Awhile back, I bookmarked a FAQ from Purdue University Extension about light and trees.
Does Night Lighting Harm Trees?
A few months ago, the Kindergarten Academy in Mechanicsburg planted new trees around the renovated school and parking lot. A few days ago, I noted many of the new trees looked in bad shape. We’ve had a hot and dry month. I thought I’d take a few minutes and check out the trees, with the schools lighting in mind, to see if the all night lights had any part in the condition of the trees. It was very surprising to find, the side of many of the trees facing the parking lot lights was brown and dying while the opposite side was still mostly green and healthy. The trees most severely affected were the Tulip Trees, as predicted by the table of tree sensitivity in the article. This happened in such a short time, over only a couple of months. I found that surprising. Even the Oak Trees were affected so I suspect, since they are low sensitivity to ALAN, it may be akin to the lightburn growers using artificial grow lights experience. The CCT of the lighting at the school measures approximately 6000K. They do not seem to be what was spec’d in the plans so I can’t be sure what brand or spec’s they have to identify the true SPD.
Just up the street from the new trees were two big trees exhibiting major stress. Again, as predicted by the Purdue FAQ, there was a street light embedded in the tree. Where the light fixture exposed the leaves to its light, that quadrant was mostly dead with brown leaves. The far side of the tree, away from the street light, was still heathy and green. The street lights are still HPS although additional street lighting at the Elmwood School, adjacent to one of the stressed trees is high CCT LED.
The Purdue FAQ does not include LED lighting of various SPD’s and I hope to get some updated information.
Once you see the effect that all night light have on trees, you can easily recognize it! Check it out and let me know if you are seeing the same thing in your communities! Amazing! Of course the question becomes, if it is doing this to trees, what is it doing to people?
– Mark
Night Lights 