# Spectrum question



## tanaka (Jan 22, 2015)

Will be making a DIY CFL fixture for my 48". Normally I'd just get all bulbs at 6500K but I've heard people also mix it with one or 2 3000K/10000K+ bulb which makes me curious which is better for plants.

Does it make a difference?


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## Yokai (Dec 7, 2014)

I use 6500k only and it seems to be fine... actually a bit too good.. have to seriously limit my hours now xD I think you'd be fine running it only at 6500k


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## Okedokey (Sep 2, 2014)

It wont make any difference beyond the way it looks. I would start with 1 of each and play until you get the right mix.


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## Xiaozhuang (Feb 15, 2012)

Okedokey said:


> It wont make any difference beyond the way it looks. I would start with 1 of each and play until you get the right mix.


Basically this, but looks make a world of difference to a tank, and I generally find mixing gives better overall colors, unless you find that 1 bulb that has perfect color rendition.


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## jeffkrol (Jun 5, 2013)

tanaka said:


> Will be making a DIY CFL fixture for my 48". Normally I'd just get all bulbs at 6500K but I've heard people also mix it with one or 2 3000K/10000K+ bulb which makes me curious which is better for plants.
> 
> Does it make a difference?


Let us think a bit backwards on this:
In the hort. world where they want to maximize output and minimize energy useage this is somewhat the current "standard"
What do you see:









The point is red is an important component in plant growth











Secondly you have no clue as th the spectral composition of "A" 6500k cfl since this is an average subject to spectral shifts of RGB output yet still equal 6500k. In other words not all 6500k are equal.









http://www.plantedtank.net/forums/showthread.php?t=649690

Ignore all this if your tank is 3 feet deep.. 

combining low K anything w/ high k anything generally 1)adds more missing spectrum and 2)adds more color contrast to your tank.

Just for fun a t12 eek: ) that has a "full' spectrum


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## Okedokey (Sep 2, 2014)

terrestrial plants can be very different beasts


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> terrestrial plants can be very different beasts


Photosynthesis is fairly primitive and the basics are fairly universal. Yes there are diffierences but considering these land plants came from the sea. well there are plenty of similarities.

Aquatic plant:











> Life, Science of Biology by William K. Purves, David
> Sadava, Gordon H. Orians, H. Craig Heller (6th Edition) Sinaur. (Fig 8.8).


http://mvoicu.hubpages.com/hub/light_role_in_photosynthesis#slide3970722


Aquatic plants can be fairly similar beasts..


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## jeffkrol (Jun 5, 2013)

A really interesting site about florescents in general:

http://donklipstein.com/f-spec.html


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## tanaka (Jan 22, 2015)

Since 6500k is lacking on the red side, would you suggest I get half 2400K and half 6500K-10000K?


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## jeffkrol (Jun 5, 2013)

tanaka said:


> Since 6500k is lacking on the red side, would you suggest I get half 2400K and half 6500K-10000K?


"I" would...



> Please note that lowest-color-temperature ("warmest") tri-phosphor lamps (generally with rated color temperature at or near 3,000 Kelvin) produce lots of orangish red light around 611 nm, and will grow plants somewhat better than other white and near-white fluorescent lamps. These will grow plants almost as well as lights made for plants, but will look brighter.


but that is just me.. As to LED's I'd give the same advice.

Note though it does depend on the exact spectra of 6500k..Some 6500k's have a good amount of red, some not..

Anyways an example of a 5500k bulb as a one size fits all:









http://www.homedepot.com/p/EcoSmart...trum-Craft-CFL-Light-Bulb-ES5M827FS/100687004

Still lowish in red to deep red..but cf's don't seem to cater to this range..


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## Okedokey (Sep 2, 2014)

jeffkrol said:


> Photosynthesis is fairly primitive and the basics are fairly universal. Yes there are diffierences but considering these land plants came from the sea. well there are plenty of similarities.
> 
> Aquatic plant:
> 
> ...


A massive over-simplification, not based on any real understanding of photosynthetic process.










Aquatic Photosynthesis: (Second Edition) By Paul G. Falkowski, John A. Raven


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## tanaka (Jan 22, 2015)

I found out that CFL are commonly only available in 2500K and 5000K. Guess I'll just go with 1 each.


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## Okedokey (Sep 2, 2014)

tanaka said:


> I found out that CFL are commonly only available in 2500K and 5000K. Guess I'll just go with 1 each.


yep


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> A massive over-simplification, not based on any real understanding of photosynthetic process.
> 
> (SNIP) for clarity
> Aquatic Photosynthesis: (Second Edition) By Paul G. Falkowski, John A. Raven


List the exact differences.. beside the lack of stomata??
not to mention many "aquatic" aquarium plants are dual nature.. i.e terrestrial and aquatic. you say "stuff" and prove nothing.
That paragraph you eluded to is an example of a massive "simplification" as it stands.. go on.. explain..
I'll start w/ the physical part, which should be really self evident:


> Totally submerged plants are the true water plants or hydrophytes. Because they are truly aquatic they have the greatest number of adaptations to life in water. These include:
> 
> The presence of little or no mechanical strengthening tissue in stems and leaf petioles. If these plants are removed from the water, they hang limply. They are normally supported by water all around them and so have no need of mechanical strengthening. Indeed, this would be a distinct disadvantage as it would limit flexibility in the event of changes in water level or water movements.
> 
> ...


Of course it is simplified.. as is any hobby.. 
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3659369/

1)


> Differences in Photosynthetic Processes
> 
> While photosynthesis is similar in both aquatic and terrestrial plants, there are a few important differences. For example, emersed plants, floating-leaved plants, and terrestrial plants extract carbon dioxide from the air, while submersed plants extract it from the water.
> 
> ...


nothing new..


> 2)Light Attenuation and Photosynthesis
> 
> Plants use the same visible light spectrum as humans (wavelengths between 400 and 700 nanometers).
> 
> However, submersed aquatic plants have a harder time getting the light they need for photosynthesis; suspended particles, dissolved substances and water depth restrict the amount of light that penetrates the water.


still nothing new.
maybe I have to make is more "simplistic"
http://www.thenakedscientists.com/HTML/questions/question/2301/


> Chris Smith - So the bottom line is that basically, there’s very little difference between the photosynthesis that’s occurring in the oceans and the photosynthesis on land because it’s all the same process. It’s just been tweaked a little bit to make use of the light that’s available and there is slightly more light of different wavelengths available out of the water than in it but the bottom line is it’s pretty much all the same.


http://www.thenakedscientists.com/HTML/about-us/who-are-we/people/chris-smith-2/

OK, admittedly not the best.. 

Maybe a bit better:


> Re: How do plants perform Photosynthesis under water?
> Date: Wed Dec 16 08:38:50 1998
> Posted By: Mark Schneegurt, Faculty, Biological Sciences, University of Notre Dame
> Area of science: General Biology
> ...


shifting a bit to algae:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2147193/pdf/389.pdf
see pg16 (404)


> Green Algae (Chlorophyta).--The experimental
> curves, so derived and calculated,may now
> be considered. Partly to test the method,since the
> action spectra of green plants are best
> ...


your trying to talk me wrong. you need to prove me wrong..I'll make it simple, just disprove this without "opinions"..

Aquatic plants respond to red light just like terrestrial plants for the most part. The fact that light is attenuated is irrelevant to aquariums of normal depths.
A full spectrum artificial like is more like daylight, and more like light received in less than 1/2 meter of open clean clear fresh water . 
Full spectrum light has the most pleasant of all overall coloring i.e there is not a gap in spectrum (re. LED's: deep red, cyan, and violet need to be supplemented) 
6500k is not magic, nor really "the" most desired "color" in CCT lighting because 1)the spectral content is punctuated and NOT like 6500k "blackbody" daylight 2)6500k can be created in any number of phosphor mixes w/out regard to spectral continuity.
Color tone (warm or cold) is a personal preference but spectral content should be considered if one is desiring to mimic nature.
Any photon is a good photon, in the visible spectrum

I could add CO2 is more important (more limiting) than light for any normal aquarium fixture.. but not relevant to this discussion.
I'll just throw this in:


> To efficiently grow such microalgae, illumination for photosynthesis, CO2 consumption, and the pH and nutrient content of the growth medium must be monitored and precisely controlled. In a closed photobioreactor, illumination is the most critical parameter because it is the most expensive factor of algae production and must be operated 24 h per day. In this research, Chlorella kessleri (UTEX 398) microalgae were grown in photobioreactors. All parameters were identical, except the source and intensity of the illumination. The light sources included red light-emitting diodes (LED), blue LED, and fluorescent lights. Growth of the microalgae was observed for seven days and the effects of the three illumination sources on cell count, cell weight, and cell size were determined. In the first experiment, in which the current of all three light sources was the same, red LED produced the highest number of cells with the highest weight while blue LED light produced the largest cells. In the second experiment, in which the light intensity was the same for all three light sources, the highest weight was again achieved with the red LED. Thus, we suggest that most advantageous production system may be to use a red light initially to produce the desired cell concentration, then switch to a blue light to increase cell size.
> http://evols.library.manoa.hawaii.edu/handle/10524/32474


Red light who the heck needs it... 











> “We have gotten much greater algae growth rates inside in the culture closet equipped with LEDs than outside or in the greenhouse even under the best days in regards to light and temperature,” he said.


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## Okedokey (Sep 2, 2014)

Wow hit a nerve did I . 

The major point here is red light will not be entering the light column in the same way as above water. The photosynthetic example of horticulture does not apply in many ways, not least, gaseous exchange, water stress and light availability. These things are crucially different. So yes, photosynthesis in aquatic plants is very different than terrestrial.



> ...the environment under water is more complex than in air and there is a diversity of photosynthetic mechanisms (i.e. C3, C4, CAM, and bicarbonate use) in aquatic species.


I would say more complex proves that your assessment that photosynthesis in air and underwater being the same is simplistic.


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> Wow hit a nerve did I .
> 
> The major point here is red light will not be entering the light column in the same way as above water. The photosynthetic example of horticulture does not apply in many ways, not least, gaseous exchange, water stress and light availability. These things are crucially different. So yes, photosynthesis in aquatic plants is very different than terrestrial.
> 
> ...


The light component is basically the same. The use of the spectrum is basically the same. Plant physiologic response to spectrum (stretch or stunt) is basically the same. ect. I really fail to see your point..

Just because some is lost does NOT mean


> The major point here is red light will not be entering the light column in the same way as above water.


 not in the way you imply.. 

You still have nothing to prove your point.. only verbal pointless babble. 

I asked you to show ONE study/reference defending your point and got..................... nothing.

Find one thing in this paper that supports your "opinion"
http://www.ncsu.edu/biosucceed/biomass/pdf/the-sun-biosucceed.pdf

Maybe adding this will help:


> If LEDR is generally enhanced under red-weighted excitation for Symbiodinium, then this might be important for shallow water corals, which are subject to high quantities of red light [50].


http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0112809
I'm giving you a small opening here..


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## Okedokey (Sep 2, 2014)

jeffkrol said:


> The light component is basically the same. The use of the spectrum is basically the same. Plant physiologic response to spectrum (stretch or stunt) is basically the same. ect. I really fail to see your point..
> 
> Just because some is lost does NOT mean not in the way you imply..
> 
> ...


As i said before, they're fundamentally different.



> Functional differences in photosynthetic ability and carbon uptake have important implications for local ecosystem dynamics allowing persistence of plants with flexibility in their exchanges of carbon, water, and energy. The distribution of photosynthetic mechanisms in aquatic plants is not based on the availability of water as with terrestrial CAM or C4 species


https://digital.library.adelaide.edu.au/dspace/bitstream/2440/47987/1/02whole.pdf


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## burr740 (Feb 19, 2014)

tanaka said:


> I found out that CFL are commonly only available in 2500K and 5000K. Guess I'll just go with 1 each.


I like 5000K. I think you'll find 2500 is very yellow and doesnt look good at all. If you "view user tanks" under my avatar, the 20H is two 5000K. Of course not all brands are gonna look the same. Those are Ulitech brand from Lowes. (They have 6500K as well fwiw).


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> As i said before, they're fundamentally different.
> 
> 
> 
> https://digital.library.adelaide.edu.au/dspace/bitstream/2440/47987/1/02whole.pdf


There use of light is NOT "fundamentally different"..in any stretch of the def. of "fundamental". AFAICT, Nothing in that paper implies anything about spectral composition. quantity, yes. Gas exchange "problems" yes. Structural differences yes..c3/CAM pathways.. ect.
183 pages and not ONE mention of light spectrum. We are apparently talking past each other.


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## Okedokey (Sep 2, 2014)

You obviously haven't read it as it discusses it throughout including the preference for the blue end of the spectrum (not red) and that photo-inhibition can occur at relatively low levels comparatively to terrestrial. 

Read again.


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> You obviously haven't read it as it discusses it throughout including the preference for the blue end of the spectrum (not red)


I never implied any different. I have continuously implied both red and blue are used and are needed by shallow water aquatics.. Esp. those that are not JUST aquatic but emergent to terrestrial adapted. OBVIOUSLY each end of the spectrum plays slightly different roles..



Okedokey said:


> and that photo-inhibition can occur at relatively low levels comparatively to terrestrial.
> 
> Read again.


Inhibition is mostly spectrum independent. JUST like terrestrial shade plants. Though spectral differences ie. high red/green has def physiological and growth changes.. Whole point of it.

and if you can't be "helpful" and point to one or a few tidbits.. forget it. I have fairly good reading comprehension. I think your taking a few things out of context.

Addendum:
First lets look at real calculated loss profile of red light in an aquarium:









PAR at the ocean surface:








http://www.nature.com/nature/journal/v407/n6801/fig_tab/407177a0_F3.html

sunlight red content:









Now we can determine roughly exactly how much "red" we are talking about:

At about 1300PAR average and a 25% red content that means 325 PAR hits the surface of a clear body of open water.

what do you think the PAR of just red is at say.. 5 feet?


> 1) Kwater - for pure water, absorption at long wavelengths dominates (>550 nm; red and IR)
> - So, IR disappears in the top 1-2 m of most lakes
> - Scattering at short wavelengths, <380 nm
> - Pure water does not absorb UV (only scatters it)
> ...












http://www.esf.edu/efb/schulz/Limnology/Light.html



> about 35% of red light (680nm) is absorbed by a 1-meter deep column of pure water


325 x .35=113 PAR JUST for red light at 1 meter of freshwater..
In nature in the "real world" .. Yes "low" in terms of terrestrial averages High in terms of tanks.. and either way NOT insignificant
At 2 meters what.. log or linear?
http://www.advancedaquarist.com/2013/12/lighting

Please clearly describe any errors..

Now we can discuss what this means (after quantifying the light)
a start:
http://aob.oxfordjournals.org/content/108/7/1299.full.pdf
http://ocw.umb.edu/environmental-ea...ght on Phytoplankton.pdf/at_download/file.pdf


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## Yokai (Dec 7, 2014)

Guise these graphs are great and all.. but just get CLF 6500k. It works. Well actually.


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## jeffkrol (Jun 5, 2013)

Yokai said:


> Guise these graphs are great and all.. but just get CLF 6500k. It works. Well actually.


Almost any light "works"...









with enough of these I could successfully grow any plants I want.. And historically they have..










working was never the question


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## roadmaster (Nov 5, 2009)

Nearly any bulb advertised as daylight or full spectrum, will have enough of the red and blues to grow plant's.
Oddly enough (to me anyway), is that many of the charts that folks go daffy over indicate the color blue to be the most capable of penetrating depth's, but most folks harp on about the red's.
6500K/10,000K or 6500K/6700K are the combos that I like.
Tried a good many combonations arriving at those that suit me.
Plant's have evolved to use what light is available so get the combo that looks good to YOUR eyes.
Weed's will manage.


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## jeffkrol (Jun 5, 2013)

roadmaster said:


> Nearly any bulb advertised as daylight or full spectrum, will have enough of the red and blues to grow plant's.
> Oddly enough (to me anyway), is that many of the charts that folks go daffy over indicate the color blue to be the most capable of penetrating depth's, but most folks harp on about the red's.


That is because "some" think red just disappears at 2 inches, or "suddenly" is not important in photosynthesis.. 
Also because blue is never an issue w/ most modern lighting.. It is just "there". White LED's are BLUE diodes coated inside w/ phosphors to make white. CF and asst. florescent are based on RGB phosphors and since blue is a heavy component in "white" are also rich in blue..regrdless of the color temp until you get to the low K ones..
Blue was an issue when incandescent lights were used which was rich in red and little blue


roadmaster7593802 said:


> 6500K/10,000K or 6500K/6700K are the combos that I like.
> Tried a good many combinations arriving at those that suit me.
> Plant's have evolved to use what light is available so get the combo that looks good to YOUR eyes.
> Weed's will manage.


K numbers give only a little indication of actual spectral content. 
and yes looking good and plants utilizing almost all light has never been a question either
For those that want a balanced to actual daylight type lighting on tha assumption "nature knows best" well then some of the more esoteric points come into play.

One thing I do know is having ample red leads to having ample visual pop.









I let my plants grow in that light (10000k white/royal blue hybrid multichip) They grew different but as expected. Short internodes, highly dissected hydrophylaa leaves ect.. Really boring color..

Early prototype rich in red ([email protected] 660nm red multichips ). JUST a crude example:









Same multichip blues, the red as stated and 6500k whites. As crisp as it was, it was still toned too blue for my taste. Plants grew fine.
The best growth that I achieved on a casual observation basis was when I was using 3500k instead of the 6500k's..
Granted an unscientifically short and uncontrolled observation..I am not alone n the LED world thinking a mix of cw/ww are the visually most pleasing (personal opinion of course) and arguably the best (w/ possibly little difference between best and better) for growth.

florescent are only slightly different..

I don't "just" pump red for growth, but also for color.

O/t but when talking about subtlties..
Led's with cyan added and without. Note green separation and richness in the top photo (your monitor may vary)


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## roadmaster (Nov 5, 2009)

Best bulb for bringing red to the tank and or highlighting red fishes such as red serpae,cardinal tetra's,red wag platy's for me was the 3200K/8000K combo.
I wasted a lot of time while searching for the proverbial "Best" bulbs for planted tank.
But this was back when I thought light alone would grow the weed's.
More growth I thought,means more light is needed.


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## jeffkrol (Jun 5, 2013)

roadmaster said:


> Best bulb for bringing red to the tank and or highlighting red fishes such as red serpae,cardinal tetra's,red wag platy's for me was the 3200K/8000K combo.
> I wasted a lot of time while searching for the proverbial "Best" bulbs for planted tank.
> But this was back when I thought light alone would grow the weed's.
> More growth I thought,means more light is needed.


I hear you. One of the reasons I went LED.. A tweak of a dial and I can change from low k to high k and add almost any toning I want to enhance any color I want (well within reason I guess) ..
To be honest, sometimes it is a curse.. you always want to tweak, whether it needs it or not..
Some higher PAR than others (dim a channel ect.) but with enough over lighting, not an issue.
concurrently if I have too much light.. global dimming is called for . W/ CO2 injection I have never found a need for less light though, except for the fact that throwing buckets of weeds out every few months seems like such a waste.. 
Not for everyone I understand.


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## Okedokey (Sep 2, 2014)

jeffkrol said:


> PAR at the ocean surface:
> 
> 
> 
> ...


 Average of 1300PAR? What chart are you looking at. That is PEAK, sunlight, at the surface. Average would be around 550PAR (RMS) and at an attenuation of natural waters of around 37% (see previous link) per meter, at 1 meter we have a total PAR of closer to 209PAR. Fine. Now lets look at what red component that equates to. The energy contained within the red spectrum is not linear to the total. So what we have now even using the 25% number you hav used is a PAR of 50 at 1m best case.

Where am I wrong on this?


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> Average of 1300PAR? What chart are you looking at. That is PEAK, sunlight, at the surface. Average would be around 550PAR (RMS) and at an attenuation of natural waters of around 37% (see previous link) per meter, at 1 meter we have a total PAR of closer to 209PAR. Fine. Now lets look at what red component that equates to. The energy contained within the red spectrum is not linear to the total. So what we have now even using the 25% number you hav used is a PAR of 50 at 1m best case.
> 
> Where am I wrong on this?


Nope you are right. I did misinterpret the graph..
But I'll get back to that in a minute:









After recalculating a bit for about 5 hours a day you have over 1000PAR or greater.. With a rough average of say 1150 over what say more than 1/3rd the day..

50PAR at one meter isn't "insignificant" in my book. And I suspect your estimate is low..See new chart..

1000PAR x .25 = 250 x .5 (2 meters) = 125PAR

Then add the effect of "shade tolerance" to aquatic plants


> Over 90% of the time light levels were below 20 mol m−2 s−1. The low LCP and Rd,area of shade-tolerant species should allow them both to conserve carbon better than less tolerant species and to gain carbon better, having net photosynthesis at lower light levels.


Yes this is for Maple seedlings..IF you can find me a solid number for aquatics, please do..
Yes I am "assuming" similarities (my "hypothesis") and unless you can give me quantitative data proving otherwise I'll stick w/ the "aquatics are like shade tolerant terrestrials" line.
You can "assume" what you want.


considering at least 1/2 a day is well over 600par, 550 is way low.......










Attenuation of red to 35% is not until 2M per the above chart.. Lets just round 1m to 30% loss of red.. 25% would really be more my guess..

So 25% of 25% of the light falling on a clear open body of water at >600PAR at more than 6 hours..37.5PAR "at least"... As I said still not insignificant..Assuming a compensation point for shade tolerant plants of say.. 10-15PAR..
Plants could grow at 1 meter w/ just red light.. Maybe not well or perfect. But that is a secondary point .

I really don't need to write a thesis to assume red light is important to useable to aquatic plants do I??











62.5 PAR just red just 1M

let us just say 50PAR of red over the course of 7 hours on average..5X the compensation point.


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## Okedokey (Sep 2, 2014)

You cannot do whatever it is you just did. PAR is already a time based metric. Having a PAR / time is a nonsense. The energy of red light is virtually all converted into infrared and is photosynthetically insignificant in most natural waters. Your 'creative' mathematics haven't changed that  

Look up Planck's law. Є= hv

Obviously all light between 400 - 700 nm is PAR. Therefore I would suggest the energy relatively to other spectrums is a factor of transmittence and Є. Under ideal situations, Є= 6.63 X 10-27erg-seconds x 6.41 x 10^14 (@650nm).

Obviously as you increase the frequency, the energy increases. So regardless, the penetration at 650nm is rubbish, and the energy is low.

Anyway, you know this, but your mathematics is broken. Either way, a 50PAR using your method is by no means best case. You would probably half this with incident angle (Fresnel'sLaw), waves, wind, clouds, reflection and so on in natural waters. You'd probably be lucky to have a PAR of 10 @ 650nm (1m).

This has all been described in Birgean Percentile Absorption. Usually between 37 - 90% ni natural waters at 650nm within 1 m.


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## roadmaster (Nov 5, 2009)

For interesting read on the topic of spectrum google,,Spectrum doesn't matter does it?at www.ukaps.org.
Could have saved me considerable wasted time/effort had the info in the thread been available to me earlier.
Much intelligent conversation in the thread .


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## Okedokey (Sep 2, 2014)

I'll have a look.


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## jeffkrol (Jun 5, 2013)

http://www.apms.org/japm/vol15/v15p29.pdf
http://www.ukaps.org/forum/threads/spectrum-doesnt-matter-does-it.26717/page-2

SSDD... 

One thing presented in the thread was a discussion of 1)CO2 is more of a limiting factor than light 2)Ethylene production (plant hormone) and distribution has "effects". Haven't looked much into it besides that thread and some discussions by Mr. Barr. I personally don't weigh it heavily. Most was done w/ stretching by such plants a rice ect. Emergents in other words and areas of stagnant water where this could be a major issue..
3)LOOK is effected by red light (fairly obvious historically)
On a more obvious level current hort. artificial light LED practices include a high proportion of red/blue light w/ much lower proportions of green/yellow ect. 
Let us say a practical example.

Ii believe I've somewhat proven that there is a fair amount of red in a natural environment AT LEAST in regards to shallow water plants (define this how you like)

Bottom line though is a healthy amount of all components found in natural light will 1)make your tank more visually appealing and 2)mimic natural conditions and 3)may have 
direct subtle to not so subtle effects on plant growth and morphology.

My own dalliance in high blue/low red proved, at least to me, there are effects..
The discussion there of PAR is funny because it is mostly a "standard" for measurement..and obviously not a perfect one. See PUR.

From the thread:


> There is also no definition of "correct". If you can grow a plant to satisfaction, wherein the plant is healthy, is algae free, has acceptable growth rate and is not suffering any malady, then can this be considered correct? If this can be achieved with a variety of color combinations then why limit one's self to a particular color combination?
> 
> Hobbyists gain confidence when they follow the instructions and are later rewarded with success. Folks do not enter the hobby because they want to study the latest science of lighting. They simply want to grow plants trouble free. But the world has too many myths and hobbyists often fall prey to those myths. The biggest myth in planted tank lighting is that 6500K is correct. This is simply not true and that has been demonstrated many times.
> 
> ...


Having the ability to adjust "spectrum to suit" adds to the enjoyment of your own viewing environment. Any adjustments will. most def. involve shifting red/blue ratios.
A tank high in blue/white has been judged (see RayII 7000k "discussions") flat. Tanks w/ higher red will always be more visibly superior (not as pretentious as it sounds) in CCT and visual impact irregardless of what one "believes" their "real world" looks like. .This is mostly due to how th light is created though (Punctated spectrum's ect. CCT vs K)

To be completely honest, and to meet the current scientific baseline, much is unknown in this regard and besides threads like this, I really do lean more to the aesthetic part than this nuts and bolts discussion of the "value" of red light.. 
And the flexibility now offered w/ LED's

It doesn't change my opinion of red, only put it at a slightly different level..
my own monthly "mostly blue" light "experiment" proved to me (at least tentatively) that the lack of red light has observable changes in plant morphology..
Be it as it may.

If one wants to pretend that the real env. for these plants is "reef lighting" so be it. Enjoy.

One more thing.. In regards to red photons:


> One would expect that blue light, having the higher frequency, and chlorophyll having a higher response to blue should generate the higher growth rate, yet, look at the data, the frequency that generated the highest growth rates is the lowest frequency, the lower response of chlorophyll and the lowest energy level. Think about that for a minute and think about the implications. So the question we should be fixated on is:


slower photons are more easily captured by the photosystem. In oher words red is more "efficient":









After all that if one believes our little plants ave evolved "beyond red"... well I guess that topic is still open. 
I certainly don't give it much credence w/ THIS subset..
o/t but interesting re: CO2 "fixation"


> Aquatic CAM
> 
> CAM photosynthesis is also found in aquatic species in at least 4 genera, including: Isoetes, Crassula, Littorella, Sagittaria, and possibly Vallisneria,[7] being found in a variety of species e.g. Isoetes howellii.
> 
> ...


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## mattinmd (Aug 16, 2014)

Okedokey said:


> You cannot do whatever it is you just did. PAR is already a time based metric. Having a PAR / time is a nonsense.


What Jeff did does make sense...

PAR is a rate of photon arrival, but to suggest that PAR is only valid when averaged over a 24-hour period is nonsense... That's like saying your car doesn't even go 50 MPH because you have to average your speed over an entire day and it spends most of its time parked. Good luck telling that to a cop who just clocked you speeding.

All rates that change can be measured on either a long term or short term basis... Neither value is inherently incorrect.

If you want to compare apples to apples, we measure tank PAR based on the short-term intensity of lighting when the lights are on. We do not re-compute PAR based on the number of hours on/off. 

If we have a light that delivers 50 PAR when it is on, but is only on 8 hours per day, so we call that 16.6PAR? Well, that's the long-term average, but it isn't how we generally express PAR.

I don't think it is sensible, much less reasonable, to try to compute the PAR of sunshine by averaging it including hours when the sun isn't shining, or to include hours when it has barely risen or is about to set.


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## jeffkrol (Jun 5, 2013)

Okedokey said:


> You cannot do whatever it is you just did. PAR is already a time based metric. Having a PAR / time is a nonsense.


Your confusing instantanous time w/ timespan.
you have 1000PAR at that second . One hour later you have 500PAR at that second.
The amount of photons in a second at THAT second so to speak.



Okedokey said:


> The energy of red light is virtually all converted into infrared and is photosynthetically insignificant in most natural waters.


(SNIP) forget it mostly redundant.. or unimportant.
you know what, it is just easier to say the Attenuation factor IS the conversion factor... and be done with it. your talking about the same thing in 2 different languages.. 
your not adding anything to what we have already been through..

nothing you have said proves it is "insignificant" ...again...

I've already said you lose a lot.. and most after 1M (and variable as well). The rest is up to you..
I did find reference to about 10PAR for deep red at 1M in a clear water lake(see I'm a nice guy.. ). Your not completely(nor did I try to imply) off base. Catch is the "insignificant" part..

Different chart from the same source:


















http://catalog.lib.kyushu-u.ac.jp/handle/2324/8148/KJ00004506757.pdf
http://www.apms.org/japm/vol15/v15p29.pdf

http://plantphys.info/plant_physiology/lightrxn.shtml


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