# Lighting Intensity vs Photoperiod Duration



## Aeropars (2 Sep 2015)

Hi All,

I wanted to start a discussion on peoples experiences on the effects of lighting intensity vs the lighting duration in the aquarium.

I've recently moved from T8 to LED (4 x Grobeam 600 over 180l 3ft tank) and I totally underestimated the power of them causing me to have massive plant melt but strangely very little algae apart from some light diatoms on my rocks. I was slightly bemused as I had a yellow tinted drop checker and was dosing EI so expected the plants to have everything then needed.

I've now gotten the tank to a point where plants have stopped melting but I'm seeing only very slow growth which makes me assume I've hit some sort of balance but to get there I've had to dim my LEDs to 10%! To get things growing better I'm going to have to increase the photo period or the lighting intensity.

I see a lot of tanks on here, particularly from the long standing pro's of the hobby where they appear to dive straight in with a lot higher level of light than I do yet don't seem to have any problems. I'd be surprised if someone like George Farmer would start running lighting so low as to what I am doing but that's what this thread is about. to understand peoples thoughts when addressing intensity and duration of light.

So enlighten (pun intended) us all with your thoughts about what to start an aquarium off with when setting up your lighting!

Personally, In my own experience I started off with about 30% intensity and a short photo period of 4 hours for bedding in but it seems that was very wrong even with good CO2 and flow.

Look forward to hearing your thoughts.


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## Julian (2 Sep 2015)

I've had a very similar experience with TMC LED's, no algae problems, just lots of plants melting which I assume to be the intensity of the lights.

Like you, I have to run them very low, although I think mine are around 25% which may even be too much. Even with an ORANGE DC I still couldn't get my plants to survive.

I've just moved house and had to start the tank all over again, got some plants coming shortly so hoping to resume my quest for a carpet of HC.

I'm actually starting to think that these TMC tiles are cursed and I should just get some T5's, or may even be something in my ADA Amazonia that's killing everything...


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## ian_m (2 Sep 2015)

Aeropars said:


> massive plant melt but strangely very little algae apart from some light diatoms on my rocks


Melting plants due to excessive light doesn't necessarily automatically cause algae especially if you frequently change water and have decent filtration. Beginners suffering plant melt and algae due to excessive light, usually aren't changing their water frequently enough and have immature filters that can't cope with the increase in bio-load.



Aeropars said:


> I've recently moved from T8 to LED (4 x Grobeam 600 over 180l 3ft tank) and I totally underestimated the power


TMC never really easily state the lumens of their LED lamps which makes it hard to compare light levels.

Any way a 3ft T8 tube is 700 lumens (Arcadia), thus I assume two tubes over 180l, is 1400lumens.

TMC use Cree XP-E LED's which are 300lumens @ 3.5W. TMC drive theirs at 12W / 5 leds -> 2.4W per LED (increases lifetime). So one TMC600 is 300 * 2.4/3.5 -> 1000 lumens. Thus with four strips you are providing 4000 lumens !!! Yikes no wonder plants are having an issue. Have they got sun glasses. . So running at 30% will give 1200 lumens about what you have with T8 tubes.

A lot of the "nice tanks" (eg Amano) are using bright'ish lights, but using open top tanks the lights are suspended. The lights are often way above the water surface, so the lumen level in the tank can easily be an eighth (or more) of the light level if the light would be at the water surface.


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## James O (2 Sep 2015)

Discussed before

From Ceg

...........Firstly, the LCP of each plant is different. Plants we call 'low light" such as mosses, ferns and so forth, have a lower LCP than stem plants, for example. Secondly, the photo reactions have a limited time span in higher plants. 8-10 hours is about the limit. After that the plants start to shut down. Algae on the other hand are opportunists and they can happily continue all day, so algae will continue to produce food while the plants have closed up shop. Extended lighting periods therefore have an impact by encouraging algae.

The way we think about light is the reason we have so much difficulty understanding it's impact. When we see light it appears to us as a continuous ray or stream of brightness, but this is not the truth of light. light is actually a series of individual pulses, in a way, like raindrops. A low intensity light is like a light rain falling gently on a leaf. A high intensity light is like a torrent, and just like a storm, high intensity light does damage to the plant photo cells as they collide with the cells.

So intensity is much more important than duration because the intensity determines the number of collisions the light particles make with the the photo receptors in the leaf. If the intensity is too weak, i.e. the number of collisions is too low, the receptors cannot make enough use of the energy. if the intensity is too high then the receptors are bombarded and actually are destroyed by the bombardment. So now, within this context, think about duration. The photoperiod will only have relevance depending on the intensity. With insufficient intensity the photoperiod has no meaning because the plant cannot make use of the weak energy and at the same time it is respiring (using energy). If the intensity is too high then the damage to the cells is occurring for a longer time, but whether short duration or long duration, damage is being incurred.

There is a phenomenon called "photoinhibition" which is a stalling of photosynthesis, and which occurs all the time that the light is on, simply because the light particles raining down on the plant inevitably damages some of the chlorophyll cells. If the rate at which collisions occur (intensity) is modest, then the plant is able to manufacture and release enzymes that repair the cells. If the collision rate is too high then more damage occurs than can be repaired by the plant in a given time period. It's entirely possible that the colors we see in plants under high lighting are a direct result of the plants attempt to minimize the rate of photoinhibition by reflecting (or fluorescing) some of the light energy it is being pummeled with.......


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## Aeropars (2 Sep 2015)

ian_m said:


> TMC use Cree XP-E LED's which are 300lumens @ 3.5W. TMC drive theirs at 12W / 5 leds -> 2.4W per LED (increases lifetime). So one TMC600 is 300 * 2.4/3.5 -> 1000 lumens. Thus with four strips you are providing 4000 lumens !!! Yikes no wonder plants are having an issue. Have they got sun glasses. . So running at 30% will give 1200 lumens about what you have with T8 tubes.



Hi Ian. Given that the LEDs are more directional that conventional lighting, woudl that equation still be correct? I ask because i had to get 4 lights to actually give the coverage of the entire substrate. SO with that in mind, not all of the lighting would overlap from each LED?


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## ian_m (2 Sep 2015)

Aeropars said:


> Given that the LEDs are more directional that conventional lighting, woudl that equation still be correct?


Its only a rough back off envelope calculation to give you an idea of light levels.

LED's are actually less directional than tubes (especially tubes with reflectors) and require quite complicated optics to get the light from the LED chip out (designed by LED chip manufacturer) and complicated optic's to direct the light in required direction (designed by TMC in this case).

There has been a lot of measurements done, in tanks, and for the calculation accuracy we require, generally putting 2 tubes (along length of tank) doubles light at bottom of tank, putting 3 triples etc.

You had to get 4 Grobeams as you wanted to cover the full length & width of your tank, which is the correct way of doing things when replacing two tubes.


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