Are all lighting watts equal??

[fandsw]

SO, I've read just about every FAQ on lighting and planted tanks I can find, so I have this simple question: are all lighting Watts equal, even if using a similar technology such as Flourescents and Compact Flourescents?

For instance, my new 72 gallon bowfront has 18 different plants in it, planted about 2 weeks ago in Flourite. It has the All-Glass Compact Fluorescent light, 2x55W 9325K bulbs. By all accounts, my plants shouldn't be doing as well as they are as I've only have 1.53 wpg. However, all my plants are showing some growth, some more than others.

It seems to me that the 2 wpg minimum rule is a little to generic, as factors such as light efficiency, temp curves, light spectrum, etc. are ignored in the 2 wpg rule. Everything I've read is that the Compact Flourescents are much more efficient that regular flourescents in their lighting, however they still seem to be held to the same 2 wpg rule. Am I missing something here?

Frank

 

[Guest]

For most purposes on tanks from 20-75 gallons the WPG rule works. Also Fluorescent watts are watts. Same for MH watts. But remember that reflectors can make a difference as well as the type of bulb. CF lights are more efficient but you still need the raw watts. You don't say what kind of plants you have and in a two week period many plants will not show the signs of light deficiencies. But if you have stem plants in there and they have not grown at least half as long as they were when you got them then they are not receiving enough light.

 

[William]

Two weeks, they could just be living off reserves that they had built up while in a healthy display tank.


I know that happened with me in a tank that was underlit, I got a plant in there.. and it absolutely FLOURISHED! Grew huge and fast, for the first few weeks... then when it ran out of reserves it had built up, it began to wilt and die.



another thing is that, there are different plants. Some require very low light, some requires very high lights.


[EDIT]
Heh, simul-post Rex

 

[Guest]

Looks like it William.

 

[loganj]

Although I'm not a planted tank guru, I can tell you a little about lights. A watt is a watt...true. The difference comes in the intensity of the bulb and the area that the light is concentrated. For instance, if you had a 4x65w PC system, the 260 watts of light would be evenly spread out over the tank. If you had a 250w MH, the light would be limited to about 2' of the tank...the areas on either side would be much dimmer. The wpg rule is a general guideline and isn't really the best guide for setting up lighting for a tank. The light from a MH is much more concentrated than a PC. A PC is more intense and concentrates the light better than a NO bulb.

 

[fandsw]

Ok, I see what you guys are saying, but here is the problem I have with the wpg rule: a watt is a measure of energy used by a device, in this case a lightbulb. The amount of watts a bulb is rated has NOTHING to do with the amount of light it generates, only how much energy it uses. How that energy is used in a lightbulb can vary greatly, in terms of heat efficiency, lux, color spectrum, etc. Two different 60W bulbs could put out a totally different type & amount of "useful" light for our purposes, i.e. a planted aquarium.

I could conceivably put together two different light strips for a tank, one putting out 1.75 wpg while the other putting out 2.25 wpg, and for the purpose of growing plants in an aquarium the 1.75 wpg could be putting out more "useful" light for the plants than the 2.25 wpg light is.

My point is this: To me, the 2 wpg rule is a good rule of thumb, but by no means is it an absolute rule. In my reading on this forum, other forums, and faqs I've seen the 2 wpg rule used too much as an absolute rule, which might cause someone spending extra money on lights to help make their plants grow while the problem might be elsewhere (substrate, fertilizers, water chemistry, plant type, etc.).

I've seen some sites that go into the scientifics of different bulbs and their light output with respect to aquariums, but they get bogged down too much in the scientifics. I'd love to see an intermediate approach, one that's a little more detailed than the wpg rule that takes into account more light bulb factors than just watts.

 

[loganj]

Well, IMO, probably the best lighting you can use for a planted tank would be either PC's or T-5's. You really don't need the intensity of MH and you'd have to set up C02 injection if you did use them. Plants don't seem to be too particular about the spectrum of the light they get. I wouldn't use actinics of course, but I've seen some nice planted tanks that were using "cool white" bulbs at around 3400K. I think as long as you stay in the neighborhood of 2 wpg using either PC or T-5 and use bulbs from 6500K to about 10000K, you'll be fine. The 6500 will have a bit of a yellowish tint to it while the 10000 would be a much whiter light. JMHO. It also depends on the depth of your tank. A deep tank will require more light than a shallow tank.

 

[fandsw]

Plants don't seem to be too particular about the spectrum of the light they get. I wouldn't use actinics of course, but I've seen some nice planted tanks that were using "cool white" bulbs at around 3400K.

That's part of my point, 2 different types of bulbs with the same wattage providing different results

I think as long as you stay in the neighborhood of 2 wpg using either PC or T-5 and use bulbs from 6500K to about 10000K, you'll be fine. The 6500 will have a bit of a yellowish tint to it while the 10000 would be a much whiter light. JMHO. It also depends on the depth of your tank. A deep tank will require more light than a shallow tank.

Another valid variable that effects the wpg rule, depth of tank. A light strip that does fine on a regular 4' 55 gallon tank would have problems getting enough light to a 55T tank.

One thing I've learned is that even considering all the different factors is that my 2x55W PC light strip will be replaced by a higher power one in the future if I really want my 72g bowfront to get the denser vegetation than I presently have, probably something like AHsupply's 2x96W kit. The wife will *shoot* me when that time comes......

Frank

 

[malkore]

a watt is a watt....a lumen is a lumen...and a lumen is a measure of light output, while a watt is just how much power the bulb consumes.

but a 40watt normal fluorescent tube puts out fewer lumens than a 36watt power compact bulb - thus the reason power compacts have more intensity than normal fluorescents.

 

[OneFishTwoFish]

So really for plants what everyone should really be concerned with is the Lumens not really watts? 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 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.

 

[TheNewGuy]

Lumens are the way to measure and get a accurate idea of how much more intensity you are going to get from one bulb type to another.

I currently am in the process of converting my 135g to a planted tank. I plan on using T-5's for my lighting. With proper reflectors and bulbs I should be able to run my tank for high and low light plants on only 3-4 80W bulbs. The intensity of the bulb and performance of the reflector are the key factors in the lack of wattage. Another added bonus is the lower power bills . BTW T-5 daylight bulbs should last about 24 mos before they start to lose their color.

HTH