In classical physics, if the source of light moves laterally, the light beam itself would also move laterally. This is because the light waves are emitted from the source and propagate through space, carrying the information about the motion of the source. Therefore, the movement of the source affects the direction of the light beam.
However, in the context of special relativity, the situation is different. According to Einstein's theory of special relativity, the speed of light in a vacuum is constant for all observers, regardless of their relative motion. This means that the speed of light is always measured to be the same value, c, regardless of the motion of the source or the observer.
In the case of a moving light source, special relativity predicts that the observed frequency and wavelength of the light will be affected by the relative motion between the source and the observer. This effect is known as the Doppler effect, which causes a shift in the observed frequency of light.
As for Einstein's light clocks, which are thought experiments used to illustrate the principles of special relativity, the movement of the light source does have implications. In a light clock, a beam of light is reflected between two mirrors, and the time is measured based on the round-trip travel time of the light beam. If the source of light in the light clock is moving relative to an observer, the observer will measure a different time compared to an observer at rest relative to the light source. This is because the relative motion affects the path of the light beam, leading to a change in the measured time intervals. This phenomenon is known as time dilation and is a fundamental consequence of special relativity.