Film stock produce only a very slight chemical change, proportional to the amount of light absorbed by each crystal. This creates an invisible latent image in the emulsion, which can be chemically developed into a visible photograph. In addition to visible light, all films are sensitive to X-rays and high-energy particles. Most are at least slightly sensitive to invisible ultraviolet (UV) light. Some special-purpose films are sensitive into the infrared (IR) region of the spectrum. In black-and-white photographic film there is usually one layer of silver salts. When the exposed grains are developed, the silver salts are converted to metallic silver, which
Ultraviolet communication in butterflies rapid opening and closing of the wings, is performed when a male approaches another butterfly; yet, males copulate with females who perform this behavior, while retreating from males who perform the flutter response. By showing that male and female wings are similar in appearance except for UV reflectance and an approaching male is exposed to ultraviolet reflection of a male's wings during a flutter response, as well as ruling out temporal differences in the flutter behavior as a cause for sex recognition, Ronald Rutowski concluded that ultraviolet light was being used as an indicator of the male sex. However, in