# Re: Lighting for a 30 high...

```>That leads me to a related question that someone might be able to comment
>on.  When these rules of thumb are determined (such as needing 2-4 watts of
>light per gallon, or 5 watts of heater per gallon, etc.), are those rules
>created using the advertised tank volumes, or the *actual* tank volumes.

Probably not too much trouble to just use the advertised volume. Most of
the time, if you are covering the area of the top of the tank OK, it is the
depth that will dictate how much lighting you need. The watts per unit tank
volume rule is really just a very rough guide, and a way to get people into
at least a useable range of lighting. It's not an absolute law, and there
are many people with light levels below and also significantly above what
the rule would say is OK and they are still growing plants well. Probably
no point worrying about precise volumes with a formula as rough as "2-4
watts per gallon".

The heating rule is pretty rough too, and it will be the temperature
fluctuations of the room your tank is in that will really dictate the size
of heater you will need. In larger tanks and tanks with sumps there are
other factors that come into play as well. The rule will get you "in the
ballpark" up to maybe a 55 gallon or so. Tanks larger than that can save
some money picking heaters sized using their expierience or by asking
others on the list what size they use. You won't need the full 5 watts per
gallon on a 120 gallon, for example, as you will on a 20 gallon to maintain
the same temperature.

>if you measure my tank's dimensions (about 48"x13"x17") and do the math, it
>comes out to about 46 gallons.  So when a person wants to determine how

It is common to use the external tank dimensions to size the tank, but I
have seen that a lot of the mass produced tanks like to fudge the numbers a
bit. Probably for marketing, but at least when you get a 55 gallon tank you
are usually getting a tank with a certain basic shape and dimensional
ratio.

>(This seems similar to the computer monitor sizing nonsense that's been
>going on for years.  A monitor labelled as 17" only has an actual 16"
>viewable size... give or take a bit.)

The classic monitor size is the distance between the centers of the
mounting holes of the mounting tabs in the corners of the tubes, measured
diagonally. As a manufacturer, this is an important number since it says
how big a chassis you will need and where you will need to drill mounting
holes. This has been a standard for a *looong* time. Now that monitors are
much more prolific though, I agree that measuring the viewable area is
probably a better measure since it is what the customer is really looking
for.

-Bill

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Waveform Technology