# how many hours of illumination is too many?



## louis_last (21 Dec 2008)

When it comes to how many hours you should light your tank for I have seen many contradictory figures, all of which presumably take into account the needs of both the plants _and_ fish, shrimp, etc. 
In a tank with _only_ flora and no fauna is there any reason why you shouldn't leave the lights on 24 hours a day to promote growth? this can certainly be done for many terrestrial species, is there any negative effects from doing so in an aquarium?


----------



## aaronnorth (21 Dec 2008)

plants need a rest aswell as fish. There will become a point at which the plant can do no more and it wont be able to carry salts around and it will die.
8-10hrs is fine.

EDIT: typing error - I mean salts not slats lol


----------



## Goodygumdrops (22 Dec 2008)

Forgive my ignorance of scientifc matters,but do plants not produce o2 and take in co2 in daylight,and the other way round during darkness?Or something basically like that.I would have thought that it was equally as important to have a period of darkness,purely for optimal plant health.
I'm sure you could push it either way.I'll look forward to the definitive answer (ceg  ) as I'm interested.
As for negatives,I would imagine algae and the need to dose more ferts (more expensive),and a higher leccy bill.


----------



## ceg4048 (22 Dec 2008)

louis_last said:
			
		

> When it comes to how many hours you should light your tank for I have seen many contradictory figures, all of which presumably take into account the needs of both the plants _and_ fish, shrimp, etc.
> In a tank with _only_ flora and no fauna is there any reason why you shouldn't leave the lights on 24 hours a day to promote growth? this can certainly be done for many terrestrial species, is there any negative effects from doing so in an aquarium?


Yes, there are a couple of good reasons. Algae are plants too and you will basically be promoting _their _growth much more so than the higher plants. As Aaron mentioned, Macrophytes only require about 8-10 hours of photoperiod. You can see this demonstrated in some stem plants as they fold up their leaves in the late afternoon.

Plant cells are always consuming energy 24 hours a day. Using energy requires the burning of carbohydrates with O2 and the expulsion of CO2 as a by-product. As a result the plant must produce carbohydrates via photosynthesis to support the cell metabolism. Photosynthesis requires the consumption of CO2 and the expulsion of O2. In order to be on the plus side of this balancing act the plant must produce more carbohydrates via photosynthesis than is consumed by all cells during any 24 hour period. During the nocturnal period the plant shifts the use of its facilities to the production of other things such as various proteins or enzymes. It's only because of the lack of photosynthesis in the dark that we observe a _net_ CO2 production and a _net_ O2 consumption by plants in the dark.

Algae don't have the complex machinery of higher plants so they have fewer restrictions and are encouraged by more light.

Cheers,


----------



## louis_last (22 Dec 2008)

Thanks a lot for the detailed explanations chaps, I wonder how the terrestrial plants that can be grown under 24 hour lighting are adapted in order for this to be possible? I know they need a day/night cycle to flower but they will supposedly just keep on going under 24 hour lighting in the 'vegetative' state.


----------



## Goodygumdrops (22 Dec 2008)

What plants are they Louis?(ot having a pop btw,genuinely interested).


----------



## louis_last (22 Dec 2008)

hemp.


----------



## Goodygumdrops (22 Dec 2008)

Oh right,I had no idea that was on 24 hours a day.Now you come to mention it though,is it grown under a different light spectrum,it's like an ultra violet lamp isn't it,like a sunbed?


----------



## Ed Seeley (22 Dec 2008)

I think it might be best not to have a discussion of the methods of growing that particular group of plants here, for obvious reasons!  Suffice to say that a number of plants grow very well under 24hr lighting and a large range will certainly do no worse than a 16 hour day.  

It may well prevent or encourage them to flower depending on whether they are short or long day plants.


----------



## Goodygumdrops (22 Dec 2008)

Well,I just didn't know anyone grew any type of plant under 24 hour lighting.I can see why they would though,so something would just grow and grow and grow.Would you want that happening with your aquarium plants though,the pruning would be a pain in the arris.
PS,sorry Ed,that's the last on the subject from me.


----------



## Ed Seeley (23 Dec 2008)

Goodygumdrops said:
			
		

> PS,sorry Ed,that's the last on the subject from me.



No prblems carrying on this discussion about plants in general, it's a very interesting subject - I just don't think discussing how that particular plant is grown is the best thing on an open forum such as ours.


----------



## scottturnbull (23 Dec 2008)

I've grown similar plants under long photo-periods. Tomatoes are very similar to the plants mentioned earlier, and during the initial growth period, can be grown in a 24 hour photo-period. It's debatable whether they actually benefit from the additional hours of daylight, or whether it's just a waste of electricity. 16 hours is usually enough, for good vegetative growth.


----------



## Ed Seeley (23 Dec 2008)

The only study I've seen on it was done at my old uni, York, where they grew Arabidopsis (a small weed used for a lot of molecular studies and other things as a model organism) under various regimes.  Those under 24 hour lighting grew so well that ran short of water and nutrients!  It's really going to depend a lot on the plant's physiology.


----------



## louis_last (23 Dec 2008)

Interesting.


----------

