Low-pressure dischage lamp and back light device using same

摘要

A low-pressure discharge lamp (1) is provided that includes a glass tube (2) having an inner diameter in a range of 1 to 5 mm and a pair of electrodes (3) disposed at end portions in the glass tube (2). The pair of electrodes (3) contain at least one transition metal selected from transition metals of Groups IV to VI. Mercury and a rare gas containing argon and neon are sealed in an inner portion of the glass tube (2). A relationship between a cathode glow discharge density J and a composition index alpha of the sealed rare gas of the low-pressure discharge lamp (1) satisfies the following expression alpha<=J=I/(S.P<2>)<=1.5alpha (where S represents an effective discharge surface area (mm<2>) of an electrode, I represents a RMS lamp current (mA), P represents a pressure (kPa) of a sealed rare gas, and alpha represents a composition index of a sealed rare gas that is a constant expressed by alpha=(90.5A+3.4N)x10<-3 >when a total of a composition ratio A of argon and a composition ratio N of neon is expressed by A+N=1). Thus, sputtering of a small-sized electrode is suppressed thereby to suppress consumption of a rare gas sealed in a lamp so as to increase a life time, and a decrease of an emitted luminous flux is prevented.