Light in Watt/Gallon or Lumen/Gallon

[qsaark]

I like to ask a very fundamental question. When it comes to light needed for a planted aquarium, it is always mentioned as X watt/gallon. While this may be correct for incandescent bulbs, it cant be true for fluorescent bulbs. as we know, fluorescent bulbs can produce light equal in intensity (lumen) to incandescent bulbs while consuming 1/3rd as little power.

Now I understand that these days most of the aquarium hoods are equipped with fluorescent bulbs/ tubes. So should we not calculate the light in lumens/gallon?

[hwchoy]

watts per gallon is a simple rule of thumb only. of course the correct measure would be the actual lumens at the substrate but how do you easily measure that? hence a simple rule based on Wpg. btw, the rules is based on fluorescent tubes.

[|squee|]

It's also difficult to measure lumens output, not something that all planted tank keepers can do.

[XnSdVd]

Hmm... i believe i came up with a semi-workable alternative some years ago. Since most FL tubes have outputs in the 70-ish lumen/watt range and 1 US gallon =3.79 liters (damn americans and their medieval units of measurement).

70lumens per 3.79gallons = 18.5 lumens/liter

So since the rule is usually 2 to 4 wpg, it's safe to say 20 to 60 lumens/liter

[hwchoy]

makes no difference actually. what is required is the actual candles per area at the substrate, and if you nitpick at the required wavelength for the plants. lumens are adjusted for human eye sensitivity. On top of that it requires us to figure the lumens efficiency for all kinds of bulbs that we are using.

planted aquaria is not such an exact science anyway.

[XnSdVd]

Heh heh, that's why i'm using sunlight

[StanChung]

If somebody can invent/produce a cheap water proof lightmeter...
Then we can ignore other variables like water clarity, height of tank etc.

[Shadow]

Can the light metter that photogrpher usually use can be use? after make it water proof of course.

[StanChung]

It doesn't measure the full range of PAR-photosynthetically active radiation but it does give a good idea of how much light a human eye can see is available.