'faint light' is correct and usable in written English.
You can use it to describe a light that is so weak that it is barely visible. For example: "The moon shone a faint light on the forest."
I could see a faint light through the keyhole.
She read, under the faint light, the Biblical story of Job.
Upon reaching my car, I noticed a faint light flickering from inside.
It would be early evening, quite dark, but with a faint light coming through windows.
A faint light is burning in my sister's window on the second floor.
With a fluorescence microscope mounted inside the cold box, they can search for the faint light emitted by fluorescing bacteria.
Still, Kino could detect a glint of desire in her eyes, like a faint light deep down a mineshaft.
We eagerly await telescopes that can analyse the faint light from these planets, seeking evidence for a biosphere.
Terrorizing inmates seems less useful than monitoring them effectively; modern video cameras work just fine in faint light.
