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Lighting for planted goldfish aquarium
To revisit this, (and cross it over to rafp, which I didn't even know
existed when I started) recommendations for lighting (based on what
particular plants require in the aquarium) are generally given in "watts per
gallon" Well, I did some research on how much light is produced per watt by
different types of lighting systems as follows:
Tungsten Incandescent: 5-17.5 Lumens/Watt
Quartz Halogen: 24
T12 Fluorescent: 50
Compact Fluorescent: 45-60
White LED: 26/70 (some prototypes are running up to 150)
Metal Halide: 85-95
T5 Fluorescent: 104
So the question when trying to judge such recommendations remains "watts of
what kind of light?"
Example: Ludwigia Repens (one of the plants in my aquarium) calls for 2-4
watts per gallon. 58-116 watts in a 29 gallon tank (my tank size). The
problem 116 watts of T5 fluorescents is about six times as much light as 116
watts of Tungsten incandescents. If the recommendation referred to
incandescents, then 20 watts of T5 fluorescent would serve. (All of this, of
course, assumes lights with spectra that are reasonably useful for the
One thing I note, the metal halide lamps, they are less efficient than the
T5's, but they do pack a lot more watts into a smaller package. Which just
goes to show that "efficiency" is not the be-all-end-all of the matter.
David L. Burkhead "Dum Vivimus Vivamus"
"While we live, let us live."
My webcomic Cold Servings
http://www.coldservings.com -- Back from hiatus!
Lighting for planted goldfish aquarium
Yes, you have correctly deduced that watts per gallon is a rough
estimate and not an absolute rule.
I think typical plant guides dumb things down in such a WPG way is
because of the perception that people are not sophisticated enough
to be able to handle a more accurate accounting of aquarium light
levels. (i.e. counting the actual photons with micro-Einsteins
per square-meter per second)
I've read that this traditional WPG number comes from Normal Output
(NO) 40 watt T12 tubes. Now the most common tube is T8, which are
at least 20 percent more efficient. T5 and T6 are at least another
20 percent more efficient than T8.
Also, WPG glosses over the fact that we really aren't interested
in the light produced by the bulb, but in light produced by the
bulb and then sent down into the aquarium. A great reflector on
linear tubes can more than double this. Also note that a great
reflector prevents light from being wasted from shining from one
tube into another tube. So, most aquaium fixture are less than
great, and I would go so far as to say not very good.
Some bulb types don't allow great great reflectors. For example
Power Compact. PC tubes always shine light from one part of the
bent tube into another (restrike) and their physical shape prevents
a pseudo parabolic reflector. So, you really have to crank up the
wattage to get good CF results. And it seems to be quite silly to
get CF aquarium fixtures for the most common linear tube length
of 4 feet. But, that's what vendors have been pushing for the
past 5 years -- go figure!
Other bulbs types do allow great reflectors. Metal halides are
something of a small point source of light, so it's quite easy
to put a super efficient reflector behind the bulb. These send
pretty much all of their light straight down into the tank in a
narrow beam. Aesthetically, this is an almost theatrical spot light
with shimmering effect. Also, when you scale up past 500 watts, the
best some metal halides are more efficient than T5 in lumens/watt.
Linear tubes also allow great reflectors. The standard commercial
T5 HO fixture that does this exceptionally well is the TekLight.
I simplify light levels by delimiting with a count of four-foot
linear fluorescent T8 tubes in front of a good, but not excellent
reflector. Low is one tube, Medium is two tubes, High is three
tubes or more. It's still just a rough estimate, and it ignores
concerns about the depth of the aquarium. For example, a single
T5 or T8 tube with an excellent reflector provides medium light to
a not-very-deep aquarium.
I think the traditional WPG "rule" will be exterminated when LED
fixtures become cost effective. The best of them are now past 150
lumens/watt. In 5 years, we might see 200 to 250 lumens per watt
from them. Here's to the future!
In rec.aquaria.freshwater.plants David L. Burkhead wrote:
: To revisit this, (and cross it over to rafp, which I didn't even know
: existed when I started) recommendations for lighting (based on what
: particular plants require in the aquarium) are generally given in "watts per
: gallon" Well, I did some research on how much light is produced per watt by
: different types of lighting systems as follows:
: Tungsten Incandescent: 5-17.5 Lumens/Watt
: Quartz Halogen: 24
: T12 Fluorescent: 50
: Compact Fluorescent: 45-60
: White LED: 26/70 (some prototypes are running up to 150)
: Metal Halide: 85-95
: T5 Fluorescent: 104
: So the question when trying to judge such recommendations remains "watts of
: what kind of light?"
: Example: Ludwigia Repens (one of the plants in my aquarium) calls for 2-4
: watts per gallon. 58-116 watts in a 29 gallon tank (my tank size). The
: problem 116 watts of T5 fluorescents is about six times as much light as 116
: watts of Tungsten incandescents. If the recommendation referred to
: incandescents, then 20 watts of T5 fluorescent would serve. (All of this, of
: course, assumes lights with spectra that are reasonably useful for the
: One thing I note, the metal halide lamps, they are less efficient than the
: T5's, but they do pack a lot more watts into a smaller package. Which just
: goes to show that "efficiency" is not the be-all-end-all of the matter.
If you have a standard freshwater aquarium, you should replace the fluorescent lamp once a year or when they are exhausted; whichever occurs first. When the lamp has become an aging, color spectrum began to change. Although this is not obvious, because the eyes are so subtle changes, will cause algae growth in your aquarium.
I am reduced to four feet of linear fluorescent tubes T9 in a good light before the designated number of levels, but not very good reflector. Low is a pipe, there are two high as three or more. This is just a rough estimate, it ignores the deep concern of the aquarium. For example, a good reflection or single-T6 T9 fluorescent tubes to provide a medium is not very deep aquarium.
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