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Turns out that you can do indoor farming these days via hydroponics and specialised LED lights. My mother, who has a large garden, warns me from exploring this as a hobby. She mentions that 'plants need to sleep too' and that having a LED light on them 100% of the time might be bad for them.

Is there any sense in this? Is it true that plants would grow suboptimally if the sun was on them 100% of the time or would they in fact grow quicker? Is there any research on this?

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The quote as phrased is a bit non-sensical really because it mostly hinges on what you define as 'sleep' or 'rest'. Plants, like most living things, including us, are far from dormant at night.

It's true that diurnal patterns govern the behaviour of most, if not all, living things that are exposed to them (1). Plants are no exception to this.

For example, photosynthesis is a 2-component process. With the so called 'dark' and 'light' reactions of photosynthesis (more correctly "light-dependent" and "light-independent"). Though both happen during the day and night, it is at it's peak during peak sunlight.

In CAM plants, to avoid dessication, there is differential carbon fixation because the stomata are kept shut during the hot daylight hours.

Respiration however, where the produced food is converted to energy, primarily happens at night.

The Khan Academy has a great 'walkthrough' of the steps of photosynthesis: https://www.khanacademy.org/science/biology/photosynthesis-in-plants/the-light-dependent-reactions-of-photosynthesis/a/light-dependent-reactions

(1). The diurnal course of plant water potential, stomatal conductance and transpiration in a papyrus (Cyperus papyrus L.) canopy https://link.springer.com/article/10.1007/BF00379885

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  • $\begingroup$ The light-independent (or 'dark') reactions take place in the light, not at night. The production of ATP and NADPH by the light-dependent reactions is not separated in time from the fixation of carbon dioxide. How would the plant store all of the ATP and NADPH? Also carbon dioxide fixation produces carbohydrate not hydrocarbon. $\endgroup$ – Alan Boyd Jul 3 '17 at 18:09
  • $\begingroup$ Right you are. Wrote that answer in a bit of a rush, edited it now. $\endgroup$ – Joe Healey Jul 3 '17 at 18:28
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Yes, as long as there is light there is photosynthesis going on. The light/dark cycle allows your plants to process what they created and rest a bit. It is good for them and encourages adequate growth.

http://www.popsci.com/blog-network/our-modern-plagues/do-plants-sleep

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    $\begingroup$ Could you please add some sources for this? $\endgroup$ – Harris Jul 3 '17 at 13:47
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Plants need no rest as long as there is a constant source of nutrients and they are kept in the right environment they will not be damaged or die or get "tired". However Plants can be subjected to the seasons where they rest in the winter ect. due to the lack of resources and essential elements.

You can however make them grow better by subjecting them to blue and red light as this is the light they respond to the best out of the whole spectrum of light.

https://www.popsci.com/blog-network/our-modern-plagues/do-plants-sleep https://homeguides.sfgate.com/24hour-light-schedule-bad-plants-95954.html

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