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-   -   watt/g rule: with or without reflector? (http://www.plantedtank.net/forums/showthread.php?t=41055)

Nix 01-18-2007 04:38 PM

watt/g rule: with or without reflector?
 
A question, please.

If we talk about watt per gallon etc. do we mean with or without reflector?
That's just a difference of 100% (or more), so it's not a small thing http://www.plantedtank.net/forums/im...on_neutral.gif

Thanks,
Nix

epicfish 01-18-2007 05:16 PM

With a half-decent reflector. All pre-made fixtures come with them.

Wasserpest 01-18-2007 05:37 PM

It's a very rough "rule".

Besides reflectors, the shape, type, and efficiency of bulbs plays a major role.

A linear flourescent bulb will allow you to reflect more of its output into the tank than a U-shaped PC bulb, and that one will be way superior to spiral compact fluorescent bulbs in terms of (reduced) restrike. A fat T12 bulb will lose more light due to restrike than a slim T5, etc.

Hoppy 01-18-2007 06:47 PM

The watts per gallon "rule" just gets you in the right ballpark for light. But, it seems that people are gravitating towards 2.5 watts per gallon, using AH Supply quality PC bulbs and reflectors, as a good amount of light. If you had just a plain white painted flat reflector, that would translate to closer to 3.5 watts per gallon needed. But, in any case it tells you that 1 watt per gallon isn't going to be enough and 5 watts per gallon is likely to be more than needed. I don't see a way to make it any more specific than that.

Nix 01-18-2007 07:06 PM

@ epicfish. Naaa. I just bought one without (idiot me). And I have a Hagen hood without one... And other countries other lighting standards with pre-mades and sets -- but that w/g rule you can find everywhere, regardless.

@ wasserpest. In a nutshell if someone says he/she has 2w/g it can mean anything from low light to high light, depending on the bulb/reflector system?

It's really rough, this rule. :)

I.e. I'm told again and again my light's too low with its ca. 1,88 w/g. But in my estimation (by the plants I grow well) it's in reality in the higher medium light sector.

Anybody with the same (frustrating) experience?

.Nix

BlueRam 01-18-2007 07:48 PM

Quote:

Originally Posted by Nix (Post 359330)
Anybody with the same (frustrating) experience?

In defense of the WPG metric it is simply easy to calculate. Sum the value for watts on all bulbs (Assume ballast power factor of 1 and efficiency of all fluorescents is the same*) and then the tank size listed on the box (ignoring that it is calculated based on outside dimensions, full to the top, and no substrate) and divide!

There are several candidates for replacement but none has really caught on.

After a while you learn to watch the plants and give them what they need.

*Assumptions as FAR from ideal!

Wasserpest 01-18-2007 08:44 PM

Quote:

Originally Posted by Nix (Post 359330)
In a nutshell if someone says he/she has 2w/g it can mean anything from low light to high light, depending on the bulb/reflector system?

It's really rough, this rule. :)

You got it. :icon_mrgr

Another glitch is the tank size... the rule is not totally linear. For smaller tanks, 2W/gal could be low light, while for large tanks it could be high light. There is also a "threshold" for really small tanks. Don't try to light your 1gal nano with a 2 Watt bulb! ;)


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