A novel cold cathode fluorescent lamp (CCFL) with an adiabatic layer suitable for backlighting of PDAs (Personal Digital Assistants) is described. The adiabatic layer (100-200mu;m) is formed between a light tube and an outer tube and is filled with low-pressure gases. This raises the temperature of the light tube to the suitable value (50-70deg;C), which maximizes efficiency even in low lamp wattage operation and in low ambient temperature. The results of experiments and heat transfer analyses show that the optimum pressure in an adiabatic layer lies between 1 Pa and 10 Pa. At a pressure of less than 1 Pa, the lamp maintains the temperature at a constant level because of the conduction loss is lower than the radiation loss.
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