the amount of light far exceeds current standards. “If you use twice as much light as is needed for a task, then half the energy is wasted”, says Hölker.

Finally the scientists recommend adopting a new definition for efficiency in urban area lighting. “We need a more appropriate measure for reporting energy efficiency, that would allow apple-to-apple comparisons of radically different lighting delivery systems”, explains physicist Christopher Kyba, also of the IGB. “For example, suburban streets with lights that are dimmed after midnight could potentially use less energy in a year than a more efficient lamp that burns at full power all night.”

According to the experts, if cities acted on these recommendations, real reductions in energy use would be possible without compromising the public experience and use of outdoor lighting. They say the goal of lighting policy should be to provide exactly the right amount of light needed, while minimizing electricity consumption and unintentional influence on people’s sleep, or on nearby natural areas.

Full bibliographic information


C.C.M. Kyba, A. Hänel and F. Hölker (2014) Redefining efficiency for outdoor lighting. Energy & Environmental Science,
DOI: 10.1039/C4EE00566J
Attached files
  • In only a few human generations, the nighttime environment has radically changed over large fractions of the Earth’s surface. Photograph of the United States at night from the International Space Station is courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center
  • Image of Berlin at night taken by astronauts aboard the International Space Station (2013, Image Science & Analysis Laboratory, NASA Johnson Space Center).
  • An example of poor lighting from the USA. A large portion of the parking lot is unlit, and waste light shines uselessly on the house façade, the tree, and into the sky. Photograph by IGB/Christopher Kyba.

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