Maybe. With discharge lamps (mains or high frequency), brightness will drop slightly with a reduction in voltage. However, Powerdown220 recommend an optimised voltage of around 225 volts and the output of the lamp is based at 230 volts, so any impact on overall light output is minimised.
Here in the UK lamps are seriously overvolted. This initially causes the lamp to burn brighter than it was intended to do so by the manufacturer. This shortens the lifespan of the lamps, and they become dimmer much faster, which is referred to as lamp degradation.
Operating the lamps at or slightly below the 230 volt design voltage slows lamp degradation, so the lamps stay brighter for longer and consume less energy throughout their lifetime.