Does the digital ballast have a dimming feature? Are you sure it's not dimmed? Anyway, as I could be wrong, I'm pretty sure a MH bulb doesn't lose strength, it just clunks out. (could be wrong)..Also, I highly doubt that it would be less bright after only a few days, that doesn't add up. Also, you may want to give it a few minutes on before you make that call. When my light first comes on, it takes about 10 minutes to achieve optimal brightness. Let it warm up a bit.