Ballasts-Light brightness?

I purchased two used (barely) ballasts. One ballast appears to work fine (light bright white). This is a straight 400 watt 120 volt ballast. The other comes with a 120-240 switch inside the 2nd unit that must be changed over manually. It appears to be hooked up correctly (120 volts). I have switched bulbs with the same result. It appears the light in the switchable unit is not as bright and a little yellower than the bright white and not quite as warm (heat given off by the bulb). Any idea on why this is occurring?

No dimmer and I actually switched bubs-one is a GE 400watt HPS and the other a 400 watt Sylvania HPS. It appears the yellower less bright bulb occurs just on the switchable unit (after switching bulbs). In other words it seems less bright in the switchable unit no matter which bulb I use.

Can anyone else be helpful in this matter? I want to make sure i don't have an electrical issue. I have contacted the manufacturer with no response. Should I be rotating the plants in the meantime (actually I have been) in order to make sure all plants are getting even lighting?

The ballasts are both the same, right? Both either HPS or MH? If not maybe that's the difference. Otherwise, I would be looking to return the second ballast.

They appear to be the same HPS 400 watt (also says HID Luminaire). The only difference is one has the ability to switch between 120-240 volts which is done internally and seems to be connected properly for 120 volts. The only other difference is the electrical cord on the switchable unit has been upgraded to meet 240 volt requirements. The difference in the lights (white vs. yellow tint) is not significant but noticeable.