  Optical conductivity spectra of La_{0.7-y}Pr_{y}Ca_{0.3}MnO_3 were
systematically investigated. For metallic samples, the spectral weight below
0.5 eV, whose magnitude can be represented by the effective carrier number
N_{eff}(0.5 eV), increases as temperature becomes lower. Regardless of the Pr
doping, all the measured values of N_{eff}(0.5 eV)/T_C fall into one scaling
curve. This scaling behavior could be explained by the theoretical model by
Roeder et al. [Phys. Rev. Lett. 76, 1356 (1996)], which includes spin double
exchange and Jahn-Teller lattice coupling to holes. With the Pr doping,
far-infrared conductivities were found to be suppressed, probably due to the
Anderson localization.
