Optimum Light Period

[ame]

Dear All

After reading Tom's post about Light intensity in ADA tanks it is clear that when it comes to light for planted aquaria ,More is not equal to better.

Another factor in planted tank Lighting is duration of lighting or Photoperiod.

I am trying to find out what will be optimum duration of lighting for a planted tank.
There must be some point in time after which plants stop photosynthesis .

If someone can share their experience it will be of great help.

Regards

ame

 

[aaronnorth]

I am not sure on the exact figure, but most say 12 hours is plenty, and there is no need to go beyon that point.

 

[VaughnH]

One bit of evidence is that some plants start closing up leaves when their preferred photoperiod is over. As I recall that has been found to be 8 - 10 hours.

 

[aquabillpers]

One bit of evidence is that some plants start closing up leaves when their preferred photoperiod is over. As I recall that has been found to be 8 - 10 hours.

I've heard that too. My latest 29 gallon low tech tank gets 9 hours of about 2.5 WPG, shows reasonable plant growth, and has no significant algae problems. I have a feeling that if I increased the period to 12 hours I'd start seeing more algae growth.

Bill

 

[ame]

Hello Friends

I have also read and followed 12,10,9 Hours of photoperiod but these again are mostly approximation like the ones we all had about Light intensity(2,3,or 5 WPG).

After Toms findings on Intensity may be we should re- think our ideas about Duration as well.

Our assumption that plants need the same amount of light intensity for this entire period of 12/10/9 Hrs may also not be perfect.

Hope Tom will read this post and enlighten us.

Thanks to all for sharing their knowledge.

Regards

ame

 

[Chiya]

Hi all,

With regards to preferred photo period, are we talking about total light intensity a plant receives? Or just 'wake up' time? Or even 'awake' time?

Case 1
Max light intensity for plant for 1 day = X micromol
If we lower the light intensity, are we able to keep the lights on longer??
This will vary the photo period drastically.
A 5WPG might need to have his lights on lesser than a 1WPG???

Case 2
I read that plants will start to 'wake up' 4 hours after continuous light and start photosynthesis. When does the 8-10hr countdown start from now?
Eg. Lights on @ 8am --> photosynthesis start @ 12pm --> plant leaves close @ 8pm regardless if light is still on.

Comments?

Regards,
Ryan

P.S. Ame, I hope you are not offended by my interruption, the low lighting thread has thrown my previous beliefs into the trash can. There are so much more to explore just on lighting alone.

 

[ame]

Dear Ryan

Good to know that we think alike.

"so much more to explore just on lighting "-I couldnot agree more.

I am hoping that someone who has tested and tweaked their light duration and intensity together will be able to show us a way.

Well looking at nature and the sun's variation in intensity over the day we can get an idea that plants do not photosynthesize all day long.

I asssume we should start the day with low intensity light and increase it progressively till noon and after 3-4 hrs of max light should reduce intensity.

But this is an assumption how do we get facts ?

Will the plant guru's share their expertise?

Thanks in advance .

ame

 

[Tom Barr]

Before running down the path of duration and intensity and modifying anything.........

Back up...............what is it that you want to do with plant growth?
Do you really and honestly want more growth and faster growth rates?
The whole point of reducing light is to reduce growth rates and demand for CO2 and nutrients.

Keep that in mind here.

If you want to increase the rate of growth, then perhaps.............but simply increasing light, or adding a bit more during part of the day is pretty simple and straight forward.

As few aquarist ever do dry weight analysis, you really cannot do much comparing with one light treatment vs another, but you can likely predict the outcomes if all else is equal(rare in most cases, but you might spot some trends as mentioned above, more light = more growth).

"Optimum light" assumes => more growth/faster growth and mostly maximum growth.

I'm not sure folks want that.
The trade off folks seem to tell me and others................... is that they want managed growth, so grow some things in at low stable light, then a bit of fast at max growth, then reduced light to reduce growth once filled in good.

Or have a bit more patience and have a slower growth tank.
Few ever asked for the fastest growth

If a farmer ask for optimum yields, this means the most dry weight harvest. For us it would mean that X plant light treatment has a higher weight/color, pigment, seed production, development etc than say plant treatment Y.

Just be careful is the question asked, ask "what is the real thing I am looking for?".

Regards,
Tom Barr

 

[ame]

Hello Tom

Thanks for the reply.

What I meant by "Optimum Light" is the minimum amount light to grow healthy plants.

After you opened our eyes about light Intensity, may be we can also test our age old belief about light duration.

What do I want ? Exactly what most folks want i.e " managed growth, so grow some things in at low stable light, then a bit of fast at max growth, then reduced light to reduce growth once filled in good"

Say for my 4ftx2ftx21 in tank I decide on 4 ,54W T5. If plant growth is not limited by light intensity(other factors adequate ,not limiting ) then will it be limited by Light duration ?

If I chose to reduce light duration to say 9 hr will that be a limiting factor ?There must be some duration above which light is wasted and some duration below which light will limit plant growth. That duration is what i meant by "Optimum period".

The whole idea is to grow healthy and good looking plants but not to waste electricity and minimise water heating due lights( my water temp reaches up to 32C in summer)

Thanks once again for the work you have done .

Regards

ame

 

[detlef]

Hi,

as Tom has pointed out every so often we should ask ourselves first what we are looking for and what our goals are before we make any decisions. As far as I am concerned I prefer a way of lighting which has seldom been dicussed so far. Most important for me is change. Change of light during the daily photoperiod like it's happening outside our glass boxes (both in intensity and color) in order to see fish and plants under different lighting conditions. I therefore have staggered intensities beginning and ending the photoperiod with very low light. After the dimmed start there is some more light then another increase before the highest blast begins (4-5 hrs only). Stepping intensities down is staggered the same way.

Total photoperiod lasts about 13,5 hrs including a very low light period at the beginning and end of each day (2,5 hrs together). This not only allows me to observe flora and fauna much longer but also under different intensities and shades of color (I am using ADA bulbs and Giesemanns "midday" which render the most pleasing combo to my eyes). Plants are very capable of adapting to different conditions so this has given me no problems in plant (or algae) growth at all as long as the high intensity blast does not exceed 5 or 6 hrs.


Best regards,
Detlef

 

[Tom Barr]

Hello Tom

Thanks for the reply.

What I meant by "Optimum Light" is the minimum amount light to grow healthy plants.

Probably about 40-50micromols seems like a safe bet, you want a little wiggle room and not go to the bone here.

After you opened our eyes about light Intensity, may be we can also test our age old belief about light duration.

Well, 6-10 hours is the likely range that will help the most. Less than this, things drop off a bit. Depends on the species but in most cases, 8-10 is best for good efficient growth. You do not get the same results from adding 2x as much for 1/2 the time............it does not work that way.............

What do I want ? Exactly what most folks want i.e " managed growth, so grow some things in at low stable light, then a bit of fast at max growth, then reduced light to reduce growth once filled in good"

Say for my 4ftx2ftx21 in tank I decide on 4 ,54W T5. If plant growth is not limited by light intensity(other factors adequate ,not limiting ) then will it be limited by Light duration ?

It can. I think it will depend on many things also though, individual plant species species, reserves the plants in question have built up etc.
I can cover Crypts (no light measured at all) for a month and they do fine if they have access to light outside the cover. They are able to draw and translocate resources.

I think this was more your point/question, but think about algae though.............they need higher light in general, so adding high intensity but shorter time frames does not help there.

But you can get to the point where you start limiting plant growth via duration as well.

But..............I think working on intensity and sticking with 8-10 hours first and getting really well known in that area should be done first.

I have no examples of nice ADA scapes with 2-4-6 hour ranges available to compare with. Do you? Would you spend 10-20K and set them up and win in the top 20 in the ADA contest?

This was low picked fruit, but we already have a good consensus about the duration, yes, it can be manipulated but do you want to go down to the bone there? Plants can and do adapt to intensity pretty good, duration? Much less so and it will be tougher to say anything more than theories...............

If I chose to reduce light duration to say 9 hr will that be a limiting factor ?There must be some duration above which light is wasted and some duration below which light will limit plant growth. That duration is what i meant by "Optimum period". The whole idea is to grow healthy and good looking plants but not to waste electricity and minimise water heating due lights( my water temp reaches up to 32C in summer)
Thanks once again for the work you have done .
Regards

ame

8-10 hours ought to do it for most plants.
You can watch and see when they "close up", like Cabomba species, you might argue that that is a sign of enough duration and adding more light is not needed.

This does occur faster at higher intensity light. How much more? Maybe 7 hours vs say 11 if you stretched it to extremes. Maybe more if you went way down on intensity.

As you approach the edge of LCP's whether from duration and intensity or some combo of the 2, you really will have more troubles and issues as many species will have different tolerances. The nice thing about all this that I did, was the fact I had some nice scaped examples with a wide range of plants that I knew of and several replicates , as well as knowing the tanks and the folks's general care and routines. So I did not have to do much work to show the tanks needed little light in terms of intensity. To test what you seek, that's a lot of work and I am not that motivated to do it, you are certainly welcomed to do it however

Regards,
Tom Barr

 

[Tom Barr]

Hi,

as Tom has pointed out every so often we should ask ourselves first what we are looking for and what our goals are before we make any decisions. As far as I am concerned I prefer a way of lighting which has seldom been dicussed so far. Most important for me is change. Change of light during the daily photoperiod like it's happening outside our glass boxes (both in intensity and color) in order to see fish and plants under different lighting conditions. I therefore have staggered intensities beginning and ending the photoperiod with very low light. After the dimmed start there is some more light then another increase before the highest blast begins (4-5 hrs only). Stepping intensities down is staggered the same way.

Total photoperiod lasts about 13,5 hrs including a very low light period at the beginning and end of each day (2,5 hrs together). This not only allows me to observe flora and fauna much longer but also under different intensities and shades of color (I am using ADA bulbs and Giesemanns "midday" which render the most pleasing combo to my eyes). Plants are very capable of adapting to different conditions so this has given me no problems in plant (or algae) growth at all as long as the high intensity blast does not exceed 5 or 6 hrs.


Best regards,
Detlef

This gives some nice aesthetic value to lighting, my client in LA does this.
I think seeing the long gradual light changes is nice myself.

But measuring it and telling someone some good hard data for all plant species, higher number of replicates etc, nice top placing scapes and their systems is rather tough. I went after the easy to measure and argue low picked fruit with the ADA example for good reason.

I simply had to falsify what some have long been claiming and give a nice scaped examples as well. I did not have to prove the min light or the duration that is optimal or deal with variations in dawn to dusk scenarios

I'm much lazier than many think. It's far easier to falsify a hypothesis folks might have than to prove what something is............

Think about that for awhile.
Seriously...................

If you can falsify it, then you know it's not due to that hypothesis (eg, must have high light) and can move on. That's something you know cannot be right because before you are several examples that clearly show it's not the case!

Showing what is the cause, the limits etc, that's harder.
Requires more work, pushes the limits of specific species tolerances etc.

Regards,
Tom Barr

 

[ER9]

i'm curious what makes aquatic plants different than terrestrial plants regarding light duration? is there in fact a difference. from my experience in the past growing terrestrial plants we would manipulate the photo period to induce flowering or vegetative growth, depending on which we preffered.

for example it was well known that anything over 12 hours photoperiod would cause most varieties of the plant being grown to go into a vegetative growth stage, mimmicking natural seasonal photoperiod changes. we also manipulated the type of light. metal halide for vegetative growth. when we preferrred to put a plant into flowering/fruiting we would cut the photoperiod below 10-12 hours and change to sodium lights.

please excuse my newbie aquatic plant growing ignorance...but it makes me wonder if aquatic plants go through similar changes under photoperiod changes? are we actually hurting some or many species of aquatic plants by cutting photoperiods below 12 hours? it also makes me wonder if algae gets a strongerhold when photoperiods go under 12 hours because aquatic plants convert alot of energy away from vegetative (quick) growth?

 

[Tom Barr]

Pretty much, they flower/change their phenology according to light duration(say when it gets to less than 11 hours, many switch gears and produce dormant structures, eg tubers........, some go to seed.

Many however respond to water levels and emeregence for flowering.
Many have hetrophylly(see Sculpthrope for more differences).

We keep the light the same, but can manipulate it.
Generally, all we wnat is vegetative growth, not tubers, seeds etc.

You got it/the concept etc down.

Algae however does the same things and does not grow well in the winter in FW systems. So less than 11 hours etc often causes many species not to grow well.

Less than 10 hours does a number of some species as well.
But plants seem fine to about 7-8 hours.

Depends on if the light is intense.

You can measure the light and the total duration in PAr units as PAr is micromols per meter ^2/sec.

So you can total up the time in seconds X the PAR reading.

This can give you some flex to go longer or shorter and still get the same relative amount of sugar produced by photosynthesis. This has obvious limits, you cannot pack all the light into say 2 hours and try to do very low levels for 20 hours.
You might want to stick around 10 hours and then go one way or the other...........most seem most interested in the shorter durations, so start with 8 hours and then give things 3-4 weeks before changing things, this is a typical time for low light adaptations.

reduce by 30 minute blocks, so to go from 10 hours to 8 might take 4 months, or 8 to 6, another 2 months.

It might work well in some species, bad in others.
Need to make sure it's not CO2/nutrients, pruning, cleaning the filter issues if you get a bad response, if not, then you can assume that the plant is meeting its demand for light.



Regards,
Tom Barr

 

[ER9]

very interesting stuff. thank you Tom you gave us alot to digest in that last response. it seems in my short time in this hobby so far that aquatic plants are much...much more demanding in many ways since we need to manipulate so many more variables, with less room for error. its starting off as a very fun but very challenging hobby.

 

[Tom Barr]

Well, the "how" is still very straight forward and rather simple.
No techy needed.

Regards,
Tom Barr

 

[Neil Frank]

Going back a few people in this thred was the question about having an extended day-lenght with lower light combined with shorter period with more intensity. Tom is correct that you cant make tradeoffs to produce some type of total light energy used by the plant. But I thought the poster was doing this to allow him to view the tanks longer without providing so much light to encourage algae.
This type of regime is important for manyof us that work an 8 to 9-hr day and who would like to look at their plant tanks before they leave in the morning and still view them for a few hours in the evening. For this situation, a 14-hr illumination period is desireable. Of course this does not have to be a 14-hr photosynthetic-period. I plan to do something along these lines with my new tanks. My 4-bulb Tek lights have capability to independently run pairs of T-5s. This allows me to have a longer viewing period and the opportunity to play with the min amount of time all 4 should be on to provide sufficient peakhour plant energy .
The need for < 10-12 hours of constant light is supported by nature. Unless you are on the equator, each hour of sunlight does not provide the same amount and quality of energy. In the morning and evening, it is less intense and has more red (due to extinction , angle and penetration). When light passes thru a forest canopy, the quality and intensity also changes.

 

[ER9]

Going back a few people in this thred was the question about having an extended day-lenght with lower light combined with shorter period with more intensity. Tom is correct that you cant make tradeoffs to produce some type of total light energy used by the plant. But I thought the poster was doing this to allow him to view the tanks longer without providing so much light to encourage algae.
This type of regime is important for manyof us that work an 8 to 9-hr day and who would like to look at their plant tanks before they leave in the morning and still view them for a few hours in the evening. For this situation, a 14-hr illumination period is desireable. Of course this does not have to be a 14-hr photosynthetic-period. I plan to do something along these lines with my new tanks. My 4-bulb Tek lights have capability to independently run pairs of T-5s. This allows me to have a longer viewing period and the opportunity to play with the min amount of time all 4 should be on to provide sufficient peakhour plant energy .
The need for < 10-12 hours of constant light is supported by nature. Unless you are on the equator, each hour of sunlight does not provide the same amount and quality of energy. In the morning and evening, it is less intense and has more red (due to extinction , angle and penetration). When light passes thru a forest canopy, the quality and intensity also changes.

i wonder if there are some type of dimmers available that can/could gradually increase/decrease light intensity on a fixture (sort of like house dimmers) over a specific time period? this would allow us to use the same bulb/fixtures and just use a dimmer. if thers not one it would be nice to see someone develope one.

 

[Tom Barr]

There are some very nice dimmers, but not in the USA.........that can do exactly what folks might want here.

Regards,
Tom Barr

 

[ame]

Hello Everyone

Let me thank all of you for sharing and adding vlaue .

We have had a far better response than I had expected(more so since it was posted in Beginners forum )

Let me try tweaking the duration and note the change in plant growth,keeping other parameters nonlimiting.

Will share my findings with all of you guys.

Tom -Hope you will entertain more beginner's question in future too

Detlef- Thanks once again.

ER 9- Using seperate timers for all lamps may be another option of staggering the lights ON/OFF.


Best wishes to all of you.

ame