effect 是名词,“影响”,搭配短语：have an effect on sth.=have an influence on sth.对··有影响
affect 是动词,“影响”,直接跟宾语,affect sth 对···有影响,且通常指不利的影响.
eg, Sandstorms sometimes affect Bejing.
Watching TV for a long time will have a bad effect on your eyes.