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 UV reflecting scales are composed of raised longitudinal ridges and perpendicular cross ribs that connect the parallel running ridges, forming a grid. The ridges possess lamellae that run on top of and parallel to the ridges and microribs on its sides. The partial overlap of lamellae structures causes thin layer interference resulting in the reflection of light with a wavelength within the ultraviolet spectrum. The other ultraviolet signal in butterflies, absorbance, was determined to be governed by pigments called pterins. In wings containing this pigment, the wings are unable to reflect ultraviolet light as well as without the pigment because