According to one embodiment, a light detector includes: a first set of light detection elements and a second set of light detection elements each being disposed in a first region on a substrate; and a first selection and integration circuit and a second selection and integration circuit each being disposed in a second region outside of the first region on the substrate. The first selection and integration circuit is configured to select a first subset of light detection elements in the first set, and integrate outputs from the light detection elements in the first subset. The second selection and integration circuit is configured to select a second subset of light detection elements in the second set, and integrate outputs from the light detection elements in the second subset.