translation.en: Before the light bulb was invented, people had figured out how to put a reflector behind it, focus it a little bit; put lenses in front of it, focus it a little bit better.
translation.zh: 在发明灯泡以前 人们已经懂得，在其后面放一个反射器 聚焦效果就会好些 前面再放一个透镜 效果会更好些