Kavita - I feel that indeed you did meet the spirit of you grandma, and it is possibly that your father really believes she is dead, so when you called him your grandma disappeared.
Nothing we sense in the world is directly known, but it is all impressions that are translated into a sense of smell, sight, hearing, etc. So the eye receives reflected light from an object that is translated into nervous impulses, which is then received by the brain which translates what are formless nerve impulses into what we feel we see. So in dreams we tend to put pictures or images collected from everyday experiences to put an interpretation on our formless dreams. We do this because we tend to have an experience of the world based on our body senses, and our dreams and communications from the dead come from a very different environment, so we put it in images and ideas we understand.
So when we dream about a dead person communicating with us it can be distorted by our view of what death is – or our associations with the dead person. So if we believe in ourselves that when a person dies they are finished it creates our own view of death, or one that is a mixture of a real communication and our beliefs. Such thoughts, even if unconscious, can cause such dreams of seeing the person we know has died being seen and assuring us that they are very much alive.
The light flickering was a sign that something unusual was about to happen - and of course the bird being alive was also a sign that the dead live on. See
http://dreamhawk.com/approaches-to-being/questions-2/#TalkDead Tony
