I'm looking for a word that refers to when a dark room is slightly lightened- for example, by a candle or a weak lightbulb, but not so much that I could use "brightened" to describe the action. "Lighten" works, but I'm wondering if there's a word that fits better in this situation.
You could say the candle caused the room to gleam:
To emit a gleam; flash or glow
with the noun gleam defined as:
A steady but subdued shining; a glow
You could also use the verb kindle:
To cause to glow; light up: The sunset kindled the skies.
These both seem to convey the slight rise in light and not complete illumination you desire.
“Soften/ed,” when used with the notions of light and visibility, is usually associated with
“[mak[ing] (something) [in the usual case, the brighter/whiter extreme of visibility]) less severe, harsh, extreme, etc.].”
(i.e., the light of the room [was] softened = the room became less bright or darker)
However, the “(something)” being rendered “less severe, harsh, extreme, etc” in M-W’s definition could also be ...
“darkness,” the other extreme of visibility.
(i.e., the darkness of the room [was] softened = the room became less dark or brighter)
Three nice (imo) examples of this use of “softened” with “darkness” (to mean less dark or brighter) found in “Google Books” include (with emphasis added):
The darkness softened as dawn came sifting through the canopy of trees.”
(from ‘The Changeling Garden’ by Winifred Elze);
“The darkness softened as my eyes adjusted to it, … .”
(from ‘Alchemystic’by Anton Strout); and
“The candle on the desk went out, and suddenly the room was engulfed in shadow, the darkness softened only by firelight.”
(from ‘Lucy's Christmas Angel’ by Sandra Heath)
The best word I can think of for the concept is glim. I'm not sure how you would use it. "The candle cast a glimmer of light into the room, just enough to make out the ..." "He saw the object by the glim of the candle." You could be playful and make up "glimmened" but that might be going too far.
Or you could use reversals and talk about "dispelling the gloom". Gloom and glim are almost antonyms.