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Re: Watts/lumens (again?)
> From: IDMiamiBob at aol_com
> Okay, guys, help me out here. When we talk about two watts per gallon,
> are we talking standard florescents? <snip> But re we talking two 40-watt
> bulbs without decent reflectors? Or are we talking about light fixture
> bulbs without bulbs without of 50%.
The guidelines have been around for a while, and I'm trying now to define
something I didn't originate, so what I say is open for debate.
In this case, the rule of thumb is that two watts per gallon of pretty much
any type of fluorescent lighting will be sufficient for the large majority
of plants. Of course, I'm not considering UV tubes or anything that
exotic. Within the rule of thumb, reflectors aren't really considered, so
you can easily use your two watts per gallon and by improving your
reflector, you can get more PAR (photosynthetically active radiation) and
lumens (visible radiation) into the tank where your plants and eyes can
> And then what happens when we go to the local lighting store and find
> Philips ultralumes, which are visibly way brighter than standard bulbs?
> Or are wealready talking about the enhanced output bulbs when we say
> that we have two watts per gallon?
Since plants seem able to use wavelengths across the visible spectra,
additional brightness out of a tube probably help them that much more.
But, when we say we have two watts per gallon, we say nothing about the
quality of the light. We're just saying two watts of fluorescent
lighting per gallon.
The nice thing about aquariums is that if you can stand the way the tank
looks and have at least that much lighting, you're probably doing pretty
good for your plants. This 'probably' is the basis for the two watts per
gallon rule of thumb.
> Okay, I know that this is just a rule of thumb to simplify our tank
> planning and layout. Yet I read numerous discussions here about
> alkalinity, pH, ferrous compounds, EDTA, etc. ad infinitum which seem to
> get really really detailed, certainly more detailed than most of us need
> to get a handle on the basics.
With each of the factors that you mention, there are a bunch of different
ways to get the desired results, and for that matter, there are a range of
results that may fit the term 'desired', depending on the aquarist's goals
for aquatic husbandry. Lighting plays into this as well. With 2w/g, you
probably won't kill most of your plants due to lack of lighting. Some may
not do as well as others, and some may die, but they may die for reasons
other than lighting.
Here are a few considerations that come to mind that directly affect
the amount of light that arrives at the plants, but are not addressed by
the rule of thumb:
Lumen output of the lights
CRI of the lights
PAR of the lights
Reflective loss due to cover glass or plastic
Reflective loss due to the surface of the water
Proximity of lights to plants
Submersed vs. emersed growth
Reflective gain for emersed growth due to the surface of the water
Attenuation due to cover glass or plastic
Turbitity of water
Depth of tank
Light piping effect
Glass vs. plastic aquarium
Algae on plants
Algae on glass
Density of plants
Substrate color and reflectivity
> Now I want some more guidelines. I have
> three tritons over my 30 gallon tank. They look twice as bright as the
> bulbs that came with the strip lights, so do they count as 60 watts each?
> I am setting up my 55 to have one F40/T12-75UL, one F40/T10-50AX, and two
> Interpet Triton 40 watters. All ofthese bulbs are way brighter than the
> standard F40/T12 bulbs. Am I overkilling it? And do you know of a website
> for Philips or Interpet where the lumens ratings for these bulbs are
> posted? Or an address I can write to?
In my estimation, you are probably doing just fine. The rule of thumb gives
you an average minimum to start with. You can go up from there, and it
looks like you are. My favorite lights are the PennPlax Ultra Trilux. I
like these because of their brightness and color (bluish-violet). They mix
well with Tritons (more purplish) and cost about the same. Having said
that, I personally don't have enough money to go buying either Ultra Trilux
or Tritons, so I go with GE Chroma 50's, 75's, CW, and PL/AQ blends.
I think that in order to know what you desire, you need to measure PAR and
lumens at the plants in different parts of your tank I have neither a PAR
meter nor a lumens/lux meter, so I just tend to start with the rule of thumb
and then tailor my lighting to meet my goals for each tank.
I know I didn't answer all of your questions, but I hope this helps,
David W. Webb
Live-Foods list administrator