In the Dark

DarkSky International is a non-profit organisation that is the world authority on light pollution. Its focus is to reduce light pollution of our night skies and reduce the harmful effects of light pollution on humans and wildlife.

The main culprits of sky glow and light pollution are streetlights, electronic advertising boards, car parks, sports lighting, commercial greenhouses and factories, with many other sectors also polluting our starry night skies.

Streetlights (as an example) use colour temperatures between 4000ºK and 6500ºK and with varying light intensities dependent on location and intended use. These can vary between 3000 lumens and 100,000 lumens per fixture.

Another source of light pollution is high-powered LED floodlights, which are widely used in all areas of exterior lighting, from residential and commercial security to heavy industrial, and are used in their millions. These products use very cool colour temperatures ranging from 4000ºK to 6500ºK or 7000ºK and beyond. They typically have a beam spread of 120°, which is the standard for Chip On Board (COB) LEDs, but rarely have the aiming of the product set correctly.

Too much light can cause veiling luminance, which is the measurement of disability glare within a scene. The incorrect use of luminaire type, mounting location and aiming can make a greater hazard, and where such luminaires would be used for security purposes would mask the hazard, rather than highlight it. Flood lights tend to be controlled via motion sensors, they can usually be substituted with good landscape lighting design.

By following a few simple steps, we can all play a part in using lighting in a more considerate and responsible way.

In landscape lighting, we also use several different accessories, including glare shields, hex louvres, and internal filters. These all help us to create the beautiful designs we do, but also further reduce light spill, unwanted glare, and potential light trespass.

The human eye is extremely good at adjusting to very low light levels, but high contrast levels need to be carefully decreased through thoughtful design.

Studies have shown that streetlights installed close to trees, and which use unnecessarily high light outputs with cool blue daylight colour temperatures, can often cause growth anomalies and unseasonal leaf drop through confusion. This repeating cycle can have a long term and devastating effect on trees and can eventually lead to death.

Plants and trees require all three ultraviolet wavelengths for natural growth, but the amount and quantity that is used in good landscape lighting design is nowhere near enough to do any harm to growth. Commercial greenhouse growing, on the other hand, requires carefully controlled lighting for both growth and flowering. It is these types of installations which use high outputs for efficiency and maximise growth. Growth inhibition, disruption of circadian rhythms, or stress response are all referred to with the excessive exposure of blue light, which applies to high colour temperature and output luminaires. Any other information to the contrary should be taken with consideration and further investigation.

A trained and experienced landscape lighting designer would use an artistic approach rather than a prescriptive one. This design principle would include safety, security and aesthetics within the overall design, meaning high-powered floodlights are not usually required.

Good landscape lighting design will typically use fixtures with wattage outputs of between 0.5w to six watts, which equates to around 30 to 600 lumens per fixture, with many fixtures being used at around the one-to-three-watt range, or 90 to 300 lumens. These ultra-low outputs are far lower than a streetlight which starts at around 3000 lumens.

Garden and landscape lighting colour temperatures between 2700ºK and 3000ºK provide the most realistic results. These colour temperatures highlight the natural colours that already exist within the landscape. 3000ºK in particular, is my preferred choice of colour temperature, with other leading landscape lighting designers around the world preferring this colour also, as it highlights most tree and shrub foliage the best due to saturation levels. This is our choice of colour as it works extremely well throughout the seasons with the ever-changing leaf colours.

From spring 2025, Foxholes Care Home in Hitchin, Hertfordshire will be opening its newly landscaped main front gardens each night for people to visit and see for themselves how good lighting design using extra low voltage and low wattage lights can enhance an area without causing damage to the night environment and surrounding wildlife.

This project will include a combination of 2700ºK with mostly 3000ºK being used via up and downlighting throughout the project. There will also be a Dark Sky setting for most areas after 10pm when the main lighting will be turned off via timed controllers. No booking will be required, so please feel free to visit. Seeing is believing. (Please note: These settings and descriptions are subject to final approval).

The five principles for outdoor lighting from DarkSky International

Useful – every light we use has a purpose in the overall composition.

Targeted – all lights are aimed with accuracy.

Low level – lights can be as little as 30 lumens or less.

Controlled – dimmed, sensors, timers, or simply off when not being used.

Warm CCT – 3000ºK and 2700ºK is perfect for landscape lighting.