Measuring light pollution

To experience real darkness in Sweden you need to go far north, for example to the area around Sarek. Other than that, there are few really dark places left. The night sky is more or less illuminated by artificial light. Light pollution, lighting that illuminates more than necessary, poses problems for astronomers who want to study the night sky or for insects that are attracted to light. But it can also lead to negative effects for humans. Research shows there may be links to cancer, sleep problems, depression and obesity. But more knowledge is needed.

"In the studies we looked at, there are generally very little information about how much light or what type of light that can be harmful. There is also a lack of good methods to measure the amount of light pollution. What units of measurement do we use? How do we ensure that the results are comparable with other measurements? Often you use satellite images without proper measurement values", says Stefan Källberg, researcher at RISE and technical manager of the National Laboratory for Photometry and Radiometry.

Lighting with a purpose

In a project ending soon, he and his colleagues have gone through the current research in the field, developed new methods to measure the amount of light pollution using a drone, and tested energy-efficient outdoor lighting that can work for both people and animals and the environment.

"We want to limit light pollution to reasonable levels and avoid spreading light where it does no good. All outdoor lighting should have a purpose. It could be to increase traffic safety, to make a walking and cycling path safer or something else."

Drone measurements

Stefan Källberg and his colleagues acquired an ordinary consumer drone, equipped it with a light meter and developed methods for quality-assured measurements of the scattered light. The drone measurements were then used in the outdoor lighting tests.

"Since we know that blue light affects insects and bats the most, for example, it would be good to reduce the proportion of blue light in outdoor lighting. But if you reduce the blue light, the proportion of red light increases, which means that the surroundings are colored red for us humans and it becomes difficult or impossible to distinguish colors. The goal is therefore to find a middle way, a light that can be accepted by people while containing as little blue light as possible."

What did people think?

Several light sources with different proportions of blue light were selected, from an orange tint to more traditional light. These were set up by a lake outside Borås along a small pedestrian and bicycle path. The regular lighting was turned off and then people walked along the route and answered questions about what they thought of the lighting.

"It is always difficult to have an opinion on light. But we can see that younger people preferred the traditional white light and thought the orange color gave an unsafe impression, while older people liked the in-between variant. Everyone agreed that it would not have worked with even redder light, it is perceived as unsafe, says Stefan Källberg."

Potential for development

Although the drone measurements worked well, there is potential to develop them in future projects.

"We have seen that our method makes it possible to get good measurement values, such as seeing which light sources contribute the most to the light in a certain area. With a more advanced drone, you could automate the process, make it fly in certain patterns and thus develop the method and take further steps towards a defined and quality-assured method", says Stefan Källberg.