In a network with Reconfigurable Optical Add/drop Multiplexers (ROADMs), transient effects from network failures trigger sudden power changes to channels, even on spans (ROADM-to-ROADM links) upstream/downstream from the failure. Some ROADMs rely on restrictive wavelength assignment rules, calledfield-of-use(FOU), to insure surviving channels meet performance objectives.Dropdepth(DD) (ratio of surviving channels) andspanoverlapcount(SOC) (length of spans of overlapping lightpaths) are two parameters defined for FOU guidelines. For a given DD, FOU guidelines specify a corresponding maximum SOC for each wavelength. Generally, a wavelength can support a longer span overlap count under a smaller drop depth restriction. However, the measured drop-depth changes as wavelengths are assigned. We propose methods to optimize transient-constrained wavelength assignment in commercial ROADM networks. Our solutions have been shown to provide 40% more channels than with typical FOU guidelines.