The present invention discloses an optical device (100) and a lighting device for illuminating two intersecting surfaces (S1, S2). The optical device (100) comprises a first light guiding structure (120) for redirecting light from a light source (200) into a first direction and a second light guiding structure (130) for redirecting light from the light source (200) into a second direction different from the first direction, wherein the optical device (100) is arranged to prevent light from the light source (200) from being redirected in a direction between the first and second directions. By positioning the lighting device (100) at the intersection of two surfaces (S1, S2) such as can be found in a step, or at a corner of a wall, or at a corner inside a closet, or on the intersection area of ceilings, the two intersecting surfaces can be illuminated at the same time with comfortable light distribution, using a simple structure that can be easily installed.