What does 6500K actually provide for plants? - Dendroboard
Dendroboard

Go Back   Dendroboard > Vivariums > Plants
Register Blogs FAQ Calendar Mark Forums Read Advertise

Support Our Sponsors
No Threads to Display.

facebook

Like Tree6Likes
  • 1 Post By Socratic Monologue
  • 1 Post By Pubfiction
  • 4 Post By jhupp

Reply
 
LinkBack Thread Tools Display Modes
  #1 (permalink)  
Old 08-13-2019, 07:49 PM
Kinstrome's Avatar
Member
 
Join Date: Oct 2017
Location: New Orleans, Louisiana, US
Posts: 321
Thanks: 31
Thanked 8 Times in 8 Posts
Default What does 6500K actually provide for plants?

(Or any color temperature, but 6500K is the most relevant.)

I understand the concept of color temperature ratings: the color of the light produced by a light source --- whether or not it emits thermal radiation --- is rated based on its resemblance to the temperature of a theoretical black body emitting that color. (So a bulb rated for 2700K is emitting the same color of light as a true black surface that is 2,700 Kelvin hot.) And I more or less understand that 6500K is the nearest color temperature to the sun at the time it is optimally bright for plants.

What I don't understand is, what nutrition does a plant actually derive from that color of light? Is 6500K just the point at which the most PAR is available for plants? If so, if PAR ratings became more widespread (or PAR readers become affordable!), would there no longer be a need to look for color temperature ratings on lights, at least for growing purposes?

Or does the color temperature of light provide some other parameter of nutrition to plants, that is totally unrelated to PAR?

Thanks for your consideration.
Reply With Quote
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 08-13-2019, 08:04 PM
Socratic Monologue's Avatar
Member
 
Join Date: Apr 2018
Location: Central WI
Posts: 784
Thanks: 33
Thanked 86 Times in 81 Posts
Default Re: What does 6500K actually provide for plants?

My understanding from old reefing knowledge is that the color temp is mostly relevant to our color perception.

More relevant to photosynthetic response is what wavelengths make up that 6500K. A certain color temp can be the function of (1) a 6500K monochromatic light source (such as some LED chips), or (2) a combination of a wide range of wavelengths (such as the sun). The latter is likely preferable for the general care of plants, and it is preferable for our viewing pleasure (since a wide range of the colors of an object are reflected).

Looking at spectral curves of various light sources can be interesting and informative. The closer those output curves match the spectral response curves of the plant (or, for reefers, photosynthetic animal) you're trying to grow, the more of the provided light will be useful to that plant.
Kinstrome likes this.
__________________
"People are like plants, they grow toward the light."
- Hope Jahren
Reply With Quote
  #3 (permalink)  
Old 08-13-2019, 08:17 PM
Kinstrome's Avatar
Member
 
Join Date: Oct 2017
Location: New Orleans, Louisiana, US
Posts: 321
Thanks: 31
Thanked 8 Times in 8 Posts
Default Re: What does 6500K actually provide for plants?

Quote:
Originally Posted by Socratic Monologue View Post
Looking at spectral curves of various light sources can be interesting and informative. The closer those output curves match the spectral response curves of the plant you're trying to grow, the more of the provided light will be useful to that plant.
I thought this was an intriguing comment. Am I correctly understanding that you're saying, in effect, that the quality of the light reflected from a plant can be used as an insight into how useful that light is?
Reply With Quote
 
  #4 (permalink)  
Old 08-13-2019, 08:50 PM
Socratic Monologue's Avatar
Member
 
Join Date: Apr 2018
Location: Central WI
Posts: 784
Thanks: 33
Thanked 86 Times in 81 Posts
Default Re: What does 6500K actually provide for plants?

I don't know the full details of how spectral response curves are measured. My very basic understanding is that reflectance is measured, as is transmittance (through the leaf), but I'm under the impression that useful information can be gained simply by determining which types of chlorophyll are present, since the spectral response curves of the different types have been worked out. Florescence also plays a role, though more so in reef corals than in terrestrial plants, I think.

Hopefully one or more of our resident plant gurus chime in soon with hard facts.
__________________
"People are like plants, they grow toward the light."
- Hope Jahren
Reply With Quote
  #5 (permalink)  
Old 08-13-2019, 09:02 PM
Pubfiction's Avatar
Member
 
Join Date: Feb 2013
Location: Port Huron, MI
Posts: 1,472
Thanks: 0
Thanked 113 Times in 103 Posts
Default Re: What does 6500K actually provide for plants?

6500k is a convention that the community has come up with. It has the property of looking fairly pleasing to the human eye and still having decent efficiency for a light (LEDs are generally more efficient if they are higher kelvin). I have a very large range of plant lights from 4k to 10k all of them grow plants just fine. If I was to go any lower the light would look awefully yellow and any higher and it would be fairly blue and washed out looking. Now there could be slight efficiency gains from certain spectre for certain plants but unless you are trying to farm one specific type of plant I doubt this will be really helpful to you. It's hard to know what to answer though without knowing what you want to achieve. You can grow plants in just rend and blue that looks like purple, you wouldnt want that for a show tank though, and you can spend a ton of money on a "high" "full" spectrum light to have the best color reproduction, you can even customize a light to your liking.
Kinstrome likes this.
Reply With Quote
  #6 (permalink)  
Old 08-13-2019, 11:10 PM
Kinstrome's Avatar
Member
 
Join Date: Oct 2017
Location: New Orleans, Louisiana, US
Posts: 321
Thanks: 31
Thanked 8 Times in 8 Posts
Default Re: What does 6500K actually provide for plants?

Quote:
Originally Posted by Pubfiction View Post
Now there could be slight efficiency gains from certain spectra for certain plants but unless you are trying to farm one specific type of plant I doubt this will be really helpful to you.
Indeed, I'm probably farming too many different kinds of plants in one more-or-less the same humidity / light / temperature setting.

Quote:
Originally Posted by Pubfiction View Post
It's hard to know what to answer though without knowing what you want to achieve. You can grow plants in just rend and blue that looks like purple, you wouldn't want that for a show tank though, and you can spend a ton of money on a "high" "full" spectrum light to have the best color reproduction, you can even customize a light to your liking.
I already bought a rather expensive LED light for a grow tent, actually. This question was just out of curiosity, as I did not understand the mechanics of color temperature very well.
Reply With Quote
  #7 (permalink)  
Old 08-13-2019, 11:22 PM
DPfarr's Avatar
Member
 
Join Date: Nov 2017
Location: SACRAMENTO
Posts: 289
Thanks: 0
Thanked 18 Times in 17 Posts
Default

In regards to what nutrition does a plant receive from light spectra, there are two general different types of photosystems: II & I. Both occur as reaction centers in chlorophyll a and are designated as P680 and P700 (respectively).

Absorption at 680 and 700 nm is the numerical part of that. The p is for phytochrome. The is the beginning of the photolysis of water to generate ATP.

How intensity plays a part, look up: action spectrum of photosynthesis.

Last edited by DPfarr; 08-13-2019 at 11:26 PM.
Reply With Quote
  #8 (permalink)  
Old 08-13-2019, 11:28 PM
DPfarr's Avatar
Member
 
Join Date: Nov 2017
Location: SACRAMENTO
Posts: 289
Thanks: 0
Thanked 18 Times in 17 Posts
Default

To the different kinds of plants, things you probably want to propagate likely aren’t that different in the grand scheme.
Reply With Quote
  #9 (permalink)  
Old Yesterday, 03:06 AM
Member
 
Join Date: Feb 2004
Location: Lincoln, NE
Posts: 347
Thanks: 0
Thanked 5 Times in 1 Post
Default Re: What does 6500K actually provide for plants?

Some generalized comments from a plant physiologist.

Socratic Monologue hit the nail on the head with color temperature. Color temperature as used in lighting is based on appearance, and as such winds up being rather loosely related to spectral composition of the light. This looseness happens partly because it's based on how it appears to our eye, which does not have a flat spectral response. And of course it has nothing to do with intensity of the light as a whole, or intensity at some particular wavelength.

For plants, we generally care about intensity (photons per unit area per unit time across a specific waveband) and for the most part do not care about spectral composition. Many find that last bit surprising given how we are taught photochemistry in school: that chlorophyll is the only pigment that matters and it absorbs light in the red and blue region of the visible spectrum, thus plants are green. But in practice, while chlorophyll is the primary photosynethic pigment, the various chlorophylls (plural in both numbers and forms) are packaged into antenna arrays associated with the previously mentioned photosystems (though these are not as described in the previous post of DPfarr) and associated with those are a variety of other pigments bound at the periphery. These additional pigments serve a few different roles, one of which ends up extending the range of useful wavelengths capable of driving photosynthesis.

The "action spectrum" mentioned above demonstrates this behavior quite clearly. These are measurements that relate light absorption at a specific wavelength to some measure of photosynthetic activity (eg carbon assimilation or oxygen evolution) when the leaf is illuminated by narrow band light at that wavelength. They are unrelated to intensity of the light and it is not predictable from just pigment composition alone. I suspect when DPfarr referred to these, they were actually thinking of a light response or AQ curve. That relates light intensity to photosynthetic activity with a specifically limited regard to spectrum (see below).

It was early measurements of action spectrum that led to the formal definition of PAR (photosyntheticly active radiation) and PPFD (photosynthetic photon flux density), and the idea that regardless of wavelength all photons with a wavelength between 400 and 700 nm have equal ability to drive photosynthesis. That means you can even drive photosynthesis with green light, despite a lack of absorption specifically by chlorophyll at those wavelengths.

To the mention of fluorescence, this is actually a very import energy dissipation pathway in plants and it is safe to say that if a plant is under illumination it is fluorescing. If our eye had a flat spectral response and we could see into the near infrared, it is possible plants would appear to glow pink to us! We are unfortunately strongly biased in sensitivity toward green light and our vision cuts out right where the bulk of the fluorescence emission that makes it out of the leaf starts.

It is also worth noting that plants have other "light receptors" that function unrelated to photosynthesis, but that can have real impacts on growth and development. Phytochrome for example, serves a role in detecting neighboring plants (by conversion between P680 and P700 in the presence of red versus far-red light) and as a result partly drives biomass partitioning between roots and shoots.
Reply With Quote
The Following 5 Users Say Thank You to jhupp For This Useful Post:
Dane (Yesterday), Encyclia (Yesterday), Eruantien (Yesterday), kimcmich (Today), Socratic Monologue (Yesterday)
  #10 (permalink)  
Old Today, 12:24 AM
Member
 
Join Date: Jan 2016
Location: Berkeley CA
Posts: 701
Thanks: 4
Thanked 108 Times in 100 Posts
Default Re: What does 6500K actually provide for plants?

Greetings,

I'll add my two cents to an especially educational thread (shout-out to jhupp's response in particuliar!)

The photon absorbance capacity of the chlorophyll photosystems + antenna complexes (and the chemical reactions they drive) is surprisingly limited. The means that photosystems exposed to light are saturated far below the intensity of noonday sun and can't make use of any remaining light energy no matter what the wavelength. The fluorescence that jhupp mentioned is necessary because a plant would burn-out its photosystem if it tried to absorb the full energy flux of sunlight striking its chloroplasts.

Last edited by kimcmich; Today at 12:26 AM.
Reply With Quote
Reply

Tags
6500k, color temperature, lights and heat, par

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Powered by vBadvanced CMPS v3.2.3

All times are GMT. The time now is 08:25 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.