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Lighting Myths
I have to say, that it is _truly_ amazing how many misconceptions about
lighting continue to be posted on this list, considering how many times
we've covered the same territory. You'd think we could at least come up
with new, novel incorrect ideas.
>Which is better? Neither. The Sun is the best and most
>unpredictable. Since most of us avoid sunlight as a main light
>source for plant tanks, we'd opt for light bulbs whose color
>temperatures very close to the Sun's. Say, 5700K.
The sun is not necessarily "best". Many aquarium plants actually come from
areas with some pretty heavy shade. And as for the color temperature, it
depends on the time of day you're discussing, and the distance from the
equator. There are other factors as well.
>If the Sun has a color temp. of 5700K, and we know C50 has
>5000K and Daylight, 6250K, the answer to which is more suitable
>for plants is obvious.
Even assuming that your first premise was correct, it isn't obvious to me.
5700K is pretty close to right in the middle between the other two.
Sue wrote:
>> I haven't yet figured out why, because the "Super Daylights"
>put out more
>> lumens and a whiter light. Could the less compact growth of
>stem plants be due
>> to the difference in spectrum? I was under the impression
>from reading this
>> list, and other information, that spectrum isn't as important
>as the total
>> output of lumens.
Joe responded:
>I have to disagree. The first thing I look for in fluorescent
>light bulbs is a color temperature as close to 5700K as
>possible. If it's 3000K(most are, like compact flourescent),
>I'd undoubtedly put the product back to the shelf and look on.
And of course, kelvin temperature has absolutely nothing to do with the
spectral output of a tube. It, again, is only a measure of how it "looks"
to the average human eye. (and since we have people who see the same bulbs
as either "orange" or "pink", you can see how accurate average human eyes are.
>> I like the color better when I mix them, 2 Supers/3 Chromas.
>>The Chromas alone
>> give off an odd tint, though not totally unpleasant.
That's an excellent, and the only reason I can think of for choosing a
certain bulb based on color.
Kelvin rating is no more an accurate representation of spectral curve than
lumens is of PAR. The big difference is that spectral curves for many
bulbs are available for the asking from manufacturers, while we have to
depend on people like Pete Mohan to give us PAR information on particular
bulbs.
When we get back to picking bulbs from the information available on the
package, we're back to the following:
*Lumens/watt aren't usually listed on the package, and will only tell you
how bright the light "looks" anyway. Except for tri-phosphor bulbs, high
lumen rating will probably yield the lowest PAR rating.
*Kelvin rating is often listed, but will only tell you how the bulb will
look to you. It's good for deciding if you'll be happy with the look of
the tank with the bulb over it. Nothing more.
*PAR - Unless you can get the readings from TAG for the particular bulb
you're looking at, or you can talk Pete (or someone else with a PAR meter)
into testing a particular bulb for you, you can forget this one. The
manufacturers don't test for this.
*Spectral Curve is rarely available on the packaging, but is usually
available from the manufacturer. This is worth digging for, because it's
_not_ that hard to get, and it actually gives you some useful information
about how it might grow plants. Ideally, for plant growth, the bulb should
have strong spikes in the red and blue areas. Many tri-phosphor bulbs will
also have a spike in the middle area, which gives them more "eye appeal"
than typical purple-ish "plant" bulbs.
*Watts are listed on every bulb, and still are adequate for "rule of thumb"
purposes. _ANY_ fluorescent bulb combination will produce adequate growth
at levels of 2-3 w/g. When assessing how many energy efficient T8's are
necessary, count the bulbs as if they had the same watt rating as SO bulbs
of the same length. For example, a 32W 4 foot T-8 can be counted as having
the same light potential as a 40W 4 foot SO tube.
People can debate their preferences all they want. I certainly have my
own. But if you're discussing anything other than spectral curve or PAR in
regards to their usefulness for growing plants, that's all they are -
preferences.
Karen Randall
Aquatic Gardeners Association