Brighter light = shorter photo-periods?

[Oreo]

I saw this posted on another forum and wanted to check with the experts about it.

Someone said that if you run higher light you should run a shorter photo-period. If this is true, at what point can you run two light cycles per day? Are two light cycles / day better then one?

Low Light ( Under 2 wpg) 10-12 hours a day
Medium Light (2.0 – 3.0 wpg) 8-10 hours a day
High Light ( 3.0 – 4.0 wpg) 7-8 hours a day
Very High Light (4+ wpg) 6 (Expert level)

2.0 Wpg 12 hours
2.2 Wpg 11 hours
2.4 Wpg 10 hours
2.7 Wpg 9 hours
3.0 Wpg 8 hours
3.4 Wpg 7 hours
4.0 Wpg 6 hours

 

[csmith]

Personally I've come to understand that plants take some time to start the photosynthetic process. It's not like an on-off process. I would think that with something like a 6 hour photoperiod you're spending more time controlling growth of algae than growth of plants.
This may sound stupid, but I've let the plants tell me what photoperiod they want. For some reason my H. kompakt and H. polysperma will actually close their top sets of leaves after about 8.5-9 hours of light, so my photoperiod is 9 hours. This seems to work as growth has been fine with these. The rest of my tank, however, is another story.

 

[Tom Barr]

WPG?

That's their advice?

Can you see an issue with like..........as in immediately?
Is WPG the best metric to measure light????

You cannot even suggest or argue any of this without having some comparable units.
I would suggest that if the units are comparable(which they are not above), then the relative growth total's per day would be close.
But is that the goal?

Why run things shorter photo peroids when you add more light?
In other words, why are you adding higher light to begin with?
Why do you add high light? => The question and the advice should START there.

So why do we add high light?
Well, faster rates of growth, when you stop adding high light, there's no growth, same as if you add low light and then stop.
The rates of growth are different, but the total will be the same.

I'm not so sure that the goal when people add high light??????????
Most add more light for faster and more total growth, not to have the same amount of growth they do with less less.

That's dumb.
Just use 1/2 the light and get to see the fish/plants for 12 hours.

That way you get far more light use efficiency, over the same time peroid and with less equipment. Also, there's much less demand for nutrients/CO2 during that time frame than trying to cram it all into 6 hours.
Why not add 6w/gal and cram it all into 4 hours? Or 8w/gal and in 2-3?

I use 1.5-2w/gal as T5/PC and use 8-10 hour ranges, or put in real comparable terms, about 40-50micromols at the sediemnt evenly sporead throughout the tank.
PAR factors all the other issues like Reflectors, bulb efficiency types etc.

High light is NOT Expert level either, high light does not impart any experience or wisdom, I'd say the oppositite actually.
Lack of wisdom.

All my tanks would fall under the low light range according to that.
A much better understanding about light and it's effect on growth is Tropica's article, they did not use wpg, they used PAR, but converted it to lumens, but you can convert it back and forth in their case for that experiment since they started with PAR.

More light does not mean better and most cases, it means worse. A real expert would tell you this.
Measuring ADA's tanks and other top scapes, including the highest ranked one in the USA, was the same as my own tanks. The ADA tanks had 3w/gal, sometimes more...... but identical PAR and evenness.

I see little utility in shorter photoperiods vs using less wattages, more effective reflectors and lighting types like T5's.
For all the pissing and moaning I see about water changes, dosing just enough, the min amoutns etc....... and CO2 issues, algae etc, not to mention fish health due to CO2 issues at higher light wattages/PAR, it's much easier to simple get the same growth with a longer time frame per day, over the course of a month, you still end up with the same total growth, so why try and pack it all into a small time space?

You gain nothing and waste/impose more hardship for labor and your aquarium plants/risk more algae and stress the fish more.
This assumes they can even measure light to begin with, rather than merely guessing and wasting excess light and higher electric bills, more algae etc.
Ignorance, speculation and guessing vs confirmation via measurement.

I'll let you decide from here.

Regards,
Tom Barr

 

[Oreo]

Tom,

What you said in the post above is basically that a watt-hour = a watt-hour whether it's delivered in 5 minutes or 5 hours it's still the same quantity of light. Makes perfect sense.

Is there any advantage to running two light cycles per day with regards to whatever it is that plants do at night? How much time do plants need in the dark for their bio-chemistry? It seems to me that theoretically plant growth could be sped up by providing only the required amount of lights-off time and as soon as the plants are bio-chemically ready start the next photo-period. Unlike our ability to increase light intensity, we can't increase the intensity of the lights-off time, but we could reduce the time-span. Two 6hr light / 6hr dark cycles sound real appealing to me just based on my own personal daily routine- especially if there's a plant-growth benefit.

 

[Tom Barr]

Tom,

What you said in the post above is basically that a watt-hour = a watt-hour whether it's delivered in 5 minutes or 5 hours it's still the same quantity of light. Makes perfect sense.

Well, you have the drive the rest of things at a higher rates/cram more into a shorter window in doing so.
This is fine, but.you end up losing/wasting light energy, adding more heat, add more CO2/nutrient stress over a shorter time frame.

I do not think that is wise approach and tells folks that more light is somehow better, more expert than something else.
Nor does it measure the PAR.......

Is there any advantage to running two light cycles per day with regards to whatever it is that plants do at night? How much time do plants need in the dark for their bio-chemistry? It seems to me that theoretically plant growth could be sped up by providing only the required amount of lights-off time and as soon as the plants are bio-chemically ready start the next photo-period. Unlike our ability to increase light intensity, we can't increase the intensity of the lights-off time, but we could reduce the time-span. Two 6hr light / 6hr dark cycles sound real appealing to me just based on my own personal daily routine- especially if there's a plant-growth benefit.

I do not think many have found much difference between split times.
I do not like it, I can see my fish when the lights are off, or just adjust the lights for the evening.
You could also run most oif the lights, then leave one on a bit longer.

I'd not bother, just set the lights for the evening when you are around more(or wheer that is for the most time).

Regards,
Tom Barr

 

[Oreo]

Still I'm curious as to if & how the plant metabolism depends on there being a dark period. For instance, I used to have a few house plants that sat under a dim fluorescent light that was left on 24hrs / day. Those plants hardly grew at all and looked pretty sickly. I also have read that the photo-period affects plant hormones and in some plants how they flower. All this makes me think that there are indeed some limits at either end of the watt-hour range. Have you done, or know of any experiments / work done studying specifically the length of dark time or the ratio of dark time to PAR-hour?

I do not think many have found much difference between split times.
I do not like it,

You would never accept an answer like this Tom. C'mon!

 

[Tom Barr]

I've found no evidence the split times help anything. But they do not seem to harm either............you can try it and see.
I've not done much regarding the veg growth, flowering and tuber production, how plants respond to shorter days etc, I have.

Regards,
Tom Barr

 

[Oreo]

Am I correct to say that even in nutrient non-limiting conditions plants can only make use of so much light in one day? Ie. leaving the lights on 24/7 is not optimal regardless of light intensity because plants do need the lights off some of the time?

If so, this is my hypothesis:

As a baseline for discussion lets say an aquatic gardener runs their aquarium with 12hrs / day of light at a low intensity "I", and then turns the lights off for the remaining 12hrs of the day. What you said above is that if this person doubles the light intensity and halves the lights-on time in the same 24hr day the result is the same quantity of plant growth. [ 12/24hrs x I = 6/24hrs x 2I ]. But these two aren't exactly the same. [ 12/24hrs x I ] implies 12/24hrs of lights off, where as [ 6/24hrs x 2I ] implies 18/24hrs of lights off. The real true equality should be 12hrs of lights off in either case: [ 12/24hrs x I = 6/18hrs x 2I ]. It seems a reasonable hypothesis that by doubling the light intensity I, 24hrs of plant growth have been crammed into just 18hrs.

Perhaps the failure of this hypothesis is that photosynthesis by itself does not plant growth make. Maybe the other chemical reactions & cellular processes involved in actual growth still take the full 24hrs and thus the day cannot be shortened. But if the day can be shortened then it is reasonable to assume that two properly adjusted photo-periods in one 24hr day would yield a significant plant growth advantage. Discovering some minimum or optimal amount of lights-off time, or some optimal ratio of lights-on/lights-off time would allow the aquatic gardener to really press the accelerator all the way to the floor, so to speak.

Or perhaps my wife is right and I'm just full of B.S. most of the time. LOL

 

[Tom Barr]

Well, the faster things go, the less efficient and the more likely something will go wrong.

With this specifically in mind...........and given you add the same energy over say 10 hour vs say 6, why not use 10 hours?
You gain nothing over the total 24 hour period and simply makes things more difficult.
I'm not clear what goal this would achieve in forcing shorter and more intense burst.

There's some MET rate issues to account for, they have limits. So do you. Do you like to sleep all day and night, then do extreme workouts for 6 hours, burning say 3000-4000 calories?
Vs say slow normal walking for 2-3 hours, other simple activity, and being up for 12 hours actively? Then get a good nights 10-12 hour sleep?

Same sort of thing, aquatic plants are best geared to about 8-12 hours of light.


Regards,
Tom Barr

 

[Oreo]

Well, the faster things go, the less efficient and the more likely something will go wrong.

Sure, I would expect that. I'm not trying to suggest mathematical precision here, only a concept.

With this specifically in mind...........and given you add the same energy over say 10 hour vs say 6, why not use 10 hours?
You gain nothing over the total 24 hour period and simply makes things more difficult.
I'm not clear what goal this would achieve in forcing shorter and more intense burst.

That's what I was thinking about / proposing in my post above. That perhaps something IS gained because of the possibility that a shorter, more intense light cycle does not require additional lights-off time. Thus the entire light / dark cycle could be accelerated. You said earlier you had not studied the how the length of the dark period effects things and I'm suggesting that perhaps there is something to be learned in that area.

(You're probably gonna need a wide-screen monitor for this. Sorry...)
Let me try describing it another way. Here's your 10hrs of light photo-period cycle laid out over two days:

00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 || 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23
on | on | on | on | on | on | on | on | on | on | on | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ || on | on | on | on | on | on | on | on | on | on | on | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __
***PLANT GROWTH MEASUREMENT----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------^

Here's what I'm suggesting happens when you go to a more intense shorter photo-period, keeping the number of lights-off hours the same:

00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 || 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23
on | on | on | on | on | on | on | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | on | on | on | on || on | on | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | __ | on | on | on | on | on | on | on | __ | __
***PLANT GROWTH MEASUREMENT----------------------------------------------------------------------------------------------------------------------------------------------------^ ||

Now, I'm not just saying the lights on/off times have changed but that the plants might actually achieve a growth rate accelerated in proportion to the number of complete day-night cycles such that at the measurement points marked above, we might expect to see an equivalent quantity of growth. This growth advantage would accumulate over the long run obviously.

There's some MET rate issues to account for, they have limits. So do you. Do you like to sleep all day and night, then do extreme workouts for 6 hours, burning say 3000-4000 calories?
Vs say slow normal walking for 2-3 hours, other simple activity, and being up for 12 hours actively? Then get a good nights 10-12 hour sleep?

Sure, I understand that. However, there have been sleep studies done on humans where they have kept people awake for days on end. Weeks in some cases, with no sleep. What they discovered was that the person then recovers almost completely after about 12-13hrs of continuous sleep. We may be driving the plants harder for the time they're awake but there's diminishing returns with additional sleep time.

 

[mi5haha]

a bunch of scholars had done tests based upon growth rate, and yields of plants by different lighting hours and intensities, including shorter lighting hours and higher lighting intensity in the past 20 years. it seems that different types of aquarium plants have different lighting compensation points. some good on 13 hours, some good on 16 hours. some not good on 8 hours.

Shorter lighting hours and higher lights may result in shorter stem plants and shorter distance between each nod.

old book knowledge. Not sure whether they are obsolete or not.

 

[shoggoth43]

Sure, I understand that. However, there have been sleep studies done on humans where they have kept people awake for days on end. Weeks in some cases, with no sleep. What they discovered was that the person then recovers almost completely after about 12-13hrs of continuous sleep. We may be driving the plants harder for the time they're awake but there's diminishing returns with additional sleep time.

I'm not sure on the weeks on end. The only one I'm aware of where they kept someone awake for a week or more was the Guiness book of records. The brain wave activity they recorded was telling. When it went nuts, he was hallucinating, when normal he was just tired. At one point at the end the activity just went haywire and he was talking normally to them. According to the man's wife, he was a completely different person after that and it pretty much tanked the marriage and brought up all sorts of ethical concerns about some of these kinds of studies ( even though this was just for the record books ).

I know there are some people who haven't required sleep at all, and I've met some who don't need a lot but that's still on the order of 5-6 hours nightly. I managed a lot of college on 3.5 hours a night but took a toll on my body in the process and I know it's common for residency students to do a 15 minute nap every 4 hours for weeks or months at a time so there's definitely wiggle room but that's animals.

The day/night period has been changing over millenia but that's such a gradual change I don't think that's even worth considering in this discussion for plants. There'd have to be some ability to up the intensity somewhat. Most likely once you hit the equivalent of midday sunlight PAR that's probably your upper limit of intensity. Anything beyond that is likely just wasted energy, but for a lot of tanks you'll likely be putting more lights on the tank than you'd want to deal with, so from an experimental side it's probably possible to experiment with this.

The "dark side" question then becomes what the "off" period is. Are you going completely dark? Do you need complete darkness or can you just drop off below LCP so the plant takes the hint and takes a nap?

-
S

 

[Oreo]

All good questions Shoggoth43.

You're right that in those human sleep studies the people started going nutty after a couple days of no sleep. My point wasn't about the hours they were awake though it was that there was a finite sleep period somewhat independent from the awake time.

 

[Tom Barr]

a bunch of scholars had done tests based upon growth rate, and yields of plants by different lighting hours and intensities, including shorter lighting hours and higher lighting intensity in the past 20 years. it seems that different types of aquarium plants have different lighting compensation points. some good on 13 hours, some good on 16 hours. some not good on 8 hours.

Shorter lighting hours and higher lights may result in shorter stem plants and shorter distance between each nod.

old book knowledge. Not sure whether they are obsolete or not.

This is highly dependent on which species we are talking about.
And these studies where NOT done on the aquatic species we typically keep.

Most use 10 hours of light on average. Some use 12, a few might use 8.
I use 8-10, but also use low light, I get plenty of growth and tight dense growth.

Regards,
Tom Barr

 

[Tom Barr]

All good questions Shoggoth43.

You're right that in those human sleep studies the people started going nutty after a couple days of no sleep. My point wasn't about the hours they were awake though it was that there was a finite sleep period somewhat independent from the awake time.

Perhaps there's a better analogy

Anyway, the metabolism rates are much faster/harder and less efficient at higher levels of light/temp etc.
I can burn say 3000 calories in 2 hours by climbing fast with a pack up a mountain.
I can also burn this same amount of calories in 8 hours by walking easily.

I'll be trashed and recovery will long, I'll have far more chance for something to go wrong, sprained, pulled, twisted, broken, cramps etc..........at higher intensity.
Same is true for the Car analogy:
Faster I go, say 60mph vs say 20mph.

60mph for 2 hours vs 20mph for 6 hours.
Same distance, I still get there in the same day. If anything goes wrong, at the slower rate, the damage will be much less.
Also, you get much bette gas miliage at 20mph.

Regards,
Tom Barr

 

[scottward]

Interesting reading. I remember having a discussion with Dianna Walstad about this type of thing a few years back after reading her book. I had a guy at an aquarium shop telling me that I should just leave my lights on continously for a few weeks to get them to grow better. So I remember talking to Dianna about whether the plants actually 'care' i.e. do they need a sleep. I have completely forgotten what the outcome of our discussion was. I think it was pretty much a case of 'don't know'. ;-)

Sorry if I'm getting mixed up here - but did I read somewhere on here something about the typical SAM utilising CO2 at the highest rate within the first 8-9 hours of the photoperiod? So then after these 8-9 hours the plants growth starts to slow down a bit?

As a side question - the spacing between nodes thing - e.g. Ambulia - is the 'larger spaces between nodes' indicating 'not enough light' old school BS or is there still some truth to that?

Scott (who likes to put his 2 cents worth in anyway even if it's actually really only 1 cent) ;-)

 

[Tom Barr]

Yes, the plants will use the CO2 for about 6-8 hours.
After that, nope, you are feeding the algae.
You can see most species close up their tips after 7-8 hours.

They are done after that.

Still, why drive real high light for 4-6 hours vs say 8-9 at lower intensity?
What are you gaining? This is more prone to algae and drives the CO2/demand much faster over a smaller time frame.

Internodal spacing is driven much much more by CO2(a lack) and there's a lot of experimental and plant molecular evidence to support this.
Plants basically starved for CO2/low O2 will try and get to the surface asap!!!!
Most any aquatic species does this via the Ethylene mediated pathway.
How plants do this is interesting. Several papers by Jackson discuss and review this.

This is why I have such dense growth even with low light that cough cough...........I've actually measured with a light meter rather than just guessing and speculating what the light might or might not be.
I've never understood how some can critique EI as guess work but then give a free pass to measuring light.

Without actually measuring it, it may or may not be high/low/med light etc.
Since they have no way to quantification, it's really a HUGE MASSIVE GUESS with error up to 300-400%.
EI at least has some user control over the error rate, lighting has none.


Regards,
Tom Barr

 

[Oreo]

So far Tom I think you're right about the 300-400% part. By all accounts I should be at medium light but based on what I'm seeing I suspect I'm well into the high-light range. CO2 is as much as the fish can tolerate so it's either too much light, or my flow is way worse then I thought. (Shouldn't be that bad at 7 turns / hr.)