An analysis of optimum photodetection for subcanier multiplexed lightwave systems is presented. The optimum APD avalanche gain, the resulting minimum required photocurrent for a given system carrier to noise ratio, and the sensitivity performance of PIN and APD receivers, are obtained. Results show that APD detection provides a sensitivity improvement in excess of 8 dB for a range of receiver noise levels from 50 ohm receivers to tuned configurations, enabling a significant increase in SCM power budget and distribution capacity.APD receivers over a range of receiver input equivalent noise levels, including tuned [4,5], untuned, an 50 ohm [3,6], receiver configurations. The results are applicable to the selection of the optimum photodetection characteristics in SCM receivers, to maximise sensitivity and signal distribution capacity.