The word "ultrabright" denotes an exceptionally bright or intense light. Its antonyms are words that imply dullness, dimness, or faintness. Some possible antonyms for ultrabright are dim, faint, weak, subdued, shadowy, or murky. For example, a dimly lit room would be the opposite of an ultrabright space. A faint glow, a weak beam, a subdued shine, or a shadowy halo are all antonyms for ultrabright. These words indicate a lack of brightness, luminosity, or brilliance, and may suggest a mood of gloom, obscurity, or mystery. Antonyms for ultrabright can be useful in creating contrast or nuance in descriptions, stories, or poetry.