CHARACTERISTICS OF OPACIMETERS ... 3.4.1 The receiver shall consist of a photoelectric cell with a spectral response curve similar to the photopic curve of the human eye (maximum response in the range 550/570 nm; less than 4 % of that maximum response below 430 mm and above 680 nm).
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photopic - of, relating to, or designating vision adapted to conditions of bright light
LD light detector The detector shall be a photocell or a photodiode (with a filter, if necessary). In the case of an incandescent light source, the receiver shall have a peak spectral response similar to the phototopic curve of the human eye (maximum response) in the range of 550 to 570 nm, to less than 4 per cent of that maximum response below 430 nm and above 680 nm.
