UV-C for mold control"7 watt light for a exposure of 60 seconds about 4 inches away from the affected leaves followed by a 4-hour dark period"

7W depending on wavelength, x4 time at least, my estimation was based on 30W so try roughly 40-50 minutes per night.

UV-B @ 280nm is enough. I'd highly advise no one who considers themselves hobby growers to ever use UV-C and certainly never below 240nm, anything under 240nm will create a lot of ozone(O3). So long as you stick to 280nm, there won't be enough latent energy to split O2 into O3. The peak wavelength to destroy fungicides is 254nm, so a mercury vapor lamp would do very well. Personally, I don't mess with anything below 280nm. Nighttime application of UV-B light 280-315 nm will effectively suppress powdery mildew by directly damaging the pathogen's DNA, with successful applications. Effective treatments involve daily, brief exposures to UV-B during the dark period, typically at a specific dose. Make sure to have no blue light or UV-A present, as this can activate repair mechanisms of organisms. For maximum efficiency, use 254nm, but that's drifting into UVC, UVB@280nm will be much safer and still highly effective. You will just need 10-15 min @280nm instead of 2-6min @ 254nm. Or thereabouts. Gluck. Applying UV-B/C two/three times per week is effective to keep it away once treated.