Hi,
All lighting is suitable for plants. If you can see the light then it's useful. The difference between the various technologies of light is simply the percentage of the energy produced by the bulb which is light and not heat or other form of radiation. For example, the energy output of a typical incandescent light bulb contains 15% light and 85% heat (infrared). The plants will use that 15% but that means a 100 watt incandescent bulb is only producing 15 watts of useful light, so it would be very inefficient to use these bulbs. All this means is that they are not efficient, not that their light output is irrelevant. The energy output of halide/HQI and so forth is somewhere around 40%-50% visible light and the rest is infrared and ultraviolet. This is a much more "useful" percentage. I'm not sure what the percentages are for LED, but does it really matter? If the percentage is low then all that means is that you need more LEDs to do the job and that you'll pay a little more for the electricity. If the percentage is high you'll just have to be more careful not to use too many otherwise you'll have algae problems.
Lord_Lucan said:
I would have thought a 200lph filter combined with an additional pump would be adequate circulation but then again I could be talikng rubbish. The feedback I am getting is that there is a massive difference in succesfully achieving a 30" tall set up against a 24" set up, would you say this is the case?
Well there are two issues involved here. The first is to have adequate flow rate, which I assume you do based on the 10X rule, but the second factor is how the flow is distributed and how effectively the CO2 is dissolved. Distribution is very tricky because inattention to flow
patterns can easily result in stagnation points and destructive interference. The energy of the pumps must be translated to a certain velocity across the surface of the leaf. The CO2 must be dissolved within that mass velocity in order to be transported to the leaf surface.
It's easier to do this in 24 inches than it is in 30 inches simply because the inertial forces acting against the transportation of a unit mass of water across these distances are more prohibitive as the distances increase.
On the other hand light energy dissipation typically follows the inverse square law, so that the energy loss is quadrupled if the distance from the bulb is doubled. The light falloff difference from 24 inches to 30 inches is about 60% which sounds like a lot, but all the plant has to do is produce more chlorophyll and to pack them more densely per square centimeter. So plants at 24 inches are less efficient food producers than plants sitting at 30 inches. Making extra chlorophyll is easy for plants but making more Rubisco to capture more CO2 is a lot harder. Ironically, if flow to the substrate is poor, it actually helps the plant that there is less light.
So when people experience failure with deep tanks they typically blame it on poor light penetration, when actually it's almost always due to poor CO2 penetration. I appreciate that the monetary outlay for the lighting is significant and that you want to make the right choice, but the only thing you have to worry about is to not exceed the energy levels. You don't have to worry about what color or what suitability. You can get bulbs to suit your taste. This is never an issue. It is excessive light energy levels combined with poor CO2 injection techniques and poorly designed flow distribution that result in deteriorated plant health and subsequent algal blooms.
If CO2 and flow distribution is well implemented, the only penalty of the light falloff for a 30 inch tank is that growth rates will be slower than if it was 24 inches. The health of the plants however will be excellent.
Cheers,