Where safety, the environment and dark skies collide: on responsible lighting of wind energy projects

Image credit: Jeswin Thomas
1683 words / 7-minute read

Summary: As the world transitions to renewable energy, concerns about both transportation safety and light pollution converge in the form of facilities like wind farms. Learn more about how these influences interact and how competing interests in both realms can find balance leaning toward better sustainability.

The world is in a precarious position at the moment. Our planet is experiencing a climate crisis. Scientists expect that its effects will become more plain in coming decades. In previous posts here, we explored how outdoor lighting and light pollution interact with environmental concerns. That includes topics such as climate change, corporate social responsibility, and the "Rights Of Nature".

The laws in many countries mandate the use of outdoor lighting because it serves the public interest. Lighting has demonstrated safety benefits and saves lives. But when lighting becomes excessive, light pollution can cause its own problems. As the world transitions to renewable energy, this can create new challenges. This post explores concerns on both sides of the issue and asks whether competing interests can be balanced in reasonable and effective ways.

More than one environmental challenge

Artificial light at night (ALAN) has several connections to environmental concerns. For one, lighting consumes electrical power. That has a significant climate impact via the burning of fossil fuels. Also, ALAN exerts pressure on species already experiencing environmental stress. That stress comes not only from climate change, but also from sources like habitat and biodiversity loss. Energy-efficient lighting like LED seems at first like a solution the first problem. But it can also contribute to making the second problem worse.

Its lower cost of operation has led to rapid adoption of LED technology in the past two decades. With this has come overconsumption of outdoor ALAN. Outdoor lighting is now perceived to be cheap and free of environmental consequences. There is evidence to suggest that had led to the installation of a lot of new and unnecessary lighting. It may have also eliminated any overall environmental benefit from the transition to LED. And it means more light in the nighttime environment, yielding further ecological stress.

In concept, the simplest solution to the climate crisis is to reduce humanity's energy consumption. But our recent history suggests that we're not going to do that. Instead, economists expect energy demand to grow coming years and decades. If so, the next-best approach is to 'decarbonize' the global energy generation portfolio. That requires finding sources of energy that aren't limited to an exhaustible fuel supply.

"Renewable" energy sources like solar, wind and geothermal harness the power of forces of nature. These forces are at work around us all the time, their energy is "free" and it yields no polluting byproducts.  We have used some, like the wind, to power our transportation for thousand of years. Yet until recently, we couldn't move that energy from where we captured it to where we wanted to use it.
Making the best use of renewables now involves constructing both facilities to collect the energy and the infrastructure needed to move it. For this reason, people who live in areas near renewable projects often oppose their construction. Often there are real concerns about the environmental impact of these facilities. When faced with the task of evaluating applications to allow them, governments have to make difficult choices. Sometimes they conclude that the benefits involved outweigh any adverse local impact. Those impacts can include light pollution.

Windmills at night near Kennewick, Washington, USA. Source: Scott Butner/Flickr (CC BY-NC-ND 2.0)

From anecdotes to data

There are certain "speciality" lighting applications that must evaluated in their own contexts. Lighting for specific public safety applications is among those applications. Wind farms, whether built on land or in bodies of water, are a particular concern.  Wind turbines are obstacles for both pilots and sailors in both daytime and nighttime. That's true whether they're in active operation or not. Countries have set rules for lighting windmills at night to reduce the chance of accidents. These rules often supersede other concerns in environmental impact assessments.

The principle underlying these rules is that certain safety concerns cannot be mitigated. As a necessary condition of permitting wind farms, they are seen as acceptable risks. These considerations have led governments to deny permission to build some projects. In other cases, the perceived benefits are too important not to permit renewable energy projects.

Neighbors often oppose wind projects on aesthetic grounds. Their concerns about property values are often labeled NIMBYism ("Not In My Backyard"). Yet there are also real concerns about the environmental impact of this lighting. Renewables projects are often built in remote locations. These are often ecologically sensitive places. Windmills can be hazardous to birds, for example, and in particular at night for migratory species. Very large wind projects involving hundreds or thousands of turbines could light up the night sky. This may happen even when the lighting employed is the smallest amount allowed by law.

So what is the real impact, and should we worry about it? Until recently there were essentially no scientific results to inform the debate. Salvador Bará (Universidade de Santiago de Compostela, Spain) and Raul Lima (Politécnico do Porto and the University of Coimbra, Portugal) just published the first significant work on this topic. They made a simple model of the visual impact of individual wind turbine lights. They used this model to compare their expected brightness to that of astronomical sources like bright stars and planets. It takes into account real-world influences like attenuation of light by the Earth's atmosphere .

Bará and Lima found that windmill lights can be very bright at short distances. Up to 4 kilometers away, medium-intensity turbine lights can exceed the apparent brightness of the planet Venus. After the Sun and Moon, it is often the brightest natural object in the night sky. At 10 km away, the lights can still be brighter than the brightest stars. They can remain visible to the unaided eye to distances as far as almost 40 km. The authors concluded that "the visual range of wind farms at nighttime may be significantly larger than at daytime, a factor that should be taken into account in environmental impact assessments".

​So far this does not address the environmental effects of these lights. The researchers also looked at the amount of illumination on the ground that the lights can cause. Except at very close range, the intensity is low. As a benchmark, the authors used the expected light intensity on the ground from a starry night sky in the absence of the Moon. They found that even the brightest beacon lights on turbines yield these conditions out to distances of only a few hundred meters. Within 5 km the intensity is almost completely negligible. That said, it could still be harmful to wildlife very close to the windmills, whether on land or at sea.

The amount of light falling on a horizontal surface at ground level (yellow curves) as a function of distance from a single wind turbine beacon light mounted 115 meters above ground level. The dotted cyan line represents "the illuminance produced by a typical moonless starry sky in conditions of astronomical night, ∼0.001 lx". Source: Figure 4, Bará and Lima (2024).

What about the night sky? "Skyglow, in absolute terms, should not be very intense far away from the poles," Bará tells us. "The luminous intensity of the standard lamps used here at nighttime is 2000 candela, and this would make less than about 24,000 lumens per beacon, something like a couple of streetlights." Of course, if designers packed turbines into wind farms, the collective effect might be detrimental to the night sky.

​In a paper published last year, Bará and colleagues considered the effect of skyglow immediately near streetlights. They found that the contribution to skyglow from an isolated, single street light is small and localized close to the light. Small wind farms may thus have little impact on the night sky in their surroundings. But that's less likely as installations grow larger.

Finding the optimal solution

What can be done about all this? Clearly there is a climate need to shift energy production away from fossil fuels and toward renewables. Almost one-third of global electricity production now comes from renewables. That percentage is steadily increasing. Certain flavors of renewable energy, like solar, don't need facility lighting at night. But they're not suitable for every condition or situation. For example, electricity generated from solar cells drops to zero at night. To reduce uncertainties, experts recommend diversifying investments in types of renewables. This ensures that no one technology dominates in an area.

To the extent that wind energy is a good option in many parts of the world, there remains the question of where to put it. The social unacceptability of wind farms near populated places is unlikely to change. That leaves locations that may be especially sensitive from an ecological perspective. At the same time, transportation safety concerns will persist and even grow.

Technology may be able to help. For example, some wind farms are now equipped with Aircraft Detection Lighting Systems (ADLS). These systems sense the approach of aircraft within a predefined volume of space around and above wind farms by using low-powered radar. When an aircraft enters a predefined detection zone, the ADLS switches on bright lighting to make windmills visible to the pilot. Once the aircraft exits the detection zone, ADLS turns off the lighting automatically. ADLS can improve situational awareness of obstructions like windmills even in challenging weather. It is sometimes deployed in conjunction with Enhanced Vision Systems (EVS) equipment. EVS combines views from infrared and visible-light cameras to help pilots see through fog, snow, and other low-visibility conditions.

At the end of the day, we can't have it all. So we have to make accommodations. Situations arise where even our best technology can't fully mitigate dangers associated with wind energy projects. But where to locate these facilities remains a choice. Decisions should consider ecological sensitivity in relation to the amount of traffic and the need for lighting. In other words, it's a problem of many variables that has more than one solution. Sometimes the answer is to not build the project at all.

Dark-sky advocates have long wrestled with such tradeoffs. It is often the case that the most "wildlife friendly light" is the one that is never installed to begin with. And yet, better lighting practices exist in the real world alongside complex social and political influences. Lighting for safety remains among the most complex of them all. As the climate crisis becomes more acute, we are again confronted with often difficult choices. The right balance between competing risks serves both the interests of nature and society. That balance leads in a direction toward a world that is more sustainable in all its aspects.