Watts vs Lumens Lighting Questions

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OneFishTwoFish

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On one of the other boards that I visit there was a lighting question asked and it started down this path but I haven't gotten a resposnse to my question on that board so I thought I would post it here too to see if anyone had any thoughts.

The question was about the rule of 2.5 wpg as minumum level to shoot for. My question was:

For plants, is what everyone should really be concerned with is the Lumens not really watts? Watts don't really provide any information as to the power of the light necessarily, just the power going into the bulb. As incandescent lights are very inefficeint what I remember is only 1/3 the power goes into the light.

For example:

A GE Standard incandescent 100W gives off 1190 Lums

florescent F40T12 40W gives off 2250 Lums

CF Plug-in 4-Pin High Lumen Biax® Item Detail uses 40W and gives off 2700 Lums.

Given that color temps were equal at 6500K wouldn't the CF but significantly better @ 40W and provide equivalent lighting as 220W incandescent (which is probably the lighting used to determine the WPG rule)?


By the way these numbers were grabbed from GE's website.
 
OneFshTwoFish,
I recently brought this point up also. I did not get a very substantial answer. That fact is a watt is nothing more than a measurement of power usage for that lamp. A lumen is the actual light output. The higher the lumens the more light output. A t-12 40 watt light and a t-8 32 watt light produce different lumens. The 32 watt t-8 will actually produce more lumens than the 40 watt t-12 will. So where does that take us? I think the wattage rule is more of a guideline than it is a rule. My 55 has two t-8 32 watt lamps. According to the wattage rule I am under wattaged for a live plant set up. My plants are growing just fine, as is the algae that I am having problems with, but that is another thread. Hope this info helps. Remember this is just the basics. You can dig in deeper with different ballasts and styles of lamps like octrons and stuff like that but it is easier to keep it simple.
 
OFTF,

I agree with muskieswen in that WPG is just a guideline. Watts merely list the power the lamp uses. It has nothing to do with the lumens of the bulb or with how much of the light actually gets into your tank.

I'm using an All-Glass Triple Tube Strip Light that uses 9325K t-8 bulbs. These are on a 75G tank. I am also using the t-12 (6500K) lamp that came with my tank. So, I have a total of 136 watts on a 75g, far below the 2wpg rule.

I am growing Rotala macrandra and Eusteralis stellata both of which are said to be difficult to grow and require very high light. They are doing very well. My plants begin pearling within 30 minutes of lights on and I've had to trim every week.

When I decided I would add plants to my tank I figured I could always add more light if the plants needed it. So far they haven't. But if they do, I'll probably get another of the Triple tube strip lights. Hope this helps.
 
Yes, wattage is measure of energy use only and says nothing about the spectrum. Lumens is measure of percieved brightness as seen by the human eye - which say something about the spectrum but not much that is useful to pants. People see green light best of all, and plants don't use green light, they reflect it - which is why they look green to us.

Wattage is not a great measure, but if you are talikng about loading NO fluorescents atop a planted tank, it is a much better measure than lumens. That because with lumens you are relying on the aspect of the tube that means least to the plants.
 
I think that the point to remember is that the advice is seldom just 2-3W/g NOF over the tank. Usually colour temperature or bulb type is also mentioned.

I agree that the W/g mneumonic isn't perfect, but we're not talking rocket science ;) . 2-3W/g of proper fluo, at least 6500K seems to be the standard recomendation. I think that with the caveat that you need the proper spectrum in the bulb, the W/g measure is fine, the evidence is certainly there, right?
 
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