The performance of Light Emitting Diodes (LEDs), including efficiency, flux level, lifetime, and the variation of color, is advancing at a remarkable pace. LEDs are increasingly used for many applications including automotive, aviation, display, transportation and special lighting applications. White LEDs are expected for general lighting applications (solid state lighting) in the near future. Thus, accurate measurements of LEDs and appropriate standards are increasingly important. This paper reviews photometric, radiometric, and colorimetric quantities used for LEDs, and discusses the current state of optical measurements of LEDs and standardization efforts in International Commission on Illumination (CIE). The paper also touches on the issue of color quality (e.g., Color Rendering Index) of light expected from solid state lighting, and the need for a new metric. The calibration facilities and services for LEDs established at NIST are also discussed.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.