Dr. Yoon describes the light emission and its propagation through the vacant space on page 252 in his textbook.
The light wave generated by orbital electron rings, propagates through
the vacant empty space in radial symmetric around them, constructing
milliards of concentric spherical wave fronts with equi-energy levels,
as shown schematically in Fig. 1-5-1.
All the wave fronts produced by oscillation of orbital electron rings
expand their spherical radii infinitely as they propagate through the
vast space of this universe. However, the energy of each wave front
does not change depending on the magnitude of their spherical radii.
All the successive wave fronts have exactly the same energy as that of
orbital electron rings performing a half cycle of their oscillation.
If this energy of an orbital electron ring oscillating a half cycle, is
E, surface areas of sequential spherical wave fronts are,
S1,S2,S3.......Sn, and the energy densities of each wave front is e1,
e2 e3 .......en, respectively, then the relation between them is

E=S1e1=S2e2=S3e3=. . . . .=Snen

Since Sn/S1=n^2, where n is integer, thus the intensity of a light beam
decreases by inverse square distance rule. A light beam is nothing but
a thinly sliced sections of these spherical wave fronts, arranged
concentrically along the propagating direction of light. It signifies
that the emission of light from its source and the propagation of light
through the space are nothing but an energy equilibrating process of
orbital electron rings oscillating in the light source. The
oscillatory energy of orbital electron rings in the source disperses
uniformly through the vacant space of this universe in order to attain
an equilibrium state. It is a natural character of energy to attain an
equilibrium state by flowing from a higher energy level to a lower one.
The energy does not need a separate energy to drive it to be
equilibrated, as though the water dam at a higher latitude, does not
need an energy to make its discharging water flow downward. In other
words, a dam storing water never provides momentum to its discharging
water to be able to flow downward. With analogy, lights never get
momentum from their source, possible to travel through the vacant space
of this universe.
Einstein assumed that light source provides momentum to its photons,
so, his photons can travel through the vacant space with the momentum
given by its source, as though a base ball flies through the sky with
the momentum given by a batter. If so, it is quite natural that the
speed of light source can change the speed of photon travelling through
the space, as though a batting energy can change the speed of a base
ball. So photons and their source have to belong to the same coordinate
system. However, it is a big mistake! The light source and the light
it emits never belong to the same coordinate system, but different
coordinate system, because the source does not provide momentum to the
light, so they can move independently with their own speed in different
coordinate system. That is why the speed of light through vacant space
is constant, and the speed of source never can change the speed of
light it emits. newedana