The lightning flash is a function within Jewish Kabbalist belief when something to be manifested is drawn very quickly through the Sephiroth (spheres of existence) to become real in the physical world. As we become more aware of spiritual matters this symbol becomes part of our vocabulary. A flash in dreams signifies a build up of energy, which may be emotional, warning us that such energy, while potentially destructive, can be used positively. Concentrated light is significant on the mundane level as a flash of inspiration in a particular project or a moment of clarity when circumstances are particularly obscure. You might like to consult the entry for Lightning for further information.