Methods for decreasing uncertainties in LED photometry Timo Dönsberg, Tomi Pulli, Meelis Sildoja, Tuomas Poikonen, Hans Baumgartner, Farshid Manoocheri, Petri Kärhä and Erkki Ikonen Published online: 21 September 2015 DOI: 10.1051/metrology/20150011001