My neighbor has floodlights shining into my garden all night. It’s annoying for many reasons, but I am also wondering if artificial light affects plant growth?
Washington State University professor and Extension horticulturist Linda Chalker-Scott addresses this issue in her factsheet, “The Myth of Night Light.” Here is an excerpt:
“When urban trees, especially street trees, are exposed to extended light periods, those leaves and buds nearest the source perceive an endless summer and keep on growing. While this phenomenon is difficult to see initially, in the autumn it is quite distinctive: affected leaves retain their green color while
those leaves under natural conditions have already started to senesce and change colors (see photo). When the first autumn frosts arrive, these green leaves die and the tree loses the resources that normally are scavenged during senescence. Recent research has demonstrated that high-intensity light sources,
such as high-pressure sodium lamps, have the greatest impact on delaying leaf senescence and subsequent dormancy of landscape trees.”
Similar information is available from Purdue University Extension, in the article “Does Night Lighting Harm Trees.” It includes a list of woody plants and their degree of sensitivity to artificial light pollution. It also mentions which types of lighting have the greatest and least potential effect (incandescent and high pressure sodium lights have a greater effect than fluorescent, mercury vapor, or metal halide). It is interesting to note that continuous lighting, as opposed to lighting that goes off at some point during the late night, is especially damaging:
“The foliage of trees grown in continuous lighting may be
larger in size and more susceptible to air pollution and
water stress during the growing season because the stomatal pores in leaves remain open for longer periods.”
There is additional information about the effects of light pollution on animals, humans, plants, and the environment as a whole, on the website of the Florida Atlantic University Observatory, and from the International Dark Sky Association.