An apparatus for processing wafers one at a time. The process includes contacting the acidic petroleum oil with a hydrogen donor solvent to thereby produce a treated petroleum oil. Illumination optics directs each of the color light beams into a corresponding light modulation assembly. In addition, overall spectrum activity can be measured. The excitation current is generated by switching the switching element with switch-on pulses that have an ON time period, and the at least one voltage induced in the detector system is measured in the area after the cut-off edge of the switch-on pulse for ascertaining the position information. The timing offset and power are reported as the result of ranging.