Light Intensity & Effectiveness. Experts please.

[AudiSteve]

I have a specific question regarding light intensity.
Assume the Water is in perfect condition and crystal clear.
If a Photosynthetic coral is placed in a tank around 6 inches from the surface in an average sized tank with 7 WPG of T-5 (using this because of even disbursement) lighting and then the T-5 lighting is increased to 9 WPG. Since the Spectral and Photosynthetic available Radiation has been increased by 2 WPG, is this increase in PAR Linear or Exponential?

 

[billsreef]

WPG does not directly translate to PAR. Different bulbs of the same wattage can have vastly different PAR. Also PAR can decrease with age in a given bulb, while the wattage remains the same. But for arguments sake, lets take use bulbs with identical PAR, in this case one bulb has X PAR. If you have 2 bulbs, you now have 2X PAR, 3 bulbs will be 3X PAR and so on. So in the case of identical bulbs, it's linear.

 

[AudiSteve]

Interesting. Now that it's been determined that (everthing being equal) increasing light is linear, could a person assume that the photosynthetic organisms ability to convert that energy to food is linear as well?

Thanks!

 

[billsreef]

This is where it get's complicated

If we are talking about corals and other organisms with symbitotic relationships with zooxanthelle algae, you have to consider several factors. One, the zoox's need a certain amount of PAR to just breakeven with their own energy needs, after that they produce excess which their host organism gets. Now I would assume that after the breakeven point is met that food excess food production is linear, however, I've not looked up any studies to confirm that and could be wrong. Another factor is the ability of host organisms to control the amount of zoox's in their cells, if light levels are low they will increase the amount of zoox's, if too much light they expell excess zoox's. There is also a point where the photosynthesis reaction can produce too much oxygen and cause cellular damage and the photosynthesis reaction needs to be reduced. So there can even be a point of too much light.

 

[pjf]

How Much is Enough for Long Photoperiod?

How Much is Enough for Long Photoperiod?

Bill,

I’d like to take AudiSteve’s question regarding light intensity one step farther with respect to MH lighting. As in AudiSteve’s original scenario, assume the water is in perfect condition and crystal clear. An SPS coral is placed in a tank around 6 inches from the surface in an average sized tank directly underneath a hood-mounted MH fixture. The fixture is my only light so for extended viewing, I plan to gradually increase the photoperiod to 10-12 hours. Assume my chiller and water flow are adequate to maintain a stable temperature.

• Will a 150-watt HQI be enough to exceed the compensation point of the SPS?
• Will a 150-watt HQI be enough to photosaturate the SPS?
• Will a 250-watt HQI be enough to photosaturate the SPS?
• Will a 250-watt HQI be enough to photoinhibit the SPS?

Thanks!

 

[MCsaxmaster]

The rate of photosynthesis for most organisms, including zooxanthellae, shows saturation kinetics up to a maximum level at a certain light intensity, levels off for a while with increasing light intensity and then begins to fall with further increasing light intensity due to photoinhibition. The response tends to have a shape like this:

This is for some kind of phytoplankter. The values aren't import here as they vary tremendously depending on the coral and the conditions to which it has been acclimatized. This depicts the shape of the response curve though.

For pjf's questions:

Will a 150-watt HQI be enough to exceed the compensation point of the SPS?

At only 6" away from this fixture, unless it is caked with salt spray, you should be over 1000 umol/m2/s and probably close to 2000 umol/m2/s (assuming a decent reflector, which these tend to come with). Yes, that is much more than enough light to exceed the compensation point for any coral.

Will a 150-watt HQI be enough to photosaturate the SPS?

Yes, most corals adapted to bright light in shallow water show max. rates of photosynthesis at somewhere around 200-400 umol/m2/s, though some may need closer to 500 or 600 umol/m2/s.

Will a 250-watt HQI be enough to photosaturate the SPS?

Yes, that set-up at only 6" away would likely cause significant photoinhibition (i.e., supersaturation).

Will a 250-watt HQI be enough to photoinhibit the SPS?

If the coral is only 6" from the fixture, absolutely yes it is.

Chris

 

[pjf]

Thanks for the excellent information, MCsaxmaster!

Where can I find references or links to publications for the information that you've conveyed?

 

[MCsaxmaster]

Sanjay joshi has done most of the work on metal lighting for reef tanks. You can find that in various places, but mostly in the archives of Advance Aquarist online mag. As for the coral photophysiology...try google scholar? This is a synthesis of many studies from many peer-reviewed journals.

 

[Steven Pro]

Dana Riddle has also done some testing of various corals in Hawaii to determine their compensation, saturation, and photo-inhibition points. His works are mostly in http://www.advancedaquarist.com/

 

[pjf]

Long & Dim or Short & Bright

Long & Dim or Short & Bright

I didn’t frame the problem properly the first time, so please allow me to restate it.

Suppose I had a deep (24"-30") but narrow SPS reef aquarium. Supplemental actinic lighting cannot be accommodated in the hood and the only light is an HQI mounted 6” above the water’s surface. To provide sufficient PAR to the corals at the bottom of the tank, I need to maximize light outage without photo inhibition of the SPS at the top of the tank located only 6” below the surface (12” from the HQI light).

· What is the maximum photoperiod and HQI wattage that can be provided without photo inhibition of the upper SPS corals?

· Should I go long & dim (e.g., 12-hour photoperiod x 150w HQI)?

· Should I go short & bright (e.g., 8-hour photoperiod x 250w HQI)?

· Is photosynthesis more efficient at low light levels (above compensation point) or at high light levels (saturation point)?

 

[MCsaxmaster]

Suppose I had a deep (24"-30") but narrow SPS reef aquarium. Supplemental actinic lighting cannot be accommodated in the hood and the only light is an HQI mounted 6” above the water’s surface. To provide sufficient PAR to the corals at the bottom of the tank, I need to maximize light outage without photo inhibition of the SPS at the top of the tank located only 6” below the surface (12” from the HQI light).

Ok, gotcha. If the corals are all at least 12" from the bulb I think you'll be ok, but even this still may be fairly bright for a lot of corals. I'd cafefully adjust them to this high intensity.

What is the maximum photoperiod and HQI wattage that can be provided without photo inhibition of the upper SPS corals?

Photoinhibition occurs as a result of light intensity, not photoperiod.

Should I go long & dim (e.g., 12-hour photoperiod x 150w HQI)? Should I go short & bright (e.g., 8-hour photoperiod x 250w HQI)?

Personally, I'd run at least a 12 hr. photoperiod. The thing to consider is the light intensity hitting all the corals in the tank. A 250 watt bulb is more likely to photoinhibit the ones at the top but will provide brighter light at the bottom. The 150 watt is less likely to photoinhibit the corals up top, but won't necessarily push corals at the bottom to maximal calcification if they need very bright light to do that (though they should do fine). If you want to grow just shallow-water corals very fast on the bottom of this tank I might opt for the 250 watt one. If you want just a nice looking tank and would be very happy with some Montipora, or Favia, or Lobophyllia, or Hydnophora, etc. at the bottom I'd probably opt for the 150 watt bulb. They'll all do fine and you'll save yourself on the electric bill.

Is photosynthesis more efficient at low light levels (above compensation point) or at high light levels (saturation point)?

Depends on many factors.

 

[pjf]

Photosynthesis versus Light Intensity

Photosynthesis versus Light Intensity

<a href=showthread.php?s=&postid=8648860#post8648860 target=_blank>Originally posted</a> by MCsaxmaster
Depends on many factors.

The graph that you posted seems to indicate a linear relationship between photosynthesis and light intensity at low and medium light levels. Then photosynthetic activity levels off well before the saturation point is reached.

Based on your graph, it appears that photosynthesis is more efficient at low and medium light levels than at photosaturation. Would this not indicate that "long & dim" is better than "short & bright"?

I would really like to see a similar P versus I graph for SPS corals that shows where the compensation point is. That chart will show if it is necessary to photosaturate the SPS corals at the top to allow the SPS corals at the bottom to exceed their compensation points. If you have a link to such a chart, I'd really appreciate your sharing it. Thanks!

 

[MCsaxmaster]

The graph that you posted seems to indicate a linear relationship between photosynthesis and light intensity at low and medium light levels. Then photosynthetic activity levels off well before the saturation point is reached.

Photosynthesis is considered to saturate at the point of intersection of a line with a slope of the initial rate of increase of photosynthesis with intensity and a horizontal line at the maximum level of photosynthesis measured. In the graph I posted the saturation intensity is about 300 uE/m2/s even though the max. rate of photosynthesis measured is at about 400 uE/m2/s. There are reasons for calculating saturation this way, but suffice it to say that in this photosynthesizer would not maintain sig. different rates at photosynthesis at 300 and 400 uE/m2/s.

Based on your graph, it appears that photosynthesis is more efficient at low and medium light levels than at photosaturation. Would this not indicate that "long & dim" is better than "short & bright"?

I misread your question a bit. The efficiency of photosynthesis at a high or low light intensity depends on many factors. The efficiency within the limited range of compensation point to saturation under a single set of conditions, however, is not so dependent. The efficiency is essentially the same between the compensation point and the saturation point (as calculated above).

I would really like to see a similar P versus I graph for SPS corals that shows where the compensation point is.

This varies drastically from colony to colony depending on the light intensities to which they are accustomed and species (over an order of magnitude difference among different colonies). You seem to be suggesting that all of the so-called "sps" corals respond in the same way or that one size fits all. This sort of thinking will cause you problems with the husbandry of these animals.

chart will show if it is necessary to photosaturate the SPS corals at the top to allow the SPS corals at the bottom to exceed their compensation points.

Any coral acclimated to the light intensity at the bottom of the tank (assuming not in a dark cave or something) will easily be able to exceed the compensation point of photosynthesis. There is plenty of light to accomplish that.

Chris

 

[pjf]

How much PAR is enough?

How much PAR is enough?

<a href=showthread.php?s=&postid=8655766#post8655766 target=_blank>Originally posted</a> by MCsaxmaster
In the graph I posted the saturation intensity is about 300 uE/m2/s even though the max. rate of photosynthesis measured is at about 400 uE/m2/s. There are reasons for calculating saturation this way, but suffice it to say that in this photosynthesizer would not maintain sig. different rates at photosynthesis at 300 and 400 uE/m2/s.

Your figures seem in line with an article by Dana Riddle, entitled “Too Much Light!” In the study, Riddle found photo inhibition in Montipora patula at only 260 µmol•m2•sec (www.advancedaquarist.com/issues/july2004/feature.htm).

Am I correctly perceiving a sea change in recent opinion regarding how much PAR is enough? In the past, aquarists have tried to duplicate natural lighting (> 2000 µmol•m2•sec). But in the recent volume 3 of Delbeek & Sprung's "The Reef Aquarium," missing are the tables that confidently show minimal lighting for each type of coral. Instead there is a reference to Riddle's "Too Much Light!" article.

The efficiency is essentially the same between the compensation point and the saturation point (as calculated above).

I am equating the slope of the P-I curve with "efficiency" here. The slope of the P-I curve decreases as the saturation point is approached. More light results in lower photosynthetic gain.

Any coral acclimated to the light intensity at the bottom of the tank (assuming not in a dark cave or something) will easily be able to exceed the compensation point of photosynthesis. There is plenty of light to accomplish that.

I believe you but I'd appreciate seeing links to studies or articles that back up your seemingly sweeping statement. Not long ago, 600 µmol•m2•sec was considered the minimum light intensity for Montipora. How much PAR is considered enough now?

 

[pjf]

Mimic Nature or Not?

Mimic Nature or Not?

In nature, SPS corals are photoinhibited by mid-day tropical sun and depend on morning and afternoon light for photosynthesis. Dana Riddle found that montipora patula is photoinhibited by only 260 µmol•m2•sec with photo-protection at ~100 µmol•m2•sec (http://www.advancedaquarist.com/issues/july2004/feature.htm).

Should we strive for photosynthesis throughout the photoperiod or should we strive to mimic the mid-day sun and induce dynamic photoinhibition with powerful MH lamps? Should actinic supplements be intended as the primary drivers of photosynthesis by reproducing the lesser morning and afternoon light?

Here’s an example of a beautiful SPS aquaria (not mine) with PAR levels that are rather high if one interprets Riddle’s article literally to mean no photoinhibition is good: