A high-efficiency LED lamp is disclosed. Embodiments of the present invention provide a high-efficiency, high output solid-state lamp. The lamp includes an LED assembly, and an optical element or diffuser disposed to receive light from the LED assembly. The optical element includes a primary exit surface for the light, wherein the primary exit surface is at least about 1.5 inches from the LED assembly. In example embodiments, the optical element is roughly cylindrical in shape. An LED lamp according to some embodiments of the invention has an efficiency of at least 150 lumens per watt. In some embodiments, the lamp has a light output of at least 1200 lumens. In some embodiments, the LED lamp produces light with a color rendering index (CRI) of at least 90 and a correlated color temperature of from 2800 to 3000 K.