Lighting for planted goldfish aquarium

David L. Burkhead · Joined: 16 Aug 2007 Posts: 26

One thing I've noticed in my research is that different plants that one
might include in an aquarium require different amounts of light. The usual
measure is "watts per gallon" which strikes me as a rather shaky measure
since it produces different light intensities for a wide, shallow tank as
opposed to a short deep one. But leave that aside for the moment, a more
fundamental question is "watts of what kind of light?" Fluorescent lights
produce more light per watt than do incandescent. And there are halogen and
metal halide lamps that have yet different efficiencies.

For comparison, direct sunlight is about 1000 watts per square meter (pretty
close to 100 watts per square foot) when the sun is directly overhead (which
technically only happens in the tropics) and becomes less intense as the
cosine of the angle between the sun and vertical. Virtually any artificial
lighting for a tank is going to be significantly dimmer than that. To
produce the sunlight of a bright summer day in my tank would require
something like 170 watts of light--more actually, since that 170 watts has
to be the energy of the actual light and not include the energy "wasted" by
the light. Figure about 400 watts for fluorescent and four times that (with
the consequent heat) for incandescent.

Obviously, you don't want anywhere close to that if for no other reason than
heat. Still, I wonder if the little 17 watt fluorescent that came with my
"starter kit" is really adequate.

So how much light does a planted aquarium really need and what options are
there to get it?

--
David L. Burkhead "Dum Vivimus Vivamus"
mailto:dburkhead@sff.net "While we live, let us live."
My webcomic Cold Servings
http://www.coldservings.com -- Back from hiatus!
Updates Wednesdays

Archived from group: rec>aquaria>freshwater>goldfish

dr-solo · Joined: 16 Aug 2007 Posts: 194

heat is the real consideration. you dont want to overheat the tank with anything
except "cool" lights. altho there isnt much difference between regular fluorescence
and "sunlight" types in terms of spectrum (both are full spectrum) there is a
difference in the intensity of certain spectrums, more blue in regular and more red
in "sun" types. the more red the better stuff looks, so get a typical light unit set
up for the size of your tank and then pop for the extra cost of one that makes the
fish and plants look good. at least with GF, most real plants wont survive long
anyway.

there are now some of those LED available, so check those out too. Ingrid

David L. Burkhead · Joined: 16 Aug 2007 Posts: 26

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
plants.)

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"
mailto:dburkhead@sff.net "While we live, let us live."
My webcomic Cold Servings
http://www.coldservings.com -- Back from hiatus!
Updates Wednesdays

ginko · Joined: 16 Aug 2007 Posts: 2

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. Smile

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
: plants.)
:
: 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.
: