Yes, ENLIGHTENMENT is a Scrabble word!

Letter values in Scrabble US: E 1, N 1, L 1, I 1, G 2, H 4, T 1, E 1, N 1, M 3, E 1, N 1, T 1.

Is it a valid word?

ENLIGHTENMENT is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

education that results in understanding and the spread of knowledge
(Hinduism and Buddhism) the beatitude that transcends the cycle of reincarnation; characterized by the extinction of desire and suffering and individual consciousness
a movement in Europe from about 1650 until 1800 that advocated the use of reason and individualism instead of tradition and established doctrine

Also: age of reason.