The degradation of amorphous silicon (a-Si) pin solar cells under prolonged illumination (Stabler-Wronski-Effect SWE) is investigated. We first measured the spectral response due to low-intensity illumination. The external collection efficiency Q is a function of the light wavelength λ and the applied voltage U. The functions Q(U) saturate for increasing reverse bias. Normalization to the saturation values defines the internal collection efficiency q. The functions q(U) for different λ cross through a nodal point with coordinates Uf, qf The voltage Uf represents the flat-band voltage of the uniform-field model. Our first SWE aspect consists of a substantial qf reduction caused by enhanced photocarrier recombination near the pi- and in-junctions. We additionally measured the photocharacteristics due to white illumination at a variable intensity ϕ The photocurrents vanish at the transition voltage Ut which is independent of ϕ for an undegraded cell. With advancing degradation, Ut decreases but Ut(ϕ) becomes an increasing function. The latter effect represents our second degradation aspect, supplementing the first one.