# Can a mid-day "siesta" be too long?



## stephanieleah (Oct 31, 2009)

Hi all

I want to lessen the number of hours I'm lighting my tank each day to experiment with the plants. Since I like the lights on when I wake up and right before bed (yes, I sit and gaze at my fishies and plants), I want to lengthen the amount of time I leave the lights off during the mid-day hours. Is it okay to leave the lights off for 4-6 hours mid-day? Will it disturb some subtle photosynthetic processes for the plants?


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## Byron (Mar 7, 2009)

Photosynthesis--the process by which plants grow by using sunlight to break down water molecules into hydrogen and oxygen, then the hydrogen binds to carbon and then oxygen creating glucose (sugar) for energy to grow and flower--requires light of a specific intensity and duration. Peter Hiscock writes that plants will be "relatively unaffected" by a light/dark/light period of 5-6 hours/2-3 hours/5-6 hours followed by 10 hours of total darkness.

Bob Fenner, a regular contributor to FAMA, writes that plants are sensitive to day lengths. "Regularity of photoperiod can be very meaningful. Experiments have shown that long dark or light periods (1-2 days) severely affect aquatic life, photosynthetic and otherwise."

Dave Huebert, a botanist at the Univ of Manitoba, writes: 
Plants are sensitive to daylength. The pigment that senses light in plants is called phytochrome, and it absorbs light in the red/far-red end of the spectrum. Research has shown that some aquatic plants are short-day plants, some are long-day plants, and some are indifferent to daylength. When exposed to the ' wrong' daylength, plants will continue to photosynthesize in the presence of light, and grow vegetatively, but will not complete their lifecycle and flower. This is true of both terrestrial and aquatic plants. Generally, it is safest to assume that tropical aquarium plants are short-day plants, which means they are more likely to flower with a duration of 10 to 12 hours of light per day. Plants which grow in temperate zones are generally long-day plants and are most likely to flower with 14 to 16 hours of light per day. 

And lastly on the scientific note, because I think this explanation makes it clear how plants tell the time, here is an excerpt from Paul Krombholz, Tougaloo College, Mississippi, and an authority on the subject: 

The distinction between describing a plant as a short day plant or a long
night plant is not important as long as the plant is on a 24 hour cycle.
If it gets short days, it will automatically get long nights. The
distinction was made because it was found that plants measure the night
length, not the day length. There is a pigment in plants called
phytochrome that exists in two forms, phytochrome red (P660) and
phytochorme far red (P700). Plants begin their nights with most of the
pigment in the P700 form, which slowly converts to P660 during the night.
The amount converted is the measure of the night length.

P660 absorbs red light, with a peak absorbance at a wavelength of 660
micrometers. When P660 absorbs red light, it converts to P700. P700
absorbs far red light, with a peak absorbance at 700 micrometers. When
P700 absorbs far red light, it converts back to P660. Daylight has a lot
more red light than far red light, and that is why the plant starts off its
night with mostly P700, the form that slowly reverts to P660. A short day
(long night) plant needs a long night to accumulate enough P660 to trigger
the hormonal sequence that leads to blooming. If the night is too short,
P660 does not build up to high enough levels to trigger blooming. The two
phytochromes are quite sensitive to light, and even room lighting has
enough red light to keep the 'clock' from running, i.e., keep any P660 from
building up. Even the relatively dim light from street lights has enough
red light to slow down the clock and give plants the "misinformation" that
the night is a lot shorter than it really is. Every November I see weeds
growing near street lights that delayed blooming and got killed by the
frosts while still in the vegetative state. Further away from the lights,
the weeds have gone to seed in plenty of time.

My conclusion would be to try your schedule and carefully observe the plant's reaction. As plants can adapt so readily, little damage will probably occur if the mid-day dark is too great, and you can always change. But from reading the above and similar, I tend to think plants may be able to adapt, provided it is consistent day to day. Consistency is the one common thread in all these articles.

Byron.


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## stephanieleah (Oct 31, 2009)

Great feedback, Byron...I'd love to know where you get all of this information (books? magazines? while preparing your master's thesis on the subject???)

It made me realize a few things:

1. I need to make sure I turn my porch light off EVERY night (it shines into the room where I keep my fish tank and there are huge windows between the light and tank.

2. Part of my light experimentation is not only total number of hours of light, but possibly also total consecutive hours of night-time darkness (because part of my plan was to keep that constant and change the siesta period).

3. My siesta period is mid-day, and starts in total darkness (curtains closed) and (when our napping kids wake up) the curtains are opened and afternoon/evening sun comes in through the window and direct and indirect sunlight hits the tank. I wonder if this could have a seasonal impact on the plants as the duration and intensity of the sunlight changes through the seasons.

4. I just need to keep using the timer so every day is consistent, and stop thinking too much about it all!


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## Byron (Mar 7, 2009)

I think from my research that your plants probably won't decline from a longer period of no tank light mid-day, but it clearly does affect them and flowering seems to be most affected. But since most of our aquarium plants won't normally flower anyway (several reasons for this, won't go into it here) the main point is that the plant will probably still grow.

I would be careful on sunlight. Diffused daylight (from windows) adds to the light over the tank quite significantly, and direct sunlight would be even more-so. But the intensity of the sunlight is the real problem; I would shade it.

A consistent point from these and other writers is to provide at least 8-10 hours of sufficiently-intense light during a 24-hour period, with or without a mid-day break, in order to maintain aquarium plants. And regular periods via a timer are best, and it is easy to see why given the plant's metabolism.

What a wonderful and complex world we live in. We take plants for granted so often, but in their own way they are as incredible a life form as animals.

Byron.

P.S. I do a lot of research, constantly, on subjects that interest me. I like to know the reason this or that works. I can usually remember having read something, but normally can't always put my finger on it when the question comes up like on the forum. One day I must catalogue my magazine articles. But the internet is a wealth of information now, and when you posted this question I just did some searching, as it is something I don't remember seeing previously. More intensive digging might find the complete answer. B.


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## Angel079 (Feb 14, 2007)

Not to hijack Steph thread here (but I am kinda  )....But along your researches on the lights Byron...You know how certain plants thrive in low light and others need higher end lights - Had you read any suggestions that certain plants need a much longer light period then others by chance (eg one type @ 6hrs and one type @12 hrs) ?

What makes me wonder about it is the dwarf baby tears. They really did nothing at all and where close to completely die off and I was ready to remove them almost, now few weeks into the siesta approch with this tank, they have exploded and are absolutely gorgeous looking and I'm wondering is that is directly linked to one another, like shorter light period at one time triggers their growths?


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## stephanieleah (Oct 31, 2009)

Point taken about the sunlit window...but since it's there, and the tank is there, would it make sense to just make sure the light is off at the time that it's the sunniest? (It's late afternoon sun and generally won't shine directly into the tank except a few scattered rays because of the trees). Otherwise I'd just need to make sure the curtains are closed

Also had a side question for both of you B and A...I'm sure I've asked this before but the more I understand about lighting needs the more I understand answers to my questions : )

I have 90 watts shining into my 30 gallon tank. It's 6700k. If I have the light on for 4 hours at 90 watts, is that the same as 8 hours at 45 watts? I know that watts is the intensity of the light, but what exactly does "intensity" mean? Strength to penetrate into cells? Energy particles per square unit of something? 

I guess I could go online but--Byron--I don't know where to look! I'm just a layperson!


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## Angel079 (Feb 14, 2007)

I's pers black the sun light filter through your window out of the tank via curtain/ blinds. I can not super scientifically give you a half pager report here now, but direct sunlight on tank does enhance certain alage to develop real well, I doubt you'd want that!?

Like I said before the duration to counter act intensity won't help much, if I had a 5w bulb hanging over my 55g and (assuming this would be possible) run it for a 1,000 hrs on end, that still would do no good for my plants health and vise versa. Specially lower light plants will simply melt in this set up of 3wpg.
IMO its comparable to ferts. If I don't use any at all and then once a year dump 4g liquid fert into my tank, its sorta obvious what'll happen there (apart from the fish, I mean the plants).


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## Byron (Mar 7, 2009)

stephanieleah said:


> Point taken about the sunlit window...but since it's there, and the tank is there, would it make sense to just make sure the light is off at the time that it's the sunniest? (It's late afternoon sun and generally won't shine directly into the tank except a few scattered rays because of the trees). Otherwise I'd just need to make sure the curtains are closed
> 
> Also had a side question for both of you B and A...I'm sure I've asked this before but the more I understand about lighting needs the more I understand answers to my questions : )
> 
> ...


Angel has correctly pointed out in her subsequent post that increasing intensity or duration does not compensate for a deficiency in the opposite. This was mentioned among some of the cited comments in my original post in this thread. There are a couple of things in this issue.

First, "intensity" is the strength of the light. It is expressed in lumens [going from memory, but I think I've got that correct] but I have never bothered with this because it hasn't--yet--been necessary for success. I started with the minimum and went up from their because I wanted the minimum necessary to achieve a healthy planted tank in which the fish would be less stressed.

"Watts" is simply the amount of energy used by the light. It has some connection to intensity but is not determinate of the intensity. Intensity is determined by the compound of phosphors that coat the inside of the tube; these "burn" to produce the light, and the type of phosphors determines both the intensity of the light and the colour rendition (kelvin). For example, most 48-inch tubes (regular T8 and T12) are 40 watts. Zoom Med make 48-inch tubes which are 32 watts, but they produce the same intensity as the other 40w tubes (so they say). The point being, same intensity, less energy used, so less expense to operate. Then there is the Life-Glo and Life-Glo 2 tubes, both 48-inch and 40 watt. But the Life-Glo is more intense light than the Life-Glo 2 because of a special coating on half the inside tube that focuses or directs the light out the opposite side only, rather than out the entire circular tube. The light entering the tank from the Life-Glo is thus more intense that the Life-Glo 2.

Thirdly, aquatic plants need light of a minimum intensity and for a specific duration. This varies, so we can speak of low light, moderate light and high light plants. But all plants have a minimum level of intensity and duration that if not met will not allow the plants to photosynthesize. This was mentioned in the comments cited in my earlier post.

If the intensity is more than the plant needs, that plant can (assuming other requirements are present) literally burn out. More usually algae takes over, because something else will be missing (carbon, minerals, nitrogen to balance the intensity). The duration of light has a minimum for each plant to photosynthesize. If the duration is less, the plant can't grow even if the light is three times the intensity. And if the intensity is inadequate, having the light on for longer will not help either. It's all about balance again.

To your tank, Stephanie, I believe 90 watts over a 30 gallon aquarium is far too much light. And 4 hours at 90 watts is not the same as 8 hours of 45 watts as I've explained. Having 90w on for fewer hours may allow the plants (or some of them, depending upon species) to grow fine, and algae may or may not be an issue. But what about the fish? As I've written elsewhere, most of the forest fish occur in dimly-lit waters and although I am not a biologist I find it impossible to think that there cannot be some detrimental effect on the fish's metabolism if it is subjected to brightness it is not programmed by nature to receive. You know how you (like all of us) are affected in a room with too bright a light. I can't read a book in the sunlight because it is too bright. Same issue for the fish.

Byron.


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