The purpose of photometry is to measure light in a way that takes the sensitivity of human visual system into account. While radiometry measures light in all spectral regions, including ultraviolet and infrared, photometry only measures in the visible spectral region from 360 nm to 830 nm, where human eyes are sensitive. Thus, photometry is essential for evaluation of light sources and objects used for lighting, signaling, displays, and other applications where light is intended to be seen by humans.
NIST's program in photometry involves maintaining the SI base unit of luminous intensity, the candela, as well as other photometric quantities; establishing national calibration standards; and educating the photometric community about the fundamentals and practical aspects of photometry and photometric measurements.
The development of revolutionary energy-efficient solid-state lighting (SSL) products has sparked the need for new performance metrics and measurement methods to address their unique construction and operating conditions. NIST has been working closely with the U.S. Department of Energy (DOE), Federal Aviation Administration (FAA), and national/international standardizing bodies to develop new documentary standards for SSL, with continued research on color quality, measurement methods, and robustness for light emitting diodes (LEDs) and SSL products. In addition, we are also developing world-class measurement infrastructure, new standard reference sources/sensors, new measurement capabilities, and measurement assurance programs to support the industry's measurement needs.
NIST makes significant contributions to SSL industry for R & D, components, modules, and final products. Activities cover
Realization of photometric quantities
The candela, SI base unit of luminous intensity, is realized with a detector-based method, dependent on the absolute responsivity of detectors. It is maintained on a group of six standard photometers, which are traceable to Division's reference cryogenic radiometer (POWR). The lumen, the unit of total luminous flux, is realized from the candela using the Absolute Integrating Sphere Method implemented in the NIST 2.5-m integrating sphere.
Research and Development
The Photometry Project is actively engaged in the research of many pertinent areas in photometry. Current projects include:
The Photometry Project provides various photometric calibration services, the Measurement Assurance Program, and the NIST Photometry Short Course.
Stakeholders and Outreach
Many organizations and agencies have interest in the research and services performed in the Photometry Project, and concurrently we have reached out to other organizations in helping to provide standards and cutting-edge research. These organizations include: