Complex sentence: Within the iconoscope, an image was projected onto a plate containing a mosaic of photosensitive granules separated from a common plate, each constituting a tiny capacitor that accumulated and stored electrical charge in response to the light striking it.
Split into simpler sentences: Within the iconoscope an image was projected onto a plate containing a mosaic of photosensitive granules. Therefore, each granule constituted a tiny capacitor that accumulated and stored an electrical charge proportional to the light striking it.