WPI vs WPG

[DongShenYin]

Here's a question: Why don't we measure light by a "watts per inch" rather than a "watts per gallon" rule? Say, 5 watts per 1 inch of depth? That way, a 10 inch tank would have at least 50 watts on it and the corals would be very happy... Hhm of course the light has to be spread evenly across the width of the tank too.

[Physh1]

These measurements INO are very vague and general to how much light is actually "needed". It really needs to focus on what you plan to keep and how the rockwork come into play. WPG would be more usefull than WPI because at least WPG give a sense of size when it comes to the tank. WPI is really vague in that sense.

 

Cameron

[DongShenYin]

Durn and here I wuz hopin ta make things easiah... like sayin a shroom needs 3wpi but a clam needs 8wpi... Oh well, back t'the drawin board!

[kryptonite]

I think DongShenYin has a very valid point. Of course wpi is a very vague rule but no more vague than wpg. Like for instance why does a 30g tank that is 18in deep need double the light of a 15g tall that is 18in deep. Depth really is a larger factor in my eyes than that of volume.

 

Good thinkin' DongShenYin, I was acctually thinking that myself earlier today as you can see I posted a question about lighting for my 15 tall earlier.

 

That's my 2 cents,

Nathan

[Physh1]

Depth is important BUT the fault in DongShenYin's theory is that is abolishes the idea of width. You need to take width into considereration when lighting a tank:D. WPG takes that into account, kinda, and therefore less vague than WPI.

 

Cameron

[kryptonite]

True dat, hehe. But width is more of a "common sense" kind of thing than depth. Width is much much easier to account for. In fact, people use his exact theory with depth on measuring for "amount of lights per foot of width" (or however you want to refer to it) every single day. I've heard plenty of people recommend using one MH per two feet of width. Aren't they using his exact theory just with width instead of depth? Who says we should combine the two into one consolidated measurement? It seems to me that we would be much more accurate by simply taking seperate measurements of both width and height for a much more concrete solution.

 

Thanks,

Nathan

[blufrogu]

i think b/c we're keeping nano reefs getting exactly the right amount of light is more crucial than a larger tank where the wpg rule seems to apply more towards. imo you should shoot for the minimum - I've run into problems before with heat (was running 36w PC on 3.5 gallons, ambient temp was like over 100 F one day). Reducing any heat source is a good thing, especially if you're running anything below a 5 gallon.

 

another thing is that with fluorescents the light is evenly dispersed by the width of the bulb. and with MH lights the source is a single point. 2 points to look into (shuffles thorugh physics notes) is that intensity will decrease exponentially with distance from an electromagnetic field of a point source. a fluoro's EM field of intensity would look like an extended cylinder. with like a spider reflector it should compensate around the front and back because the distance traveled by the reflected rays are shorter than in the middle, therefore intensity of the reflected waves should be higher along the edges. but unless it's a circular pendant reflector it shouldn't help the width lighting for a MH light and also if your tank is rectangular.

[DongShenYin]

I've also read that the wpg rule should be tossed in favor of the watts fer square feet rule... That we should use 40-70 watts per square feet, or something like that. But I guess unless you switch the lights around and clinically test your corals under each type, its all theoretical?

[Cyber]

Hello,

 

I think the definition of light vs tank must defined base on the ratio between the wattage of the light and the distance of the light to the spot right underneath the light.

 

Let's take it to the extreme. A 10gal with the light 1' from the bottom of tank has different intensity when compared with the same 10gal with the same light but the light now is 2' from the bottom.

 

So the true definition of how much light should be "how X wattage that all the live stock receive from Y distance" from the light. For example, to keep a clam, the user must place the clam 1' from a 175W light. Of course PC and MH give different intensity too.

 

The clam thing is just an example, dont bite me

 

Just a thought,

Cyber

[yellowtang]

I was thinkin about the exact same thing last nite...(i need to decide on lights for my 29gal.)

[Kites315]

Use depth for the wattage of lamp, and width and lenght for the number of lamps, just my opinion

 

Kyle

[DongShenYin]

And how does one calculate that? 10 gallon tank = x number of lamps with y wattage? The viables of x and y dependent on the animals kept....? Anyone map this out?