The present invention relates to an optical amplifier and the like comprising a structure for effectively suppressing transient output signal power fluctuations caused by delays in control. Based on the analysis, the logging speed is increased if all the sensors justify it, and is reduced if any of the sensors require a reduced logging speed. Each printhead module includes an ink distribution member that is attached to the ink reservoir. The controller also includes a gate drive device electrically connected to the power device for regulating operation the power device. A method for equalizing the illumination of light sources for a digital image test member, and an apparatus and method for testing the color of a digital image uses the illumination equalizing device. The electrode for one embodiment may be used for an electrochemical sensor or sensor cell.