hours of dark


Prolific Poster
Aug 2, 2005
I was wondering how dependant on dark periods plants are. I know they use 02 at night, but if the lights were left on, would this prevent them from doing so? All algae issues aside, are there any ill effects to leaving lights on 24 hours a day? If so, how do plants in the north cope when they get 24 hours of light at certain parts of the year?


Ian H

Guru Class Expert
Jan 24, 2005
Shipley, West Yorkshire, UK
Re: hours of dark

It is generally considered important that plants get a dark period. It isn't a rest period as such, but due to the absence of photosynthesis a modified chemical reaction occurs. I have read that the majority of plant growth occurs during lights out, although I have never observed this on a scientific basis.

Some plants physically start to close their leaves even before lights out in my tank. I've always assumed that this is a mechanism to reduce the light falling onto the leaves.(They are ready for bed :) )

In the main the plants we use in our tanks are tropical or semi tropical. These plants are used to roughly equal photo periods of light and dark.