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This fourth paper of the Series is devoted to photon fluctuations in the light output of distributed feedback (DFB) lasers. Statistics on laser photon fluctuations are collected from numerical solutions of noise driven rate equations. The approximate formula for the variance of the photon fluctuations, presented earlier , is also applicable to the DFB laser. Compared to the single-cavity injection laser, the DFB laser has the following features. 1) The order of magnitude of the photon fluctuations of the single lasing mode of a DFB laser is comparable to the fluctuations of the total power output of a single-cavity laser. 2) Contrary to single-cavity lasers, which cannot be made to Operate in a single longitudinal mode even under idealized conditions if they are driven by short current pulses, DFB lasers will readily deliver a single, pulsed mode. Thus, if thermal effects and backreflection of scattered light can be controlled, there will be no mode jumping during pulsed operation.