[laglad]

It could be that the rise of 'enlightenment' word occurences in the 1960s refers to the enlightenment as the Buddhists and Zen practitioners speak of it instead of the European context of the word. The rise would map with the counterculture movement of those times which we're still living in.

[lsy]

I thought this might be the case too, but the n-grams for "enlightenment", "Enlightenment", "the Enlightenment", and "The Enlightenment", etc. are all quite different. Lowercase "enlightenment" doesn't show the same pattern as capital-E or with the definite article.