Improved Photometric Standards and Calibration Procedures at NIST
1Optical Technology Division, National Institute of Standards and Technology, Gaithersburg, MD 20899-0001.
Summary
NIST now bases photometric units on a cryogenic radiometer, improving accuracy for luminous intensity (candela), luminous flux (lumen), and luminance. This detector-based approach enhances calibration services and reduces uncertainties.
Area of Science:
- Metrology
- Photometry
- Radiometry
Background:
- NIST previously relied on standard lamps for photometric unit realization.
- A need existed to improve the accuracy and traceability of photometric measurements.
Purpose of the Study:
- To establish detector-based photometric units at NIST.
- To reduce uncertainties in photometric calibrations.
- To expand NIST's photometric calibration services.
Main Methods:
- Established a detector-based luminous intensity unit (candela) using an absolute cryogenic radiometer.
- Realized luminous flux (lumen) and luminance units based on the new candela.
- Utilized standard photometers for illuminance realization and calibration.
- Developed a new absolute integrating sphere method for luminous flux realization.
- Employed an integrating sphere source for luminance unit realization.
Main Results:
- All NIST photometric units are now traceable to the cryogenic radiometer.
- Standard photometers with large dynamic range simplify illuminance measurements.
- Detector-based methods have reduced photometric calibration uncertainties.
- NIST can now offer a wider range of photometric calibration services.
Conclusions:
- The adoption of detector-based methods has significantly advanced NIST's photometric capabilities.
- Traceability to the cryogenic radiometer ensures consistency and accuracy in photometric measurements.
- The new methods provide more reliable and versatile calibration services for industry.
