I think there's something buried deep in the human psyche which equates the light with "good" and the dark with "bad". It probably harks back to when we were nomadic hunter-gatherers being hunted ourselves by the animals around us, almost all of which had and still have better night vision that we poor generalised human-type people-things.
Our ability to make and to control fire was the great leveller which enabled us to survive, particularly once we left the African savannah and ventured out into less hospitable terrain. It enabled us to ward off attacks by predators and it was also used as a tool for hunting as well as cooking. I saw a TV programme quite recently in which it was shown that cro-magnon man almost certainly used fire to drive woolly mammoths over cliffs in the periglacial regions during the ice ages. We also know that neandertal man used fire effectively. And, of course, fire = "light", and light = "good".
Yet the association pair light = "fair", in the sense of "light-coloured", and that being desirable, is a sometime thing. How many of those of us of the caucasian persuasion lie out in the sun whenever possible to try to get a tan? Being too pale is seen as a sign of something like unhealthiness. Having said that, it's not only the Michael Jacksons of this world who aspire to being paler than they were born. If you read the matrimonial sections of Indian newspapers you see a lot of ads for and by women who have "wheat"-coloured complexions. And the ads for skin-lightening potions of various kinds and dubious provenance are legion.
