The luminous thread which is dancing rhythmically within the cubical atom is the basic source of cosmic effulgence. The cubical effulgence of the atom is called ‘luminous atom’ know as ‘microbode’ (cubical cell). It is described as OM-light. The Mundakopanisad provides a wonderful description about this:
The ‘OM’ in its aural and luminous streams rises above and above…and turns itself into the universe. These risings, or surges and transformations, called Omkara natana (dance or rhythm of OM).