Lightning in a dream denotes unexpected changes, which are taking place or are about to take place.
This may be the sudden realization of a personal truth, or of a more universal awareness. Often such a revelation has the effect of knocking down the structures we have built in as safeguards in our lives.
Alternatively, we may have to make changes in the way we think while leaving our everyday structure and relationships in place. Lightning can also indicate strong passion – such as love – which may strike suddenly but be devastating in its effect. You might also like to consult the entries for thunder / thunderbolts and weather.