Light is build up out of different frequencies, layer up on layer: Red + Green + Blue = white. In physics the term photon is used to describe the smallest entity, it is the lowest number on the plank's scale.
Light is considered a wave that travels through space. From the 8-formation particle concept, one could see light as a flock of birds or a shoal fish moving through the Aether. The compression and size of the group defines the possible frequencies it contains.
By using a prism light can be split up, when it passes the lattice of the glass' atomic structure, bending the incoming light into different observable bundles / formations / frequencies: Low (Red) - Medium (Green) - High (Blue)