Richard:
Lumens is a measure of human perception of brightness. In professional horticulture, source intensity is always measured in Watts.
I agree, that giving brightness only in lumens is stupid.
Full spectrum (300-800nm) graph should be given with each light to be able to calculate any brightness standard.
Now to theory, there are
MORE THAN ONE spectrum to lumen conversion standards, which makes brightness given with only lumens and no standard allready obsolete (not to talk about cheap lumen meters that calculate it based only on one peak value!). When we were converting at out faculty we used
CIE 1978 standard, so probably this is used the most?!
IMAGE: CIE 1978 standard:
And for me even PAR is ridiculous to use as each individual plant has its own spectrum absorption and reflection characteristic. The only literature I was able to find to measure each plant's individual "PAR" is one really old book from times that they did not have electronic spectrometers.
On wiki
Luminosity function is written about converting. All one needs to do to convert from real spectrum to lumen is to integrate alongside spectrum graph from cca 400nm to 750nm using CIE 1978 curve and multiply with 683.002lm/W if using relative CIE 1978 graph.
To convert from spectrum to PAR, different curve is used (at stated above in one post), but I do not know exactly which units and maximum value is used for PAR.
IMAGE: PAR conversion:
Have a nice day,
Ziga
P.S. to admins
PNGs uploaded to gallery are uploaded as blank images
