Lighting for Biodiversity

In Sweden, the city of Stockholm is taking a bold step to control the impact of lighting on biodiversity in the region.
The project, which is set in the forest area of Årstaskogen, involves integrating presence detection and tuneable colour temperature lighting.


By 2040 the Swedish capital of Stockholm aim to become climate-positive and fossil fuel free.
The master plan involves not only reducing its carbon footprint but to nurture a healthy environment for its residents and wildlife.

To make this happen, Stockholm has crafted an “Action Plan for Biological Diversity in the City of Stockholm.” This is a ambitious initiative that has created many projects aimed at preserving and enhancing biodiversity within the urban environment.

The project is a collaboration between multiple departments at the City of Stockholm including, the Environmental Administration and the Traffic Office.

The initiative launched in 2022, with the first phase set to conclude in mid-2024. The overarching goal is to establish guidelines for lighting practices that harmonize with and support biodiversity.

In 2022, the city began pilot projects to trial projects based on international research and investigations. The central goal was to evaluate how colour and presence-controlled lighting would affect the activity of the local bat population within the Årstskogen nature reserve area, located in the heart of Stockholm.
An important aspect of the project is to ensure that ecological considerations remain at the forefront, which is made possible by the close collaboration with the municipalities Environment Agency.

Colour temperatures in regard to the enviroment

CitiSun Dual Colour installed in Årstaskogen

CitiSun Dual Colour installed in Årstaskogen

CitiSun Dual Colour

CitiSun Dual Colour

OrangeTek's CitiSun Dual Colour luminaire was selected and installed in Årstaskogen along with our Active Light presence detection nodes.

This dual colour luminaire, one of the first of its kind, has the ability to change the colour temperature balance using smart street lighting controls and sensors.

Today, there are a number of choices to make regarding different colour temperatures.
Where we see the greatest demand today is monochromatic amber, 2200K and 3000K. We believe combining these blue spectrum free and white light sources offers a considered balance between safety for the population and the environment.

Worth noting:

Monochromatic Amber - is advantageously used as a signpost, in combination with a presence sensor. Or for special needs to be used at a defined part of the year, to show consideration for, for example, bats during mating season!
- No blue light content.
​- Low energy efficiency and colour reproduction, but relatively good contrast!
​​ - Not intended to replace functional lighting!

2200K – about 10% less energy efficient compared to 3000K, still relatively good lighting performance and operating economy!​

Technical Solution

Two technically innovative solutions were tested to evaluate the impact of lighting on the local bat population in Årstaskogen.

Option 1: In this first option we equipped the luminaires with two different colour temperatures, 3000K (warm) and 2200K (warmer). Both light sources were activated at dusk with the 3000K source turning off five hours prior to and after midnight.
The 2200K light, which gives less blue light, aimed to see if a cost-effective lighting solution could still provide good enough illumination while being more favourable to the bats.

Option 2: In the second option we equipped the luminaires with monochrome amber LED lights at 620nm and 3000K. The amber LED lights remained active through the whole night, while the 3000K was controlled by presence sensors and illuminated an area of 150-200 meters before and after the detection location.
The very small biological impact of the amber LED made it ideal as a guiding light, but for safety and sense of security, the 3000k lights were the optimal choice. 


Forest road in Årstaskogen

Forest road in Årstaskogen




CitiSun Dual Colour

CitiSun Dual Colour

Illuminated wild rabbits of Årstaskogen

Illuminated wild rabbits of Årstaskogen

Install Sites

Two areas, or rather roads, which for the project was named “the brook” and “the forest,” were selected for testing.  In the summer of 2022 pre-measurements of bat activities were made. Around “The brook” bats had been obvserved in the past and the area had previously been illuminated with luminaires at 3000K. "The forest” was before always completely unlit but for safety and security reasons it called for illumination.
In the summer of 2023 new measurements were done to give understanding about the impact of the new lighting solutions.
Additional to measurements of lighting, audio boxes was installed to record the sounds of the bats. This provides a better understanding of the activity in the area.

For “the forest” the lighting solution Option 1 was applied while “The brook” was equipped according to Option 2. 
This way the test result will give the best, broadest information on how these
new solutions affect the enviroment and it's fauna.

In the area of Årstaskogen 56 animal species was identified, and Stockholm as a whole hosts 11 different species of bats. 
This makes it clear that the project and the results that come out of it is of great importance for a bright future of the biodiversity.


A bright future

As 2024 have just begun the project is as we speak alive and kicking and the collection of data is ongoing. It is estimated to be finished and reported in the middle of the year.

One thing to take note of is that the lighting solutions presented in the project are based on studies and reports. No information or plan is set in stone and the project is open to new information that could refine its guidelines or arrangements. The project is based on thorough site investigations by professional ecologists.

The Swedish capital is surely taking big steady steps toward a climate-friendly, fossil-free future while also supporting biodiversity and enviromental conservation. 
The testing in Årstaskogen gives us hope for the safety and well-being of both wildlife and nature and when the project is concluded it will hopefully show that even urban lighting can play a huge role in supporting biodiversity.

OrangeTek are delighted and honored to provide this innovative project with our luminaires and knowledge and we are crossing our fingers that the commitment by the city of Stockholm and us will make way for further improvements of enviromental friendly ligting solutions across the city.