High-resolution observations of downwelling spectral irradiance in the wavelength band of 350-2500 nm carried out using Spectroradiometer at Thiruvananthapuram (8.5°N, 77°E), a coastal station located in the southwest Indian Peninsula adjoining the Arabian Sea, have been used to investigate the instantaneous spectral aerosol direct radiative forcing efficiency (ISADRFE) and its variation with solar zenith angle. This study shows that, during the pre-monsoon season (March-May), magnitude of the ISADRFE maximizes at the wavelength of ~460 nm around noon, with mean values ranging between -270 to -330 Wm-2μm-1τ500 -1 at 15°<SZA<50°. The wavelength at which the ISADRFE peaks as well as the spectral width of the peak increases with solar zenith angle (SZA), especially at SZA>70°. About 47% of the to the total (broad band) instantaneous shortwave aerosol radiative forcing is contributed by the photosynthetically active radiation at solar zenith angle of 20°, while the corresponding percentage contribution decreases to ~40% at SZA of 75°. At solar zenith angle of 20°, ~8% of IADRFE is contributed by the wavelength bands above 1.5 μm, while at SZA of 75°, the corresponding contribution is ~17%.