I understand (1, 2) that whether and how much time a plant needs to be in the dark depend on the type of plant. What's the answer for the olive?

The reason I ask is that my city shines lights up on the branches and leaves of an olive tree on my corner all night and I wonder whether that's unhealthful for it.

2 Answers 2


I think the jury's still out for a final verdict on the effect of light pollution on plants. In the UK, many of our street lamps have been replaced with LED lighting - research is ongoing in the matter of how that may affect plant growth when compared to the old sodium lighting. I found this article https://www.sciencedaily.com/releases/2015/03/150316093003.htm which may of be of interest, but it is not an exhaustive study of the effects on all, or even many, plants, it just has a general conclusion that light pollution has some sort of impact on plant growth and flowering, Although intensive study of this subject needs to be carried out, in the UK, whether that happens or not is dependent on whether a particular university department has sufficient funds and interest to pursue it. Any studies so far have been funded by the European Research Council, so it's unlikely studies will continue here in the UK, given the intended unhelpful act of Brexit. With luck, perhaps other European countries will commit to the research.

  • This study seems to imply (but not explicitly state) the the higher intensity LEDs don't have the same effect of low-intensity sodium vapor lamps. I would also assert that the color spectrum of the two different lamps has an effect as well. Now, we don't know much about your "spotlight" other than you label it as a spotlight. Knowing the size, lamp type, etc will get a better answer.
    – Tim Nevins
    Commented Dec 5, 2017 at 18:17

Night lights are not lights. These are so low in power (compared to sun) that they should have no effect (but on nocturnal insects). Especially if it is indirect light or street lighting. Look at full moon (especially if there are moving clouds), and you will notice that also moon will have a larger effect. Spot light for monuments are some more difficult (stronger).

  • I specified in the question that "my city shines lights up on the branches and leaves of an olive tree". This is not ambient city light: it's spotlights on the tree.
    – msh210
    Commented Dec 5, 2017 at 10:23
  • @msh210 I never wrote about diffuse light, There are so many type of luminaries in the cities. For a precise answer you should really give more details. The power is very low in any case, compared the sun. Just our eyes adapt so much that we doesn't realize it. Commented Dec 5, 2017 at 14:44

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