Let us talk light

[TyroneGenade]

Thanks for the reply Defdac. So, the lux value is ultimately irrelevant and what is really important is the PUR (3rd column from the right) as a sign off how just how much energy is actually usable? Anyone have a table of minimum PUR to grow certain plants?

If one visits http://translate.google.co.za/transl...n%26safe%3Doff they give Lux values for the plants, which is about as useful as W/gal (i.e. meaningless). It would be nice having info on what level of PUR is needed to grow particular plants. I have a total of 40-58 PUR over my tank assuming 85% reflector efficiency and no light escaping. Does this classify as low, medium or high light? Which plants need what PUR to grow well assuming the correct CO2 levels?

[Plantbrain]

Thus, a measure that only weights the blue and red parts of the spectrum is needed for being able to measure a lamps true photosynthetic power. This is PUR. A PUR-meter will give lamps with high Lux low values, and lamps with much blue and red high values. Within reason. It takes accessory pigments into consideration ofcourse.

How much consideration? How much fudge factor is in that?
This is assumption needs to include the entire living growing plant which has a light harvesting complex that can be modified and captures all sorts of light including green light and yellow etc.

Plants and light are not static things, as the plant grows up and out, the light changes. They adapt at the whole plant level, the tissue level and at the chemical level.

You are not going to escape that issue or error ratio. You can get close, but then you are as close as PAR meter. Few aquatic species have PUR data, there's a ton available for PAR however.

Now if you want to compare bulbs, I suppose....but few bulbs have ever been tested with growth rates independent of other factors for aquatic plants as far as PUR/PAR etc.

Do you know of any? The choice between bulbs may not be
that significant at the end of the day in terms of the difference between PAr and PUR.

"Plant" bulbs have not been shown to perform significantly better than say "cool whites" in terms of growth rates. Unless you have some new studies??

Show me the differences in terms of an aquatic submersed plant growth that adapts, changes through time and has more than molecules of chl a to catch light.

Regards,
Tom Barr

[essabee]

Thks esaabee, can you suggest what will be the wattage if I chose a 2-tube light set for my 3-footer.

2 X 39 Watts T5 HO = 78Watts total

[defdac]

Anyone have a table of minimum PUR to grow certain plants?

No will probably not find one either. I know Tom Barr aka plantbrain likes about 30-40 µmol/m² PAR to get most plants running smoothly and with low growth rates (easier maintenance).

If one visits http://translate.google.co.za/transl...n%26safe%3Doff they give Lux values for the plants, which is about as useful as W/gal (i.e. meaningless). It would be nice having info on what level of PUR is needed to grow particular plants.

It's not black and white here. It's not that Lux is useless. It's almost as useful as PAR.

I have a total of 40-58 PUR over my tank assuming 85% reflector efficiency and no light escaping.

That sounds ok! Think you will be able to grow any plant with those figures.

How much consideration? How much fudge factor is in that?
This is assumption needs to include the entire living growing plant which has a light harvesting complex that can be modified and captures all sorts of light including green light and yellow etc.

Plants and light are not static things, as the plant grows up and out, the light changes. They adapt at the whole plant level, the tissue level and at the chemical level.

You are not going to escape that issue or error ratio. You can get close, but then you are as close as PAR meter. Few aquatic species have PUR data, there's a ton available for PAR however.

This entirely misses the whole point of the calculator - but also assimilates it since you can add any action spectrum you want for any species. It's up to you as a user of the calculator.

The two action spectrums I have added is for Elodea and Zooxantheallae.

I guess you could argue that other green underwater plants might have a different looking action spectrum, but it will not be much off. Heck the Zoox and Elodea is not much off - it will ALWAYS be much better to shoot down blue and red light with a little of green/yellow to make things look nice and behave normally - than it would be to use green light.

Now if you want to compare bulbs, I suppose....but few bulbs have ever been tested with growth rates independent of other factors for aquatic plants as far as PUR/PAR etc.

Do you know of any? The choice between bulbs may not be
that significant at the end of the day in terms of the difference between PAr and PUR.

"Plant" bulbs have not been shown to perform significantly better than say "cool whites" in terms of growth rates. Unless you have some new studies??

That is totally true and also what the numbers from the calculator actually says with a big sign "IN YOUR FACE GroLux-engineer!". It's also painfully clear that the most bang for the buck will be the reflectors, not what type of bulbs you select. It's there. In the calculator. Some bulbs are less efficient but you will be able to grow plants will all of them...

Now I will tell you something cool:

1) Lux-meters are cheap.
2) Their sensors have almost perfect alignment to the photooptic curve.
3) You know what bulbs you have.
4) You have a calculator where you can calculate PAR, PUR and.... Lux.

Some lateral thinking later and you will see that you can use your cheapo Lux-meter as a PAR or PUR-meter with the help of the calculator and it will be with high certainty be more exact than the cheapo PAR-meters...