True the ati's and giesemann are the best but cost a pretty penny or two....
I've been doing a bit of reading about this because I'm also a skeptic on having a bunch of T5's and T8's to get high lighting requirements. But the way that I see it is that there is a lot more to the lighting requirement. Essentially our aim is to try to simulate sunlight (when lighting is concerned) and its effect at the sea bed. And this brings a whole lot of factors into account. We need to account for not just the intensity of light but I'm sure the spectrum of light that enters the tank. In this case I think is when MH's "shines out" from the rest. I know for a fact that water absorbs certain spectrum of light so this could also have a slight factor for deeper tanks. And I'm also not too sure what is the spectrum of light in terms of non visible rays from lamps. This I still need to look up.
Yes our closest measure comes from plant growth spectrum usage and is called PAR,now different globes produce different PAR and this is where it can get complicated as you need a PAR meter...now even this system is flawed as it is now believed that corals use a spectrum of light more in the PUR range so here testing kits etc are very very out of reach so for now unfortunately we cant go that deep into the exact details,In real world conditions though results seem to indicate that the more lumens a bulb produces then the more PAR/PUR it produces in general(although globes like ati and giesemann are the exception and produce a bit more PUR per lumen) so for the purpose of lighting a reef tank without becoming a mad scientist with expensive PUR meters etc who wants to find out how deep the rabbits hole really is
The reason for this is simple,fluorescents and mh that peak in a certain wavelength still give of lower levels of light in other areas of the spectrum like red,green etc but leds ALMOST ONLY give of light in a specific wavelength so now this forces us to start closely evaluating the actual spectrum needs of our corals and many are setting up experiments to show how much of each spectrum is ideal for corals to thrive especially sps,so far its been difficult to pinpoint as most results seem to show that certain colours like red are needed but only in a small portion which is hard to quantify since even LED's of the same make and model etc will give of different quantities of light per watt FOR DIFFERENT COLOURS!
I've also been doing a bit of reading in terms of the definition of the parameter Lumens and what I can gather is that its the intensity (luminous flux) of light multiplied by the "area" at which it shines on. I'm not going to any detail but I think this is what's also misleading when it comes to looking at this parameter for aquariums. Because the "area" at which light is emitted for a flourescent light bulb is essentially more than a MH (since the light is directed downwards) which is maybe why the intensity of light in terms of lumens is more for the MH than for an equivalent set of T5's and T8's in a marine aquarium.
I feel that its NOT misleading at all its a standard and gives the light a proper measurable value irrespective of if its a point source of light(mh) or a larger area that the light is being rendered from.The only time this will become a factor to consider is due to tank dimensions as in certain deeper tanks it becomes easier to provide enough even with t5 especially if the tank is very wide,when the tank is narrower yet deep then the point source(mh) becomes more practical...coral/anemone placement would also determine this as anemones like magnificas benefit more from a mh directly above it than t5 above it.
Remember t5 is also directed downward using reflectors so its simply a matter of the usage situation.
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