# Optimizing the photoperiod



## Gomer (Feb 2, 2004)

This sorta stems from the Amano's approach at lighting thread.

Most people tend to use 10-12hr full light photo periods. I know for a fact that by the 10 and 12hr mark there are some plants that either stop photolyzing for the most part, or considerably slow down their photosynthesis. You can see this in some plants that close up towards the end of the photo period despide the lights still being on.

So my question is this. Is there some sort of general window of time that you want to keep the lights on a tank for to keep photolysis at a maximum and not have plants start to "go to sleep early".
I figure that this could 
a) give plants a foot up over algae since at the end of the reduced photo period, non of the plants slacked off
b) allow for less day to day growth on high light tanks yet still maintain healthy plants.

Any opinions on an optimal* photo period?

*Please ignore human wants of being able to see their tank light up at 7am before going to work and have the lights on till 7pm when they are home from work...etc etc.. 

Hope I am clear on my thoughts [/url]


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## gnatster (Mar 6, 2004)

One would have to observe the plants and determine the plant(s) that close up last and tailor the photo period to the needs of the late closer. Once determined set the time for slightly shorter period and then you would maximize the time the lights are on and not be lighting unnecessarily.

This optimal period would probably vary from tank to tank taking into consideration lighting type and intensity and a other growing conditions, including but not limited to, CO2 levels and available nutrient levels.


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## Gomer (Feb 2, 2004)

only some plants would close up..others, regardless of how much or little light, will not close up. many don't pearl as well, so judging them can be quite tough. 

As for tank specifics, lets consider this a prototypical 3wpg PC tank who's size makes the wpg scale appropriate.


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## pineapple (May 4, 2004)

Plants in general are odd things in that they adapt to their environment. One extreme example is the Eucalyptus tree which is an evergreen in Australia. Eucalyptus has been planted all over the world and when eventually it was planted in Russia, with its ice cold winters, the eucalyptus became deciduous.

Presumably, aquatic plants are also able to adapt to regular periods of light as well and continue to photosynthesize as long as all the chemicals needed for that reaction were present. The concept of a plant getting 'tired' and needing a 'sleep' after a hard day in the light is somewhat hard to prove. But I would not sneer at the concept. Something akin to it probably exists.

Providing enough light for plant growth, but not too much must be the aim. Hopefully viewing periods fit in with the biological schedule.

Rotala walichii and Rotala rotundifolia both exhibit nictinasty (close leaves during low or no light period) slightly after the lights come on (6:00am) and before the lights go off (5:45pm).

Experiment only would determine the optimum period for plant growth (or to facilitate less pruning or aims such as less algae) in a certain environment, with selected plants etc. What might be suitable for a Rotala sp. forest, might not work so well with a Ludwigia sp. flower bed.

Most aquatic gardener's lighting is expressly for viewing because they cannot afford dual lighting systems with high and low light on separate timers (not to mention that is a new idea here in America for many of uss).

A good topic. I can follow your line of thinking lately.

Andrew Cribb


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## Gomer (Feb 2, 2004)

> A good topic. I can follow your line of thinking lately.


Are you saying that I am normally an incoherant babbler? :mrgreen:

Any perspective from any of you plant scientists?

[/quote]


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## HeyPK (Jan 23, 2004)

The fact that some plants start to close up about an hour before the lights turn off should NOT be interpreted as evidence that they have stopped photosynthesizing or that they will only photosynthesize for a period that is one hour shorter than the photoperiod they are getting. 

Lets say we have some plants on a 12 hour photoperiod. They start closing up after 11 hours. If you reduce the photoperiod to 11 hours, you will find that they will start closing up after 10 hours. If you increase the photoperiod to 16 hours, you will find that they will start closing at 15 hours.


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## anonapersona (Mar 11, 2004)

HeyPK said:


> Lets say we have some plants on a 12 hour photoperiod. They start closing up after 11 hours. If you reduce the photoperiod to 11 hours, you will find that they will start closing up after 10 hours. If you increase the photoperiod to 16 hours, you will find that they will start closing at 15 hours.


Is this just a theory or are you saying you have done this and seen that this was the effect?


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## JLudwig (Feb 16, 2004)

Related topic....

Can you push some plants too hard? I have some dwarf Lobelia, Blyxa japonica, and H. polysperma var 'Tropical Sunset' that seem stunted, they also seem to do better growing in another plant's shade, I think I may be 'cooking' them. I need to work out some lighting changes but I do want to try an Amano style light period to see if it fixes this problem/

Jeff


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## HeyPK (Jan 23, 2004)

> Is this just a theory or are you saying you have done this and seen that this was the effect?


No it is more than a theory of mine. I have seen that plants adjust to a 16 hour photoperiod and begin to close up about an hour before. Besides, it is a well known phenonemon. Plants are known to have various circadean (about a day) rhythms. If a plant is out of synchrony with the day-night cycle it will take a few days up to a week to get back in synchrony. If a plant is kept under constant conditions, 24 hours a day, constant light or constant darkness, the rhythm of opening and closing leaves will continue, but will gradually get out of synchronization.


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## niko (Jan 28, 2004)

Plants closing:
I tend to agree that the closing of the plants does not necessarily mean they have stopped photosynthesising 1 hour or so before that. But I don't have any scientific base for my view.

Even if the light is still on some plants close anyway. I think it's just common sense to turn the lights off about that time.

Remotely similar to the plants closing at night is the increased bubbling in the afternoon. I have seen tanks that bubble only 30 min after the lights come on in the morning, but the heaviest bubbling that I've seen has always been in the afternoon. So it probably makes sense to tailor the light period or intensity to that natural fluctiations.

The above being said there is an APC member from Asia I believe that has a sump full of aquatic plants that get light only during the night while the plants in the tank get light during the day. From what I understand the plants in the sump are doing well despite the reversed light phases.

That is probably a good example of how well the plants adapt to changing light periods.

Light period too long:
I have an experience that doesn't really lead to any conclusions but it's somewhat interesting. Maybe one conclusion would be that plant tissues need the dark period for proper development.

I set up a 30 gal. tank with 110 watts of CF (3.7 wpg) for a friend of mine. The guy let the lights on 24/7 for about 4 weeks, never turned them off. There weren't any algae at all, after a month the tank was as clean as the day it was set up. But there was not much plant growth either. No fertilization other than the initial 10:1 N and some TE.

The only weird thing were the leaves of Hygro corymbosa. The new leaves were long and thin with the looks, color, and transparency of dark green jell-o. Hairgrass and Java Moss hardly grew but were nice green. Hygro polysperma grew mostly down by the substrate, and with normal leaves.

Strong light for a few hours a day:
Do you think that the stem plants would benefit from only MH or HQI as Amano is doing? What about using strong CF lighting instead?

--Nikolay


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