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 conseque