naman;25251 said:
I know and support what you say, but I can't get why you say "PPFD also changes throughout the day"?
PPFD is a cumulative value - all the light which plant get per day. May be you have been in a hurry and mean PPFD is not the same every day?
But we talk anout tanks, not lakes.
Sure, it's just a density. It does not mean that it is the same all day long.
Nor everyday either. This is because plants grow every day(per day) and throughout the day(say per hour, per minute etc). If you want the total, you'd need to measure the leaf as it grows and moves through the aquatic weed bed.
Let me further explain by asking some questions to folks in general here:
Do plants grow throughout a day?
Some plants grow very fast, some several cm per day, some do not but get shaded by those that do.
The
canopy changes very rapidly in aquatic systems.
Thus so does light/PAR/PPFD and any parameter you wish to consider through space and time.
PPFD changes as you move around in the aquarium.
You can measure this and reptile link supports this via the inverse square law.
Take a look at Sanjay's article and most Reef articles are about 20 years ahead of FW plant hobbyists in general, both in testing and measurements.
Sanjay's Reef Lighting Info Pages
Poke around on there and get a feel for the lighting calculator, the spectra plots.
I think if you are interested in coming up with a light calc to avoid measuring, you need this data but it still has some serious assumptions and plants grow much faster than cormals in general(but not macro algae!)
All in all, measuring light is neither simple nor easy.
youi need to be specific in the question you ask with respect to light.
One simple discrete point does not tell you much, several over time start to tell you a much better story.
Most folks use one discrete point in space and time.
My advice to Vaughn and anyone, is not to do that, measure over time/space.
Using light bulb maker's spectral data, or initial readings assumes a lot.
Distances from the plants change radically.
Growth rates and formations of the canopy also can go from zero to exponential back to near zero over a growing season or if you neglect trimming your tank.
You need to take many samples in an aquatic weed bed.
Since many folks do not trim daily, typically let's assume 2-3 week time frames, maybe less for a non CO2 method, how might the PPFD change over that time frame?
How might the Spectral Flux Density change as well?
Leaves absorb different wavelengths and wood and rocks reflect light etc, as does water, angles, distance that the user uses above their tanks to light source etc, different light sources also produce very different patterns.
HQI vs say LED vs T5's.
Are the SFD the same for these also?
Ideally you'd measure FSD for each point and this can be done.
But "PAR" just averages them together, which is okay and an easier number to haggle with for most folks.
Does PPFD change with respect to time as bulbs change over months and there is variation between bulbs, electrical sources driving the bulbs etc?
Lots of questions
As for w/gal/day rule - this is forces aquarist to remember about PPF per day (it's a good sign
Per
second or per day, PAR per unit time still beats the snot out this method. It's not that much better than w/gal.
You still have the same total amount of energy, and this can change a lot of things, say compress it into 2 hours? Or 16 hours?
Then that rule falls apart.
Now if you simple suggest if you use higher light, try using it for 8-10 hours and if you have low light, 12 is fine.
However, you still have
no reference standard to compare the light sources other than watts here between each other.
No "rule" can avoid that.
That's why measuring your tank
in situ is critical.
Vaughn saw this rather quickly when he moved the meter around at Kyle's aquarium the other day. Sometimes you can learn a lot more in person than all day on the web.
You still are left with a large degree of error when you discuss light comparisons and aquatic plants. Much more so than the errors associated with EI.........
Without this folks often say "I use low light - 1wpg", while their plants get the same amount of energy for growth as his nabour's with 2wpg.
This is "why" I say it is a little bit better than wpg rule.
Yes, but the details of the information rather than a one shot rule is far more informational and useful. I do not rely too much on such rules.
I suppose it's a little better,m but it's not precise or that useful really anyway, which is why I use a PPFD meter and also use a spherical probe for lake studies.
Reflections etc likely play a large role in our tanks, but I'll stick with 2D dynamics for now. The sphere probe is extremely expensive, the Apogee is a relative cheap and many clubs/hobby groups can buy one and then share it to do data collection.
I often suggest that local clubs sell their plants on line to raise funds for high grade testing equipment and that they make a set of reference standards to share amongst their membership.
This helps folks learn much faster and better.
To be fair, W/gal/day is a good "quick rule of thumb" to estimate what you have without mesurements,
Yea, which is the same exact deal with EI!
So I find it ironic Edwards tries to hedge things with light while telling everyone how terrible and inaccurate EI is and how you are just guessing.
The main input of energy that drives CO2, all nutrient uptake is light yet he does not bother to even measure it in situ?
Humm........
The same applies to CO2, but it's not really something that cheap to measure accurate. I can measure reconstituted RO water using sodium carbonate and assume it to be all carbonate KH.
Then use pH and measure KH with a digital tritrator.
I've done this.
Then I added peat little by little over time and maintained the same CO2 flow rate.
But the CO2 dissolved meter method I suggested some time ago are made and there are LCO2 meters which get around all these RO/KH/alk variations and allows me to measure CO2 independent of such different in aquariums, tank to tank etc.
Then you can put it all together very well with high accuracy and precision.
If you are missing one large variable like light, you are really dead in the water and cannot compare independent observations.
Measuring nutrients is fairly easy compared to that.
But with organic fractions and influences and whether it's bioavailable or not?
Even that can get more complex.
Still, to answer such questions and to make sure our test are valid, you need to check. Then you go back and see how the model looks to use for predictions.
If all you consider for PPS or EI are the nutrients alone, then you will have the same poor correlations/poor success/plenty of algae.
Now plenty of folks do this and blame the method, however, lean EI vs rich EI, or non CO2, or PMDD, or ADA, or Dupla all work under some conditions.
Knowing what those are is key, but very few decided to measure and test it.
but we must not forget the type of lamps and reflectors and other factors you mentioned. We can't measure everithing and everytime... and don't need that to grow lush plants after all.
Yes, we have to account for bias in our assumptions in any model(rule).
You got it!
You are just right, we can't take it as a precise rule.
Many folks know that, I hope, so I simply do not see any need in posting everytime all that factors you mentioned in last post so I omit 'em.
haha!
You crazy guy you
Will you do the patterns
like ADA's?
Will you try to do the same with
Super-Spreader® ?
I think we can have some use from this devise.
naman
Yes, I can, wait till Vaughn gives me the light meter back, I might drag the LiCOR out for some measurements at home or at another clients.
Since the tank is 1.3 meter's deep and we have 1000W MH's and can vary the light with sequential screens, that would be a nice tank to measure.
But I can show a much more relevant measure at home as a group of plants spreads out over say 2-3 weeks. Sorry to rehash over some of this stuff, I think out loud and have go through and ask myself each question.
This often helps me and other folks learn it. I'm fairly sure you have a decent understanding and if not, you will go get it.
Thanks,
Regards,
Tom Barr
