Complex sentence: Some early proponents of DST aimed to reduce evening use of incandescent lighting--once a primary use of electricity--today's heating and cooling usage patterns differ greatly, and research about how DST affects energy use is limited and contradictory.
Split into simpler sentences: Some early proponents of DST aimed to reduce evening use of incandescent lighting, once a primary use of electricity. Today's heating and cooling usage patterns differ greatly, and research about how DST affects energy use is limited and contradictory.