Thanks everyone. It is a 4w incandescent, it is meant to be a night light so it is very dim, one of the reasons I went with this bath fan unit. T
There is no minimum load on the instruction sheet, only max load. It does say "No intended for use with electronic ballasts". I guess I assumed the incadecently 4w night light was not a part of the 18w florescent electronic ballast - maybe I was wrong on that. It does say it is intended for magnetic rapid start ballasts only. This is the Decora PR
It sounds like I should give the commercial sensor a try since it can be used for electonic ballasts and it also has 3 wires (white, black, ground).
Link to the fan http://www2.panasonic.com/webapp/wcs...del=FV-08VKML2