Ray, beam are comparable when they denote a shaft of light.
This conception of light as a shaft is fixed in our language but is not always in keeping with modern scientific views of the nature of light.
Ray suggests emanation from a center or point in the manner of the spokes of a wheel; its typical application is to one of the apparently thin lines of light that seem to extend from a radiant body (as the sun or a candle) or that are flashed from a reflective surface (as of steel or a mirror glittering in the sun).
Beam implies not a line but a long bar; it suggests therefore a bar made up of a bundle of rays of light; thus, a beam of white light is split by a prism into rays of light of the various colors of the spectrum.
A small beam is sometimes called a ray .