Backlight module and lens thereof

A backlight module for a liquid crystal display includes a reflective sheet, at least one light source above the reflective sheet, and a lens above the light source. The lens has a light-permeable surface at the bottom, a light-reflecting surface formed on the top of the lens, two side surfaces connecting the light-reflecting surface and the light-permeable surface, and a diffusion surface formed at the center of the light-reflecting surface. Profiles of the light-permeable surface and the light-reflecting surface are concave. The diffusion surface is convex. The lens of the invention allows light emitted by the light source to diffuse more uniformly.

This application claims the benefit of Taiwan application Serial No. 094100833, filed Jan. 12, 2005.

BACKGROUND

The invention relates to a backlight module, and in particular to a lens of the backlight module for a liquid crystal display.

Several lamps make up the backlight of a direct type liquid crystal display. During manufacture, the number of tubes increases to maintain luminance in larger displays.

Referring toFIG. 1, a backlight module comprises a diffuser11, a frame12, a reflective sheet13, and lamps14. The diffuser11and the reflective sheet13are fixed by the frame12. The lamps14, between the diffuser11and the reflective sheet13, generate light emitting directly or reflected to the diffuser11by the reflective sheet13and passing through the diffuser11. Because luminance between the lamps14and reflective sheet13of the conventional backlight module1differs, the brightness of a display is not uniform. Although increasing distance d between the lamps14and the diffuser11solves the problem mentioned above, thickness of the backlight module is increased, affecting display quality.

Referring toFIG. 2, providing an additional diffuser11aalso solves problems. The thickness of the sum of the diffuser11aand the diffuser11increases and the haze of the diffusers11and11ablurs the outline of the lamps14. Applying diffuser11anot only increases the cost but also the thickness of the backlight module1. Overlapping diffusers11and11afurther affects output of the light source. Increasing the number of lamps14to maintain luminance also increases costs.

SUMMARY

Embodiments of the invention provide a backlight module comprising a reflective sheet, at least one light source, and a lens. The light source is located above the reflective sheet. The lens is located above the light source and comprises a light-reflecting surface, a light-permeable surface, two side surfaces, and a diffusion surface. The light-permeable surface is located at the bottom of the lens, with a concave cross-section thereof. The light-reflecting surface is above the lens, with a concave cross-section thereof. The side surfaces connect the light-reflecting surface and the light-permeable surface. The diffusion surface is convex, formed on the central axis of the light-reflecting surface. Light from the light source is reflected and scattered by the lens to normalize light distribution and to make backlight module output lighten uniformly.

The lens of the invention comprises a light-reflecting surface, a light-permeable surface, two side surfaces, and a diffusion surface. The light-permeable surface is located at the bottom of the lens, with a concave cross-section. The light-reflecting surface is above the lens, with a concave cross-section. The side surfaces connect the light-reflecting surface and the light-permeable surface. The diffusion surface is convex, formed on the central axis of the light-reflecting surface.

DETAILED DESCRIPTION

Referring toFIGS. 3 and 4, the bottom of a lens21is a light-permeable surface211. A cross-section of the light-permeable surface211is concave. A light-reflecting surface212, adjacent to the light-permeable surface211, comprises a front reflective layer215and a rear reflective layer216. A cross-section of the light-reflecting surface212is concave. The side surfaces213are translucent or transparent and connect the light-reflecting surface212and the light-permeable surface211by an inclined angle. The diffusion surface214is convex, formed on the central axis of the light-reflecting surface212. The light-permeable surface212comprises a space217in the center of the light-permeable surface211, for accommodating the light source30.

Referring toFIGS. 3,4and5, the backlight module (not shown) comprises a reflective sheet40, light source30, a diffuser50, and a lens21. The lens21is located above the light source30. The light source30is located above the reflective sheet40. The lens21is located above the light source30. The lens21comprises light-reflecting surface212, light-permeable surface211, side surfaces213, and diffusion surface214. The cross-section of the light-permeable surface211is concave. The light-reflecting surface212, on the light-permeable surface211, comprises front reflective layer215and the rear reflective layer216. A cross-section of the light-reflecting surface212is concave. The side surfaces213are translucent or transparent and connect the light-reflecting surface212and the light-permeable surface211by an inclined angle. The diffusion surface214is convex, formed on the central axis of the light-reflecting surface212. The light-permeable surface212comprises a space217in the center of the light-permeable surface211, for accommodating the light source30. A diffuser50is disposed above the lens21.

The light source30generates a rear beam301and a front beam302. The rear beam301is emitted to the reflective sheet40and reflected therefrom to the diffuser50. The front beam302is emitted to the lens21directly.

The front beam302comprises a reflective light beam303, a direct diffused light beam304, and an indirect diffused light beam305. The reflective light beam303is emitted from the light source30, reflected from the rear reflective layer216of the lens21, emitting to and reflected from the reflective sheet40, and emitting to the diffuser50.

The direct diffused light beam304is emitted from the light source30, passing through the lens21, and scattered to the diffuser50by the diffusion surface214. The indirect diffused light beam305is emitted by the light source30, passing through the lens21, scattered to and reflected from the front reflective layer215by the diffusion surface214, and emitting to the diffuser50.

The side surfaces213are translucent or transparent. A first side light beam306is emitted from light source30, passing through the lens21, and emitting to and through the side surfaces213, and emitting to the diffuser50. A second side light beam307comprises light that fails to pass through the side surfaces213and then returns back to the lens21.

Via the lens, the invention provides various light beams comprising the front beam302including the reflective light beam303, the direct diffused light beam304, and the indirect diffused light beam305, the rear beam301, the first side light beam306, and the second side light beam307, generating normalized light distribution, decreasing inconsistent luminance between light source30and reflective sheet40.