The phrase "a long darkness" is correct and usable in written English.
It can be used to describe an extended period of time characterized by a lack of light, hope, or positivity.
Example: "After the storm passed, the village was left in a long darkness, with power lines down and no streetlights to guide the way."
Alternatives: "an extended gloom" or "a prolonged shadow".
Like a candle lit in the long darkness of a winter's night, peace starts with a single, incendiary act.
"No one had told Hannie that the real winter followed on behind the solstice, no one had explained the deep dead winter after Christmas, when the light hardly grew and the cold and the long darkness closed like a shroud on the land".
The geographic area at high latitudes beyond the polar circle is characterized with long darkness during the winter (polar night) and with a long summertime insolation (polar day).
Imagining that late December night of long darkness, you can almost hear these youths of Vermont tramping up to the isolated farmhouse to intrude upon the sanctuary stillness.
In an autobiography completed shortly before his decision to resign, Slabbert wrote: "When I look towards the future, I am fearful of the long darkness that may await us all.
"When the long Darkness spreads itself over the country, many hidden things are revealed, and men's thoughts travel along devious paths," a west Greenlander told the explorer Knud Rasmussen sometime around 1904.
By John Updike The New Yorker, November 14 , 1964P. 52 It comes upon me as strange, after the long darkness of self-absorption & fear & shame in which I have been living, that things are beautiful, that independent of our catastrophes, Nature, that which exists without guilt, continues, like grape leaves in the sun or a blue jay on a twig outside my cottage window.
A long period of darkness separates the Middle and Neo-Elamite periods.
In interviews this evening, members offered the bleak view that their country was on a long slide toward darkness with no visible solution, and no hope.
Many economists, when we saw the plan, knew immediately that Greece was beginning a long journey into darkness that would last for many years.
