The standardisation of light and photometry – A historical review

Abstract

This paper investigates the technological challenges and solutions to defining a reproducible standard for light together with its measurement, from the 18th to 21st century. The arrival and subsequent need to quantify gas lighting led to development of improved measurement methods, which in turn demanded more reliable standards of light, evolving from candle and flame standards to incandescence, and eventually the current radiometric definition. The progression is similarly traced from the plethora of early comparative visual photometry methods through to modern semiconductor instrumentation. The problem of heterochromatic photometry is also examined.

Photo-Oxidation of Therapeutic Protein Formulations: From Radical Formation to Analytical Techniques

“…Lumen as the photometric International Systems of Units (SI) derived unit of luminous flux, is a measure of the total quantity of visible light emitted by a source per unit of time. It takes into account the sensitivity of the human eye i.e., the luminous flux differs from power (radiant flux) in that radiant flux includes all electromagnetic waves emitted, while luminous flux is weighted according to a model (a "luminosity function") of the human eye's sensitivity to various wavelengths [25]. One lumen is defined as the luminous flux of a 1.464 mW at a defined wavelength of 555 nm with 100% efficiency.…”