Yea the point of a dimmable ballast is clear and simple imo I have a few dimmable ballast that all have a job 50% when the young ones first see the light at a lower hight then 75% after a short while then up to 100% when they r in full flow and finally 110% when your plant's are near the end.I have 8plants that r near finishing and have boosted the ballasts to maximum 660 watts and can clearly see a difference in my plants with the extra power being applied so isint it simple enuff if you have it use it to full effect otherwise just buy a cheaper standard ballast........and no I have never heard of a ballast that diminishes in use when running on a lower setting same applies with the bulb.....