halation

noun

1. (countable, uncountable)The action of light surrounding some object as if making a halo.

   “She was, as you know, to the west-ward of us, and the sunset was making a great flame of red light to the back of her, so that she showed a little blurred and indistinct by reason of the halation of the light, which almost defeated the eye in any attempt to see her rotting spars and standing rigging, submerged, as they were, in the fiery glory of the sunset.”

2. (countable, uncountable)The blurring of light around a bright area of a photographic image, or on a television screen.

   “As the result of a series of experiments on halation carried out with backed and unbacked plates, ordinary film and stripping film, Ernest Marriage concludes that there are two varieties of halation, one due to reflection from the support and the other due to spreading of the light in the film.”

   “Halation, properly speaking, is the reflection and diffusion, within the film, from the lighter areas to the adjacent darker ones.”

   “Halation can be prevented or diminished by using an absorbing layer between the sensitive emulsion and the support (anti-halo undercoat) or on the back of the support (anti-halo backing).”