The present invention relates to a composition comprising a blend of a luminescent polymer and a low molecular weight viscosity modifier, which has an emission maximum in the range of 350-480 nm, contains no exocyclic double bonds, and modifies the viscosity of the polymer without substantially altering emissive properties of the neat polymer. When a toner sensor detects that toner is out, and further a door sensor detects that there is a possibility that a toner bottle has been replaced, a toner replenishment rate is calculated from the rotational speed of a motor for rotating the toner bottle, and timing in which image formation is to be resumed is determined based on the toner replenishment rate. A n-well and a deep n-well surrounding the p-well on the sides and bottom. Each signal value of a set is acquired during a same ordered time segment.