Lighting / Spectrum topic

ctyank

Junior Poster
Jun 17, 2006
19
0
1
Durham, NC
I've been running around with the idea that lighting in the blue spectrum is better for red plants. That conclusion comes from the following progression:
* Plants primarily respond (photosynthesize) to light in wavelengths not visible to the human eye, i.e. infrared and ultraviolet.
* Plants reflect back colors that they do not absorb (or use). Most plants reflect back green which is in the heart of the human-visible spectrum.
* Plants can't really control the rate at which they photosynthesize. However, one thing some can do is change color from green to red.
* Photosynthesis is most efficient using Red light. If a plant turns red, it cuts down on its growth by reflecting back infrared light.
* If a red plant isn't using green (human visible) light or red light, then it must use ultraviolet light.

Do I have that right? So, for example, throwing 100 watts of actinic light at a 20 gallon tank with only R. Macrandra would be better than using 100 watts of say an Aquasun bulb or any of the mid-day bulbs on the same tank.

Thoughts?

Thanks. - Chris
 

VaughnH

Lifetime Charter Member
Lifetime Member
Jan 24, 2005
3,011
94
48
85
Sacramento, CA
Re: Lighting / Spectrum topic

My thought is that you can do an interesting experiment on this and tell us your results! As far as I have read, actinic bulbs don't help aquatic plants much at all, and infrared doesn't penetrate water very far, if at all, so it is of no benefit to plants. I think UV does penetrate water pretty well, so it is likely to be beneficial to plants. But, you can try all of this experimentally and all of us will benefit.
 

Tom Barr

Founder
Staff member
Administrator
Jan 23, 2005
18,696
747
113
Re: Lighting / Spectrum topic

ctyank said:
* Plants primarily respond (photosynthesize) to light in wavelengths not visible to the human eye, i.e. infrared and ultraviolet.

No, this is wrong, plants use light energy in the 400-700nm range.
Chl that feeds PS is only operative at 660-700nm.
Blue light will filter down and lose energy, even though some pigments and chl itself will absorb a little better at the red/blue regions of the spectrum, but you do not gain red color from this, you do have a different preception of your own sense of color, but the plants, the amount of red pigment is typically the same.

* Plants reflect back colors that they do not absorb (or use). Most plants reflect back green which is in the heart of the human-visible spectrum.

So what color does a red plant reflect back then?

* Plants can't really control the rate at which they photosynthesize. However, one thing some can do is change color from green to red.

No, they most certainly do and must control the rate of PS!!!
Pigment changes are only one adaptation.
the color change is due more to nutrient levels than light in our tanks.
The light is stable, the NO3 levels often are not.

* Photosynthesis is most efficient using Red light. If a plant turns red, it cuts down on its growth by reflecting back infrared light.

Yes, it's most efficient, but that does not mean it looks good to us.
Few like yellow/red colored light.

IR light is given off by anything exposed to heat.
Police can track people with IR at night running through the woods.

I'm not sure why you think red plants reduce IR light.
Reflection of the light in the IR range would mean that the plant would not absorb IR wavelengths, which are outside the red visible spectrum.

You cannot see this range of light un aided.

* If a red plant isn't using green (human visible) light or red light, then it must use ultraviolet light.

Do I have that right? So, for example, throwing 100 watts of actinic light at a 20 gallon tank with only R. Macrandra would be better than using 100 watts of say an Aquasun bulb or any of the mid-day bulbs on the same tank.

Thoughts?

Thanks. - Chris

No, plants will not use UV light either, they use 400-700nm range.
Red plants do use red(but a fair amount is relfected, but plants do not need a lot) and green light also(other pigments can and do absorb green light, not as well as say red), and blue.
They are adaptable.
Given time, say 1-4 weeks, algae and plants will adapt to a given light nm range within the 400-700nm range.

That light does not reflect what is our own aesthetic for the "best color" though.

Many think redder = better.

This is sign of stress as the redder color is produced.
NO3, rather than light will get plants redder.

This was shown and number of years ago on the APD.
Light can change your preception, but as far as growth rates, plants do not care that much.

Cool white bulbs grow plants equally as well as any pricy plant bulbs.
There are numerous studies that support this also as well as the NO3 effect on aquatic plants in relation to anthocyanins and chlorophyll.

Regards,
Tom Barr
 

Wet

Lifetime Members
Lifetime Member
Aug 25, 2006
395
0
16
USA
Re: Lighting / Spectrum topic

Any input on the talk of supplemental actinic/03 lighting producing shorter internode space and bushier plants? Assuming a properly fertilized/CO2/etc tank, of course. Thank you.
 

Tom Barr

Founder
Staff member
Administrator
Jan 23, 2005
18,696
747
113
Re: Lighting / Spectrum topic

In terms of practical hobby based experiences, experimental and in theory: => no.

There is far more that suggest neighboring plants and shading from wood/other plants will lead to longer internodal distances.



Regards,
Tom Barr