Disclosed are a light unit and an illumination system using the same. The light unit includes a top plate, a bottom plate, and at least one light source module located between the top plate and the bottom plate. The bottom plate includes a specular-reflection region and a diffuse-reflection region. The diffuse-reflection region includes a first reflective pattern that reflects incident light via Lambertian distribution and a second reflective pattern that reflects incident light via Gaussian distribution.