The obvious question to ask is why do you think its dimmer? Are you comparing two bulbs side by side? One after the other? Or just remembering what the old one looked like? And what was the old bulb, another Gavita?

If the old bulb when right through to failure then I'd expect a new one of the same specs to be significantly brighter, up to as much as twice as bright although your eyes might not perceive it that way.

The ballast should last through several bulbs as a minimum but there are reasons why it might not. A moderate dimming of the bulb is not what I'd expect from a failing ballast.

Thanks, shrubs. The light is obviously much dimmer to the eye, maybe not even half as bright. The first new bulb was almost blinding. The new ones are not even close to that. These are the new bulbs compared to the one that burnt out.

What woud cause the ballast to fail? Have the 600W Lumatek digital ballast.

Sounds like it's the bulb. Your sure they are HPS in the right wattage?

-- If the Capacitor is partially failed, then the light will be dim. Try replacing the Capacitor. Make sure use use the same UF rating as the old one.