Methods of measuring intensity in photoelectric spectrophotometry are discussed, and conditions for maximum reasonably precise utilization of amplifier galvanometer response are experimentally investigated. For a spectrophotometer having four light sensitivity ranges, differing by approximate multiples of ten, it is shown that, if proper grid bias is used on each range, deflection is proportional to incident light intensity within ±0.5 percent for applied grid potentials from 0 to 0.3 v. With a suitably selected galvanometer system, deflections measure light intensities from 1.0 to 106 arbitrary units over the whole response range of the instrument. It is also shown that for applied grid potentials from 0 to 0.5 v, the deviation from linearity does not exceed ±1.5 percent.
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