[DJ88]

IMO neither are really accurate.

With W/gal it is misleading.. As is W/ft^2. With both all you get is a ratio. With no real reference. It makes it seems that 400W of NO is the same as 400W of MH. Which it isn't. Not even close.

With W/ft^2 you are assuming you have the same intensity over all of the surface area of your water. and you don't. Especially if you have a MH. the intensity is focused over one spot mainly. With tubes it is spread out even further. With this spreading of the light over more area the intensity decreases massively.

As with any measure of light in a tank the main concern is how DEEP your tank is and how that light penetrates it. With each type of lighting your intensity increases and therefore the depth at which the light penetrates goes further. This is going from NO to VHO to PC and then MH. The light coming out of a tube(NO & VHO) is pread out over a long length. So you can only say that for each inch of a 48" NO tube it has approx 0.8333 w per inch of tube and that is radially. A MH puts out 400W of light in an element that is approx 2 inches long. As a guestimate that is 200W per inch of source. Can you see where I am getting at?

For example I had 320W(at one point 400W) of NO light on my old 90 gallon tank. The few corals I tried existed, nothing more. Most receeeded. But I had no growth and had to have them inches below the surface even for that.. in my 33 I have MH and VHO. And get explosive growth on most every SPS I put in. That is the only way to describe it. They are the same depth or in most cases deeper.

The intensity of the light in your tank decreases exponentially as you penetrate. So IMO both ways of measuring are kind of deceptive. The only way to really compare lighting is to measure the actual intensity of the light in various spots of your tank and then make a visual representation of this data. An easy way to do this manually would be to sit down and figure out small areas of your tanks water surface and sit and look at what light sources are above that spot. Even there you have a problem with this as light sources emit light radially. Not all in one small beam. You can assume that all of the .83W/" of NO is going down. But we know it isn't. This is where reflectors are useful. But even then there is light lost. If it all went into your water the inside of your lid wouldn't be lit up.. [img]images/smiles/icon_wink.gif[/img] I know, semantics but you get my point right? The only way to know how much light your tank is recieving is to measure it at the waters surface and all over the surface. Then show this in a graph to aid with passing this information across.

IMO adding how much wattage you have and using an arbitrary figure to create a ratio isn't a useful way to express how much light you have. There are too many variables.

I say just use your eyes and decide if you have enough light for what you are hoping to do by gaging it against a similar tank that is successful with what you hope to keep. Follow others leads. ie MH for SPS, Clams, LPS and softies, PC for softies n some LPS, NO for fish only. Even then it is dependant on how deep the light has to penetrate.

Did you get all that?? [img]images/smiles/icon_wink.gif[/img] [img]images/smiles/icon_biggrin.gif[/img]

[ 17 November 2001: Message edited by: DJ88 ]