# Question about Lighting Cycles or Intervals for Planted Aquariums



## jay973 (Aug 14, 2007)

What are the benefits of lighting cycles high/low continuous/intervals for planted aquariums? Why would one choose one over the other?

I've recently changed my lighting configuration over my 120 gallon and I was wondering how to optimize growth vs the balance of viewing. I have 2 80w T5 GE 6500K which I don't care for the color, makes reds look green, and 2 55w GE 9325k which makes it easier on the eyes when viewing when both are on.

I keep my lights on 10hrs a day (just because that's how I ran 4 55w PC's). I currently have the PC's coming on 1hr before the T5's and staying on 1hr after the T5's giving the max light output for my hood at 8hrs. I don't know if this is to much light yet since I'm only on my 4th day with the new configuration, but since algae would be an indicator I figured I'd ask before it gets to that.

I've heard of lights being turn off low max off max in a cycle or switching low max low max. What's the logic? In one of the case the person was using MH lights and had heat issues so turning them off was an option. Are there benefits to one over the other?


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## hoppycalif (Apr 7, 2005)

A lot people think there are benefits, but as far as I know, no one has done a controlled test to find out for sure. The main benefit, if it exists, would be a reduction in algae.


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## jay973 (Aug 14, 2007)

Thanks Hoppy, I guess that's why it is hard to get responses for these questions. I'd like to here from people who do one or the other and start our own informal study. I don't believe I'm the only one with the question.

With so many people in the hobby I think we can get a pretty good census.


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## hoppycalif (Apr 7, 2005)

Getting a "census" is easy. Just post a poll question and let people "vote". That doesn't really tell you a lot though. To really find out if a split lighting period has an effect, good or bad, you need to set up some identical tanks, get them growing identically, all treated exactly the same, then change the lighting on half of them to the split period you want to test.

So, to do this you first need the room and the tanks and the time. Then you need to be able to get multiple tanks all growing alike. And, finally you need very good observational skills to notice the effects you are looking for. I strike out on all of those criteria!


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## jay973 (Aug 14, 2007)

"I strike out on all of those criteria!"

You and me both. I didn't think it would be so challenging maybe there's a government grant or something. Or we can petition a study unlike how many times pigs pass gas or something...LOL

We have to have members in high places for support.


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## cs_gardener (Apr 28, 2006)

My reason for having a split lighting period is so I can see my tanks both in the morning and evening. There is a 3 to 3.5 hour lights out period in the middle of the day when I'm at work. I keep the same schedule on the weekends as I'm usually out an about then as well. If I'm home it's a good time to do tank maintenance. I don't know if it helps keep algae down, but it doesn't seem to do any harm.


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## hoppycalif (Apr 7, 2005)

cs_gardener said:


> My reason for having a split lighting period is so I can see my tanks both in the morning and evening. There is a 3 to 3.5 hour lights out period in the middle of the day when I'm at work. I keep the same schedule on the weekends as I'm usually out an about then as well. If I'm home it's a good time to do tank maintenance. I don't know if it helps keep algae down, but it doesn't seem to do any harm.


That is the practical reason for a split lighting period, and I have seen several posts here by people who do it for that reason. I'm hoping someone will rise to the challenge, set up an aquatic plant room, with a dozen identical 10 or 20 gallon tanks, each with the same lighting fixture, same substrate, same plumbing set up, planted with the same plants, and do the testing. Then we can all learn from the results.


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## jay973 (Aug 14, 2007)

Catherine,

That's interesting how long are your lights on for? Are they at max output all the time or do you have a high and low during the 2 intervals?

Have you ever had your light on a continous cycle? If not would you consider changing your lighting for a few weeks to see if you notice a change?

My tank isn't mature enough at the moment for me to try since I only changed the lighting configuration less than a week ago, but it is something I certainly want to try myself in the next couple of months.

The control environment Hoppy is suggesting is ideal if we get any takers.


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## BryceM (Nov 6, 2005)

Over the past few years I've seen lots of ideas here about lighting strategies and essentially all of them are presented without any evidence to show that their particular method is best. It's pretty clear that people are having success with all sorts of ideas.

If the idea is to mimic nature, it's probably best to have a low-high-low setup. Some have suggested that afternoon thunderstorms and cloudcover are common in the tropics and have made the argument that this favors a high-low-high schedule.

My personal preference is to use just enough light in the tank to provide enough for general viewing for about 12 hrs/day. About 1 wpg is fine. A mid-day blast of 3-5 wpg is used for about 4 or 5 hours to "feed the plants", even those in partially shaded locations. Intense light brings out the best coloration in plants too. This method is more or less what Amano does with his metal halide tanks and it works well enough for me. I'm of the opinion that it helps control algae while still allowing a period of insane light levels, but there is absolutely no proof that this is true.

My low-level lights don't come on until 10 am and they go off around 11pm. I'm pretty busy in the morning anyhow and this lets me enjoy the tank in the evening.


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## cs_gardener (Apr 28, 2006)

Well, I have 7 tanks and the light times are similar but not exact depending on the tanks needs and how well I remember the "standard" time setup when programming a timer. They all come on between 6:30 and 6:50 (helps to get me out of bed  ). Off between 11:30 and noonish. Most are back on by 3:30 although 1 comes back on at 5. Off again between 9:30 and 10 (one turns off at 8 - different tank than the one that comes on at 5). When the lights are on they are on full power, I don't have a high light period. 

The two tanks with the shorter lighting periods have had algae problems when the lights were on longer and since shortening the lighting period the algae has almost completely cleared in one and is gradually diminishing in the other. On my 29 gallon I have a 2 x 65w fixture and the front light is on in the morning and the back light is on in the evening. The fixture was a great deal on ebay and I couldn't resist but I don't need 130w on the tank! I figure it's best to even out the wear on the fixture by switching from one bulb to the other. It's the tank that doesn't come back on until 5pm because it does get additional sunlight from the south-facing window it's in front of (not direct light, I keep the blinds tilted so it's just bright, indirect light). Three other tanks get some bright morning sunlight so I try to take the sunlight into account when setting up the timing for the lighting.

My tanks are never completely algae free and it's not a condition I strive for. As long as the algae is minimal and not growing rampantly and smothering the plants, I'm fine with it (mostly) because I can keep it within my tolerance levels. My tanks also have a soil underlayer and except for gluteraldehyde (generic Excel) I don't dose regularly - I tend toward the low-tech side of things.


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