PURPOSE: To prevent unstable discharge and provide a stable visible light by making lamp input voltage of an external electrode type fluorescent discharge tube in a chopping wave form having a specified duty ratio and supplying it to a lamp.
CONSTITUTION: A specified amount of rare gas such as He, Ar, Xe, and Kr is sealed in a tube type glass bulb, and in addition mercury vapor is sealed if necessary. A phosphor 6 is applied to the inner surface of the glass bulb, part of the phosphor 6 is removed to form an aperture 7. A plurality of line-like or belt-like electrodes 2-4 are formed on the outer surface of the glass bulb, other than an effective luminescent surface corresponding to the aperture 7. High frequency voltage from a high frequency power supply unit 5 is applied to the electrodes 2-4 to light a fluorescent lamp. An external electrode type fluorescent discharge tube is lit by forming lamp input voltage in a chopping wave form having a specified duty ratio, for example about 80% duty ratio. The high frequency power supply unit has a high frequency oscillator using a transistor and a step-up transformer.
INOUE MASAKI
TAGAWA KOJI
KUMADA TOYOHIKO
