Spread illuminating apparatus with irregular interval of grooves of light reflection pattern

摘要

There is provided a spread illuminating apparatus to suppress the appearance of moiré fringes. A light reflection pattern of a transparent substrate is composed of grooves of substantially triangular in section and flat portions adjacent thereto. The light reflection pattern is formed substantially parallel to the optical axis of a bar-like light source and the depth of the grooves increases gradually in proportion to the increase in distance from the light source. The interval of the adjacent grooves (the groove interval) is set to vary irregularly. Thereby, the relation between the interval of grooves and the interval of mosaic pattern of liquid crystal cells is not definite, and the appearance of moiré pattern can be suppressed. The variation ratio of the groove interval is set to range 25% to 85% of the average groove interval