Lighting Guidance

September 12, 2018

Lighting Guidance

Insects around metal halide light Pat Waring

Most rivers in the London region are designated as wildlife corridors. The Thames as a Site of Metropolitan Importance for Nature Conservation (SMINC) has the highest designation. Yet throughout the night it receives wasted and unwanted light pollution from residential and commercial properties.

Light from buildings spills more than 200 metres onto the river Thames and the vegetation lining Barge Walk. Light affects the wildlife corridor, illuminates the water, and the tree canopies that only bats (and other wildlife) are using.

Bats such as Daubenton’s bat use river corridors to move to their foraging areas and roost sites. Light pollution causes fragmentation of the corridors and inhibits movement of light shy species. Bat retinas are specifically adapted for low light conditions.

Insects form the basis of bat prey. They are also important for all bird species in order to feed their young. Insects can be attracted to light. Lamps with a high ultraviolet (UV) content can “hoover” up to 75% of the insects from a habitat. This is called the vacuum effect. Around one third of these insects will die.

The Bat Conservation Trust state:

that smarter lighting, rather than less lighting, is key to mitigating the effects of light pollution. Light should only be erected where it is needed, illuminated during the time period it will be used, and at levels that enhance visibility. Any bare bulbs and any light pointing upwards should be eliminated. The spread of light should be kept near to or below the horizontal.

Narrow spectrum bulbs should be used to lower the range of species affected by lighting and light sources that emit ultra-violet light must be avoided. Reduce the height of lighting columns as light at a low level reduces ecological impact. For pedestrian lighting, low level lighting that is as directional as possible should be used and below 3 lux at ground level (preferably 1 lux).

Other solutions:

Light shields: trees and vegetation should be retained as they act as light shields.
Don’t use reflective surfaces under lights;
Use controlled management systems (CMS) to switch off the lights when not in use; dimming capacity, lumimotion - if it is near sensitive habitat.
Lights should have appropriate shielding, back plates, barn doors, its done in LBRuT (LB Richmond);
No lighting of historic buildings or structures;
Concerts with lighting, fireworks etc. should only be scheduled for the end of August, we found the smoke affected the bats more than bangs; and
Use narrow spectrum, avoid white and don’t use UV light to minimise the range of species affected by light

Any new lighting proposal, which may have an impact on a water body or green space, should be accompanied by a statement to show that there will be no impact on any species that may be using that water body or green space. A statement should demonstrate as to how any impact will be mitigated. This statement may require evidence such as a bat survey. Post development monitoring may also be required.

Lights should not be on automated switching but should be extinguished after the last user. So basic- but now ignored - as these sites are managed by a mixture of Trusts and Friends Groups so there should be something in the wording of the lease/management agreement to state that car park lights should be switched off as soon as possible.

When designing lighting, start at the feature (the river) and work backwards with 0 lux at the feature. This may mean using low transmittance glass on windows, sensors and vegetation screening. Black netting can cut down some transmission from sports pitches, unfortunately its mainly used to cut down glare for people not wildlife.

Case study: Warren Footpath

The Thames Landscape Strategy’s London’s Arcadia Project implemented a lighting system designed at 20 lux ambient light level (lower than the standard 55 lux) with LEDs at 30 watts (streetlights are normally about 70 watts). Dimming regimes were installed and individual lights dimmed to the lowest level, when the lamps were not in use. The system works because it is dynamic in nature and spillage can be directed away from the features used by bats, i.e. the vegetation and water remain dark. This broad spectrum light however can still be seen by bats and will alter their behaviour.

A study in the Netherlands is experimenting with narrow spectrum light which may have less of an impact on bats though may not suit all human situations where colour definition is needed. see more downloads page https://www.furesfen.co.uk/recommendations/ including Spoelstra-et-al_2017_Response-of-bats-to-light-with-different-spectra.pdf

Urban gradient