Thomas C. Larason

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We describe how the National Institute of Standards and Technology obtains a scale of absolute spectral response from 406 nm to 920 nm. This scale of absolute spectral response is based solely on detector measurements traceable to the NIST High Accuracy Cryogenic Radiometer (HACR). Silicon photodiode light-trapping detectors are used to transfer optical(More)
The Système International des Unités (SI) base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps to be carried out with a relative expanded uncertainty (coverage factor k = 2, and thus a 2 standard deviation estimate)(More)
The Système International base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps with an expanded uncertainty of 0.46%, almost a factor-of-2 improvement. A group of eight reference photometers has been constructed with(More)
Adenovirus is regarded as the most resistant pathogen to ultraviolet (UV) disinfection due to its demonstrated resistance to monochromatic, low-pressure (LP) UV irradiation at 254 nm. This resistance has resulted in high UV dose requirements for all viruses in regulations set by the United States Environmental Protection Agency. Polychromatic,(More)
Increasing commercial, scientific, and technical applications involving ultraviolet (UV) radiation have led to the demand for improved understanding of the performance of instrumentation used to measure this radiation. There has been an effort by manufacturers of UV measuring devices (meters) to produce simple, optically filtered sensor systems to(More)
Ultraviolet (UV) reactors used for disinfecting water and wastewater must be validated and monitored over time. The validation process requires understanding the photochemical properties of the pathogens of concern and the challenge microorganisms used to represent them. Specifically for polychromatic UV systems, the organisms' dose responses to UV light(More)
Polychromatic UV irradiation is a common method of pathogen inactivation in the water treatment industry. To improve its disinfection efficacy, more information on the mechanisms of UV inactivation on microorganisms at wavelengths throughout the germicidal UV spectrum, particularly at below 240 nm, is necessary. This work examined UV inactivation of(More)
A cryogenic radiometer-based system was constructed at the National Institute of Standards and Technology for absolute radiometric measurements to improve detector spectral power responsivity scales in the wavelength range from 900 nm to 1800 nm. In addition to the liquid-helium-cooled cryogenic radiometer, the system consists of a 100 W(More)
The illuminance responsivities of two transfer standard photometers have been directly determined from their spectral responsivity calibrations at two different calibration facilities of NIST. The main characteristics of the two photometers, and their calibrations are described. The spectral and broad-band (illuminance) responsivities measured at the two(More)