I want to know if detailed work has been done to study growth of plants under florescent lights/ selected narrow bandwidths of light. As I understand it all florescent light emit in 2 or more narrow bands of different wavelengths. The K value of these lamps is an average. What are effects of different groups of these bandwidths on the plant growth, internodes spaces, leaf shape, colour etc???

Hi,
That is not really an accurate statement. The peaks you refer to are simply individual frequencies that have the highest energy compared to the other frequencies across the bulbs output spectrum. This may produce what we perceive as the bulb's characteristic "color" but in reality the bulb emits energy in most or all of the other wavelengths. If you were to compare the energy of those peaks with the total energy of all wavelengths it would be a small ratio. It is the area under the curve that determines to total energy output of the bulb.

Based on the spectral quality of the light plants will produce various pigments to adapt to the conditions with very little loss of efficiency. This may be expressed as hue or color changes but other than that I don't believe there are any other differences in growth rates or other physiological differences as a function of frequency. Any differences are more likely to occur as a result of differences in CO2/nutrient availability or due to light intensity.

I've grown the same plants under different bulb types and have not observed any significant differences.

These examples aren't scientific by any means but more illustrative. The first image is L. aromatica grown under T5 Daylight + Interpet Triplus. The second image shows clippings from the first grown under Daylight + Osram 840 which is an orangy bulb found in office buildings. Other than minor color differences I saw no difference in form, such as internodal distances or leaf aspect ratio etc., or in growth rates. In fact, in both cases, for this plant internodal distances varied more significantly as the distance from the light increased. From a practical standpoint therefore you can simply get the bulb colors you find makes the plant most attractive.



Cheers,

Would a particular color temperature be more likely to bring out reds or browns in a plant as opposed to greens?

While I do not know much about aquatic plants/botany I do know that in general plant leaves have two different types of Chlorophyll, types a and b. Each has an optimal absorption region at different wavelengths. Now if your bulb has a majority of the energy distributed in regions outside of these wavelength regimes, the plants would have to "work" harder to utilize the light energy for photosynthesis. I guess it is plausible that they could manufacture necessary pigments/chemicals so as to be able to utilize the light that they receive. This could very well also possibly cause a difference in appearance, but I am not sure if this is actually the case.

This article : http://www.aquaticplantcentral.com/f...osythesis.html

has some useful information, although I do not really know how scientifically accurate it is.

Carissa, from purely an optics standpoint, bulbs with a distribution such that they have a large percent of energy in the red end of the spectrum would bring out the red in these plants. This is simply because there is more red light for these plants to reflect. In addition, everyone's eye has slightly different sensitivity to colors and so while some color temp bulbs may look perfect to you, they might not necessarily look the same for other folks. Of course color temp has no real meaning in comparing different bulbs as it is some sort of averaging effect and is not really a true color temperature (like that for a black body radiator).

Whether different bulbs have the capability of bringing about color changes in the plants, more from a biological point of view, in that whether they would induce the plants to adapt and change their pigment/chemical constituents so as to better utilize the light from the bulb is a different matter and I don't have a good idea for whether this does happen.

Additional to the Chlorophyll a and b there are accessory pigments - carotenoids, xanthophylls, and flavonoids, and many others that absorb other wavelengths to convert the energy of those wavelengths. There are also pigments which reflect harmful wavelengths such as IR and UV.

The Barr Report Newsletter March 2005 discusses Photosynthesis.

"...Blue light stimulates malate synthesis in guard cells. Under red light, guard cells synthesize glucose and sucrose mainly; this metabolic pathway is deactivated by blue light, and metabolism switches to starch degradation and malate biosynthesis..."

Evidently, red light stimulates CO2 fixation while the addition of blue stimulates organic acid, amino acid, and protein building.


"...These other pigments allow a much greater range over the spectrum than Chlorophyll alone. SAMs can and do change the concentrations and type of these pigments to suit their
environment. Algae essentially do the same thing at the single or colonial cell level. Thus changing the spectral output does not gain the aquarist an advantage over the algae.. Furthermore, green microphytic algae have the same pigments as the SAMs..."

This is more or less consistent with what I observe. I see no difference in bushiness or legginess as a result of spectral variation. This makes sense because the spectral emission of the sun is wide and changes during the day being red(ish) in the morning blueish at midday, however due to the local environment of a plant at any given location, the spectral quality that plant receives can vary wildly from that of the sun due to shade or reflection. It would therefore be self defeating for a plant to only be able to use one or two narrow bands of light.

Cheers,

Thanks a lot! Great post and a good point about variations in light conditions in nature. Obviously plants need to be able to adapt...if they didn't they wouldn't be around to begin with.

So ceg4048, while growth isn't affected by variations in the light colors, have you noticed them taking on different colors? Do red plants take up the red pigmentation more strongly if they are exposed to a particular type of lighting?

^ That's what I want to know. Also, does red light mean lower K and blue, higher? My 10,000 K bulb really looks red when it shines on things, but actually it's probably more along the purple line so perhaps it's actually very blue?

I am sorry if I find the answers are slightly misdirected. How plants react to natural light, including the diurnal and seasonal variation in the spectrum is its natural adaptation to the environment. In the aquarium, especially the indoor aquarium, the plants do not receive natural light but we provide it with artificial light. MH or other incandescent bulbs do provide light very much like natural light (enough like the natural light for the range of adaptness of the plant). Florescent lights do not provide a light like the natural light, but being more efficient, especially the new range of fluorescents, fluorescents are very popular with aquarist. Among aquarium supplies are several premium priced fluorescents.

What I want to know is- has any detailed work on their effect on plants been done? If so where can I find it?

Well, I'll have to disagree with this and I think that perhaps the answer renders the question of MH versus T5 moot. There is absolutely no way that the spectral output curve of a Metal Halide lamp can in any way be compared to that of the sun - and I mean NO WAY. A review of the following website will reveal sample spectral plots of the sun superimposed on the plots of typical MH bulbs=> Facts of Light – Part 2: Photons by Sanjay Joshi - Reefkeeping.com

You can see on the very last plot on that page where the sun emits a fairly fat curve of all wavelengths across the visible spectrum in more or less even distribution although there is about a 40% higher peak value at blue (450nm) than at the far right where red is (700nm). In any case the curves are not even remotely close. In fact the spectral plot of the representative MH bulbs used on that plot looks pretty much like the spectral plots of typical daylight or higher Kelvin T5 bulbs. I mean, you could argue about the peak photon emission values or at what wavelengths the peak values occur etc. but MH compares quite similarly with T5 in terms of the shape of the plots.

Marine life is more finely tuned to specific wavelengths than freshwater plants so simply on the basis of these spectral plots I can't see any reason why MH versus T5 would generate any significant morphological or physiological differences in plants. There may be more detailed studies out there than I am aware of though.

So to the best of my ability to interpret, the question seems to boil down to: will my plants behave differently (flower, send out shoots etc) or grow differently if they are subjected to sunlight versus MH versus T5? Well I don't have any hard data to answer that nor do I know of any studies specifically detailing that. It would surprise me if there were differences between sunlight versus artificial light and, based on the spectral plots, it would completely blow me away if it turns out that there were differences between MH versus T5 but plants never cease to amaze me so I'll keep an open mind.

One other thing to consider is that many of our plants in nature are only flooded for half the year, grow emersed during the dry season and, they are almost always subject to nutrient deprivation or nutrient limiting so that any differences in growth patterns and behavior in the field versus in an aquarium should not be attributed only to what kind of light the plants receive. The ecology in our tanks has nothing to do with the plants indigenous ecology.

The whole question of Kelvin temperatures is a sticky one because the Kelvin temperature model originate from the thermodynamic concept of "black body radiation" wherein a theoretical "black body" emits certain wavelengths based on it's temperature. At room temperature it emits wavelengths in the infra red regime and as it heats up the emitted wavelengths become shorter. Just like the rainbow color sequence, the black body emits in the sequence: ROY G BIV as its temperature increase (red orange yellow green blue indigo violet). Roughly, the ROY range is something like 1000K-5000K and BIV range starts at around 10,000K.

For reference Kelvin degrees of temperature (K) is equal to Celsius + 273 so that 0C=273K and that 0K= -273C which is termed absolute zero (i.e this is as cold as it gets in the entire universe)

I also don't have any controlled data that maps specific color changes in any given plant as a function of bulb K temperature. It's just too tedious and many of my plants exhibit color changes as they grow under the same bulb type so it would be tough to correlate a specific color change with a certain bulb type.

Intensity seems to have as much to do with the color change but each intensity value also has spectral components so that when a plant has grown to 8 inches tall even though it is under the same bulb it's receiving more red or more blue than when it was only 4 inches tall so this could trigger the pigment redistribution. There are too many variables to contend with. I have A. reinikii growing under orange Osram 840 on one side and under blue/cool white on the other side. The first one looks orangy sitting in the tank of course but when I trim both and remove the clippings they look more or less the same to me under the sunlight.

Cheers,