Re: Lumens and spectrum

["Wayne Jones" <waj at mnsi_net>]

Katie wrote:

I'm sure this topic has been beat to death, but I need some
reassurance...
There's too many opinions floating around on the Internet.

I reply:

Well you are probably going to be even more confused after reading the
various replies here.

Katie wrote:

1. Is comparing lumens the best way to judge lamp output for AQUATIC
plants? Is
lumens the most imporant out of other factors like CRI and Kelvin?

I reply:

None of these factors tell you much about how well plants will like the
light. Aquatic plants are so adaptable they seem to do well under almost
anything as long as there is enough of it. Some of these things can give
you clues as to how good a lamp might be for growing plants but nothing
definitive. For instance if two lamps have identical spectrums but one
lamp had more lumens than the other then the lamp with the greater lumen
rating would be producing more plant usable light. Or if a lamp has a
very high CRI then it is probably a full spectrum lamp. The Kelvin
rating might give you a slight idea of the spectrum of a lamp. A high
Kelvin rating means that it probably has more blue in the spectrum than
it's lower Kelvin brothers.

Katie wrote:

2. Do AQUATIC plants make use of all available light including the green
at low
light levels like 2-4 wpg ?

I reply:

From a plant growing point of view the ideal lamp would have a spectrum
that exactly matches the average photopic response of the plants you are
growing. Now I have not much of an idea of what that might be and I
doubt if anyone else has much of an idea either. It depends on the
individual plants most of which have probably never been tested. Maybe
they do use green, maybe they don't but lamps with wildly different
spectrums will grow the same aquatic plants very well. I think that when
all is said and done that sunlight is probably the best light source for
plants. So if I had to guess which lamp is the best I think it would be
the lamp with the spectrum that most closely matches the suns spectrum.
Just this morning the sun was shining directly in my tank and I was
thinking how much better it looked than when lit with artificial
lighting.

One thing that should be pointed out however is that while plants don't
seem to be picky about the quality of light they recieve, people are
very picky indeed.  Things like lumens, CRI and Kelvin are very accurate
indicators of how you will percieve a light source. You can use these
inicators to pick whatever lamp you like and the plants will almost
certainly be happy too. Most people like lamps of about 5000K to 6500K
with a CRI of at least 80. If you choose a high lumen lamp then the tank
will appear brighter than if you choose a low lumen full spectrum lamp.
Just make sure you have enough of it for what you are trying to do.

Wayne