This work examines the impacts of the diurnal radiation contrast on the contraction rate of the radius of maximum wind (RMW) during intensification of Hurricane Edouard (2014) through convection-permitting simulations. Rapid contraction of RMW occurs both in the low- and mid-levels for the control run and the sensitivity run without solar insolation, while the tropical cyclone contracts more slowly in the low-levels and later in the mid-levels and thereafter fails to intensify continuously in the absence of the night phase, under weak vertical wind shear (~4 m s^-1). The clouds at the top of the boundary layer absorbs solar shortwave heating during the daytime, which enhanced the temperature inversion there and increased the convective inhibition, while nighttime destabilization and moistening in low-levels through radiative cooling decrease convective inhibition and favor more convection inside the RMW than in the daytime phase. The budget analysis of the tangential wind tendency reveals that the greater positive radial vorticity flux inside of the RMW is the key RMW contraction mechanism in the boundary level at night, due to the enhanced convection. However, the greater positive vertical advection of tangential wind inside of the RMW dominates the RMW contraction in the mid-levels.