What was Edison thinking when he invented the light bulb? Did it occur to him that his bright invention would deprive millions of healthy sleep patterns for the rest of time? Before electrification, we tended to go to bed when it got dark, to avoid the tedium of stumbling into furniture by the feeble light of oil lamps or candles. We pretty much went to sleep when most animals did. Sure, bedtime changed with sunset times throughout the year, but people practiced natural ‘sleep hygiene’. We evolved to function in this way, after all.