# Duration VS. Intensity



## old 97 (Jul 25, 2011)

Ever heard of a DLI ?
http://www.licor.com/env/newsline/2013/01/daily-light-integral-dli-measurement-using-li-cor-light-sensors/

Why is it when if I leave a fixture on tank "A" ( at 20 Par ) for 24 hours I get hair/stringy algae.

Yet the sunlight can blast through the window for hours at 250 PAR on the same tank without any noticeable effect ?


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## Zapins (Jul 28, 2004)

Interesting site, but I am not sure what you are concluding after reading the site.

Are you saying that cumulative light exposure determines algae growth?


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## niko (Jan 28, 2004)

And how is it that you can have a tank that is in complete darkness for 23 hours of the day and receives only 1 hour of very strong light (96W 2" over a 40 gallon breeder tank) and the plants are intense green, grow slowly, look perfect and there are no algae in sight because the Amano shrimp are extremely hungry all the time?

And how is it that a tank can receive only 30 min of sunlight sideways in the morning and the rest is ambient light and still manage to fill itself with plants in a few months? Starting from seeds left over in the substrate, no CO2, no fish, no ferts.

And how is it that the open sea gets scorched by the sun all day long but there are no algae in sight miles around?


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## old 97 (Jul 25, 2011)

niko said:


> And how is it,,
> 
> And how is it that ,,,.
> 
> And how is it that ,,


Yes, I have seen this as well.

One stereotypical response that I see often, reads - "you have algae because the lighting is to bright"

Yet even under relatively 'dim' light (under 10 PAR) after a few days of continuous light I get hair/string every time.

Like Niko mentioned I too can supply ridiculous amounts of light intensity; albeit for brief periods without inducing algae. -also in a non circulated, no ferts, non CO2, no love tank.

Is it true that photosynthesis is the preparation of the dinner, respiration is the dining process ?

Something tells me that CO2 + H2O → C6H12O6 + O2 in kinda hard to avoid but, I am curious why manipulation of the delivered DLI in regard to duration yields different results (grows algae→doesn't grow algae) 
Do plants and algae have a difference in the respiration process?


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## Zapins (Jul 28, 2004)

old 97 said:


> Do plants and algae have a difference in the respiration process?


There are a lot of differences between algae and plants even at the chloroplast level, but the basic processes are similar.


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## Darkcobra (Nov 23, 2009)

It may be that plants require a minimum amount of light intensity to perform photosynthesis efficiently, and at 20 PAR, they're not receiving it regardless of the number of hours. Takes at least 8 photons being converted to electrons, before they can be put to use processing one molecule of CO2. This must be done within a reasonable amount of time, as electrons slip away easily; and at low light, losses due to this are probably significant.

It may be that since plants have good capacity for storing energy in the form of sugars, they prefer to spend the day collecting, and the night growing. In tanks where growth rate is fast enough to notice on a daily basis, I only see growth after the dark period. You're not providing night in the experiment you describe, which is unnatural, and probably not a condition to which plants can efficiently adapt.

In either case (or both), the plants are disadvantaged, and not able to fully exert whatever anti-algal properties they might possess. They're probably not particularly healthy either, and that encourages algae.

Plus algae, having much smaller storage capacity, doesn't seem to have any preference for growing at night. It uses what it collects to grow immediately, and uninterrupted light allows continuous growth.

For a more meaningful duration vs. intensity test, exclude the extremes. 4 hours of 80 PAR vs. 8 hours of 40 PAR is a good example.


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## Zapins (Jul 28, 2004)

I like your thoughts on the OP Darkcobra, there is certainly a minimum threshold for photosynthesis - this is why the watts per gallon breaks down with very small tanks and very large tanks. Though plants do grow day and night 

Have a look:


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## Darkcobra (Nov 23, 2009)

Cool video! Yep, that's growing day and night for sure. Maybe I just never noticed the daytime growth, because my nighttime period is twice as long - double the amount of growth is twice as noticeable.


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## TropTrea (Jan 10, 2014)

You have to keep in mind that plants have both a photosynthesis and a respiration cycle. When the two are in balance for the specific species and the proper nutrients are available then growth is the healthiest. When you mess with this balance you can be hurting one species but improving another species health.

The old school used to look at algae thriving in an environment of high phosphates and the color of the algae was an indicator on the light level. With higher quantities creating green and even blue-green algae. I'm not sure if this has been proven completely false today.


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