It’s a noun, not an adjective. If you say, “I’m bright”, that’s an immodest (and possibly inaccurate) statement. But “I’m a bright” says that you don’t believe in God, more strictly that your view of the world is naturalistic, free of what its inventors describe as “supernaturalism and mystical elements of all kinds”. The term has only recently been coined by Paul Giesert and Mynga Futrell, two educators from Sacramento, California. They modelled it on gay, to provide an umbrella term for a potential coalition of all those who felt themselves isolated and without political influence in the USA because they professed no religious belief. The philosopher Daniel Dennett has taken it up and publicised it in newspaper articles, from two of which the quotations below have been taken. Somehow, I don't think it's going to catch on.
Whether we brights are a minority or, as I am inclined to believe, a silent majority, our deepest convictions are increasingly dismissed, belittled and condemned by those in power — by politicians who go out of their way to invoke God and to stand, self-righteously preening, on what they call “the side of the angels.”
New York Times, 12 Jul. 2003
Look on the bright side: though at present they can’t admit it and get elected, the US Congress must be full of closet brights. As with gays, the more brights come out, the easier it will be for yet more brights to do so. People reluctant to use the word atheist might be happy to come out as a bright.
Guardian, 21 Jun. 2003