How do I fix dimmer lights?

I have two dimmer lights connected to the same switch. When I turn them on only one is able to fully brighten. It is still getting power, but can't reach it's full capacity. It reaches it's brightest point when the dimmer switch is turned half way. When the switch is turned to 100 percent, then the light has almost no brightness. The brand of the lights is Portfolio. Does this sound like a problem with the light? Or a problem with the switch?