How Do Outdoor Lights Affect Bats?

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The short answer to how do outdoor lights affect bats is that they change how bats hunt, fly and travel at night, and the effect depends on the species. Some bats gather at bright lamps because the lights draw insects toward them. Other bats avoid lit areas almost completely. A study of LED street lights found that brighter light increased activity in the first group and reduced it in the second. Lowering the light level, rather than removing it, was enough to keep the light-averse group active in the study area.

Quick answer

Light-opportunistic bats, such as Pipistrellus pipistrellus, increased their activity at brighter street lights in the study we opened.
Light-averse bats in the genus Myotis were less active under higher light levels.
At the lowest lit level tested (25 percent of original output), the study did not find a significant effect on either group.
Outdoor lights that are bright, unshielded or left on all night are the ones most likely to change bat behavior. Shielding and dimming are the two practical controls the sources describe.

The person typing “how do outdoor lights affect bats” wants

A clear answer about whether a porch light, yard lamp or path light will hurt bats, and what to change if it does. The short answer is that it depends on how bright the light is, where it points, and which bats live nearby. The sources below answer part of that question. They do not give a single safe lumen figure for a backyard, and this post does not invent one.

What the street light study measured

The most detailed source we opened is a 2018 field study published in Royal Society Open Science and archived by PubMed Central. The researchers set up four lighting levels on existing LED street lights in a suburban area: 0, 25, 50 and 100 percent of the original output. The researchers then recorded bat activity at each level. The paper states its main result directly: “Higher light intensities (50 and 100% of original output) increased the activity of light-opportunistic species but reduced the activity of light-averse bats.”

The same study reports that the 25 percent level behaved differently. In the paper’s words, “Compared to the unlit treatment, the 25% lighting level did not significantly affect either P. pipistrellus or Myotis spp.” The authors suggest that this middle setting may give people enough light for their needs while leaving dark corridors for bats that avoid light. They put it this way: “it is possible to achieve a light intensity that provides both economic and ecological benefits by providing sufficient light for human requirements while not deterring light-averse bats.”

The study is about street lights in one place, so the result is not a direct measurement of a patio lamp. Still, the mechanism it describes applies to any outdoor light: a bright source can draw in insects, and the bats that eat those insects come with them, while bats that avoid light stay away.

Why some bats come to the light

Insects are attracted to light, and some bats feed on the insects that gather there. The paper explains that some bat species are “light opportunistic” because they “feed on the large numbers of insects attracted to lights.” This pattern is sometimes called the attraction-by-insects idea. In the study, the feeding buzzes that signal a bat catching an insect increased at the brighter levels. The researchers found “significantly more feeding buzzes at 50% and 100%, compared with the 25% lighting level.”

For a homeowner, the lesson is that a bright light can change which bats are near your yard and what they do there. It does not mean every bat in the area will benefit. The study records feeding activity, and it does not say whether the bats that gather at lights are healthier or more numerous over time. The sources we opened do not cover that question.

Why light-averse bats move away

Bats in the genus Myotis avoid lit areas. The paper notes that these species “seem to be negatively affected by all types of street lighting.” When light levels were higher, activity by this group fell. Dimming can create darker routes. The authors write that dimming “might create dark refuges that light-averse bats could use for commuting and foraging in urban areas.”

This matters for a yard that sits between a wooded area and a house. A lamp that lights the whole path can block a flight route that bats used before. The study does not measure a specific yard, so it cannot say how much a particular lamp would affect a particular bat colony.

Bats in protected landscapes

A master’s thesis from Boise State University, hosted on the National Park Service site, studied artificial light and bats in Grand Teton National Park. The thesis opens by noting that “Bat and insect populations are at risk globally,” which is the reason the park studied the question. It compares bat and insect activity under different light colors and reports that red light does not seem to be an effective method of promoting bat activity. The thesis is a park-based study with its own conditions, and it should not be read as a rule for every outdoor light. We cite it here as a second source that the topic is active research and that color and intensity both matter.

Practical steps the sources support

Use less light. The bat study shows that the brightest level produced the largest change in activity. Lower output is the simplest control the sources describe.
Shield the fixture. The reduction of light spill is the main point of full-cutoff fixtures, which direct light down rather than out. A shielded lamp keeps the dark edges of a yard dark, which is where light-averse bats fly.
Use motion sensors. A light that turns on only when someone walks by avoids hours of constant illumination. The logic is the same as the street light study: less time lit means less light spill across the yard at night.
Keep dark corridors. Leave some areas unlit, especially along hedges, tree lines and water. Those edges are where many bats forage and commute.

If you are choosing between a bright floodlight and a motion-activated one, our post on solar motion-activated flood lights covers what the listings state about sensors and output. Our guide to solar security lights with motion sensors covers the detection settings the listings describe. Neither page measures bat activity.

How we chose

This post answers one question with the sources we could open and quote. We looked for a peer-reviewed field study on bats and artificial light, and for a second readable source that covers bats and outdoor light directly. We used the PubMed Central copy of the 2018 street light study and the Boise State thesis hosted by the National Park Service. We did not use news summaries of either source as evidence. Every quoted sentence was checked against the fetched text of the page it comes from. We did not look at product listings for this post, because the question is about the light itself, not a brand.

What we could not verify

We could not verify a safe lumen, lux or wattage level for a home yard. The sources do not give one.
We could not verify how bats in North America respond to the LED street lights used in the Bristol study. The study was done in a suburban area in the United Kingdom, and the species named are European genera.
We could not verify whether bats that feed at lights gain or lose over a full season. The sources record activity, not survival or population change.
We could not verify the effect of warm-colored versus cool-colored outdoor lights on bats in your area. The thesis compares light colors in one national park, and the results are specific to that setting.

FAQ

Do outdoor lights hurt bats?

The evidence shows a mixed effect. Bright light increased activity of bats that feed on lit insects and reduced activity of bats that avoid light. Dimmer light, at the level the street light study called 25 percent of original output, did not significantly change either group in that study.

Will a porch light attract bats?

A porch light can draw insects, and bats that feed on those insects may come to the area. The sources we opened describe this for street lights. They do not measure porch lights specifically.

Is red light better for bats?

The Grand Teton thesis reports that red light does not seem to be an effective method of promoting bat activity. That is a finding about bat activity in one park, not a guarantee that red bulbs are safe for every species.

What is the simplest change I can make?

Lower the output and shield the fixture so light falls on the area you need and not on hedges, trees or open sky. The street light study supports reducing intensity, and it found the lowest lit level did not significantly change either group in that study.

Should I turn off all outdoor lights?

The sources do not say that. They describe the effect of light levels and light color. Keeping lights for safety and use is a reasonable choice when the light is shielded, dimmed and used only when needed.

Are bats in my area light-averse or light-opportunistic?

Local species matter, and the sources name only a few. A regional bat group, a state wildlife agency or a university extension office can tell you which species live near you.

Bottom line

Use the least light that does the job, shield it so it points down, and avoid lighting the dark edges of your yard where light-averse bats fly. The street light study supports dimming to a middle level, and it found that the unlit and lowest-lit conditions were the most different from the brightest ones.

Sources

Rowse, E. G. and Harris, S. “Effects of dimming light-emitting diode street lights on light-opportunistic and light-averse bats in suburban habitats.” Royal Society Open Science, 2018. PubMed Central, https://pmc.ncbi.nlm.nih.gov/articles/PMC6030271/ (opened 2026-10-30)
Cole, H. “Understanding and Mitigating the Effects of Artificial Light on Bats and Nocturnal Arthropods in Grand Teton National Park.” Master’s thesis, Boise State University, December 2022. National Park Service, https://home.nps.gov/grte/learn/historyculture/upload/Cole-access-final-2.pdf (opened 2026-10-30)