# Maximum Photoperiod Plants will Utilize



## jeffkrol (Jun 5, 2013)

Yes but your question is complicated and light isn't the major cause of algae.

First you need to understand if there are other limiting factors such as nutrients including CO2.

Then you need the info. plant profiles of which will hit the saturation point at what light output.

Also need to figure the DLI. Daily light integral.

http://w3.marietta.edu/~spilatrs/biol103/photolab/globexpl.html

Most aquatic plant light saturation points have afaict not been determined. Most "shade" plants still have saturation points well above what one normally sees in an aquarium. 

Sadly the below chart doesn't give exact illumination levels.


https://1gt3sd9flvb3kwgha3wmyhbu-wp...016/09/Light-Compensation-Points-1024x706.jpg


Oops wrong graph.

https://cdn.shopify.com/s/files/1/0...hotosynthesis_Curve_2_grande.png?v=1569911215


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## Deanna (Feb 15, 2017)

I’ve often wondered the same thing and thought of it more as a question of “Is there a point where light intensity, e.g.; identifiable PAR/PUR values, and photoperiod combine to damage plants?” I don’t believe that I’ve reached such a point, with my setup, if one exists. So, I will describe what my plants are exposed to, regarding light.

First, CO2 is unlimited; I run it 24/7 and target an ~30ppm level. I also have never detected macro (includes Mg and Ca) limitations. We can’t effectively measure micro levels, so I can’t affirm my belief that they are not limited.

I have two photoperiods, separated by a 3-4 hour siesta. I say “3-4” because each photoperiod has a half-hour ramp to/from zero artificial light (ambient room light can allow plants to photosynthesize). I am not implying that a siesta is beneficial. I think it is, but haven’t proven, to myself, that it is.

The first photoperiod has about 40 PAR at the substrate (14” of water) for two hours (viewing purposes only), again surrounded by half-hour ramping. The second photoperiod has about 120 PAR at the substrate for seven hours (same ramping). PUR values are very high. I haven’t gone beyond these variables only because there is no point: no one is in the room enough to enjoy it, outside of those hours.

With the above settings, I have seen no detrimental effects with my plants. However, my plants are all stems, with the exception of some Dwarf Sag and DHG (mini). I have noticed that some stems (my Limnophila Aromatica, Pantanal and Wallichii) begin to close-up when the light begins to dim during the last photoperiod. This is something they learn to do. They also did it when my PAR values were much lower and when that second photoperiod was shorter, so it is triggered by a learned response to their end-of-the-day life, and is not photo exhaustion.

With these settings, I also have no algae. Some people would say that’s a lie, but I can’t see any in my tank (I had plenty in the past). I don’t attribute this entirely to plant health, although I think it is the majority of the reason. I believe that my snails do enough damage to the surface biofilm to do the rest of the algae inhibition.


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## Tiger15 (Jan 7, 2018)

I would say 10 hour is likely the maximum beneficial period plants can utilize, based on reports from Dutch growers that certain stem plants will close up beyond 10 hours. Non-stem plants may respond differently and we won’t know as they show no signal. 

Lengthening the photo period is not a compensation for insufficient intensity. But shortening the period is fine with sufficient intensity to control algae. Some aquascapers reported that they can achieve lush growth free of algae for just 6 hours a day.

Low light plants can suffer from too high light intensity. I’ve seen YouTube tour of aquatic plant nursery green house in which low light plants are covered with sun screen. I don’t know if low light plants in high light aquarium will suffer as artificial light is no where near sunlight intensity.

I schedule split photo periods for my viewing, 4 hour in the morning, and 4 hour in the evening with 7 hour siesta period in between. I don’t know if a siesta period is beneficial or not to my plants as I have CO2 and no algae.


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## Jah410 (Feb 11, 2019)

Deanna said:


> I’ve often wondered the same thing and thought of it more as a question of “Is there a point where light intensity, e.g.; identifiable PAR/PUR values, and photoperiod combine to damage plants?” I don’t believe that I’ve reached such a point, with my setup, if one exists. So, I will describe what my plants are exposed to, regarding light.
> 
> First, CO2 is unlimited; I run it 24/7 and target an ~30ppm level. I also have never detected macro (includes Mg and Ca) limitations. We can’t effectively measure micro levels, so I can’t affirm my belief that they are not limited.
> 
> ...


I've also noticed that same learned behavior from some of the same plants. Also rotala rotundifolia. In the past, if I change the photoperiod, it would take them about 3 days to relearn the new light cycle. Quite interesting I thought. 

I am kind of following a similar approach to you. I basically EI dose and keep co2 high. I've also got a lot of cleanup crew to hopefully keep algae down from here on. 

I may try lengthening my max intensity slowly based on what you've said.


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## Jah410 (Feb 11, 2019)

Tiger15 said:


> I would say 10 hour is likely the maximum beneficial period plants can utilize, based on reports from Dutch growers that certain stem plants will close up beyond 10 hours. Non-stem plants may respond differently and we won’t know as they show no signal.
> 
> Lengthening the photo period is not a compensation for insufficient intensity. But shortening the period is fine with sufficient intensity to control algae. Some aquascapers reported that they can achieve lush growth free of algae for just 6 hours a day.
> 
> ...


I'm curious about the 10 hour max. Wonder if that's just learned behavior, or if it's actually the limit. 

Also I've have wendelov Java fern in the past under the same light but for 10 hours (didn't know how strong my light actually was). It actually fried the plant. Tried twice and both times the leaves actually crisped. Didn't melt!


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## Baysha (Apr 22, 2020)

My low tech tanks are on about 15 - 16 hours of light a day (I haven't gotten to programming the timers yet, I switch the lights on and off manually so it's not always at exactly the same time). Plants are doing great, red plants are red, no algae. Interesting that both of you mention stem plants closing up, I have never seen this behavior.

Diana Walstad recommends a photoperiod longer than 12 hours with the explanation that shorter photoperiod might slow down the growth of some plants because it basically means "winter is here". But I think it's not the whole story - most high-tech people use shorter photoperiods and their plants are growing like crazy. So maybe it's a combination of other environmental factors? High-tech versus low-tech? I don't know. Would be interesting to find out! Anyway, long photoperiod works for my tanks and I love that I can admire them from early morning to late evening.


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## Quesenek (Sep 26, 2008)

To throw a wrench in the 10 hour thing.

I have a low tech tank that I run a NICREW ClassicLED Plus at about 40% on. The photoperiod is around 15 hours and the plants don't fold up like they do in my high tech tank.

My high tech tank even running 30 4000k Luxeon LED's over my 55 gallon at 100% for 10 hours a day for a month, the plants didn't fold up until after the lights were off.
There was no difference from running everything at normal levels. Same was true for Sunplus CW, but I didn't try the 100% thing for as long as the 4000k LED's.

It wasn't until I installed some Cyan/DR/Violets into my DIY setup that my plants said they had enough at around 11 hours photoperiod that they started folding before the lights were off.

Whether the plants were utilizing the light, I have no idea, but they were still pearling and they were still open.

As jeffkrol said, the main issue with high intensity lighting is Co2 levels and stability. When Co2 is the limiting factor coupled with high intensity lighting, it causes an unstable system and unstable Co2 = Algae.


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## Deanna (Feb 15, 2017)

Baysha said:


> Diana Walstad recommends a photoperiod longer than 12 hours with the explanation that shorter photoperiod might slow down the growth of some plants because it basically means "winter is here". But I think it's not the whole story - most high-tech people use shorter photoperiods and their plants are growing like crazy. So maybe it's a combination of other environmental factors? High-tech versus low-tech? I don't know. Would be interesting to find out!


It's all about the light. The high light levels used in high-tech tanks drive growth much more strongly than in low-tech. However, we have to add CO2 and higher levels of other nutrients, to keep up with that growth, or the plants will burn themselves out, in a manner of speaking. The dying/struggling plants, then, would bring on algae.

Additionally, in high-tech tanks, there is much less forgiveness for inconsistencies in supplying the plants what they need. We can supply high light for 12 hours or more, but it needs to be consistent or imbalances start to have a negative effect on plants. The same goes for CO2 consistency and somewhat with the other nutrients. Low-tech tanks are much more forgiving in this regard and, therefore, easier to maintain.


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## Tiger15 (Jan 7, 2018)

Not all stem plants but the fine foliage type such as Ambulia, Cabomba or Hygro polysperma react to opening and closing. The reporting of 10 hour maximum photo period are from Dutch gardeners with high light CO2 setups. The response from low to medium tech setups is likely different due to influence of multiple variables. I have no idea how non stem plants react as there is no readable signal I’m aware of.


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## jeffkrol (Jun 5, 2013)

Deanna said:


> It's all about the light. The high light levels used in high-tech tanks drive growth much more strongly than in low-tech. However, we have to add CO2 and higher levels of other nutrients, to keep up with that growth, or the plants will burn themselves out, in a manner of speaking. The dying/struggling plants, then, would bring on algae.



Total agreement w/ dying/senescent plant material will cause algae issues. spores need ammonia to germinate and cannot use any other Nitrogen sources I'm aware of.


As to "burning out"... well light on the surface of a lake and open stream can push 2000 PAR at the surface..Good lights might push 500 PAR at the tank surface or w/ marine ones 1000PAR.


Emergent forms of aquatics will see full daylight (granted it's not constant over the day cycle) but don't usually burn themselves out (exposing shade acclimated ones will of course) but CO2(atm) is really a lot higher than your 30...like currently 400ppm-ish.


SADLY the below pdf doesn't list algae tolerance to high CO2 levels..
http://osse.ssec.wisc.edu/curriculum/earth/Minifact6_Carbon_Dioxide.pdf


As far as I "know" some streams can have higher CO2 levels than a lake but I suppose the oxygenation factor comes into play.


Obviously ind. species and their "predispositions" matter.


As to another point brought up above.. studies show some plants can do fine or even better w/ a 24hr light cycle. Of course these studies were done on terrestrials where CO2 is never limiting..

Guess one can think of duckweed which sort of shares the best of both worlds and how crazy prolific it is at high PAR levels..


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## Deanna (Feb 15, 2017)

jeffkrol said:


> As to "burning out"... well light on the surface of a lake and open stream can push 2000 PAR at the surface..Good lights might push 500 PAR at the tank surface or w/ marine ones 1000PAR.
> 
> 
> Emergent forms of aquatics will see full daylight (granted it's not constant over the day cycle) but don't usually burn themselves out (exposing shade acclimated ones will of course) but CO2(atm) is really a lot higher than your 30...like currently 400ppm-ish.


Yup: I was afraid that using that “burn themselves out” phrase might be too violent. Although you clearly see the meaning, others might not realize that the intent was to imply that high light can cause a plant to exceed the supply of nutrients necessary to maintain its’ health.


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## Tiger15 (Jan 7, 2018)

Getting burnt means that the plant is damaged by high light. I know immersed grown Java fern and Anubias in green house need sun screen protection, and shade loving terrestrial plants like Hostas can get burnt under full sun. 

But submerged grown plants have water protection so it is not the same. According to Jeffcroll chart, when light reaches the saturation point of a plant, growth will plateau out, not implying burnt out.

https://1gt3sd9flvb3kwgha3wmyhbu-wp...016/09/Light-Compensation-Points-1024x706.jpg

Has anyone experienced low light plants get burnt out by high light under water?


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## Jah410 (Feb 11, 2019)

Jah410 said:


> Tiger15 said:
> 
> 
> > I would say 10 hour is likely the maximum beneficial period plants can utilize, based on reports from Dutch growers that certain stem plants will close up beyond 10 hours. Non-stem plants may respond differently and we won’t know as they show no signal.
> ...


I mentioned this earlier.


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## Quesenek (Sep 26, 2008)

Tiger15 said:


> Getting burnt means that the plant is damaged by high light. I know immersed grown Java fern and Anubias in green house need sun screen protection, and shade loving terrestrial plants like Hostas can get burnt under full sun.
> 
> But submerged grown plants have water protection so it is not the same. According to Jeffcroll chart, when light reaches the saturation point of a plant, growth will plateau out, not implying burnt out.
> 
> ...


From some googling on java fern it seems like if given the needed levels of nutrients and Co2 it doesn't care about the light levels that we typically provide for aquariums, and it will grow relative to the amount of light and nutrients its receiving.

I think there might have been a misunderstanding on the term low-light plants, what I've been able to find is that this only really means that the plants can grow in low light levels, not that they're specifically low light plants in our aquariums relative to what they would receive in nature.
The main issue that we run into with placing slow growers (low light plants) under high light is that the leaves might find themselves covered in algae from the light accumulation, just like substrate or hardscape.


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## jeffkrol (Jun 5, 2013)

Tiger15 said:


> Getting burnt means that the plant is damaged by high light. I know immersed grown Java fern and Anubias in green house need sun screen protection, and shade loving terrestrial plants like Hostas can get burnt under full sun.
> 
> But submerged grown plants have water protection so it is not the same. According to Jeffcroll chart, when light reaches the saturation point of a plant, growth will plateau out, not implying burnt out.
> 
> ...





> when light reaches the saturation point of a plant, growth will plateau out, not implying burnt out.


Right but what is the cause of the slowdown? Lack of say CO2 or a nutrient? Or more uncontrollable factors such as the rise of toxic O2, enzyme shortage ect.
Sadly it's all sort of co-mingled.


Really got to keep in mind "high light" in an aquarium can be like 100PAR.. High light outdoors or in a greenhouse can be 750-2000 PAR.
Not to mention outdoors has a ton of damaging UV and baking IR..

Sooo oddly our "high light" is low light to terrestrials.
And spectrum is "softer"..

*AND (some) plants can adapt..*


> Other shade-tolerant species (e.g., iripilbark tree) show moderate (Oberbauer and Strain, 1986) or large (e.g., coffee; Friend, 1984) increases in light-saturated photosynthesis under a high light regime during development. Capacity to adjust maximum photosynthesis to utilize the light regime in which they were grown was demonstrated for 14 early-, middle-, and late-successional species grown in full sunlight and in the shade (Bazzaz and Carlson, 1982).



In a sense we sort of look at it as backwards..
Certain plants can tolerate shade.. some can't 







> Shade-intolerant species tend to respond to high light regimes with much increased photosynthetic capacity. For example, the rate of light-saturated photosynthesis of seedlings of such shade intolerant species as idigbo, afara, and obeche grown at high light intensities was approximately twice as high as that of shaded seedlings. By comparison, seedlings of the shade-tolerant kuka showed little change in photosynthesis whether grown at high or low light intensities.





> Shade tolerance, defined as the ability to survive and grow under low light, plays an important role in the succession of forest plant communities. The mechanism of adaptation of plants to shading has become an important topic in ecology research. In this paper, we reviewed shade tole-rance of various forest plants and examined their adaptability in terms of morphology and physiology, and discussed the plasticity on growth traits, biomass distribution, crown structure, leaf morphology and physiology, leaf anatomical structure, photosynthetic parameters, carbohydrate allocation, water and nutrient utilization related to shade tolerance of forest plants. Finally, we discussed some problems with previous studies, and proposed possible future research issues.



Look at it another way..
https://www.ledtonic.com/blogs/guid...and-your-plants-ppfd-photoperiod-requirements


DLI for ferns ect is 4-6.


DLI for 100 "PAR" over a period of 10 hours is 3.6...
https://www.waveformlighting.com/horticulture/daily-light-integral-dli-calculator


300 "par" over 10 hours is a DLI of 10.8


> Shade plants (annuals and perennials) 6-10




https://pubmed.ncbi.nlm.nih.gov/29733159/
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/shade-tolerance




now after all my blah blah blahing..
An article on the favorable conditions for algae growth..
http://www.jlakes.org/config/hpkx/news_category/2016-03-22/1-s2.0-S1364032115004839-main.pdf


I'll let the more ambitious go through the whole thing..


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## jeffkrol (Jun 5, 2013)

Tiger15 said:


> Lengthening the photo period is not a compensation for insufficient intensity. But shortening the period is fine with sufficient intensity to control algae.


Again though let's not talk extremes..


> Very high PPFD levels over a short duration of time or very low PPFD levels over a long duration of time are rarely ideal for good growth.


Kind of a wishy washy statement.. 
https://www.ledtonic.com/blogs/guid...and-your-plants-ppfd-photoperiod-requirements

Obviously commercial growers need to maximize return for energy input soo they need much more specific standards than most aquarists..
And again their low light is generally our high light.. 



> Your grow light produces 500 PPFD at 18" from the plant according to your grow light PPFD chart/light footprint.
> If the lamp's distance is increased to 20" from the plant, it produces 400 PPFD at the canopy.
> If the lamp is lowered to 15", it's producing 700 PPFD. By looking at the chart we see that ~25 DLI is achieved by exposing the plant to 500 PPFD over 14 hours but also when exposing the plant to 400 PPFD over 17 hours or 700 PPFD over 10 hours.
> *Choose a combination that fits both your grow set up but also your plant's minimum and maximum PPFD limits.*


Lengthening the photo-period can be a worthwhile thing..

50 "PAR" over 12 hours is a DLI of 2.16
Same as a 100 "PAR" over 6 hours..

100 over 12 is 4.32
Still.. "low light" in the real world.

For fun








Pretty "flexible"

now 1000"PAR" for one hour is, math wise the same as 100 "PAR" for 10 hours but since you probably max out the photo-systems it's prob only equiv to 400 effective PAR over 1 hour and a 
DLI of 1.44..
Would be an interesting experiment..


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## Tiger15 (Jan 7, 2018)

Here is what expert says about optimum light duration:

_LIGHT DURATION

Minimum of 5-6 hours for new tanks that want to minimize triggering algae.
7-10 hours is common for average, stable tanks.
10+ hours; marginal gains to plant growth rates, increased chances of algae incidence. Suggest using moonlighting/lower powered display lighting if extended lighting hours is desired for viewing purposes._

https://www.advancedplantedtank.com...vent-algae-growth?_pos=2&_sid=8e5d6d79a&_ss=r


and explanation of light compensation and limitation ( saturation) points:

https://www.advancedplantedtank.com...adv_light_and_co2?_pos=1&_sid=25a8d9483&_ss=r


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## Baysha (Apr 22, 2020)

https://acquariofilia.org/english-articles/af-interviews-diana-walstad/5/


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## jeffkrol (Jun 5, 2013)

From the op:


> I'm running a hightech setup with a light dimmer that ramps to 100 percent intensity for about 4 hours flanked by 3 hours worth of 70 percent flanked by 7 hours at 30 percent
> (Ed note 14 hours)
> 
> I'm not having an algae issues currently.


https://www.aquariumgardens.co.uk/the-fight-against-algae-38-w.asp



> Algae normally appears when there is an imbalance in nutrients, CO2, oxygen and light. For example, too much light but too few nutrients and CO2 will cause algae. Poor distribution of CO2 and nutrients is also a common cause of algae. It is talked about widely that that lowering nitrates and phosphates (two vital nutrients) will reduce algae outbreaks, when actually, algae thrives in a low-nutrient environment. This is a myth and should be avoided in planted aquariums.
> 
> Here are the main reasons why we get algae in our planted aquariums:


You can't talk about duration without talking intensity, nutrients and plant maintenance as well as considering species to a certain extent.



> I'm not sure if 10 hours of low say 40 micomol vs 7 hours of higher 100micromol is better for the plants, but the energy we can calculate...


Tom Barr
https://barrreport.com/threads/mininum-photoperiod.5944/


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## Tiger15 (Jan 7, 2018)

jeffkrol said:


> From the op:
> 
> You can't talk about duration without talking intensity, nutrients and plant maintenance as well as considering species to a certain extent.
> 
> ...


True. Light intensity, CO2, plant species, and nutrients all have influence on what is optimum photo period that ranges from 4.5 hour claimed in Barrreport to 12 hour advocated by Walstad.

_heck my tanks got a 4 1/2 hour photo-period and i still get 1/2" a day growth on some of my plants. shorter photo period also prevents algae growth such as GSA especially with tanks that have higher light_


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