Importance

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Abstract

A single side-sealed metal vapor discharge lamp is disclosed which includes a discharge tube having a sealed section at one end and a discharge region defining envelope at the other end, a pair of metal foils sealed at the sealed section and a pair of electrodes, the discharge region of the discharge tube containing a rare gas for starting and a filled gas containing mercury and light emitting metal. The electrodes are each comprised of a rod connected to the metal foil and a coil of at least one turn mounted on the forward end portion of a bent end portion of the rod, the coils being oppositely spaced apart by a predetermined distance in the discharge region. The coil is formed of a higher melting point material than a surface material of the forward end portion of the bent portion of the rod. With the length from the bent portion to the forward end of the rod indicated by L1, the length of the coil by L2 and the wire diameter of the coil by d, the following inequalities are satisfied: L1.ltoreq.3d and d/2.ltoreq.L2-L1.ltoreq.3d. According to the lamp, it is possible to firmly mount the coil on the corresponding rod, to reduce less scattering of a material of which the electrode is made, to prevent blackening on the tube wall, to obtain a better starting characteristic and to enhance a lumen maintenance factor.

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First Claim