New bulb for sure, start any calibration with a factory bulb from M&R. That way you know that variable is starting from the optimum point. Set taps correctly first.
I believe you can set the LTU to Seconds on your control panel. Ron?
1 ltu = 1 sec. this way downline you can run off a 60 ltu test to see if it equals one minute. When the times start getting to 50% more like 90 sec = 60 ltu its time to replace the bulb.
John is right on the taps, you need to have it tapped to your voltage to get strong light.
Al