A lamp assembly is provided, that utilizes a light source including an LED element without cutting part of light therefrom and capable of forming a luminance distribution where the light with a maximum peak portion can be arranged substantially at (i.e., at or near) the cutoff line, thereby improving light utilization efficiency. The lamp assembly with an illumination direction can include a light source including an LED element with an emission surface, and a projection optical system for projecting an image of the light source in the illumination direction so that a desired light distribution pattern can be formed on a virtual vertical screen. The light source can have a rectangular shape having long sides and short sides, and can be configured to provide a luminance distribution on the emission surface such that a luminance peak portion is provided at or near one of the long sides.