Lighting question?

[Dave001]

Hey everyone,
Just looking into lighting for my 125g tank, been doing a bit of reading and have come across a lot of conflicting info.
Most people say 3wpg of light is needed for plants, but of what type of lighting is that rule based on?

To better explain my question.
Based on the info I've found on the net comparing different systems of lighting and there light output, and working on my tank requiring 375w of lighting, I've calculated that 375w of incandescent lamps (3x100w + 1x75w), has the same light output as 80w of fluorescent lamps (2x40w 48 inch T8's), which has the same light output of a single 50w metal halide bulb.

Now I'd consider 2x 48inch 40w fluorescents to be standard fish only lighting for my tank, so I take it the 3wpg rule is not based on incandescent lamps, and is maybe based on fluorescent lamps, but I also see people advising the use of 150w of metal halide for a 55g tank, which would equate to 240w fluorescent lighting, you can see why I'm confused.

I already have 2x 48inch 28w HO T5's (which is suppose to be equivalent to 2x 48inch 36w T8's) on my tank, and was planing on adding the same again to the hood (so 4x 48inch 28w HO T5's), but now I have no idea what to do.

Thanks for taking the time to read, and any replies would be greatly appreciated.

Thanks,
Dave

 

[budrecki]

I have a new 180g and I am having the same proble. Trying to figure out proper lighting for livr plants is not as easy as 2-3 watts per gallon.


If anyone has a simple answer I would love to hear from them.

 

[beviking]

"375w of incandescent lamps (3x100w + 1x75w), has the same light output as 80w of fluorescent lamps "
Are you speaking of lumens? Plants could care less about lumens (a measure of what people see).

The wpg rule is based on normal flourescent lighting. Many experienced aquarist classify low light and high light plant tanks as "easier" to manage than the mid-level light tanks. At 3wpg, you can grow most plants. If you start out with 1.5wpg, your choice of plants is limited and if you want to switch later, that's a hassle, which is why most say 3wpg (which is considered high light). With high light tanks, you would inject CO2 and dose nutrients providing optimal growing conditions for plants which makes it hard for alge to thrive.
I have no experience (practical or reading) with T5's but if they are "equivalent to" 48" T8's (which I do use), I'd say 4 over the tank is marginal. O.k. if you're injecting CO2. Some higher light plants won't do too well. But your tank is 6' long correct? Do you plan on having 1' at each end underlit or 2' at one end darker?
Do you plan on keeping high light requiring plants? Are you prepared to do the required maintenance required to keep a high light tank? I'm not trying to disuade you from anything, just enlighten! :laugh:

 

[Dave001]

First off, thanks for your reply, beviking.

Are you speaking of lumens? Plants could care less about lumens (a measure of what people see).

I would have thought plants would care more about lumens (a unit of measurement quantifying the amount of light emitted from a light source.), then watts (a measurement of how many joules/sec an electrical device consumes power). But that's why I asked for help.

The wpg rule is based on normal flourescent lighting.

Thank you, now I have something to work with.

Many experienced aquarist classify low light and high light plant tanks as "easier" to manage than the mid-level light tanks. At 3wpg, you can grow most plants. If you start out with 1.5wpg, your choice of plants is limited and if you want to switch later, that's a hassle, which is why most say 3wpg (which is considered high light). With high light tanks, you would inject CO2 and dose nutrients providing optimal growing conditions for plants which makes it hard for alge to thrive.
I have no experience (practical or reading) with T5's but if they are "equivalent to" 48" T8's (which I do use), I'd say 4 over the tank is marginal. O.k. if you're injecting CO2. Some higher light plants won't do too well. But your tank is 6' long correct? Do you plan on having 1' at each end underlit or 2' at one end darker?
Do you plan on keeping high light requiring plants? Are you prepared to do the required maintenance required to keep a high light tank? I'm not trying to disuade you from anything, just enlighten! :laugh:

My tank is only 4ft long, and I don't plan on keeping many plants at all, just a few assorted broad leaf plants, swords and java fern, just enough for my Discus to feel comfortable in. I currently do daily water changes of 50% (which will have to change with the additon of plants), so I think i'm up to the maintanance required.
As you say, switching over to better lighting is a hassle later on, so I'd rather just do my homework and get it right in the first place, just in case I'd like to add more plants later on.

Thanks again,
Dave