In Paradise Lost, Milton said that in hell "No light, but rather darkness visible / Served only to discover sights of woe".
By Peter Bradshaw
There is something very Miltonic going on at your local multiplex at the moment; darkness visible is what popular cinema yearns for.
Everything is dark nowadays. There's The Dark Knight, the latest, madly successful Batman movie; it's nothing to do with the camp silliness of the 60s TV show or even the relative gaiety of the Tim Burton movies.
This Batman returns the film franchise to the crepuscular gloom of the original comic book: it does what it says on the tin - it's dark, dark, dark.
Dark equals grownup; dark equals sexy, dark equals real
The Joker is a homicidal psychopath given to threatening people with knives and guns. The whole thing is so dark you can hardly see your hand in front of your face.
Dark is absolutely de rigueur for superhero movies nowadays.
Spider-Man is relentlessly angst-ridden and the first X-Men film actually began at the gates of Auschwitz.
Or there's Harry Potter, something else for which the brightness dial is twisted resolutely anti-clockwise.
When that franchise first started, it was quite a jolly experience: now it's dark - because Harry has grown up, you see.
Then of course there's James Bond. When Roger Moore had the job - and indeed when Sean Connery did - you would get the odd quip, the flirtatious interlude with Moneypenny, and each and every violent encounter would be topped off with a nonchalant wisecrack; it was virtually an action movie tradition.
But in the new 007, Quantum Of Solace starring Daniel Craig, there are no jokes, no smart remarks. Bond is just a ruthless killer, driven by rage.
Once again, pop culture's great dark shadow has fallen.
Dark is a term of approval, even of awe, shorthand for a vaguely defined, cloudily understood quality that is thought to improve a film franchise, and make its pre-dark manifestation look silly and babyish.
It isn't pessimism exactly, but a self-conscious super-cool cynicism and a deadpan refusal to be shocked by its own increase in violence.
No more post-kill quips for the modern James Bond
Dark equals grownup; dark equals sexy, dark equals real. Dark is the new black.
Or is it? I can't help thinking that these movies aren't really dark.
You want dark? We'll rent a DVD of Ingmar Bergman's Cries And Whispers and afterwards I'll read aloud Philip Larkin's poem Aubade. There - that's really dark.
A couple of lines of Aubade will make Christian Bale's Batman whimper with fear, or it would if he's got any sense.
I can't help thinking that "dark" is a fashion accessory driven by the movie world's preconception of its grungy demographic: the tickets and DVDs are bought by boy-men aged from 12-24 who dress in "dark" clothes and play "dark" computer games in their dark bedrooms.
This is a fan base whose psychological angst is to be indulged.
I'm a fan of Bond and Batman, and to a lesser degree I can see the potency of Potter - but I think "dark" is becoming a convenient alibi for a lack of tonal variation, a lack of light and shade. In real life, there is happiness as well as sadness, triumph as well as disaster.
These things are no less real for happening scarcely, or at any rate, more scarcely than we would want. But they are there, and they have to be represented, for the bad things to mean anything.
But "dark" is a luxury we can afford in the good times. When the sun is shining and the birds are singing and property prices are climbing then "dark" is fascinating.
If you thought Batman was dark, you should try Ingmar Bergman
But when you've lost your job and your stakeholder pension is valueless, ambiguous mean'n'moody superheroes who may be super-villains aren't necessarily what you need.
Perhaps bright and jolly films will come back into fashion and the caped crusaders will go back to zooming around in silly outfits and say things like "Holy Recession, Batman, our life savings in Iceland have vanished, we need to cheer this place up".
The "dark" mode may slipping away into eternal night.