# Staged vs. continuous light schedule



## niko (Jan 28, 2004)

This post is about the important differences between the two approaches in lighting a planted tank. The two approaches result in very different internal (metabolic) state of the plants. This is not a post that is necessarily meant to tell you which light schedule is better. When you are finished reading you will know two things - how a planted tank can be controlled more precisely and how it can be more stable.

First off - the terms that I use:

*"Staged" light schedule*
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There is a midday "peak" in the light intensity. Before and after the peak the tank is lit with enough light to make it appealing to the eye.

Peak intensity: 2 to 4 times increase compared to the non-peak lights

Peak duration: Between 2 and 5 hours.

*2 hour peak:*
For slow growing plants; 
When trying to reduce an algae outbreak; 
Slowing down the plant growth without sacrificing plant health.
*4 hour peak: *
The normal peak duration for most tanks (with medium to fast growing plants)
*5 hour peak:* 
To force fast growth.

Note: There is no significant benefit from increasing the light very gradually (stepless increase and decrease with precise electronic controls)

*Continuous light schedule*
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8-12 hours of continuous light.

Intensity: 1-5 watts per gallon

* 1 watt per gallon:* 
Slow growing plants
*2-3 watts per gallon*: 
Most commonly used
*3+ watts per gallon:* 
Fast growing plants (lots of trimming, increased water column fertilization)

Allright, most of the above is common knowledge. I wrote it just in case someone misses a detail here and there. It appears that there have been quite a bit new people in the local planted tank scene.

And now the important information:

Source: 
http://www.controlledenvironments.org/Light1994Conf/1_1_Geiger/Geiger text.htm
Scroll down to the title "Metabolic Flexibility".

Ok, most people can't really decypher what is being said in that section. Much less to see how it applies to the control and stability of a planted tank. Here it is in simple terms:

Fact 1:* Plants do not care what is their light schedule.*
Staged and contiounous light schedule produce the same amount of plant mass at the end of the day.

Fact 2:* Plants restructure their internal functions depending on the type of light schedule.*

Fact 3:* Under continuous light plants make food from CO2 with only 60% of their maximum efficiency. *
During the peak of a staged schedule the plants make food with 100% efficiency. 
(Don't forget - at the end of the day both light schedules produce the same amount of plant mass. 
The Continuous shedule does this slower, but for longer - throughout the day.
Staged schedule does this fast, but for a short time - only during the peak.)

Fact 4: *The food production is regulated differently depending on the light schedule.*
Staged schedule: The light regulates the food production.
Continuous schedule: Biochemicals regulate the food production.
(Don't forget - at the end of the day both light schedules produce the same amount of plant mass.
The plants have different ways to make the same food.)

Fact 5: *Plants respond to stress differently depending on what was their light schedule.*
Continuous light schedule: The plants continue to make food 4 hours after being treated with weed killer.
Staged light schedule: The plants stop making food almost immediately after being treated with weed killer.

Ok, so we have 5 interesting fact. Simply put the plants rearrange how they function internally depending on how they receive the light. But how is this important for the control and stability of a planted tank?

Here's how:

In a planted tank system that is setup to provide the plants with food while preventing algae outbreaks there is an intentional limitation of the food resources. Historically this has been a Phosphorus limitation. But no matter how well you clean your water from Phosphorus sooner of later the algae finds a way to grow again.

Staged light schedule has proven to be very beneficial part of a system geared toward reduced algae growth AND optimal plant growth.

During the peak of staged schedule the plants start photosynthesyzing within minutes after the strong light is turned on. It takes them anywhere from only 2 up to to 15 minutes. Look at Fact #3: With staged light schedule it takes the plants a very short time to start function at their maximum rate. 2 minutes to go from 0 to 100%! It's almost as if you have a switch to turn them on (or off) just by using the light intensity.

Algae can also function very well under strong light. Full limitation of algae growth in an aquarium by reducing any nutrient is a bad idea. Especially if you also want to grow plants. In a good planted tank system most of the nutrients are where the algae can not get to them - in the substrate. But algae can still fluorish with minimal amounts of food floating in the water. What algae can not do is to store the food they make during the peak hours. Plants can. And they use that food to grow when it's dark!

[As a side note we have to note that just like the biofilter can turn into an Ammonia production facilty if things are wrong the plants themselves can actually induce algae growth. If the plants are stressed (starving for example) they can actually release nutrients through their leaves. Have you even had short fuzzy algae cover the leaves of your plants? Food was being released from the plant leaves because of stress. Short fuzzy algae growing on plant leaves is a sign of starvation. So it is important to not stress the plants. Feed them well. "Good plant growth = no algae", remember?. But also - feed them wisely.]

*So here we have it - how a planted tank can be more precisely controlled and more stable;*
During the peak hours both algae and plants kick in high gear. They make and store food.
During the low light hours of a staged schedule the plants and the algae do different things. Algae has little stored food and starts to have issues pretty quickly if there is not enough light. The plants on the other hand can last a long time without light because their storage is better. And they use the dimly lit part of the day AND the night to grow! The next day there is more plant mass... and less algae.

-->*The control* that a staged schedule provides:
The plants can be "conditioned" to kick in high gear almost immediately after the strong lights come on. The CO2 supply is also staged to be maximum during the peak light hours. So plants start to make and store food as soon as the strong lights come on. And they stop making food and start to grow as soon as the strong lights are off. Algae on the other hand hangs around after the strong light has been turned off. Waiting till tomorrow when another 3 hours of strong light will help them a little but not too much.

The aquarist that maintains a low level of Phosphate in the water (less than 0.1 ppm) can easily reduce it even further should algae appear. This will quickly reduce but not eliminate the algae growth. A low level of P also ensures that if the aquarist does not do anything the algae will self-limit itself pretty soon after they decide to explode. The food will get hard to find. Now think of what happens to this built-in self control if the P was say 1.0 ppm? And the tank was lit for 12 hours straight? With bright lights (2+ wpg)?

In an optimal planted aquarium system there is a 3-rd level of protection against possible algae outbreaks: Lots of Nitrogen. Normally the N is in the substrate where the algae can not easily get it. But what is more important to know is that without enough N the plants have trouble if there is an accidental drop in the CO2 supply. Please do not assume that your CO2 supply is 100% efficient 100% of the time. That is not so. But with enough N the plants will adapt just fine to a possible drop of CO2. So a lot of Nitrogen is an insurance against possible CO2 shortage. How much N is enough? Either provide an infinite supply of N from the substrate ot maintain a ratio according to Redfield. (Note that the Redfield ratio of NO3O4 is about 20-25:1). This is all fine but what does N have to do with staged light schedule and control? Well, only 3 hours of strong light and plants that are prepared for a possible drop of CO2 by having enough N is a good combination if we are talking about control. Control AND stability actually.

-->*The stability* that a staged schedule provides:
First off it is important to remember that noone really knows exactly why when the plants grow well algae disappears. As you saw above the staged light (and CO2) schedule may provide a reasonable explanation. But it does not explain extreme cases of stable tanks that are left unfertilized and without maintenance. Also it does not explain cases of tanks in which algae literally falls apart within 2-4 hours when introduced to the tank. But the fact remains - it is only common sense to match the plants' natural processes with a light schedule that results in a system providing optimal plant growth and reduced algae. A system that has very few chances of failing: A stable planted aquarium.


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## Michael (Jul 20, 2010)

Niko, I have two questions:

1. Would you comment on the "siesta schedule"? As explanation, I keep most of my aquaria on this lighting schedule, and have almost no algae. One tank and several nanos are located in windows and therefore cannot be kept on a siesta schedule. These have algae problems. (I keep a lean water column and rich substrate in all.)

2. I distrust the "watts per gallon" measure of light intensity for many reasons. Do you have PAR equivalents for these?

Thanks for a very interesting post!


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## fishyjoe24 (May 18, 2010)

I ask the same questions... I also did a siesta on one of my tanks and that helped with algae.. also i think to help with algae is to have a lot of plant mass straight off the bat when first setting up the tank... so many times do I see planted tanks with people saying it's heavy planted with just a few plants here and there, and i say you need a lot more plants.


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## niko (Jan 28, 2004)

Michael,

Siesta:
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In the last few days I've been looking for actual scientific articles that have to do with the reasons to do or not do a midday "siesta". I'm still looking. Don't want to post a hasty opinion about it. 

What I've found so far is data showing that both plants (terrestrial) and algae have a natural peak of the photosynthetic activity around noon. This peak is not uncheangeable (unnatural light schedule changes it for example). It appears that a midday siesta would lead to reducing the amount of food that algae makes when exposed to light. Meaning that they will have less to eat and grow when it's dark. Same goes for the plants too. Bottom line, from what I've read so far - it looks that a midday siesta is a variation of the staged light schedule used by ADA and others. Same idea - mess with the algae because they can't store food very well. The midday siesta seems to be geared toward having the tank lit when you are home in the evening and not really based on a natural advantage.

The entire idea to have a midday dark period apparently originated from a German company (Dupla) that knows aquatic plants very well. But what Dupla publishes on the Net is somewhat naive - they claim that in the tropics often there is a midday rain and overcast skies. That is the only reason they give to do a midday light siesta. Emulate a rainy sky every single day? Pretty simplistic reasoning but I do not want to dismiss it easily and I want to find out more about the whole idea.

As a side note: The idea of limiting the plant and algae functions by manipulating the temperature is not a bad one either. I found an article that talks about temperature and photosynthesis. The relationship is very strong even with 5F difference. Of course it is not very practical for aquarium use compared to turn on/off a light bulb. So how about a temperature siesta? And if someone has forgottten or not noticed - ADA suggest lower temperature for the first week or so when starting a new tank. The idea is to give the plants time to adjust before making them grow fast (lower temperature limits the algae growth too.)

PAR:
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It is not everything it is thought to be. Nor are watts per gallon, no way. I used watts per gallon in the original post of this thread because most people think in watts per gallon. It would have been better if I used something like the word "intensity". The idea is that the peak in a staged light schedule basically blasts the tank with light that is 2-4 times stronger than the normal light. Watts, PAR, number of bulbs - the idea is the same.

I will post soon why PAR may not be the ultimate way to measure aquarium plant light. It makes sense for it to be but there are some considerations.


During all this reading I realized how many statements in this hobby are questionable. It is very rare to quote a source of the statements. Also, as in everything in science, one or two articles do not mean that things are the way these articles draw their conclusions. In any case one can make more sense of it if actual scientific articles are quoted and explained in layman's terms so more people look into the issues. This hobby has no authorities - be it now-how or aquascaping design (ADA included). So scrutinizing is up to anyone that cares to do it.


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## digital_gods (Apr 23, 2010)

Niko, keep up the great research! 

Have a couple of comments. I understand where DRUPAL is coming from in regards to the mid day siesta. When I was in Belize during the summer time, the rain would come in just after lunch between 1-3pm. They were never long. It down poured for 30-60 minutes and then cleared up to blue sky. I think if you just dropped your light to low for an hour just after your day burst, that would simulate the tropical rain. 

As far as light measurement goes, par is a good way to measure with traditional lighting. The saltwater reefers have found that par measurement does not accurately work for LEDs. With LEDs being directional, they have gone back to using lux. You take the luminous, the spread/lense angle and the distance all into consideration. 

Now with staged lighting, I'm wondering would this save energy in the long run?


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## Michael (Jul 20, 2010)

Your comments on siesta make sense. I've never believed that stuff about mid-day rainstorms.

Yes, PAR is not the ultimate measure of light because the meter's sensitivity to different wavelengths is not exactly the same as a plant. Given all the new technologies, it still seems to be such an improvement over watts/gallon. But I see your point in using it to complare the intensity of the light during the mid-day burst with other times.


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## fishyjoe24 (May 18, 2010)

Michael said:


> Your comments on siesta make sense. I've never believed that stuff about mid-day rainstorms.
> 
> Yes, PAR is not the ultimate measure of light because the meter's sensitivity to different wavelengths is not exactly the same as a plant. Given all the new technologies, it still seems to be such an improvement over watts/gallon. But I see your point in using it to complare the intensity of the light during the mid-day burst with other times.


yes, just read my par collect reading at the top of the tank, and how much the par meter jumped up and down at the top of the tank before slowing down....

and also see how much the blue high specturm didn't do much..

also wouldn't a siesta be cutting off different chlorophyll photosynsis periods?

Chlorophyll a is used for oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light.

chlorophyll a - helps absorb light energy.

chlorophyll c1 helps with gathering light but is not used in photosynsis

c2 and c3 I don't have any info on and we would need to get phil to answer..


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