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Light at night: Which characteristics of street lights are important for insect diversity and bat activity?

 

This project aims to provide information on how different characteristics of the luminaires and the light color affect insects and bats. For this purpose, artificial light sources were set up for the first time in dark locations where artificial light has had little effect so far. Information on the effects of light on animals is crucial for taking measures against light pollution.

 

Modern LED luminaires help achieve energy-saving goals. Their brightness can be adjusted (dimmed) as desired. The more they are dimmed, the more energy is saved (40% dimmed = 40% energy savings).

Dimming of LED lights can be controlled electronically as needed. Street lights can be programmed to emit 100 percent of the amount of light only when necessary, for example, when there are cars on the relevant section of road (Fig. 1). This saves energy and makes an important contribution to darker nights, because the day-night rhythm is important for many plants and animals.

 

But LEDs can also have negative impacts on the environment. Cold-white LEDs, which have a bluish glow, save a particularly large amount of electricity, but attract numerous insects that react to blue light. The insects are trapped by the light and die. This is less the case with warm white light colors (Fig. 2).

 

Two species of moths attracted to night light

 
 
 

The design and shape of LED luminaires also affect how visible the light is, potentially having a negative impact on living organisms (Fig. 3). What influence the shape of the luminaire has on the environment is still poorly understood.

In this experiment, we investigate luminaires with different properties and how they affect the diversity of insects and the activity of bats. The latter are important natural enemies of insects.

 

We have chosen three dark sites (Lägeren, Birmensdorf, Alptal) where there is normally no artificial light. We test two designs of enclosures, one with a screen that distributes the light and one without. We also vary the light color temperatures (warm white, white, cold white) and light intensities (50% or 0% dimming).

Insect traps are mounted under the lights (Fig. 4) (see also: How does an automatic insect trap work?). This allows us to determine the number of flying insects attracted to the lights. We use ground traps to catch insects and other invertebrates running on the ground. Bat acoustic signals are recorded (echolocation).

 
 

What's New? This project will provide results on the effects of individual and combined luminaire characteristics (light color, light intensity, and light emission) on insects and bats (Ex. Figs. 5-6). Such information on combined effects of light properties is a prerequisite to effectively reduce light pollution.

The experiment will be conducted during the next 3 to 5 years to measure the longer-term effects of LED lights on insect life.

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