According to one embodiment, a light detector includes a plurality of elements. Each of the elements includes a first semiconductor region, a second semiconductor region, and a third semiconductor region. The second semiconductor region is located on the first semiconductor region and has a higher first-conductivity-type impurity concentration than the first semiconductor region. The third semiconductor region is located on the second semiconductor region. The elements are arranged at a first period in a second direction crossing a first direction. The first direction is from the first semiconductor region toward the second semiconductor region. A quenching part is electrically connected with the third semiconductor region. Multiple lenses are located respectively on the elements. One of the lenses is positioned on one of the elements. A refracting layer is located between the elements and the lenses. The refracting layer has a first thickness.