Power Balance In The Positive Column Of Narrow Bore T2Low-pressure Mercury Discharges

Fluorescent lamps, which are based on low pressure mercury discharge, are among the major light sources for indoor lighting and play an important role in lighting. Compact fluorescent lamps (CFL), featuring compact structure and high efficiency; have played significant role in general lighting. In recent years, T2compact fluorescent lamps with outer diameter7mm have shared more portion of the market. However, researches on lamp discharge characteristics mainly focus on lamps with larger diameters (T4-T12), but seldom on lamps with small diameters. Since the current density inside the T2fluorescent lamps is much higher than that in lamps with larger diameters, ambipolar diffusion will lead to mercury depletion along the axis of the lamp tube, and subsequently influence electric and photometrical output properties of discharge. While China manufactures85%of the CFLs over the world, a series of regulations are implemented which propose requirements of greater performances to the products in EU market. Therefore, it is necessary to study fluorescent lamps with smaller diameters in order to optimize the designs of T2compact flourescent lamps. The energy losses in the positive column of low-pressure mercury discharge includes radiation, heating of gases and volumn losses. In this dissertation, the radiation power and radiant efficiency of strong spectral lines in the positive column of discharge are measured by Koedam factor method for T2Ar-Hg and Kr-Hg low pressure lamps. The dependence of discharge properties on the cold spot temperature, discharge current, filling composition and filling pressure is discussed. Furthermore, a1-D fluid model is applied to analyze energy balance in the positive column of the T2low pressure mercury discharge lamps, and results obtained from the model are compared with those from the experiments.In Chapter1, the basic principle of fluorescent lamps and the development trend of lamps with smaller diameters are introduced firstly. Then, the researches on T2mercury discharge lamps are proved necessary and important as a response to the current status and challenges for China’s industry of fluorescent lamps. After the previous researches on modelling and experiments of low pressure mercury discharge lamps with different diameters are reviewed, main tasks and innovations of this dissertation are stated.In Chapter2, the concept and physical meaning of Koedam factor are explained. The methods to obtain Koedam factors for lamps with large diameters are reviewed. A small ganio-radiometer is designed and manufactured. In the experiments, the Koedam factors of strong spectral lines at254,365,436and546nm of the T2lamp discharge column are measured. The cold spot temperatures are20and50°C for Ag-Hg lamps, and30and50℃for Kr-Hg lamps. All the lamps are operated at the currents of40,100and160mA. The comparison of the experimental results with those derived from Monte-Carlo simulation by Lawler et al reveals that Koedam factors will decrease with the decreasing diameters and will increase with the increasing current, and that Koedam factors are less dependent on cold spot temperatures. Spectral lines at254nm are found to yield the maximum Koedam factors.In Chapter3, The procedure and experimental setup are described in detail for measurement of radiant powers inside the positive column by Koedam factor method. The radiance of the spectral lines within the range of200-1000nm at different cold spot temperatures and currents is obtained by means of irradiance relative calibration and radiance absolute calibration. Then radiant power and radiant efficiency can be calculated with the Koedam factors obtained in Chapter2. Since the radiation at185nm is easily absorbed by oxygen at atmosphere, the radiant powers at185nm can be indirectly derived from the ratio of radiance of185nm to radiance of254nm. A vacuum monochromator is applied to obtain the radiance of185nm and that of254nm on different conditions. A deuterium lamp radiance standard is applied for calibration. Besides, the uncertainty of the experimental results is analyzed in detail.In Chapter4, the radiation powers and radiant efficiencies of the eleven spectral lines (at185,254,297,313,365,405,408,436,546,577,579nm) for T2lamps are measured. The dependence of input powers and radiant efficiencies on cold spot temperatures, discharge currents, rare gases and their filling pressure is discussed. For the radiation at254nm with current100mA, the optimum cold spot temperature for radiant power is50℃, and the cold spot temperature for maximum radiant efficiency is higher. The optimum filling pressures for T2Ar-Hg discharge and Kr-Hg discharge are5Torr and7Torr respectively. Krypton is filled in the low pressure mercury discharge lamps to reduce input power and increase radiant efficiency at254nm. Though visible radiation from mercury atoms is very low compared with radiation at254nm, it is still very important for the research of energy balance in the discharge column. In addition, mercury depletion along the lamp axis cannot be neglected.In Chapter5, power balance in the discharge column of low pressure mercury discharge is analyzed. The energy input into the discharge column is consumed in the form of radiation loss, gas heating loss and loss at the wall. In this dissertation, a one dimensional fluid model developed by Petrov et al is applied to analyze the detailed discharge process. According to this model, radial distribution of the electrons is taken into consideration, and the radiation process is evaluated with coupling coefficients of different infinitesimal elements in the discharge space. When the cold spot temperatures are over40℃, the model prediction agrees well with the experimental results. But at lower cold spot temperatures, there is big deviation between experimental results and model.