Outdoor lighting and biodiversity: how to light without erasing the night

Lighting without erasing the night means using only the light that is needed, in the place and for the period it is needed. Excessive intensity, high colour temperatures, beams aimed at the sky and running all night alter the behaviour of insects, birds and other animals, as well as reducing the natural legibility of the garden.

Paths, steps and entrances call for safety. Trees, walls and water can be given scenic lighting, but they do not all need to be lit at the same time. A plan based on hierarchies reduces power and avoids a visually flat garden.

The first sustainable decision is to remove points that have no function.

Shielded luminaires directed downwards reduce light spill. Blue-rich light should be avoided, but colour temperature alone does not make an installation harmless: intensity, duration and the area lit are just as important. Sensors, timers and scenes allow the light to be switched off after the period of use.

The choice should take account of reflection off pale paving and water, which can amplify the effect.

Hedges, copses and boundaries connected to the landscape should keep unlit zones. Even in a lit garden, it is possible to create dark continuity for movement and shelter.

Maintenance should check the aim of the luminaires as the plants grow. A spotlight that was unobstructed at first may end up hidden and be redirected towards the crown.

The lighting should be reviewed as trees and shrubs gain volume. Branches may start to intercept beams, reflect light towards windows or create very intense patches. An annual night-time inspection makes it possible to correct angles and remove luminaires that no longer serve a function.

It is also worth measuring actual hours of use. If a path is no longer used after 11 pm, keeping the whole network lit until morning adds no safety. Scenes and gradual switch-offs give a better answer.

Lighting every tree, keeping the network on until morning and using more intensity than necessary are common mistakes. Beams aimed at the sky, at water, at tree cavities or at sheltering areas should also be avoided.

At Diaplant, the lighting is fine-tuned on site, at night, after installation. The test makes it possible to reduce points, correct angles and preserve dark zones without compromising paths and entrances.

Good outdoor lighting does not compete with the night. It makes use safe and reveals a few elements, letting the rest of the garden breathe.

• How do nature-based solutions contribute to biodiversity in cities? (2025).
• European Commission. Pollinators and EU Pollinator Monitoring Scheme. (2025).
• Owens, A. C. S.; Lewis, S. M. The impact of artificial light at night on nocturnal insects: A review and synthesis. (2018).
• Boyes, D. H. et al. Towards a mechanistic understanding of the effects of artificial light at night on insect populations and communities. (2022).
• Colours of the Night: Spectrum-Specific Impacts of Light Pollution on Biota. (2025).