Quote Originally Posted by oldmac
BTW for everyone; while I was gone I oversaw a side by side by side experiment that had UVb from start of veg to flower to finish, Uvb for just flower period and no UVB at all. We used 5 different strains and the results are interesting. I will try to post it all in the comming days.
More than interested on hearing about it, bro :rasta:

You are right, there is no LED growing lamp using UVB LEDs, which are very expensive (one can cost more than all the rest of the lamp). Those using "UV" LEDs actually are using near UVA, and mostly, violet (no ultraviolet) LED.

UV tecnically starts below 380nm. Although LEDs emitting in 390-410nm, which are the vast majority used on LED growing lamps, are barely visible, they are not UV, and that band effect is accounted on all botany literature as deep blue, not as UV. I do no expect large differences in biological effects than 450nm blue effect for these LEDs.

There is actually avalaible true UVA LEDs (peak emission 360-385nm), but i think little manufacturers (if any) is using them. They are mostly avalaible on low power LEDs. UV LEDs needs especial optics in the encapsulate of the chip because most materials do yellow when exposed to UV. In general UV are much short lived than blue LEDs and output degradation is faster.

Anyway, efficiency compared with royal blue LEDs is greatly reduced.