Complex sentence: He then determined that he could reverse the process and reproduce the recorded sound from this photographic strip, by shining a bright light through the running filmstrip, with the resulting varying light illuminating a selenium cell.
Split into simpler sentences: He then determined that he could reverse the process and reproduce the recorded sound from this photographic strip. He achieved this by shining a bright light through the running filmstrip, with the resulting varying light illuminating a selenium cell.