Applied Photometry: Review of Retrospective and Reality Part 2: LED Challenge to Photometry

This is the second part devoted to review of modern applied photometry. In the six paragraphs of part 1 of this publication1, the oneness of candela and Watt realization and short history of artificial light sources up to LED intervention was observed. Activity of international expert’s community in field of light and optical radiation measurements was discussed. The replacement of traditional sources of general lighting and signalling by radiation sources with LEDs, which have a spectral distribution of light emitting characteristics different from traditional light sources, has raised a number of issues in the metrological support of optical radiometry and applied photometry related to the oneness of the reproduction of units of energy and photometric quantities based on Watt.