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Where are the fireflies?

Biodiversity By Roxana Rakhshani, Senior Lighting Designer – 06 February 2023

Illuminated firefly on a rock against a dark sky


Roxana smiling to camera stood in an office space

Roxana Rakhshani

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When was the last time you saw a firefly? The answer to this question is most likely “never.” However, when asked "How often do you see insects gathered around lamps?", your answer is probably “always.”

While artificial light at night (ALAN) allows us to increase the duration of our activities through the night, it has seriously affected the environment for many nocturnal species by interfering with their natural daily and seasonal light cycles. Most of us are too busy to consider the small creatures living around us, the impact of our habits on insects and the reason we need to act responsibly towards them.

Importance of insects
Listed below are some of the main reasons we should consider the importance of insects in our lives:

  • Pollinating plants: It has been estimated that around 80% of UK plants are pollinated by insects. This figure includes human food and crops. Any impact on the insect population will directly affect human beings’ direct food supply.
  • Breaking down and decomposing organic matter: Nature’s way of dealing with waste is through insects and micro-organisms which involves turning dead animals and waste into healthy, fertile soil. Although not all insects are involved in this process, by reducing the number of insects, the natural waste cycle will be affected.
  • Animal food: The diets of many birds, fish and mammals consist of insects. If they were to die out, our ecosystems would collapse.
  • Human food: Two billion people around the world consider insects a normal source of food, as they are packed full of protein, vitamins, and minerals.
  • Diseases: Although it might not sound positive, insects can spread illnesses and diseases. These illnesses are a natural way of controlling populations of varied species. Reduction or increase in insect population may lead to a change of balance in the population of other species.

Insects and lighting

Insects, like the rest of the natural world, are sensitive to light. Phototaxis is the term used for the movement of species when exposed to light. Insects with positive phototaxis are attracted to light while negative phototaxis applies to insects that are repulsed by light.

Artificial lighting alters these natural behaviours in nocturnal species:

  • Feeding: Insects with negative phototaxis cannot survive without darkness and are therefore unable to find food in the presence of artificial lighting.
  • Navigation: Compared to artificial lighting, moonlight and starlight are directional. Artificial light sources throw light in various directions, making it impossible for the insects to navigate. This results in them dancing around a light source that will eventually kill them.
  • Predator avoidance: Using darkness for safety is a natural way for nocturnal insects to avoid predators. Overly lit spaces make it hard for insects to avoid predators - this will cause a significant reduction in their population.
  • Reproduction: Some insects use the polarisation of light to find the water they need to breed, as light waves line up when reflected from a smooth surface. The reflection of artificial lighting from unnatural surfaces produces a false effect for insects. Some of these insects such as mayflies, only live for a day, and end up laying their eggs in the wrong place, which will cause disruption to their entire population.

Smart design

Unlike many other types of pollution, lighting is the easiest to address. In theory, once a light is switched off the problem is solved, and nature will find its way to recover gradually. But this is easier said than done. The increase in human population makes it impossible to entirely switch off all the lights. However, although the use of artificial lighting is inevitable, there are a few steps that can be taken to minimize the negative effects.

  1. No lighting: Human eyes adapt to darkness. Our provisional eyesight enables us to navigate in the dark using minimum light. Overusing light endangers human evolution through the loss of our primitive ability to navigate in the dark.
  2. Colour temperature: White LED lights are designed to create a daylight effect. The use of LEDs on the blue side of the spectrum alters insects’ night-time activities by affecting their day/night sensors. Studies show that the reaction to colour temperature varies between different insects. Although the common belief is that insects are more affected by cold light, studies show that some species react to the warmer spectrum as well. The use of biological study prior to the design provides a better understanding of the suitable colour temperature for different environmental areas.
  3. Control systems: Use of control systems alongside smart sensors will provide the opportunity to control both colour temperature and illuminance level at the same time following the surroundings and natural light. The lights can be switched off or dimmed when needed and the colour temperature can be changed depending on the season and time of the day.
  4. Avoid flickering: The use of high-quality and compatible LEDs and drivers can reduce the visible and non-visible flickering that has a significant effect on all species including humans.
  5. Design: When designing the lighting layout, it’s vital to locate lights for minimal interruption with the natural habitat. Reducing light spills to the background and the use of focused lighting integrated with architectural details can reduce the negative effect on insect habitat.
  6. Blinds and curtains: Simple use of blinds and curtains at night-time will reduce interior light spills into the exterior space. Curtains and blinds can be connected to the control system and programmed using an astronomical time clock or daylight sensors.

Most of the written standards are guidelines, not mandatory. There clearly is such thing as over-lighting, hence why we, as lighting designers should ask ourselves the most important question - “Does it need to be lit?”