'darkling' is rarely used as it is an old fashioned word for 'dark' MEANING OF DARKLING AS AN ADVERB: In the dark. AS AN ADJECTIVE: Occurring or enacted in the dark. Dark; dim. AS A NOUN: The dark: Example: "She carried some rugs for me through the shrubbery in the darkling" (H.G. Wells).

I've never used the word darkling in my life. I can guess at its meaning, but unless you're trying to be poetic, you should simply use the word dark.