Hi..

There's lots of talk about Light. Kelvin, spectrum, what's best, what's not ..

But is there anything outthere with some substance? other than hearsay, opinions and grapevine talk?

Many people suggest using Grolux, plantlight IE low kelvin light, but I also heard that originally the grolux/plant light were designed to help terrestrial flowers increase budding, and then later they were picked up by aquarists..

Using low K tubes look ugly, and you have to combine it with higher kelvin tubes.. but in order to properly combine them, you really need to make 100% sure that each tube/bulb or whatever, actually reach all the plants.. there's no point in having 2 different tubes if they only reach 50% of the plants each..

What's your take on Kelvin?

I understand that the spectrum is more important than kelvin.... bulbs or tubes with an allround high spectrum are better....


Do you, Tom, anyone, have anything scientific on this? any papers? anything I can look up?

I am tired of people's opinions on this.. I want hard facts.. or at least something that's been tested...

I think the general consensus is that it doesn't matter whole lot what bulbs you use, since plants can adapt to quite a variety of spectrums. Anecdotal evidence suggests that it doesn't matter a whole lot, other variables have a much greater effect on plant growth than spectrum or kelvin. As far as evidence, it's a difficult thing to test, since you have to control for so many variables, I'm not aware of any tests that have been done that would provide application to our purposes. If there are, I would like to see them too.

Hard facts need hard data.

So........that means rates of growth.
Not colors that we like, that might be more a psychological test of aquarium light preferences

Not my cup of tea.

The questions we often ask as researcher's is what is it that we are testing and what do we hope to answer?

Will this data and test tell us what we want to know?

I'm not clear on what K ratings mean to plants.
The entire spectral spikes over 400-700nm, which are sometimes shown, these can be somewhat informative.

Still, hard to compare.
So you really are left with this opinion.
So this is not bad as some seem to suggest either.

I pick the lights that look the best to my eyes and that is that.
Easy.

The rates of growth based on micromoles if equal will be the same.
The studies do show that. But when you move into opinions and marketing garbage..........all bets are off.

But they also do not mean that much in terms of the plants.

So I'd suggest not getting too excited about it, and choosing something that you personally like.

Regards,
Tom Barr

I agree. Finding the right light.. for your eyes, is the important bit..

I am actually trying to find something to either support or discredit some of all the rumors, opinions etc. that float around in forums etc.

I see so many suggest plant tubes.. low kelvin.. red light tubes... it helps photosynthesis etc. it's the best for plants, it makes the plants more red ..

all these opinions are just that...opinions, hearsay and make believe.. Is there nothing concrete somewhere?

It would be impossible to develop the hard data you seek. We all use bulbs that are far from being black bodies, so the color temperature of the bulbs is mostly a marketing number. The fluorescent bulbs most of us use have spectra made up of various spikes at various frequencies, and of various heights. That light is nothing like natural.

To do a meaningful test you would need to test each spike in the spectrum, alone or in various combinations with other spikes, or with a true black body background spectra. You would have to make sure the PAR values for each combination were the same, an impossibility by itself, since the PAR values vary widely throughout any tank. When you finally got done you would still have to select an available bulb, with whatever color temperature and spectra the manufacturer uses. Then, you would soon find that the spectra varies as the bulb is used for hundreds of hours. Finally, you would need to be satisfied with how the light looks to your eyes or you would be unhappy even if the bulb resulted in great plant growth.

So, this is an area where we just pick what looks good to us, with only some wildly inaccurate numbers to help us make our decision. Fortunately our eyes are designed to make things look like we are used to them looking, so almost any bulb will soon look natural to our eyes.

I do agree. What I am searching for is some reasoning for using grolux tubes for instance...

Hi Martin,

since you seem to be very interested in the topic I've pulled out what I've found on the net over the last couple years.
It's indeed not much as others have already stated and you have to do some googling also. Sorry about that but for some
of the research papers/discussions I don't have the URL's anymore.


1. Photosynthesis, action and absorption spectra using bacteria

Botany online: Photosynthesis - Light Reactions

users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/ActionSpectrum.html


2. Experiments carried out using algae suspensions

"On the action spectra of photosynthesis and spectral dependence of the quantum efficiency",
Y. Zeinalov, L. Maslenkova, Bulg. J. Plant Physiology, 2000, 26(1-2), 58-69


3. The following research was done using terrestrial plants

"Light signals and the growth and development of plants - a gentle introduction"

Pedro J. Aphalo, 2001, Dep. of biology and faculty of forestry, University of Joensuu, Finland


4. Tom has done a nice summary also in one of his newsletters. Give it a good read if you have not done already. You also might want to look out for the extensive reference paper list at the end of this report.
Well, I just realized that the attached pdf seems to have disappeared. Tom, please help!

"Phytochrome, Photoreceptors and their Roles"



Best regards,
Detlef

Years ago I found that Grolux bulbs supply more red light to the tank, and that was very pleasing to look at, not because of the plants, but because the red colors of the fish really looked great. So, for a few years I used one Grolux bulb in the mix of bulbs I had on any tank I had.

Now that I have learned to grow plants - not real well, but I can grow them - I like having some red light over the tank to make the reds in the plants look great too. In my opinion that is the attraction of the GE 9325K bulbs. It isn't science, just esthetics.

There was a nice paper done comparing the plant buylbs to those of cool whites.
It basically said that there was no difference in relative growth rates which is the main criteria for comparing preferences or which is better(with higher biomass accumulation = better).

This is a good post from one of the old SFBAAPS members:

Re: Watts, lumens and hogwash

Critical experiments show that maximum growth of most plants under cool white fluorescent lights will be equivalent to or better than that obtained under the blue-red phosphors. Work by V. A. Helson, Canada Department of Agriculture, Ottawa; and J. W. Bartok and R. A. Ashley, University of Connecticut, indicate that there is no advantage to the use of blue-red fluorescent tubes except for aesthetic purposes. Some of the names of these special tubes are Grolux, Plant-Gro, Plant Light, Vita Light and Optima. The higher cost of these fluorescent tubes may be justified on experimental or aesthetic grounds but is hardly warranted on the basis of plant growth.

So there you go.
Now while this cited some extension guy.............this is just rehash from his statement above, I've not found the specific study, I do recall seeing it once and the RGR's of the plants.

With time, most every plant will adapt pretty well to a number of spectra outputs.

So the original claim is valid and the question is answered.
The bulb makers and all the other folks making Gro lux bulb claims are pretty much full of beans near as anyone can tell.

That said, I chose bulbs based on what I like.

Regards,
Tom Barr

Now we're getting somewhere.. thanks for these links.. I found the 'krib' exchange on this as well... good reading..