I'd be surprised if they actually increase or decrease the intensity of the light. On the older NuArc unit I have, those dials would be to determine the actual exposure (in units of light -- not time). There is probably a sensor that measures the about of light (UV) that the bulb is putting out (fluxuations in voltage, heat of the bulb, etc varies the bulb's output). When you set the dials for a certain setting, the actual time of an exposure might vary, but the amount of light hitting the paper will be the same. Mine is a 1000 Watt fellow that I also have not got around to using yet.
I am assuming your v28-1200 is a 1200 Watt beast -- so I would think that the number of units of light will be low for a platinum print...I would do a test print in 5 unit intervals (5-10-15-20-25) to start with. It will depend on your negs (conventional developers or pyro, density, etc).
That is the best I can do for you -- perhaps someone who has actually used a 1000 Watt or 1200 Watt light source will chime in soon!
Vaughn