Patent ID: 7368916

Claim:
A method for making capacitive measurements of cathode fall potential in a fluorescent lamp, the fluorescent lamp containing an electrode, the method comprising: determining a magnitude of a plasma potential associated with the electrode at a reference point; measuring a cathode fall potential waveform associated with the electrode; and determining a respective magnitude of each of a plurality of points along the cathode fall potential waveform based on the magnitude of the plasma potential at the reference point, wherein measuring the cathode fall potential waveform comprises measuring the cathode fall potential waveform using a capacitive measurement apparatus comprising an electrically conductive sleeve that surrounds a portion of the lamp that contains the electrode, and an operational amplifier having an output terminal and first and second input terminals, wherein the first input terminal is electrically coupled via a shielded cable to the conductive sleeve, the shielded cable comprising an electrical shield, and wherein the output terminal is electrically coupled to the second input terminal of the operational amplifier and to the electrical shield.