Patent ID: 7064490

Claim:
A compact self-ballasted electrodeless discharge lamp comprising: a bulb filled with discharge gas containing mercury enclosed in the bulb in the form of mercury element, not in the form of amalgam, and a rare gas; an excitation coil installed near the bulb; a ballast circuit which supplies high frequency power to the excitation coil; and a base that is electrically connected to the ballast circuit, wherein: the bulb, the excitation coil, the ballast circuit and the base are formed into an integral part; the bulb has a virtually spherical shape or a virtually ellipsoidal shape; a recessed portion to which the excitation coil is inserted is formed on the ballast circuit side of the bulb; the recessed portion has an opening section on the ballast circuit side, and has a tube shape with a virtually round shape in a cross section thereof, with a portion positioned on a side opposite to the opening section of the recessed portion being provided with a function for suppressing the convection of the discharge gas; a largest diameter of the bulb is set in a range from not less than 60 mm to not more than 90 mm; a bulb wall loading of the bulb during a stable lighting operation is set in a range from not less than 0.07 W/cm 2 to not more than 0.11 W/cm 2 ; a ratio (h/D) of a height (h) of the bulb based upon an end face of the opening section in the recessed portion to the largest diameter (D) of the bulb is set in a range from not less than 1.0 to not more than 1.3; supposing that a distance between a top face of the recessed portion positioned on the side opposite to the opening section of the recessed portion and a top portion of the bulb facing the top face of the recessed portion is Δh, and that a diameter of a portion positioned on the side opposite to the opening section of the recessed portion is Dc, the following relationship is satisfied: Δh≦1.15×Dc+1.25 mm; the excitation coil is constituted by a core and a coil wound around the core; and a center portion of a portion around which the coil is wound in the longitudinal direction of the core is positioned within a range that is apart from a plane on which the largest diameter of the bulb is located by a distance from not less than 8 mm to not more than 20 mm toward the ballast circuit side.