A study on the relationship between CCFL's characteristics and gas pressure

Summary form only given. A continuous improvement in the lumen output and efficacy of the cold cathode fluorescent lamps (CCFLs) generally used for the backlight of LC-TVs and notebook PCs is always expected. The lumen output and efficacy can be improved by controlling the electric field intensity in the discharge plasma by changing gas pressure. Therefore it is very important to grasp the relationship between the CCFL's characteristics and gas pressure. The authors investigated the influence of gas pressure on the cathode fall voltage (CFV) and the electric field intensity of the positive column. The lamp used for this measurement had an outer diameter of 4 mm, and a length of 200 mm. The electrodes used here were Ni-plate and Mo-plate, which had a length of 5.2 mm, a width of 1.7 mm and a thickness of 0.1 mm. The enclosed gases were Ne-Ar and Ne- Ar-Hg, whose pressures were 8 kPa, 5.3 kPa and 2.7 kPa. The measurement results show mainly three points. The first is the difference in the relationship between the CFV and gas pressure with regard to the presence of the mercury. The CFV of the Ne-Ar lamp reaches a minimum at 5.3 kPa, while the CFVs of the Ne-Ar-Hg lamps decrease with a rise in gas pressure monotonously. This difference is caused by the variation of the sheath thickness arising from the presence of the mercury. The second point is that the CFV of the Ni- electrode lamp is higher than the Mo-electrode lamps' whether the mercury is present or not. This is caused by the difference of gamma coefficients between Ni and Mo. The third point concerns differences in variation of the characteristics of the positive column when gas pressure changed. The electric field strength increases with a rise in gas pressure whether the mercury is present or not. This is caused by the increase of the elastic collision loss between electrons and atoms. The absolute value of the electric resistance per unit length of the positive column in Ne-Ar-Hg lamp increases with a rise in gas pressure, while the values of the Ne-Ar lamps do not change. The difference is considered to be caused by variation of the ratio of elastic collision loss to radiation loss.