JohnnyToke
Member
gramsci.antonio said:lumens are useless to confront bulbs with different spectrums, but are quite useful with bulb of the same spectrum.
You can see this way (very simplified):
F(x) is a function, where x is the frequency of the light and F(x) is the output of the lamp at that frequence.
Then a lumen meter sample the light over 256 different frequencies, and mutilply the value of each frequencies for a different number T(i) and then divide for the sum of all the T(i) numbers.
By this way, some frequencies count more than others: the greater the associated T(i), the more important the frequence will be.
This is done because to the human sight some frequencies are brighter than others, therefore we can think as if it is introduced a correction vector T, i.e.:
Lumen=L(F, T)=<F(X.i), T(i)>/||T(i)||
l
where F is a function that represent the source of light that varies over the spectrum and efficiency of the lamp, L belong to the positive real, T the correction vector, and i the n-th sampled frequency.
But we are thinking lamp for plants, and and not for human sight. We know just the Lumen and not the function F, therefor T become an error vector and not a rescalation, making Lumen an useless factor when dealing with lamps with a different F, but it will be still useful when confronting lamps with the same F, since the error vectors will delete each other.
Conclusion: A CMH with 182 L/w and the same spectrum, is twice as better as a CMH with 90 L/w, since the efficiency is doubled.
very well written. It makes more sense now. Excellent post.
thanks
JT