Question on dimming Vivosun MH/HPS ballast

[mkono87]

I picked up a 600w version from a buddy who said that he did switch it too the 400w setting in the beginning few weeks. I immediately thought was not a good idea. After looking at the vivosun website, im under the impression that if both the ballast and bulbs are 600w, changing the lumens is not an issue and is designed to do that. Can anyone comment on this? The ballast clearly indicates it dimmable.

 

[TorturedSoul]

My experience with a different brand of electronic HID ballast (which may not at all be relevant, but who knows, lol?) :

I own one of the adjustable Lumatek 400-watt ballasts. It'll run a 400-watt bulb at 400 watts (or 10% or so "overdriven," if the user wishes). It'll run a 250-watt bulb at 250 watts. It will also run a 400-watt bulb at 250 watts. This reduction in wattage, if I remember correctly, causes a slight but measurable shift in the spectrum of the bulb's output - but this wasn't anything that I could detect with my (poor) eyesight. Running a 400-watt HPS bulb at only 250 watts did not seem to shorten its useful life. However... I ran 400-watt MH bulbs at 250 watts and they didn't seem to last all that long. They'd work fine for a while - easily long enough for the average vegetative growth period - but then simply fail to light up one day. I don't know whether this was a shortcoming with the ballast, the bulb, all MH bulbs... or just one of those things that "is." I do remember that the HPS bulbs I used were branded as Lumatek bulbs, but I assumed that a different company actually manufactured them. I'd love to stumble over a case of them, though.