Q. Why does a woman wave her hands in front of her when lighting Shabbat candles?
A. Blessings should be said before performing the action. However once you have said the blessing over the candles you have already made it Shabbat and it would be a transgression if you then kindled a light.
The compromise is to light the candles, cover your eyes during the b’rachah and then remove your hands so that you enjoy the lights after the blessing has been said.