View Full Version : Lighting - Effect of Different Spectrums on Plant growth
02-04-2009, 02:29 PM
Up until about 4 or 5 years ago the prevailing wisdom at APD and other sites was that the intensity of light was more important for plant growth than the spectrum of the bulb, within broad limits, of course.
I haven't seen that idea mentioned lately. Is it valid or have we become smarter in the last few years?
02-04-2009, 04:20 PM
Intensity is a poor word to use really. A CF bulb is about as intense as you can get with huge power in a small area but on its own doesn't give the spread needed for a whole tank.
The spectrum has been argued about and still is argued about. I'm a non believer. lol
I would say that high light / low light is also out the window these days. We are starting to see that the most important thing is good light and well spread rather than huge amounts of light.
The people who have lower (I hate to use this term) WPG but use several tubes spaced well get just as good if not better growth than the people who use high WPG but CF bulbs.
What I mean is someone who used 2 30W T5 linears getting better growth than someone who used 1 x 65W CF.
I personally would call it more a case of high CO2/low CO2 and as long as light is 'good' and not necessarily high then the same results can be achieved.
Its the old assumptions problem. I added more light and the growth was better and faster. Lets roll back. The CO2 was increased along with the lights? Of course. So how come everybody assumes it was the light increase when the CO2 (and nutrients) were also increased? Because thats what we've always heard and understood.
Therefore my belief is once you hit a decent level of a light i.e. 2WPG with a good spread of light over the tank and not all focused in one area then growth and condition is CO2 led.
I do have to admit I hate CF bulbs. lol. For the very reason of focusing to much light in too small an area.
02-04-2009, 05:55 PM
So instead of intensity we're left with non limiting light? :)
As long as your plants are above the limiting levels of light ( ideally across the spectrum but you can grow plants in some pretty odd colors of light ) then it's really not so much a high/low or anything issue. It's really just figuring out what it is that you want to bottleneck the system with. In most cases it's easier to do that with light and usually accidentally/inadvertently done most often with CO2?
I find the WPG thing to be kind of tough to deal with and I'd be happier if there were something along the lines of X watts of T5 is good for N area down to Y meters from the bulb. I don't know if you can simplify that to X watts of bulbtype to Y meters from bulb. I wouldn't think so because then you'd have someone hanging a single fixture in the tank and wondering why only one side is working.
Maybe something like 12x24" "blocks". that way a four foot tank would be 4 "blocks" if it's 24" wide but only 2 "blocks" if it's a 55 Gallon size so you don't have people stuffing 4 T5s on it thinking they need that kind of light. If they want to that's another matter entirely. Then you could drive the amount of wattage by the distance to the light source.
I recall reading something 15 years ago from someone who did light studies on lux and reflection/absorbtion in water. I seem to remember 15% is just reflected right off the water surface. I don't know how that tracks with the other values people see and I don't remember fresh/salt or clarity on the water or any surface agitation.
The big problem is that for what I want to do with LEDs I have no real idea of how watts of T5 compares to the LEDs, or the PC lights or the MH lighting. I'll admit the MH lights are pretty much a no go out of the gate just due to the wattage and heat they'll give off. Although this winter I could have used an extra space heater in the living room. Still, it would be nice to have a better formula or guideline to use instead of wpg.
02-04-2009, 06:29 PM
What I am suggesting is that over a certain level of light as long as it is well spread, then no more is needed.
IMO This is shown where plants in a low light setup with non limited nutrient and CO2 shut up shop before the photoperiod ends just as they do in high light setups.
Light is one of those arguments that noone is really happy with and everyone has their own ideas on whereas in the main (especially on here) I think we are all on the same wavelength with regards to non limiting CO2 and nutrient.
02-04-2009, 06:48 PM
There's a min amount of light required.
Once you hit that, then adding CO2 is helpful.
Adding more light simply increases CO2 demand, more nutrient demand, thus you have more growth at progressively higher light intensities.
This is a trade off.
Most aquarist want good to moderate growth of any species they chose to grow, not the highest maximum yield. That's too much work and such systems are harder to maintain.
So we accept slower growth rates and easier management.
SuperColey1is pretty well astute on this topic:D
Spread, CO2, nutrients and other issues are part of this.
We are light limited in terms of growth for most tanks, a few might be PO4, NO3 or CO2 limited.
Still, since light is the largest energy input for most, it makes the most sense to limit it to control growth rates. It also makes the most sense to maximize the spread, the PAR/PUR, and of course our own aesthetics for color.
As lighting is the most stable parameter we can add and control in an aquarium and drives everything else, it should be the best choice of managing the system, not limiting PO4, even non CO2 systems are more dominately light limited than they are CO2 limited.
I think our color perception plays the most role in opinions about light, not actual rates of growth. I know of no planted aquarist other than myself that does dry weigh analysis, Tropica and Ole and few others do, but they are in the trade business.
So it's rather difficult for most aquarist to even compare other than their own sense of color, which is............mostly what they care about anyway, so that is often enough to support the argument :p
I cannot argue with that:cool:
I can compare dry weights between light sources however.
I can compare amounts of red pigment etc.
02-05-2009, 08:14 AM
Its the age old '4WPG is needed to make a foreground carpet' statements.
The problem is most hoods have a flap at the front. The lights are in the centre and rear (if there are 2.)
People who have luminaires have them over the centre.
Therefore what is the problem with carpets? They need super highlight because the spread is not goo enough. Move the luminaire to the front and see what happens. That carpet is now growing under 1.5WPG. Surely not. How is that possible?
So you can see what my point is.
If you are using tubes in a hood at the rear and centre with your flap at the front then the rear and centre are getting most of the light. the foreground is geting the least amount of light which defeats the object because that is where you want the most light.
It also means that the centre and rear grows much faster than the foreground.
So in summary if it is reversed and the tubes are front and centre then the foreground gets the light it needs the centre does too and the taller plants at the rear that are closer to the light are not hurt by this move!!!
Ideally get the tubes spaced equally so that they aren't both in one position or at the front or at the back.
Try it and see for yourself. It works. :)
Thats one reason why I made my own LED setup. I now have 15 lights spread over the whole tank so everything should be getting good light and it should maximise the spread. Instead of having 30W along the centre of the lid and 18W in the rear. I have 14W rear, 14W centre and 14W front (1.27WPG)
No carpeting plants in there though to prove this to you, my breeding corys want open sand in this are. lol
02-05-2009, 03:11 PM
ADA tanks grow carpet plants with low lights; this was posted by Tom a while back after he used his par meter at one of their events. Also if the spread isn’t that good why not raise the light up a bit? I use cf and i simply mounted it in my DIY hood vs the weak coralife fixture. Moved it from 4'' above water to 9'' and not only is the spread better, but the carpet plants are carpeting :). Another issue that has already been discussed is the tendency of light to bend when it strikes the water surface, so even though the bulb may not be directly above the tank it still gets a lot of light to areas further away. I do have to agree that plants directly below the bulb will get more light but think of what types of plants we typically put directly under the bulb? Tall plants right.. So it’s obvious that they seem to grow better, since they are a heck of a lot closer to the water surface and thus the light source.
02-05-2009, 04:20 PM
You are right about the ADA tanks but they use MH which is mounted further away than fluorescent and the spread is therefore much better whilst still being quite intense.
With fluorescents you have to remember that yes the spread will get better if you raise it you are effectively reducing the light level whilst raising it. If you are already using 1WPG for example (I was using 0.9WPG T5HO until recently) then raising it will reduce the actual light further and you may have to add more light in there dependent on how high you raise it.
The tall plants at the back is exactly what I mean. If a 'stock' hood was reversed and the 1/2 lights that were in the rear half were now at the front then the tall background plants would still be getting the light they need whereas you would now be giving the better light to your carpet.
As the hood is the background/midground can block out a lot of thelight from the the tubes. Of course MH luminaires can avoid this problem.
02-05-2009, 04:55 PM
I've found that the T5 lights I have are much better at evenness and they are the same PAR but only 2x the wattage.
I have to raise the MH's higher(Aqua Medic German with good reflectors etc), to get about 80 micromols across the bottom, at the top about 200. With the T5's, I can lower the light about 6" more inches and get better spread and more light.
So........watt for what, perhaps similar, but in practical spread and efficient use of my electric? The T5's kill MH's by 2:1 for even a cheap T5 system vs an expensive pricy MH set up(not the weak ADA MH's).
02-05-2009, 05:51 PM
I have to agree. lol As much as I warble on about spread I was using a single 30W T5HO over my 33USG for the last 2 years and it was awesome. That was what leads me to say that T5HO with good reflectors are easily 2 x the (aargh) WPG rule. They are ust much more efficient. The LEDs are beating them though!!!
However I was not attempting a carpet and most of my plantmass is in mid tank (attached to hardscape. lol)
02-05-2009, 07:38 PM
Well, I can measure a T5 and then compare the PAR in ADA type tanks etc to justify light intensity:
So if I have that amount with any light system, I know I can grow a nice carpet of E. tennellus, HC, gloss or hair grass, all of which grow well in this tank.
I just measure with the PAR meter and adjust.
02-05-2009, 07:43 PM
Tom you've seen that tank in the flesh. Are those lights over the foreground like it seems from the picture. I don't mean I am judging from looking at the lights themselves. I am looking at the substrate level and the front is well lit and the rear a little darker!!!
Are they 'giving' the best light to the carpet?
02-05-2009, 08:37 PM
I think you could get better lighting using T5 personally.
I think they would agree as well, but it's not as "clean and high tech looking"
But a nice T5 suspension light can be done as well.
I modified my T5's and did the nice wire suspension.
The light in the tank above is pretty much 40-50 micmols over the entire surface anywhere, well, other than the top of the rock in the center etc, but the plants all have very similar PAR.
So whether you use T5, MH's, normal FL's, LED's etc, you know the intensity requirements for these plant species.
This is far more useful and answers the relevant question and allows us to test and use a specific light for a specific foreground goal etc.
And that, not all the other heehaw, is the bottom line.
The rest is mere aesthetics.
You might want HQI's, they look nice etc, away from the tank more etc and not care about electrical cost, efficacy of light per watt, spread etc etc.
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