An outdoor overhead lamp assembly uses light emitting diodes to provide illumination for an area to be illuminated. The lamp assembly includes a unitary housing, which may be formed from a single casting. The housing includes mechanical mounting structure for mounting the housing to a mast arm. The housing includes an electrical compartment for housing electrical components and connections. Heat sink fins are formed on the integral housing that provide for thermal control of the electronic components and LED modules within the lamp assembly. The LED modules are mounted to aiming platforms within an optical compartment for the assembly. An external lens provides environmental protection for the LEDs and their individual lenses. The housing may also include structures for mounting decorative coverings or “skins” to accommodate different aesthetic requirements.