Mercury Vapor Lamp Starter?

[MNBobcat]

Our outside yard light comes on with a low glow one night and full bright another night. I replaced the daylight sensor after it would not come on at all. Does anyone know if they have a starter/ballast in them and if its built into the bulb? I'm trying to understand if all I need to do is replace the bulb or if I'm going to have to replace the whole light.

Thanks.

 

[hosspuller]

Need a new bulb or ballast. The ballast is the starter.