Can someone give me the formula for calculating PUR? I've finally grasped the concept of PUR and PAR and their importance so I want to figure them out for my tank and see if I can improve my lighting.
Thanks

I just use PAR and use a PAR meter and that's the end of it for me

Apogee makes a very nice PAR meter that's water proof etc to 6-8ft etc.
I have one and a LICOR.

Regards,
Tom Barr

So is there a low tech way to calculate PAR? I have 6700K bulbs in my 4x96w PC system but I'd like to know my PAR to see if these are really that good or not. I know they look good but I would like to get the max PUR out of my lights as possible.

Ivo use to have qa nice run down and I think some other folks spents gobs of time and effort to get at it and use a model.

I spent some $ and can test in real time, in specfic cases, at specific plants, at specific depths etc, with a lot less guess work, time and effort.

That's a trade off.

One I gave some thought too... and also given the lack of light measurement in this hobby, a painfully poor black hole, decided to do something about it.

I see some carry on about testing and measurements of little things such as NO3, Fe etc, but they do not measure light.

Kinda of funny when they bad mouth me suggesting water changes and known volume/weights to target a NO3 levels but they do not even own a light meter

Regards,
Tom Barr

Try to contact Daniel, he might be able to give you some formula.

www.defblog.se


Best regards,
Detlef

I dont know if you really can 'calculate' PUR. You'd have to measure it, I mean its a property of the light and depends on its spectral distribution and intensity across a given range. To 'calculate' it youd need some accurate data if not measured by yourself, from someone else or the company, and either a whole lot of math by hand or a program to interpolate the data.

As I understand it, LUX is weighted towards human sight, PAR is unweighted and accounts for all wavelengths 400-700nm, and PUR is weighted towards plants photosynthetic regions. The idea of PUR is good, but i've not seen any bulbs really measured with it and I have yet to hear of such a meter - is there such a thing experts?

My router seems to have gone down so you can't reach my blog or my PUR-calculator.

I calculate PUR exactly as outlined in this article:
Aqua Botanic-light bulb comparison
"Steps to calculate tabulated quantities"

It uses a photosynthetic action spectrum, which is an average of how most plants use the radiation. Crazy Loaches is right that it thus can't be calculated *exactly* for one single plant - but it will be very near.

Take a PAR-meter and put a filter on it that filters the light exactly like a photosynthetic action spectrum and you will get the PUR-value.

Can be done either optically or digitally.

A lot of things that can be done are not of great value to actually do. Plants can adapt well to a wide range of light intensities and light spectra. So, there is little to be gained by pursuing an accurate measure of just the light that is most effective for plants. On the other hand, if you enjoy the science involved, and that is part of the pleasure this hobby provides to you, then there is no reason not to seek such light measurements. This is a hobby, so enjoyment is the goal.

Would you in the same way say that plants have adapted to a wide range of nutrient levels so there i little to be gained by pursuing an accurate measure of just the nutrients/levels that is most effective for plants?

If not, why is that?