If the light bulb was the way the speaker is, and you couldn't focus or sharpen the edges or define it, we wouldn't have that, or movies in general, or computers, or T.V. sets, or C.D.s, or DVDs -- and just go down the list of what the importance is of being able to focus light.
如果灯泡和喇叭一样 不能聚焦或限定它 我们就不能播放幻灯片，电影 电脑或电视机 又或者CD和DVD，等等等等 其重要的特征都是 能聚焦