It takes minutes for a general spectrophotometer to scan a visble spectrum range, but such a device cannot satisfy the occasion where a dynamic spectrum is to measured. Though OMA system has come into existence to meet the demand of measuring dynamic spertrum, OMA cannot be applied for gencral purpose for its expensivenees. A photograph tube is both practical and reliable photo-electric converter. For one thing, it is of low cost, for another, it is convenient to mcasure dynamic spectrum if a feasible scheme compatible with its performance has been worked out.