Range and Error of Densitometers for Emission Spectroscopy

Present day densitometers are arranged to measure the proportion of the incident light that is transmitted by the photographic image of the spectral line. The readout is generally a galvanometer with a linear scale or a recorder which is also linear, although occasionally the strip chart may be printed in logarithmic units. A peculiarity of the transmission densitometer is that the measurement is inverse to usual electrical instruments in that the smaller the excursion of the needle the larger the quantity measured.