LAMP HAVING BLEACHABLE COATING TO PROVIDE VARIABLE ATTENUATION
Original Publication Date: 1999-Feb-28
Included in the Prior Art Database: 2004-Apr-09
Xerox Disclosure Journal
Disclosed is the addition of a bleachable dye coating to the surface of a fluorescent lamp in order to compensate for normal reduction in light output over lamp life. Aperture fluorescent lamp output is known to decay over time. The principal mechanisms for this decay are discoloration of the reflector coating that forms the aperture, consumption of the mercury that is the excitation mechanism, reduction in phosphor efficiency, and deposits of material evaporated off the electrodes. In document illumination systems, this reduction in output leads to a decrease in exposure, as a significant problem in analog copying machines. In digital copying machines (scanners), there is often a capability of electronically correcting for the decrease in illumination, however, there is a corresponding reduction in the signal-to-noise ratio. In addition, the correction means often has limited dynamic range so it is advantageous to restrict the amount of variation due to the lamp. The proposed addition of a dyed coating on the surface of the lamp will bleach out over time, compensating for the reduction in output.