Diffusion Sheet with Localized Regions for Even Illumination

The diffusion sheet is divided into a first region with first diffusion characteristics and a second region with second diffusion characteristics. The first region corresponds to the outer circumferential section and has higher diffusion capability to redirect oblique light toward the center. The second region corresponds to the light-emitting diode position and has lower diffusion capability to prevent excessive scattering. This local differentiation allows efficient light distribution without increasing power consumption.

The patent changes the diffusion parameters of the diffusion sheet by creating regions with different diffusion characteristics. The diffusion coefficient or scattering angle varies spatially across the sheet, with the first region having parameters optimized for capturing and redirecting oblique light, and the second region having parameters optimized for direct light transmission. This parameter variation resolves the contradiction by optimizing light path efficiency rather than increasing light source intensity.

The patent merges the diffusion function and the light redirection function into a single diffusion sheet structure. Instead of adding a separate reflection sheet, the diffusion sheet itself is designed with spatially varying characteristics that enable it to perform both diffusion and redirect oblique light toward the center. This integration reduces device complexity while maintaining improved light utilization.

The diffusion sheet is designed to perform multiple functions: it diffuses light from the light-emitting diode, redirects oblique light toward the center, and controls the overall light distribution pattern. By making the diffusion sheet multi-functional through regional differentiation, the patent eliminates the need for additional components like reflection sheets, thereby reducing device complexity while improving light utilization efficiency.