While reading this article online something said on it made me wonder.

Also, there have been suggestions and a Dawn / Dusk type of ramp up and down to simulate the slow changes in the sun have value, but we have not seen solid universal data in this regard to date...

It made me wonder if we are simulating the sun in a dark room for growing the plants with the help of red, blue, and a little bit of far-red light, what will happen to the plants if we keep the ideal conditions for which the plants carry out photosynthesis whole day? Does it affect its yield or the plants die out quick?

I am an engineering student working on indoor farming, my knowledge of botany is the same as a high school student. So if I am wrong please tell me.

  • $\begingroup$ Do plants 'stay awake' or fall asleep? $\endgroup$ – user438383 Apr 11 at 16:14
  • $\begingroup$ During the night they are mostly inactive. $\endgroup$ – Momobear Apr 11 at 16:17
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    $\begingroup$ Welcome to Biology SE! I'm afraid that your question as currently posed is a bit confusing. Can you please try to explain more of the context of your question and what you understand about the mechanisms at play? $\endgroup$ – jakebeal Apr 11 at 16:21
  • $\begingroup$ @Gurkirat perhaps edit your question to say 'active' (and maybe specify what kind of activity), since plants don't go asleep or stay awake. $\endgroup$ – user438383 Apr 11 at 16:44
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    $\begingroup$ I don't know the "correct" answer (I don't think one answer covers all plants) but I have lost plants under lights when I have forgotten to cycle (on/off). They had water, food and fresh air, but some need darkness to perform optimally. Certainly blooming is often day-length related; some plants need short days, some need long. $\endgroup$ – anongoodnurse Apr 12 at 5:09

Ideal conditions for photosynthesis

You mention ideal conditions to carry out photosynthesis, I would just like to point out that this includes carbondioxide levels, temperature, and nutrients as well as light.


As anongoodnurse mentions performance might be measured by blooming which, in most flowering plants, has a day-light related component. However, for general growth increasing daylight over the 'natural' day length can often increase yield.

Daylight Cycles

The important point to note is that plants do 'ramp up' at dawn getting ready to start photosynthesizing (for some plants with temporal photosynthesis mechanisms (see CAM photosynthesis) this can be even more important). The reason plants do this is because plants can suffer from 'photobleaching' which can be considered similar to sunburn in humans, if they are not ready for sunlight. Getting 'ready' can involve lots of things including opening stomata (pores) to let CO2 in, changing which metabolic pathways are active, and moving about chloroplasts inside cells. Plants 'figure out' how and when to ramp up based on circadian rhythms which work well on 24 hour clocks and slight changes over time. Thus 12 hrs to 16 hrs can be a big change, particularly if the change happens by lights coming on earlier. Additionally, the 24 hour 'clock' means that plants will do better with 18hr light then 6hrs dark cycles than 36hrs light 6 hrs dark, because the total cycle length should be about 24hrs.

Photosynthesis Side Effects

Finally, constant photosynthesis does take its toll on plants as photorespiration accompanies photosynthesis. In C3 plants (most crops) this can reduce photosynthetic output by 25% whilst creating ammonia as a byproduct. The ammonia needs to be detoxified as a build up in the cell can cause cell death. Thus plants need enough 'respite' from photosynthesis to deal with photorespiration byproducts or they will suffer.

  • $\begingroup$ Thanks a lot, I was looking for an answer like this $\endgroup$ – Momobear Apr 12 at 21:29
  • $\begingroup$ Adding my thanks, too. +1. (Only had a vague idea of the need for darkness, but not the consequence of its absence.) $\endgroup$ – anongoodnurse Apr 14 at 1:44

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