Embedding sustainability into the design of street lighting

Light pollution is an increasing problem and Artificial Light at Night (ALAN) affects nature in many ways. The Norwegian Road Authorities (SVV) initiated a collaboration with the Norwegian Institute for Bioeconomy (NIBIO) and the University of South-Eastern Norway (USN) to find measures that can help reduce the negative impacts of road lighting on the environment and nature. While USN has looked more generally at sustainable lighting design and ways to reduce the negative effects of road lighting, NIBIO has focused on how road lighting affects insects. We study how the light from roads contributes to light pollution, with the final aim to know more about what measures most effectively reduce the negative effects of road lighting. In this pilot study of light levels in two transects beside a road, the results show that the light levels decreased relatively fast as the distance to the light source increased. Thus, the direct light from the road lighting might not be the most prominent addition to the light pollution in the open landscape. On the other hand, the measurements showed some light influence from the road up to around 160 meters from the road, although the levels were low. While the light was below the detection limit, the light source was visible as a point source at a very large distance. This observation addresses the question of whether organisms are influenced by the average light energy per area, or the intensity of a source as observed from a distance (irradiance vs. radiance). Additional sources of light pollution may affect the result, such as unshielded private light sources and sky glow. This project aims to find measures that can help reduce the negative impacts of road lighting on the environment and nature. We study how the light from roads contributes to different components of light pollution, like skyglow, light trespass and luminance from the light source.


Introduction
Road lighting contributes to light pollution in large areas of Norway, especially because this is one of the few countries that uses road lighting on highways.As research shows how light pollution harms nature (1), the need to look at solutions to reduce light pollution has emerged.Between 1992 and 2017, light pollution increased by 49% worldwide (2,3).However, artificial light at night affects (ALAN) nature in many ways, and most species are affected, but in different ways.ALAN can affect foraging, reproduction, habitats and migration.(1,4,5).There are ways to reduce the negative effects of this type of pollution on nature (6), like limiting the light levels, installing timers, managing the spectral power distribution, and shielding the luminaire.This project was initiated by the Norwegian Road Authorities (SVV) in 2021, and the collaboration includes the Norwegian Institute for Bioeconomy (NIBIO) and the University of South-Eastern Norway (USN).The aim is to find the most appropriate and effective measures that can help reduce the impacts of road lighting on the environment and to be able to evaluate the zone of influence on insects from road lighting.USN is responsible for the part considering sustainable lighting design and ways to reduce the effects of road lighting in Norway.NIBIO focuses on how road lighting affects insects.In the initial part of the study, pilot studies of existing light levels in the side area of the road were performed.This specific work concentrates on the distribution of street lighting into the landscape, and the different components of light pollution, such as skyglow, light trespass and direct light from the luminaire.
Figure 1 Illustration showing some of the considerations that must be taken when designing sustainable street lighting, where insects are the main focus in this project, other species are also affected, and so are the view of the natural starry sky and northern lights.Ill.Jamal Safi.

Method
To gain insight into the distribution of light beside roads, a pilot study was conducted on Haldenveien in Frogner, close to Oslo, the 25.10.2022 between 19.00 and 21.00.Light measurements were done on two transects beside the road.One in the forest and one on a partly open field.On the field, the measurements had to be taken on the side of the field, to not destroy the crops.The road lighting was the most prominent light source in the area, but some farms with luminaires were present at a distance of a few hundred meters.The transects were on opposite sides of the road.The forest transect had the light pole closer, and the light distributed from the back of the luminaire, while the transect on the other side of the road was further away from the light pole, and the light distributed from the front of the luminaire.The measurement was taken horizontally at 1.5 meters.First measurement was taken beside the road and then repeated every 10 meters, increasing the distance to the road, until we reached a place where the light meter did not indicate any further decrease.The weather conditions during the measurements were temperature around 5 degrees C, overcast and cloudy (approx.80% cloud cover).The light measurement was carried out by Lysteam AS with the light meter GL Spectis 1.0 Touch + Flicker (GL Optics, Poland).The instrument can give full spectra and thus, the measured illuminance can be re-calculated to express irradiance or spectral irradiance.In the presentation of data in this article, photometric units are used since the weighting spectra for ecological effects are mostly unknown.Images were taken to show the situation in the field we were analysing.The luminaire at the road was a Philips BGP764 LED 360/740 DM32 SR with an output of 205 W and a stated colour temperature of 4000 K, measured colour temperature was 4062 K.The results showed that due to the road optics, designed to avoid stray light, the light levels decreased relatively fast as the distance to the light source increased, especially in the forest, where, not surprisingly, the trees shielded the lights.The direct light from the road lighting might not have been the most prominent addition to the light pollution in the open landscape, however, the measurements did show some light influence from the road up to around 160 meters from the road, although the levels were below 0.1 lx.We also know that moonlight (with light levels up to 0.1 lux) affects many species, like rodents, who forage during new moon (7).The reflected light from the asphalt contributes to light pollution and affects greater distances.The strong luminance directly from the light source might also be affecting insects and animals.This light is seen at very long distances, while not being measured on an illuminance meter.
There were several additional sources of light pollution in the area that may have affected the result, such as an unshielded light source on a nearby farm, sky glow from both Oslo/Skedsmokorset and Oslo Airport Gardermoen.At transect 2, 160 meters away from the road, the measured light towards the unshielded light source of the farm (seen in the picture, Figure 5) and towards the airport was greater than when the light meters were directed towards the road.In transect 1, 50 meters away from the road, the light levels were slightly higher measured up towards the cloudy sky (0.002) than measured towards to road (0.001).

Conclusion and further work
The most important result of the light measurements was that the observations provided a basis for ideas and discussion about the focus for further work.1.Although the light level was below the detection limit, the light source was visible as a point at a very large distance from the road.This observation addresses the question of whether organisms are influenced by the average light energy per area, or the intensity of a source as observed from a distance (irradiance vs. radiance).2. The preliminary measurements gave some indications of how far from the road the streetlight affects the light environment, but this needs to be verified with more measurements under different types of weather, with greater control of other factors that affect light pollution, different types of road fixtures (lamp types on the road, car headlights), and light pollution from sources other than the road.Here, for example, cubic light measurements in combination with luminance photos can be useful.This can give insights into what factors of light pollution affect an area most, the direct component, the reflected component from the ground, or the sky-glow, which is highly dependent on the particles in the air.

1 .
Transect 1, forest:  The results from the light measurements showed that the light levels dropped from 8.2 lx by the road, to 0.25 lx 10 m from the road.At 50 m from the road, the road light did not influence the measured light level, due to a natural shielding of trees and bushes.On the other hand, light reflected from the cloud-covered sky could be observed when the light meter was directed toward the zenith.Also, at some positions, you could see the high luminance point from the luminaire.

Figure
Figure 2The two transects and the location of the measurement area.

Figure 3 2 .
Figure 3 Illuminance in distance from the road, forest-transect.

Figure 4
Figure 4 Illuminance in distance from the road, partly open transect.Distance (m)

Figure 5
Figure 5 Image from approx.160 meters from the road, with light from streetlamps, private outdoor lighting and sky-glow.