The features of the electroluminescence spectra in amorphous silicon p-i-n diodes were ecxellently explained by dispersive-transport-controlled recombination. The misunderstanding to the efficiency and peak position of the electroluminescence for many yera was thereby clarified by the theory. The experimental methods of local states in the intrinsic layer of a-Si-H solar cells studied by the electro-luminescence were described in detail. The studied results showed that the defect energy distribution exhibited a single narrow peak when the samples were prepared by diluted silane using hydrogen, while the defect energy distribution was wider with double peaks in the samples deposited by pure silane.