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.
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.
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).
