This graph shows several points of interest on the UVA/B spectrum, plus shows the erythema curve. This curve is actually designed to show the damage potential to human skin, but it applies to all living matter. The higher the line, the more potential "damage" that wavelength can cause. We put damage in quotes, because the goal isn't to damage the plant as much as expose it to those wavelengths to illicit a response, so the plant will react to prevent damage. When speaking of cannabis, that reaction is to create more THC, cannabis's natural sun block. For tomatoes and peppers, it would be to create more terpenes and flavanoids, plus a thicker flesh, which is it's protection mechanism.
Virtually all UVB lamps cut off at about 300nm (shown by the blue line), so they don't produce any light from 280nm to 300nm. This is unfortunate, as this means they not only miss out on the most potent part of the UVB spectrum, where the reaction is highest, but they also miss out on producing light to trigger UVR8. The only exception is the Flower Power
lamp we sell, which uses special, patented glass and can reach down to 280nm. Any UVB light will help, but producing significant light in this 280-300nm region will guarantee premium results, and insures you are working WITH the plant biology.
The point of this graph is to show you that not all UVB is the same. As you go from 320nm towards 280nm, it rapidly increases in power, in damage potential. The atmosphere filters out all wavelengths smaller than 280nm, but light from 280nm to 300nm is allowed through the atmosphere, and should be in any serious horticultural UVB lamp. Otherwise, you are cutting out 50% of the spectrum, and the half that has the greatest effect on plant biology.
Notes: We are used to using 280nm-320nm being defined as UVB and 320-400nm being defined as UVA, but other definitions exist. The European regulatory agencies consider 315nm to be the dividing line for UVA/B rather than 320nm. Many agencies consider 380nm-400nm to be "violet" and not "ultraviolet". None of these definition are "more right" than the others, they are just different. Being a US based corporation, our definitions are based on FDA regulations and accepted limits.