Grandmother's body seemed to resemble an electromagnetic field. The house in which she appeared was solar heated and well insulated. I typically only needed to use the furnace at night. I have wondered if a well-insulted house might build up electrostatic charges which would have made it easier for her to appear, but then again maybe not. I have wondered about the use of the word light to figuratively express physical consciousness.
Light travels as both a wave and a particle.
The nervous system in the body creates networks where particles of matter travel as waves enclosed in the neurons. It might be possible for a spirit body to create channels of spirit consciousness that travel naturally up and down the body, layered in the head as the physical body does. There are a number of stories circulating about people who have near death experiences. Many of them happened in a hospital so that their brush with death can be verified. It is interesting to me how much longer are their stories, than the time that is recorded as being in a near death state.