The Greek Dark Ages appear to have ended when trade with other areas of the Mediterranean once again started to flourish.
One of the major causes of the end of the Dark Ages appears to have been technological. This was the set of advances that allowed the Greeks to start to use iron. The use of iron was important both for war and for farming. New iron tools allowed the Greeks to farm more efficiently. This allowed them to support a larger population and to have more goods to trade with other peoples of the Mediterranean.
As this happened, Greek culture started to flourish once again. The Greeks developed an alphabet derived from the Phoenician alphabet and started to write. Their art started to revive and they made much more elaborately decorated pottery along with other things such as bronze artworks. This was the age of Homer, where epic poetry was important.
The cultural changes, then, are material changes in the tools, weapons, and art of the Greeks. These changes showed that the Greeks were becoming more prosperous and were moving out of their dark age.