What was the "Enlightenment"? Cultural, spiritual, philosophical, political and societal movement beginning around the 15th century, that placed the individual human being with special emphasis on his capacity for thought, as the center piece of responsibility for the development of the shared human condition within and across societies.
Embodied especially in artistic and philosophical works, applied to politics and governance, the seed of the scientific and industrial revolutions, and with a celebrated connection to ancient cultures.
Some enlightenment personae in no particular order: Erasmus, Montaigne, Machiavelli, Michelangelo, Luther, Da Vinci, Kepler, Descartes, Galileo, Brahe, Newton, Locke, Hobbes, Rousseau, Montesquieu, De Tocqueville, Kant, Hegel, Clausewitz, Smith, Mill. (I just realised I'm not going to try and list everyone who deserves to be included, I do not have the capacity for that task)
I think it's fairly arbitrary, but there is a certain kind of loss of innocence from there on out in western philosophy, Marx, Nietsche, Weber, Schmidt and Arendt for example are hard to place in the same sphere with those above. In my mind a key task of philosophy now is to find a new connection to this lost innocence of free flowing unburdened thought from previous centuries, kind of the way these classic enlightenment figures sought connection with the ancient world.
The discovery of the unconscious mind of psychology and neurology is a complete new frontier in itself, and definitely marks out the beginning of a new phase in philosophy and society. Great many things are changing and a new enlightenment maybe about to begin right now.