Insects | Amphibians | Reptiles | Birds | Mammals | Humans
The effects of night lighting on wildlife have been
known for hundreds, even thousands, of years. Hunters and fishers
have used torches, lamps, and other light sources to attract their
quarry to them, so powerful is the effect of light on some
species. Gas-lit lighthouses have long had the reputation of
attracting marine birds by the thousands, as well. But only in the
past century, with the advent and spread of electricity, has the
problem of artificial night lighting become so pervasive.
All animals and plants on this planet (including
humans) are genetically adapted to regular day/night/seasonal
cycles that have, in many places on the planet, been completely
interrupted by the glow created by artificial lights. Although some
animals may capitalize on the lighting, many suffer its effects,
and one hundred years is not enough time to genetically adapt to
To understand the affects of artificial light, we must first
understand the difference between diurnal and nocturnal creatures.
Diurnal species are species that are primarily awake during the
day, and sleep at night. These include animals such as bees,
squirrels, songbirds, and even humans. Nocturnal animals sleep
during the day, and move about at night. These include animals such
as moths, bats, frogs, and cats. Artificial light affects
both, but in different ways.
Artificial light has several general effects on wildlife:
- Attracts some organisms (moths, frogs, sea turtles), resulting
in them not being where they should be, concentrating them as a
food source to be preyed upon, or just resulting in a trap which
exhausts and kills them.
- Repels some organisms, excluding them from habitat where they
might otherwise make a living. Makes it a form of habitat
- Alters the day/night patterns, resulting in not getting enough
sleep, not having enough down time for the body to repair itself,
alters reproductive cycles.
Humans can go inside and turn out the lights out to prevent
these issues, but the frogs in the pond by the streetlamp can't.
For animals that are very site specific, it's not an option to
move. They just get eaten, or fail to reproduce. For those that can
move, as more and more lighting encroaches on dark areas, the areas
that are dark enough to move TO become fewer and further between.
Artificial lighting is another form of habitat loss.
Keeping the light LOW (mounting the fixture as
low as possible) and SHIELDED (fully shielding the
light so bulbs and/or glowing lenses are not visible) cuts down on
the amount of glare and light visible to the animals, so that there
is less opportunity for them to get trapped, repelled, or have
their day/night patterns altered. Keeping it LONG
wavelength (ambers and reds) actually makes the light that is
visible seem dimmer to nocturnal animals that primarily use rod
vision. The rod system's peak sensitivity is at 496 nm, so a low
pressure sodium light, with its emitted light at 589 nm, should
seem 1/10th as bright to an animal using purely rod vision vs. an
animal that uses rods and cones to see (see Publications:
Ecological Consequences of Night Lighting, p. 33).
Changing to LOW, SHIELDED, and LONG wavelength lights also results
in energy savings. For instance, lights that are lower and shielded
often result in more lumens (light) being focused onto the ground,
rather than wasted illuminating the sky above the light.
Additionally, some long wavelength light sources such as low
pressure sodium lights and amber LEDs use a fraction of the energy
of their mercury halide, incandescent and even fluorescent
For more information on specific groups of animals affected by
artificial lighting, click on the links below: