Metal Halide vs. LED Rates of Photosynthesis

[A. grandis]

I was looking through some PowerPoint presentations for a particular slide and found this. Frankly, it was so long that I had forgotten that I even did the experiment - Iwasaki MH rate of photosynthesis versus that of blue/white LEDs. This was determined using a Li-Cor PAR meter and a Walz PAM fluorometer.

Interesting discussion and great graphic to start with!
One thing that I've learning about scientific experiments is that the material and methods are as important as the abstract and discussion to take the conclusion.
Any conclusion in what is the "best" for photosynthesis in this case needs to take serious consideration at the variables and what was used (lamp, wattage, ballast, reflector, spectrum/PAR, etc..) to find the numbers, right? Also the "advantages and disadvantages" between the two sources of light, which in reality are just physical differences in nature.
While intensity and distribution of photons is what most likely dictates the balance in what the sensor will capture to translate to a graphic, we need to have in mind that metal halides will offer safer levels of greater intensity than most LEDs available and used over aquariums. That said, and knowing that halides will allow more intensity than LEDs before the coral reacts against it (photo inhibition), the saturation of photosynthesis allowed will also follow this logic, but that is directly dependent on intensity/PAR.
In a balanced system, the amount of lighting will also play with chemistry/nutrients for the balance of photosynthesis' saturation, so probably that would play some in the variables for reef aquariums in the long run. Good question here is to know what was the coral in this experiment used to in terms of light. That would play with any conclusion as well IMO.
Bottom line here is: Iwasaki 6500K 250W is literally a PAR monster bulb, considered by many the most powerful bulb for growth ever produced, and if that LED was on the bluer side (less PAR) and with inferior intensity, comparison would be tricky to determinate anything logical comparison. This is just an example. Not to mention what species of coral/zooxanthellae was used.
I would love to have more info on this anyways. It's always a great pleasure to see your works published, @Dana Riddle !

On the side, I would love to hear your opinion about what many call the "gaps in the spectrum" regarding LEDs as well. I wish we could understand that better.

I truly hope this thread will be a great reference about photosynthesis and, to add to it, the importance of spectrum in any comparison.
Thanks!!!! Aloha!

 

[xiaoxiy]

we need to have in mind that metal halides will offer safer levels of greater intensity than most LEDs available and used over aquariums. That said, and knowing that halides will allow more intensity than LEDs before the coral reacts against it (photo inhibition), the saturation of photosynthesis allowed will also follow this logic, but that is directly dependent on intensity/PAR.

Quite the opposite was seen in this specific experiment. Under Dana's study conditions, Pocillopora under LEDS did not undergo photoinhibition until the intensities were MUCH higher light intensity than the photoinhibition PAR under the halide. From eye-balling it, photoinhibition started at 300 PAR under halides but didn't occur until almost 500 PAR under LEDS. Moreover, at light intensities above 200 PAR, the Pocillopora under LEDS experienced MORE photosynthesis than under Halides. In other words, LEDS allowed more more photosynthesis at higher PARS and photoinhibition wasn't seen until intensities got even than those under halides.

Good question here is to know what was the coral in this experiment used to in terms of light. That would play with any conclusion as well IMO.

Pocillopora

 

[Bpb]

Something I wonder. Is it possible perhaps that under equal par levels, the led will be providing much higher Intensity in the blue range, relative to the iwasaki which will be green and yellow dominant? Yes…yes I understand the iwasaki has a wide and full blue/violet/uv production in the relative spectral distribution, but would that only be as beneficial at much higher par levels?

Would the iwasaki need to be hitting upwards of 500+ par to take advantage of its blue range? Is it perhaps providing less blue than the led competitor at equal par levels?

 

[J1a]

Something I wonder. Is it possible perhaps that under equal par levels, the led will be providing much higher Intensity in the blue range, relative to the iwasaki which will be green and yellow dominant? Yes…yes I understand the iwasaki has a wide and full blue/violet/uv production in the relative spectral distribution, but would that only be as beneficial at much higher par levels?

Would the iwasaki need to be hitting upwards of 500+ par to take advantage of its blue range? Is it perhaps providing less blue than the led competitor at equal par levels?

I agree with you. Imo there are two sides.

One: the intensity of the spectrums which allows photosynthesis to take place;
Another: the intensity of the spectrums which cause photo inhibition. Which is just as important.

The lumped PAR value, imo, does not tell the full story.

In the era where mostly fixtures use similar light bulb and spectra, PAR is a good measurements because an iwasaki will be an iwasaki (until it ages.. at least), and sun will be the sun. Now when LED are really mainstream, spectrum can really vary. Even for a same light fixture, the user can, and likely will, set the spectrum according to their preference.

And. I wonder if any one has done this: given a same light model, how much does the spectrum vary from one unit to another, even under same setting? It would be interesting to find out.

 

[Mellotang]

Where does one even find a 250 iwasaki color arc any more?

I haven’t seen any iwasakis for sale in a long time

I believe they were discontinued

 

[Bpb]

Where does one even find a 250 iwasaki color arc any more?

I haven’t seen any iwasakis for sale in a long time

I believe they were discontinued

Correct they’ve been discontinued. I believe Hamilton still offers a 6500k 250/400/1000 watt lamp last I checked which wasn’t long ago

 

[hart24601]

While many of these ideas are great and valid, I think it’s also easy to for interpretation of what Dana was doing. He can correct me if wrong but it was just a curiosity trial to see what happened long enough ago blue/white LEDs were standard and those MH bulbs were the “standard for growing”. Not an in depth study or deep level experiment.

it is very interesting and raises a lot of questions of course particularly with the old blue/white LEDs which didn’t contain any spectrum under royal blue.

 

[Mellotang]

I would buy a case of iwasakis if I could

I’m not sure of the spectrum on the Hamilton 65k

what made iwasaki so nice was the big spike in violet/blue combined with the rest of the spectrum

I have never seen another 65k that had that violet blue spike similar to iwasaki

For me iwasaki saturated with actinic and blue T5 gave the best color and growth on many high light loving sps

 

[oreo54]

I would buy a case of iwasakis if I could

I’m not sure of the spectrum on the Hamilton 65k

what made iwasaki so nice was the big spike in violet/blue combined with the rest of the spectrum

I have never seen another 65k that had that violet blue spike similar to iwasaki

For me iwasaki saturated with actinic and blue T5 gave the best color and growth on many high light loving sps

Well build an led version .
This is a bunch of 6500k " fresh fish" cobs and viosys violets 420's vs an Iwasaki 6500k (. 3 jaggy lines thanks to Sanjay).

Tailor the violet channel to taste.
Dotted line is ocean at 1 m.
Grey background is daylight.

 

[Mellotang]

Not the same

 

[Mellotang]

I have duplicated iwasaki spectrum and the extra blue violet with GHL Mitras and the results were ok

I think it has to do with the halide in
The giant reflector creating a uniform blanket of light

 

[oreo54]

Not the same

I or anyone else haven't tested it to say how well it competes soo ?

 

[oreo54]

I have duplicated iwasaki spectrum and the extra blue violet with GHL Mitras and the results were ok

I think it has to do with the halide in
The giant reflector creating a uniform blanket of light

The DIY design uses native 120 degree spread.. It is NOT a Mitras..
Besides when you have cut the spectrum down to "daylight" look you have cut par significantly..
Above was designed for full color full output with dimming of course..

Certaintly not saying it is "perfect" btw..
Prior to adding the Viosys the green area in the composite spectrum is what is def. SHORT in daylight led's vs Iwasaki.

 

[J1a]

Imo it's exceedingly challenging to consider both spectrum and the optical geometry concurrently. Having multiple independent variables just makes hypothesis testing very difficult.

 

[Mellotang]

Would be interesting if you could run iwasaki n diy LED side by side, same water, two different tanks plumbed together, same coral, same flow and see what happens

 

[Mellotang]

Part of me feels that if LED we’re doing the same thing as halide we wouldn’t even see these discussions anymore

I think some of it due to the fact that the majority of reefers have never even run halide and saw the results first hand

I just find halide sps tanks to be more stable, have more natural growth forms, sps corals just get depth of color and overall health I’ve never duplicated with LED

it is just my preference

I have done amazing things with LED but my preference for ease of growth, aesthetics and overall stability it’s halide all day for me

 

[Mellotang]

How do you measure rate of photosynthesis?

if we are doing a study to measure rate of photosynthesis wouldn’t it make sense to
Use same spectrum and intensity

 

[oreo54]

Imo it's exceedingly challenging to consider both spectrum and the optical geometry concurrently. Having multiple independent variables just makes hypothesis testing very difficult.

IF you have the par and hang both high enough the geometry equals out..
Most rays striking the tank surface will be perp. or close to it..
Yes it is complicated..

To be clear I don't expect either to be sig. better than the other.. The difference would be interesting.

Actually the above ff COB's have even better and cheaper replacements in the high K high CRI race..
It's an old design.

 

[Mellotang]

Also curious if this experiment was run in NSW...

If it wasn’t I’m sure there would be other contributing factors that affect rate of photosynthesis and the corals ability to utilize certain wavelength and intensity

 

[hart24601]

Part of me feels that if LED we’re doing the same thing as halide we wouldn’t even see these discussions anymore

I think some of it due to the fact that the majority of reefers have never even run halide and saw the results first hand

I just find halide sps tanks to be more stable, have more natural growth forms, sps corals just get depth of color and overall health I’ve never duplicated with LED

it is just my preference

I have done amazing things with LED but my preference for ease of growth, aesthetics and overall stability it’s halide all day for me

I do hope MH is around a long time so reefers have options. More options the better to suit the person. Myself always hated halides, T5 when came out seemed like such a step forward and now I prefer LEDs but again, personal preference. Choices good to have. I think debating is a natural part of the hobby even over matters that are not practically noticeable. As Adam from battlecorals posted - who’s mortgage is paid by selling corals: