Technical Innovations To comprehensively evaluate the impact of lighting on the local bat population , two distinct technical solutions were developed and tested :
Option 1 : This approach involved equipping luminaires with two different colour temperatures , 3000K ( warm ) and 2200K ( very warm ). Both light sources were activated at dusk ( approximately 1000 + 1000 lumens ), with the 3000K source turning off five hours before and after midnight . The 2200K light , emitting less blue light , aimed to explore whether a simpler and cost-effective lighting solution could still provide adequate illumination while being more favourable to bats .
Option 2 : In this configuration , luminaires featured monochrome amber LED lights at 590nm ( approximately 500 lumens ) and 3000K ( around 2000 lumens ). The amber LED remained active throughout the night , while the 3000K component was controlled by presence sensors and illuminated a section of 150-200 meters before and after the detection location . The amber LED ’ s minimal biological impact made it ideal as a guiding light , while the 3000K source was essential for safety and enhancing the sense of security .
On-the-Ground Measurements Two distinct park roads , “ the brook ” and “ the forest ,” were selected for measurement and observation . Pre-measurements of bat activities were conducted in the summer of
2022 . “ The brook ” had previously been illuminated with round radiant luminaires using ceramic metal halide at 3000K and bats had been observed in this location in the past . In contrast , “ the forest ” had remained unlit , but accessibility and safety concerns had prompted calls for illumination . The bat activity measurements for both sites were again conducted in the summer of 2023 , providing crucial data for evaluating the impact of the new lighting solutions .
Audio boxes have been installed to record the sounds made by bats . Once the data and sounds have been evaluated , the city will be able to better understand the different bat types , quantities and activity in this area .
Looking Ahead “ The brook ” has undergone a transformation with lighting according to Option 2 , while “ the forest ” now utilizes the lighting solution from Option 1 . These test results will offer insights into the effectiveness of these different lighting configurations and their ecological implications . Moreover , this experiment could inform future lighting decisions across the city .
Committed to Sustainability It ’ s important to note that these lighting solutions are based on reports and studies , rather than established scientific consensus . The project remains open to new information that may refine its guidelines . All adjustments for biological diversity are founded on thorough site investigations by ecologists , who provide guidance on species and their lighting sensitivity . The project is also exploring how residents utilize the routes in terms of their experiences and feelings of safety .
A Rich Tapestry of Life With 56 unique animal species identified in the area , including 18 near-threatened , 5 vulnerable , and 3 endangered , Stockholm ’ s commitment to preserving biodiversity is evident . This project takes on added significance as the city is currently home to eleven species of bats , constituting 79 % of the bat species observed in the county and 61 % of those observed in
LIGHTING
the country since 2000 . Prominent among them are the northern bat , the pygmy pipistrelle , and the water bat .
A Brighter Future for Biodiversity It is anticipated that the findings should be reported in the middle of 2024 once the evaluation of field observations and data is complete . In the meantime , data collection is continuing .
Stockholm ’ s forward-thinking project is a beacon of hope for environmental conservation , hoping to demonstrate that even urban lighting can play a vital role in supporting biodiversity . With innovative approaches and a commitment to sustainability , the city is taking strides toward its vision of a fossil-free , climatepositive future while safeguarding its natural treasures .
Parts of the project have been enabled by a new luminaire called ” Citisun Dual Colour ” by OrangeTek . 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 .
It serves as a promising example of the future of lighting , designed to minimize environmental impact and prioritize the well-being of both wildlife and the community . By shedding light on the delicate balance between human needs and the needs of nature , Stockholm is pioneering a more harmonious coexistence between city life and the wild world beyond .
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