The history of technology is endlessly interesting... 

Fun fact: "Blackout curtains were invented to keep light from escaping, not the other way around as they’re used today."

Research @ Atomic | @astorventures, @mohrdavidow, @kernel0x, cs @harvard

"With a completely dark city, the German bomber planes struggled to see where to drop their bombs and many historians credit millions of lives saved to the blackout efforts."

 h/t Glimpse

"Without sophisticated tracking systems, German aircraft relied on sight during bombing runs and so the European Allies instituted blackouts and recommended blackout curtains."