Highly accurate short-circuit current measurements of photovoltaic devices require spectrally adjustable radiation sources. This paper presents an optical setup, which is able to generate and adjust the spectral irradiance in the wavelength range from 355 nm to 1200 nm with an optical resolution of 7 nm to 15 nm. A grating light valve (GLV) is used as a spectral shaping tool. We prove the highly resolved spectral shaping capability by matching the spectral irradiance of the generated radiation to the AM1.5g reference solar spectral irradiance distribution, slightly smoothed to consider the limited bandwidth of the spectrometer. Remaining deviations are mostly lower than the spectral measurement noise of 0.5 % to 3 %.