Lumens and lux are photmetric units...
Photometry- is the science of the
measurement of
light, in terms of its
PERCEIVED brightness to the human eye. It is distinct from radiometry, which is the science of measurement of
radiant energy (including light) in terms of absolute power. In modern photometry, the radiant power at each wavelength is weighted by a
luminosity function that models human brightness sensitivity. Typically, this weighting function is the
photopic sensitivity function, although the
scotopic function or other functions may also be applied in the same way.
mW are radiometric units...
Radiometry- is a set of techniques for
measuring electromagnetic radiation, including
visible light. Radiometric techniques characterize the distribution of the radiation's
power in space, as opposed to
photometric techniques, which characterize the light's interaction with the human eye.
In photometric quantities every wavelength is weighted according to how sensitive the human eye is to it, while radiometric quantities use unweighted absolute power.
PAR µmols are...
Quantum- Which is basically identical to radiometric but a step closer to plants...it measures only 400-700nm(only Photosythetically active radiation) as compared to 380-850nm(all visible) that radiometry measures.
PAR in µmols actually is just fine in accuracy...or mW...both are equal really.
What I assume you mean by PAR isn't the best...is that a handheld "par meter" isn't the best. And that is because of the calculations to convert it to µmols it does internally and has a slight error based on nm's of the light. A spectradiometer will give an accurate µmol count that is just as accurate as the mW it also give.
If a par meter gave a mW read out, it would be off too. It's not PAR µmols that is not perfect...it's the device that takes the measurement.
And with all that said...a handheld par meter...even with the error...is 10000X better and more relevant than lumens.
What do you think is the best to use?
EDIT: You can send in a spectral chart of a light to apogee and they can calibrate the meter to the spectrum so it's accurate.
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