小虎做完了所有的作业,兴奋地打开电视,电视上正播放着一台精彩的文艺晚会,小品、相声、魔术、歌舞,应有尽有。看着看着,小虎突然对一个问题很感兴趣:舞台上的灯光为什么会慢慢的变暗,同时又会有一两盏灯慢慢变亮?小虎知道,暗下去的是背景灯,亮起来集中照射到舞台上正在表演的演员的灯是追光灯,是为了让演员的表演显得突出(见图1)。他不明白的是,这些灯怎么可以随心所欲的变亮或者变暗? Tigers done all the homework, excitedly turn on the TV, television is playing a wonderful variety show, skit, comic dialogue, magic, song and dance, everything. Looked at the tiger suddenly was very interested in a problem: why the stage light slowly dimmed, while there will be one or two lights slowly lit? Tiger know that the dark is the background light, light up The light that focuses on the actors performing on the stage is chasing lights to make the actor's performance stand out (see Figure 1). What he does not understand is how these lights can be brightened or darkened at will.