| 摘要 |
PURPOSE: To lessen the light absorption loss by a supporting case of a light emitting tube by specifying the relation between the whole length from the tip of a base to the tip of the light emitting tube and the light emitting tube exposed length from the tip of the light emitting tube to the supporting case. CONSTITUTION: Four straight tubular bulb 1a are so arranged in parallel as to be positioned at four corners of an approximately square shape, the insides of the bulbs are connected one another at each edge part with connecting parts 1b, 1c to give one bent discharge route, and filament electrodes 5 are formed in both ends of the discharge route to give a light emitting tube 1. One end of the light emitting tube 1 is supported by a supporting case 3 in which a cap 4 is installed and a lighting circuit 2 is so housed in the supporting case 3 as to set the consumption electric power to be 16 W or lower. The length L from the tip of the cap 4 to the tip of the light emitting tube 1, the light emitting tube exposed length D from the tip of the light emitting tube 1 to the supporting case 3, and the average value θ of an angle formed between the center axis of the apparatus and a tangent line from the luminous center on the center axis of the apparatus and parted from the tip of the light emitting tube by D/2 to the surface of the supporting case are so determined as to satisfy the following relations; D/L<=0.55; 2θ<=57 deg.. |
