means Light is the visible radiant energy that lets us see, or anything bright, pale, or not heavy depending on which sense you mean.

from Two different words wearing the same coat. The 'brightness' sense comes from Old English 'lēoht,' from a Proto-Germanic root tied to a very old Indo-European word for shining, the same ancient family that gave Latin 'lux' and Greek 'leukos' (white). The 'not heavy' sense comes from a separate Old English word, 'lēoht' (or 'līht'), traced to an Indo-European root meaning easy or nimble, a cousin of Latin 'levis' (light in weight, source of 'levity'). English simply let the two settle into one spelling.