JPS6476602A - Back-light apparatus - Google Patents

Abstract

PURPOSE: To obtain high luminance and to reduce uneven luminance when the height of a diffusion plate is three times as big as the diameter of a fluorescent lamp when viewed from the front, by forming a reflecting mirror by a perpendicular incidence part, a reflecting mirror part and a multiple reflecting mirror part. CONSTITUTION: A back light for a transmission display body 12 such as a liquid crystal display device is composed of a diffusion plate 1, a fluorescent tube 8 and a reflecting mirror. The reflecting mirror is formed by a perpendicular incidence part 3, an inclined incidence part 9 on a parabola, which intersects the intersection point 4, and has a straight line 7 intersecting the center of the tube 8 in parallel with the straight line connecting the intersection point 4 of the line 2 to indicate the height of the plate 1 and the incidence part 3 and the intersection point 6 connecting the line 5 to indicate the diameter of the tube 8 and the plate 1 as a symmetric axis and the center of the tube 8 as a focus, and a multiple reflecting part in parallel with the straight line intersecting the end 10 of the plate 1 and the incidence part 9, and fluorescent light reflected by the incidence parts 3, 9 and fluorescent light reflected by the multiple reflecting part and additionally reflected by the incidence part enter into the plate 1. Thereby, when the height of the diffusion plate is almost three times as big as the tube diameter, luminance is high when viewed from the front and uneven luminance is reduced.