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 (Light My Way) naked eye and ultimately unknowable to the human intellect." Conversely, Steve Stockman, author of "Walk On: The Spiritual Journey Of U2", sees "Ultraviolet" as being about Bono's wife Ali Hewson, and "how when he feels like trash, she makes him clean," but says there is good reason to interpret the song as being just as much about God. The song's title supports this view: indigo and violet rarely appear in song lyrics as frequently as other colours, while ultraviolet represents an unseen wavelength beyond the visible spectrum. As such, the title evokes the image of black light or an invisible