【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】 .

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