Despite the fact that there are multiple light sources in this photo, including one that is not artificial; you have still met the challenge beautifully with the one (I am assuming) artificial one that matters.
If I am not mistaken the challenge is for a single artificial light source...the sun hardly counts as artificial. In any case the composition is terrible...there is no reason to have the leaves in the foreground lit by a flash...if you cut off the leaves you have a decent sunset image...but again...that wasn't the challenge...
Use a single, artificial light source to dramatically light the subject of your choice.
I'm sorry, but I must consider the sunset as a second source.
If it is a plant in front of a poster, forgive me.