# More thoughts on Color Temperature



## i4x4nMore (Mar 31, 2008)

Recently, I've been seeing posts in which people express that Color Temperature is an important factor when choosing fluorescent bulbs to grow plants - whether it be T5 NO/HO, PC, CF's, or other fluorescent variants.

In response, I have been replying with my opinion that it doesn't matter so much whether one uses 3000K, 4100K, 6500K, or 10000K because these values don't really tell you the actual amount of red and blue wavelengths that are present in the spectrum of the fluorescent bulb. A large part of my opinion also stems from the fact that bulbs of different color temperatures from the same manufacturer tend to give similar measured PAR values.

But after thinking about my responses, I wondered if I was answering with too broad of a stroke and, hence, implying that color temperature doesn't matter at all to plant growth.

In more strict terms, I've read that color temperature does affect the different stages of plant growth in areas such as: the seedling stage, vegetative growth stage, and the budding/flowering stage. In a simplistic view, it is the duration and relative amounts of red versus blue wavelengths that affects these growth stages.

Where things get a little confusing regarding color temperature is that fluorescent bulbs have a highly "constructed" light spectrum compared to natural sunlight. A fluorescent spectrum is a mixture of lower power frequencies combined with very narrow higher power spikes . These spikes are engineered to appear at specific frequencies within the spectrum. I presume it is the relative intensities of these spikes that can dominate the perceived color temperature of the bulb, as in the "Tri-Phosphor" bulbs. A light spectrum like this bears little resemblance to the spectrum produced by natural sunlight. So, to make sense of all this, we have to know what component of the fluorescent spectrum is actually important to plants in terms of photosynthesis and growth stages: Is it predominantly the spikes of the spectrum that matter? Or is it the wider range of lower power frequencies that have more of an effect?

Fluorescent bulbs are mostly designed for human vision. Very few bulbs are engineered specifically for photosynthesis - but they do exist. To humans, those bulbs appear pink-ish in color because they are designed specifically to produce red and blue wavelengths, with very little emphasis on the green/yellow part of the spectrum where our eyes are most sensitive. Hence, those bulbs look dim to us, and the objects they illuminate look off-color to us... but I imagine they can provide a fair amount of PAR for plants. But I am suspicious whether these bulbs provide any real advantage over the bulbs that are designed more for human vision.

Among other goals, the makers of fluorescent bulbs for aquariums are trying to meet several objectives: generate a lot of lumens, create good color reproduction, and provide photosynthetic energy for plants/coral. Generating a lot of lumens and having a high color-rendition-index (CRI) are aspects intended mostly for humans, and how humans see. And I think most of the engineering emphasis is placed in these two categories. The fact that these bulbs produce some photosynthetic energy seems almost like a by-product or an afterthought to me - except for the rare bulbs that are designed specifically for photosynthesis. 

Of the three objectives listed above, generating lots of lumens has less to do with photosynthesis because lumens are a weighted measure of light in the green part of the spectrum where our eyes are more sensitive. More green light means more lumens - and, as a result, the light will appear brighter to humans. This is, in part, why most fluorescent bulbs have a large narrow spike in the green part of the spectrum.

How the CRI affects photosynthesis and, ultimately, growth stages is where things get a little gray for me. I've seen that manufacturers produce fluorescent bulbs at different correlated color temperatures (from 3000K to 10000K), but all having a fairly high color rendition index (CRI >82). But, as a counterpoint, greenhouses use both sodium vapor and mercury vapor lights specifically for controlling plant growth... and these lights have a terrible CRI. Even a lot of common metal halide bulbs have a low CRI despite the fact that they are good at growing plants. So, a high CRI doesn't seem to be a dominating factor in affecting growth stages or photosynthesis either.

If you combine all of the above ideas with the fact that most people are just trying to get their plants "to grow at all", I tend to respond that the correlated color temperature of fluorescent bulbs is not a significant factor. It's a broad stroke indeed... but I think mostly correct unless you are specifically trying to trigger different growth stages in the plants.

Just my thoughts... would love to hear your ideas.

Cheers.


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## Bigk (Jan 31, 2010)

Interesting post, but lighting is only one key stage to plant growth. Plants get their "food" through photosynthesis but still need nutrients for growth also. What experience have you personally had with lighting?


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## Hoppy (Dec 24, 2005)

Lighting is the plant growth accelerator pedal. High light drives fast plant growth. Low light drives slow plant growth. To complicate this, CO2 also drives faster plant growth, so low light plus good CO2 drives faster growth than low light without good CO2. The other nutrients must be available or the plants can't all grow at the faster speed the light/CO2 are driving them at.

The best argument for the relative unimportance of color temperature and CRI for aquatic plant growth is that so many people use so many different lighting setups with many different bulb combinations, and grow aquatic plants very well. Until someone makes the effort, and spends the time and money to do a series of good controlled tests I don't see how we can ever be sure about what the effect of different light spectra are on aquatic plants.


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## i4x4nMore (Mar 31, 2008)

Bigk said:


> Plants get their "food" through photosynthesis but still need nutrients for growth also.





Hoppy said:


> The other nutrients must be available or the plants can't all grow at the faster speed the light/CO2 are driving them at.


Right. For this discussion, I am assuming non-limiting nutrients and non-limiting CO2 - which can be provided by the Estimative Index approach and CO2 injection. In addition to dosing the water column, I also assume the use of a fertile, loamy, soil substrate. The combination of the two should cover all the bases. With nutrients and CO2 in ample supply, one should be able to change an aspect of the lighting and see how it alone affects the plants.

I agree that the overall intensity of the light affects the rate of growth. Given ample nutrients, more photons from the same light source would give more photosynthesis. But in this discussion, I'm more targeting how the balance of frequencies of those photons might affect growth patterns - not the overall intensity. 

Or to put it more succinctly: 

1. Does the color temperature of a fluorescent bulb really affect the balance of red and blue wavelengths within the bulb's spectrum? 
2. And... Can chosing a different color temperature of fluorescent bulb allow one to trigger or enhance different growth stages of an aquatic plant?
3. In fluorescent bulbs, how are CCT and CRI and PAR related to actual plant growth, given non-limiting nutrients/CO2?




Bigk said:


> What experience have you personally had with lighting?





Hoppy said:


> ...so many people use so many different lighting setups with many different bulb combinations, and grow aquatic plants very well.


Early on, I was stubborn-headed and was driven to prove to myself that almost any light source with the appropriate intensity could be used to grow aquatic plants. I am not inclined to the look of a fluorescent light source - although they have gotten better. Since my main goal was to produce a stunning, relaxing aquatic display, that precluded the use of fluorescence because I was sensitive to it.

As a result, I went down a path of setting up lighting configurations that included everything from incandescent, halogen, all flavors of HID, and sunlight. I quickly was turned on to PAR as a means of quantifying and comparing the photosynthetic energy provided by these sources regardless of their wattages and relative spectrums. So, I spent a lot of time and effort observing the effects of PAR on plants. For example: How much PAR is needed to grow Glosso as a carpet? How much PAR is needed to turn Rotala Macrandra red? How much PAR can I have in a non-CO2 tank with soil before algae sets in? etc. 

But my questions were irrespective of color temperature because I was just trying to get the plants to grow - analagous to hitting them with a blunt light stick. I never really investigated what effect duration or color temperature had on the plants. They were growing without algae, I was having to trim them a lot, and I was pleased.

To be well rounded, I finally did start testing and using fluorescent sources: PC, CF, T12, T8, T5, T2, NO, HO, high CRI, low CRI. And I was a little bit curious why so many hobbyists seemed convinced that you "must use 6500K" when choosing a fluorescent bulb. Where did this idea get rooted? Why is it circulated? It is contrary to all of my experience... if all we're talking about is getting a plant to grow and look mostly healthy.

Even though I had good results in growing plants in color temperatures ranging from 2400K to 15000K, it started to feel a little bit incorrect to imply that color temperature doesn't matter at all. On some level, it must have some impact whether it be flowering, reproduction, leaf size, leaf density, plant color, or other aspects.

If we were discussing the use of a true full-spectrum light source, such as a black body radiator, then the color temperature of that source would have more of a correlation to the relative spectral power distribution between the red part of the spectrum and the blue part of the spectrum. But this correlation doesn't seem to exist for fluorescent sources.


Cheers.


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## epond83 (Feb 19, 2009)

It seams you two know more then I, however I'll had what I've read.

6500K looks good and does produce plant growth, so it is understandable why it is often suggested to use. Color tempature is the apparent color of the bulb. As mentioned fluorescents are a few spikes on a color spectrum chart that combine to look a certain way, giving the color temp. Different spikes can produce the same color temp. making it not the best judgment to pick the most effecient bulb. With that said a bulb could be producing enough light in area's needed for plants but not be the most effecient spectrum "blunt light stick."

I usually figure out how many watts i want, given the light source. Then i pick a bulb based on the spectrum chart, most decent bulbs have these and if they don't it's probably not one i want. As mentioned plants need spikes in the blues and reds so this is what I look for.

I don't remember where i got this but i made a note of it and i think it came from a bio major or something.

Chlorophyll a uses 430nm and 662nm
Chlorophyll b uses 453nm and 642nm
Carotenoid uses 449nm and 475nm

Red light has more energy so i would think that side is more important. Also red leaves use the blue side more so that is important to rememeber.

So i found where i saw that info, a discusion about color temp on another site http://www.aquaticplantcentral.com/forumapc/lighting/26955-color-temperature.html


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## archer772 (Nov 13, 2009)

The way I understand it is that par values are readings that acure only in the 400nm-700nm range so wouldnt any bulb regardless of the K rating be good for plants as long as they have a good par rating??


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## Diana (Jan 14, 2010)

I use a mix of bulbs, usually one 'plant' bulb and one Cool White or Daylight bulb, with the goal of enough of the reds and blues that plants use but a natural looking tank. Most of the tanks are near a window, too, for some sunlight or at least some cloudy sky for several hours a day. 
Between the 2 bulbs most of my tanks have roughly 2 watts per gallon, but not all of it in the optimum range for plants. Never the less I think I am at the maximum light that I can handle, and need to improve the CO2 levels.


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## Bigk (Jan 31, 2010)

I think the key is experimenting and you seem to have had your fair share of experience. I hope some clearance comes from this thread and a lot of people open up to experimenting so that information like this becomes frequent.


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## i4x4nMore (Mar 31, 2008)

epond83 said:


> 6500K looks good and does produce plant growth, so it is understandable why it is often suggested to use.


I would split the point and add that 6500K only looks good [to humans] if the light source has a high CRI >85. A fluorescent bulb can have a low color rendition index and still have a CCT of 6500K. And, "producing growth" with 6500K doesn't mean that it is "best growth" that might otherwise be achieved with a different arrangement of frequencies in the light. And by "best growth", I don't mean the speed of growth. I mean the attributes that define the plant as being healthy and true to its native form - its propagation abilities, how/when it flowers, and the shape and density of it's leaves, etc.



epond83 said:


> Different spikes can produce the same color temp. making it not the best judgment to pick the most efficient bulb. With that said a bulb could be producing enough light in area's needed for plants but not be the most efficient spectrum "blunt light stick."





epond83 said:


> As mentioned plants need spikes in the blues and reds so this is what I look for.
> 
> Chlorophyll a uses 430nm and 662nm
> Chlorophyll b uses 453nm and 642nm
> Carotenoid uses 449nm and 475nm


I would be inclined to argue that the plant doesn't respond solely to narrow bandwidth spikes in the spectrum, but rather, wider "bumps" centered around those wavelengths you've listed. My intuition is that plants evolved under continuous, full-spectrum lighting and, hence, use a range of frequencies. I am uncertain if a plant would respond well if you gave it ONLY those wavelengths and nothing else.




archer772 said:


> The way I understand it is that par values are readings that accrue only in the 400nm-700nm range so wouldn't any bulb regardless of the K rating be good for plants as long as they have a good par rating??


Ah, this is an interesting point... and something I've wondered about. An ideal PAR meter gives equal weighting to all wavelengths within 400-700nm. To my knowledge, it doesn't give emphasis to red photons or blue photons or green photons. So I've always wondered if you could take a light source with a measured PAR value and magically add just green photons to it... it should produce more PAR. But, the added green photons wouldn't benefit photosynthesis... and that seems counter intuitive to what "PAR" is. Either I'm looking at it too simply, or there is another aspect of PAR measurements that I'm missing. I haven't been able to determine this with the information given on manufacturers websites.

Additionally, a PAR measurement isn't going to reveal the ratios of red wavelengths to blue wavelengths in the light. Nor does it imply anything about the relative amounts of other wavelengths... So, by extension, it seems to be irrespective of the color temperature of the source.

So by that, your statement would appear to be true. But the seed has been planted for me to wonder if PAR is enough of a metric to predict the growth characteristics of aquatic plants. It doesn't seem to be enough for people who grow fruiting or flowering plants indoors.

Hence the spark if interest 

Cheers.


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## archer772 (Nov 13, 2009)

i4x4nMore said:


> Ah, this is an interesting point... and something I've wondered about. An ideal PAR meter gives equal weighting to all wavelengths within 400-700nm. To my knowledge, it doesn't give emphasis to red photons or blue photons or green photons. So I've always wondered if you could take a light source with a measured PAR value and magically add just green photons to it... it should produce more PAR. But, the added green photons wouldn't benefit photosynthesis... and that seems counter intuitive to what "PAR" is. Either I'm looking at it too simply, or there is another aspect of PAR measurements that I'm missing. I haven't been able to determine this with the information given on manufacturers websites.
> 
> Additionally, a PAR measurement isn't going to reveal the ratios of red wavelengths to blue wavelengths in the light. Nor does it imply anything about the relative amounts of other wavelengths... So, by extension, it seems to be irrespective of the color temperature of the source.
> 
> ...


I agree it doesnt differentiate between the different wave lengths but most of the better T-5 bulbs will have a graph of sorts that will show the wave length peaks to help make the decision if a person is looking for specific wave leangths at least IMO.


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## epond83 (Feb 19, 2009)

i4x4nMore said:


> I would split the point and add that 6500K only looks good [to humans] if the light source has a high CRI >85. A fluorescent bulb can have a low color rendition index and still have a CCT of 6500K. And, "producing growth" with 6500K doesn't mean that it is "best growth" that might otherwise be achieved with a different arrangement of frequencies in the light. And by "best growth", I don't mean the speed of growth. I mean the attributes that define the plant as being healthy and true to its native form - its propagation abilities, how/when it flowers, and the shape and density of it's leaves, etc.


 I agree with this, I left my statment a little open. Your points are valid which is why I do not buy bulbs bassed CCT. But I can understand why people who have not read as much or tried other bulbs might think 6500K is the best bulb, not knowing this is a wide range of spectrums and CRI





i4x4nMore said:


> I would be inclined to argue that the plant doesn't respond solely to narrow bandwidth spikes in the spectrum, but rather, wider "bumps" centered around those wavelengths you've listed. My intuition is that plants evolved under continuous, full-spectrum lighting and, hence, use a range of frequencies. I am uncertain if a plant would respond well if you gave it ONLY those wavelengths and nothing else.


 This is the information that i have seen as to the wavelenghts that the different Chlorophylls use. The red end does have more energy in it since the waves are moving at a faster rate so it is somewhat understandable why they would use this type of light. But yes I'm sure they need more then just those peaks, an experiment using LED's in those wave lenghts would be interesting. However they full range does have an effect, more so the shifting which alows plants to know when to blume and push summer growth. Also some plants prefure morning light which has more blues, while others prefure evening light which has more reds.


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## plantbrain (Dec 15, 2003)

Th accessory pigments surrounding Chl a/b offer a wide and adaptable range of wavelengths. So the plants can live in a wide range of PAR and wavelength types.

Plants can use this wavelength difference to tell if they are next to rock blocking light, or if it's another plant's leaf blocking the light and take appropriate growth action.

Growth rates differences are not very significant even on the best day between color temps, they really do not give you that entire spectrum graph either, you need that entire graph and then study energy efficiency converted into growth.

What is the highest watt per unit of growth for a set of given wavelengths?

The fancy plant bulbs do not offer any significant differences between them and the cool whites as far as growth.

What we percieve or the coloration and morphology might change, but the overall growth does not.

So it's more about aesthetics, not plant preferences, growth rates at that point.

So PAR works well and the meters are cheap relatively speaking.
It's not perfect, but it's better than the alternatives and makes comparisons much easier to do.

That said, I've seen some nicer growth and color using different bulbs with the same PAR. Am I sure that it's not something else? Some other factor? Not entirely, but it seems there's a bit to it. 

I have gottne better reds using different bulb types and the GE 9235 and the Gieseman powerchromes seem to do very well there.

Aesthetics play a role for us, the other factors do also, so it's hard to tease this part and answer things.

Regards, 
Tom Barr


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## Guy (Sep 30, 2009)

epond83 said:


> The red end does have more energy in it since the waves are moving at a faster rate so it is somewhat understandable why they would use this type of light.


Can you explain this? Why would a longer wavelength carry more energy? I would expect the opposite. I would think Ultraviolet, X-rays, and Gamma with their shorter wavelengths to carry a lot more energy than longer waves like infrared.


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## epond83 (Feb 19, 2009)

Um yeah brain fart sorry. Yes less energy in red end but more heat...


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## Guy (Sep 30, 2009)

epond83 said:


> Um yeah brain fart sorry. Yes less energy in red end but more heat...


I have only anecdotal evidence but I've experienced more plant growth with light on the red end of the spectrum. It probably depends on the specific species of plant. I just never considered wavelength energy to be a factor.


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## plantbrain (Dec 15, 2003)

FYI, all wavelengths used to drive photosynthesis ends up at P680(nm) in the LHC in plants for PSII or in PSI as P700(nm). The higher energy shorter wavelengths give off heat and fluorescence resonance as this occurs. 

Blue light can help open up stomata, far red causes other changes etc, but the actual PS is done via the 680 and 700nm(or anything higher).

A good discussion is found at most College Bio web sites, commonly taught stuff to very bored but willing students interested in a good grade, but less so in plant basic biology.

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.html

I like this one better:

http://employees.csbsju.edu/hjakubowski/classes/ch331/oxphos/olphotsynthesis.html

This teacher has it right and makes the point that green light still drives plant growth.

http://plantphys.info/plant_biology/photopart.shtml

Read through it.
It helps to better understand plants and not the marketing gibberish often hocked by light bulb makers.

Regards, 
Tom Barr


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## i4x4nMore (Mar 31, 2008)

plantbrain said:


> This teacher has it right and makes the point that green light still drives plant growth


Is this the reason that green wavelengths are not filtered out in a PAR meter? Based on what I've seen about the meters, it seems that green wavelengths contribute to the overall PAR value as much as the other wavelengths.

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Thanks Tom, and everybody, for the discussion and the links. I figured sooner or later that I would have to dive into the texts... just felt like keeping it a bit interactive at first and see what experience has brought to other hobbyists.
Also, I wanted to be sure that I wasn't passing along incorrect information regarding all of this - which is very easy to do once you get an idea stuck in your head.

So I guess it's time to hit the books.
See you on the other side.

Cheers!


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## Guy (Sep 30, 2009)

While studying Tomato Plants I was surprised to learn that there's a significant photosynthetic wavelength peak at 437nm. But most people one the fish boards tell me that blue light provides no benefit to plants and is strictly for looks.

I've never been able to reconcile this and I've never been convinced that plants can't use blue light because it seems to grow some plants just fine for me.

The concept of "antenna pigments" is new to me but it explains my observations on using blue light in my aquarium.


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## Hoppy (Dec 24, 2005)

I'm far from a botanist, so two things stood out for me in the link that I read: One is that the sun provides far more light than any plants need, so there is no reason for plants to evolve for maximum efficiency in using light. The second is that we see plants as green not because all green light is reflected, but because more green light is reflected than for other colors. Since our eyes emphasize green/yellow colors, the green light that is reflected looks brighter and more green than it would if our eyes had a flat response to light spectra.

This tells me that plants use the whole spectra of visible light, absorbing significant amounts throughout the spectra. And, that explains, for me, why people succeed in growing very nice plants with such a wide variety of lighting products. Differences in the light spectra should therefore be only a secondary concern.


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## plantbrain (Dec 15, 2003)

Guy said:


> While studying Tomato Plants I was surprised to learn that there's a significant photosynthetic wavelength peak at 437nm. But most people one the fish boards tell me that blue light provides no benefit to plants and is strictly for looks.
> 
> I've never been able to reconcile this and I've never been convinced that plants can't use blue light because it seems to grow some plants just fine for me.
> 
> The concept of "antenna pigments" is new to me but it explains my observations on using blue light in my aquarium.


The energy is lost and filters down to P680. Tomato has specific pigments that like that nm range that optimize fruit and growth production. They love full sun and have many issues.

Other species might have another optimal nm range, but most of these are subtle and we cannot control the sun easily at an agricultural scale. For aquatic plants, we can.

While there's a dip in PS some for green light, PS still occurs in those bans as well. PS is not absent at all.

Now as Hoppy is saying, maximum efficiency is required for submersed low light plants where the light is 50-100 less than terrestrial tomato. When something is a few orders of magintude different, well, things change.

Horticulture where we can manipulate and alter things is very different than natural systems of agricultural ones where there's little issue with CO2 or light.

Regards, 
Tom Barr


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## i4x4nMore (Mar 31, 2008)

Hoppy said:


> One is that the sun provides far more light than any plants need, so there is no reason for plants to evolve for maximum efficiency in using light.


Unless you're a little struggling plant at the bottom of a rain forest canopy 



Hoppy said:


> This tells me that plants use the whole spectra of visible light, absorbing significant amounts throughout the spectra. And, that explains, for me, why people succeed in growing very nice plants with such a wide variety of lighting products. Differences in the light spectra should therefore be only a secondary concern.


Yes, that's a significant conclusion that I also arrived at after reading about the info that Tom posted: "...all wavelengths used to drive photosynthesis ends up at P680(nm) in the LHC in plants for PSII or in PSI as P700(nm)." The info at http://plantphys.info/plant_biology/photopart.shtml was a good read with some nice supporting charts and graphs. Hope to dig into it some more soon.

Cheers.


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## Hoppy (Dec 24, 2005)

i4x4nMore said:


> Unless you're a little struggling plant at the bottom of a rain forest canopy


I didn't think of that, nor of the fact that "low light" plants tend to grow where there is far less light, so they probably did evolve towards maximum efficiency for using light. As Tom Barr once noted (I think it was him) light that filters down through a forest canopy tends to contain a lot more green light than bright sunlight does. So, those plants would almost have to have evolved to make the best use of that green light.



> Yes, that's a significant conclusion that I also arrived at after reading about the info that Tom posted: "...all wavelengths used to drive photosynthesis ends up at P680(nm) in the LHC in plants for PSII or in PSI as P700(nm)." The info at http://plantphys.info/plant_biology/photopart.shtml was a good read with some nice supporting charts and graphs. *Hope to dig into it some more soon.*
> 
> Cheers.


I hope you do dig into that stuff, just to round out your knowledge more so you can help all of us understand it better. But, anything that resembles going back to school and studying subjects I have no knowledge of has as much attraction for me as BBA does.:wink:


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## wadesharp (Nov 27, 2009)

hey when you guys say "6500k..." what is the "k" kelvins??


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## epond83 (Feb 19, 2009)

yes kelvin, in lighting there is a color chart that realats kelvin to bulb color. Low kelvin like 2800 will be more yellow, 6500 is more white mid-day and 15,000 is blue.


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## wadesharp (Nov 27, 2009)

thanks we where talking about kelvin's in my chem class and i stumped my teacher on this so i was just making sure i was correct on what i was saying


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