question about par and spectrum

[Detritivore]

hello,

i have been wondering; if you took a prism and broke the visible light spectrum into its constituent colors, would the yellow end of the spectrum have more PAR than the blue end?

thanks

[mesocosm]

Greetings All !

A general definition of PAR ...

PAR is the range of light (400-700nm) that can be photosynthesized by plants. It coincides with the range of visible light.

The acronym PAR stands for photosynthetically active radiation, but the term PAR does not include the full range of light that can drive photosynthesis in all living organisms. If it included photosynthetic green bacteria, purple bacteria and Heliobacteria, PAR would extend into the near infrared zone. These bacteria live in environments such as the bottom of stagnant ponds, sediment and ocean depths. Because of their pigments they form colorful mats of green, red and purple. These organisms must make use of the leftovers discarded by the plant kingdom, in this case, light outside the PAR range.

Extracted From:
http://en.wikipedia.org/wiki/Photosy...radiation_(PAR)

More specifically ...

Radiation which drives the process of photosynthesis. Wave band is 380-710 nanometres.

Extracted From:
www.scotland.gov.uk/cru/kd01/lightgreen/ccsnow_11.htm

(I) The electromagnetic spectrum ...






(II) The absorption spectrum of some photosynthetic pigments ...




It should be noted zooxanthellae don't contain chlorophyll b (IIRC ... Jake, please correct me if I'm wrong about this). Rather, they have chlorophyll a, chlorophyll c, beta-carotene (a carotenoid), peridinin, diadinoxanthin (a xanthophyll) ... among others. It should also be noted that there are accessory pigments involved, not the least of which is a xanthophyll called zeaxanthin which is involved in a photoprotective response called "fluorescence quenching."


(III) Absorption (%) vs. Rate of Photosynthesis (%) ...

hello,

i have been wondering; if you took a prism and broke the visible light spectrum into its constituent colors, would the yellow end of the spectrum have more PAR than the blue end?

thanks

This is how the wavelengths of visible light breaks down ...

red:~625-740 nm
orange:~ 590-625 nm
yellow:~ 565-590 nm
green:~ 500-565 nm
cyan:~ 485-500 nm
blue:~ 440-485 nm
violet:~ 380-440 nm

So the "yellow end" is in the 565-590 nm range ... and the "blue end" is in the 440-485 nm range. Look at image (III). A "general" interpretation shows:

Rate of Photosynthesis between 565-590 nm (yellow end) = ~ 25% - 40%.
Rate of Photosynthesis between 440-485 nm (blue end) = ~ 75% - 85%.

So ... you're going to see a "higher PAR" (as measured by the rate of photosynthesis %) at the "blue end" as compared to the "yellow end."

Tragically ... it's not so simple. The PAR "value" of a given light source can change dramatically, depending upon the photosynthetic pigment that's being examined. Consider images (II) & (III) again ... which PAR should we talk about? The one for chlorophyll a, or for carotenoids? And there's more involved than just the photosynthetic pigment ... so the actual specimen's characteristics ... not to mention the medium that the light is passing through ... come into play. Which PAR "number" should be put on a MH light's box? ...

...


It might also be noted that the "concept" of PAR may not be quite as straightforward as is oftentimes suggested in reefkeeping-cyberspace. PAR can be viewed as an "effect", rather than as a measurement of a quality of the intensity of light (as is typically suggested). Don't get me wrong ... the measurement is the measurement, physics "works", and people can read their meters ... but it's the "cellular machinery" that demonstrates the effect. Change the cellular machinery components, and you change the "effect." Do people seriously believe that the cellular machinery ... photosynthetic pigments, zooxanthellae density, cellular pigments ... to name but a few ... are the same in corals? And we're just talking about photosynthesis ... what about photoadaptation ... what about photoprotection?

The emphasis on two narrow wave bands in the common discussion about reef lighting makes for relatively good "marketing" discussions and product assessments ... but it seems to me that this overlooks the role of accessory pigments, and the utilization of other wave bands in the rate of photosynthesis.


JMO ... HTH

[jsbzmcdaniel]

Well ya didn't have to put it in such easy terms ya know!

[mesocosm]

Greetings All !

Well ya didn't have to put it in such easy terms ya know!

Well ... hehe ... I'm trying ...

And I've discovered that pictures help ... ...

[Orion76]

Good old Gary, sure knows how to turn a simple question into a confusing answer :p

[mesocosm]

Greetings All !

Good old Gary, sure knows how to turn a simple question into a confusing answer :p

What did you expect ... rubber biscuits? :destroy:


JMO ... HTH
:bootyshak

[mesocosm]

Greetings All !

... would the yellow end of the spectrum have more PAR than the blue end?

thanks

So people want simplicity, eh?

How 'bout this as an answer to the original post ... "No." Short ... precise ... not confusing ... just the kind of thing you can get anytime in other cyber-spaces ... sans invective masquerading as humor ...

... is this really want you want from me? ...

... hehe ... keep dreamin' ...






To continue ... ...

"Because we are typically concerned with providing light to our aquariums primarily for the photosynthetic needs of the corals, the most appropriate measure is the quantum units, and, more specifically, we need to know the amount and quality of light available for photosynthesis. This measure of the amount of light that is frequently used is called photosynthetically available radiation (PAR), ..."

And ...

"The term PAR refers to the amount of light that falls in the range that is suitable for photosynthesis."

And ...

"The primary benefit of light to corals is the conversion of PAR into the energy required for photosythesis by the symbiotic zooxanthellae in the coral tissue to produce food. Photosynthetic pigments in the zooxanthellal cells carry out the collection of the light energy, such that they efficiently absorb light in the 400 to 700 nm range. The zooxanthellae contain various types of pigments: chlorophyll a, chlorophyll c and the carotenoids, such as Beta carotene, peridinnine and dinoxanthines. The pigments in the cells will absorb different wavelengths with different efficiencies. The absorption spectrum for zooxanthellae has been shown to have a broad peak in the 400 to 500 nm waveband (blue-green) and a narrow peak in the 650 to 700 (red) waveband. "

- Dr. Sanjay Joshi

Extracted From:
Photosynthesis and Photoadaptation

BTW, the above referenced article should be required reading ... ... JMO.


Just trying to fill in the data set ... ... hehe ...


JMO ... HTH

[Orion76]

Come on Gary, don't keep us in the dark with your cliff notes, tell us the full story

[GTR]

Greetings All !




What did you expect ... rubber biscuits?

Hey... leave me and my profession out of this!

SteveU

[dphinsx2]

So do our corals get more par from our actinic lights then they do from our 10k mh lights? Should we be running our actinics less then lets say 12 hours a day?

[coralite]

The yellow end of the spectrum is practically useless, as is green (a combination of blue and yellow light).

PAR is a measurement of the available energy from light that is usable in photosynthesis. The PAR spectrum ranges from roughly 400 to 700 nm. There is more energy in the shorter bluer wavelengths and it is more efficient to tansform high energy (shorter/bluer) wavelengths into lower energy (longer/redder) wavelengths. That is why we see our coras fluoresce greens and reds when we punch them with strong actinic blue light. Although Chlorophyl a is a commonly used benchmark for PAR efficiency, there are different versions of the pigment with their efficiency attenuated red or blue.
There is no way to meet the exact photo demands of a coral because its particular ChlA and accessory pigment suite will be very specific to an intensity and quality of light.

If you recall Dana Riddle's monochromatic light experiment wherein he used blue and red leds to expose corals to the same amount of differently colored light, the areas of pocillopora exposed to red light bleached and those exposed to blue light turned pink. I agree with Dana's explanation that the red light caused a reduction of zoox because it was a lot more efficient at driving photosynthesis.

not sure if I answered any questions here, just tried to clear up Gary's mess :smoker: Thanks for holding it down meso!