A glass tube of aluminosilicate glass, with high dielectric constant K∼6.0 and low dielectric loss tan δ∼8.0×10−4, was investigated for the external electrode fluorescent lamps (EEFLs) of a dielectric barrier discharge. Compared with conventional EEFLs made out of borosilicate glass tubes with K∼(4.9−5.3) and tan δ∼(2.3−2.4)×10−3, the efficiency of the aluminosilicate EEFL increases by 15%−25% even at high luminance above 20 000 cd/m2 and the pinhole stability of the aluminosilicate EEFL also improves remarkably. In a soda-lime glass EEFL with a high dielectric loss tan δ∼7.0×10−3, the luminance and pinhole stability deteriorate even with a high dielectric constant K∼7.2 at room temperature, because the value of tan δ escalates as the temperature on the external electrode increases due to the dielectric heat dissipation.

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The properties of longitudinal and transverse discharges are investigated with the use of external electrode tubular lamps, with respect to the characteristics of current and voltage, luminance and spectral radiation. With the mercury-rare gases, a high luminance of over 10 000 cd m−2 is readily obtained in the longitudinal discharge with a long positive column where the spectral radiations from Hg are dominant. However, the luminance is extremely low, a few hundred cd m−2, in the transverse discharge with a short gap where all kinds of atom species are ionized and the intensity of the spectral lines from Ne and Ar is rather high. With pure Xe and a mixture of Xe, the transverse discharge is superior to the longitudinal discharge in that the breakdown voltage is low and the luminance for a high pressure above 200 Torr is relatively high.