SCL Talk on Photometric and Radiometric Measurement

The Standards and Calibration Laboratory (SCL) organized a talk on photometric and radiometric measurement on 6 March 2015. The speaker was Dr. Teresa Goodman of UK’s National Physical Laboratory (NPL). In the beginning, Ms. Brenda Lam (SCL) introduced the background of the speaker. Dr. Teresa Goodman is a Principal Research Scientist in the Optical Radiation Measurement Group at the NPL. She has more than 30 years of experience in R&D associated with the realization, maintenance and dissemination of optical radiation measurement scales for sources, detectors and materials. Dr. Goodman currently serves as International Commission on Illumination (CIE) Vice President Publications.

Dr. Teresa Goodman introduced her talk contents included Applications, Measurement principles, quantities, units and methods, Reference standards and traceability, Sources of error and uncertainty and brief the history of NPL.

Optical Radiation and “Light” principles were briefed. The following wavelength ranges were mentioned: UV-C (100nm – 280nm); UV-B (280nm – 315nm); UV-A (315nm – 400nm); Visible (~400nm – ~780nm); IR-A (780nm – 1400nm); IR-B (1.4um – 3um); IR-C (3um – 1mm). There were three measurement parameters included Artefact being measured, Spectral resolution and Measurement geometry.
Spectral = distribution of radiation as a function of wavelength
Broad band = weighting or radiation by a function such as eye response function or erythemal action spectrum

Then she introduced the measurements in terms of colour appearance “Colorimetry” (CIE 1931 Standard Observer function) and other weighting functions included Photobiological hazards, where actinic UV hazard for skin and eye; Near-UV hazard for eye, Retinal blue light hazard, Retinal thermal hazard, Infrared radiation hazard for eye and Thermal hazard for skin.

Dr. Goodman mentioned the measurement geometry which is determined by the optical system used on the input side of the measurement instrument. “Geometry is important for materials” she said because of interaction involved Refraction and Scattering which changed travel direction of radiation. During this measurement, we needed Standard Geometries.

After that she stated the measurement sources and detectors and equipment such as Goniophotometer and Integrating Sphere. The following setup was the basic measurement of intensity and illuminance.

The summary of different measurements’ Pros and Cons was shown in the following table.

Dr. Goodman also introduced the calibration and reference standard requirement to us. Reference lamp needed to have reproducible output under controlled operating conditions, easy to align in correct orientation and good wavelength coverage. We needed to consider the spectral differences and stray light.

Finally, she introduced NPL history to us. NPL has founded since 1900 with more than 450 specialists in Measurement Science. The photo showed NPL opening in 1902 and speech at that time was “The object of the scheme, I understand, is to bring scientific knowledge to bear practically upon our everyday industrial and commercial life, to break down the barriers between theory and practice, to effect a union between science and commerce.”

Mr. Dennis WK Lee (Head of SCL) moderated the Q&A Session.

I took a photo with Mr. S.T. Yip (Safety Officer, University Safety Office, CUHK).

After the seminar, Mr. Dennis Lee led me to visit their new accredited Photometric and Radiometric Measurement facilities. Photo showed different types of standard lamps.

The in-house design for swapping UUT and Ref during measurement was briefed. It enhanced the efficiency of measurement.

At the end, I took a photo with Dennis in front of the integrated sphere.

Reference:
SCL - http://www.itc.gov.hk/en/quality/scl/about.htm