Which one "effect on" or effect in" is the correct way to be said or both ways are correct??? why?? examples please.(I have seen it both ways but don't know how to use in or on after effect.) Thank you before hand. Emotion: big smile
Well, I'd say "effect on" is what I've seen mostly.

Or may be, "effect in" could be used in sentences like - That policy came to effect in December.
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I think you mean effect as a noun and not a verb. "John was able to effect real change" is a verb. "John's promotion had a significant effect on the company's morale" is a noun. The use of "effect" as a noun is usually followed by "on" meaning "result or consequence." You could also say, "What would be the effect OF turning all the lights off at 10pm?" That also alludes to result or consequence of an action.

Effect can also be used as a noun to mean sound, lighting, scenery etc in a play or movie: as in "The director portrayed the mood by utilizing special effects, rather than words."

So it varies depending on the way in which you use it.