The term was first commonly used in early photography to distinguish light that would expose the monochrome films from light that would not. A non-actinic safe-light (e.g., red or amber) could be used in a darkroom without risk of exposing (fogging) light-sensitive films, plates or papers.
Early 'non colour-sensitive' (NCS) films, plates and papers were only sensitive to the high-energy end of the visible spectrum from green to UV, i.e., shorter-wavelength light. This would render a print of the red areas as a very dark tone because the red light was not actinic. Typically, light from xenon flash lamps are highly actinic, as is daylight as both contain significant green-to-UV light.
In the first half of the 20th century, developments in film technology produced films sensitive to red and yellow light, known as orthochromatic and panchromatic, and extended that through to near infra-red light. These gave a truer reproduction of human perception of lightness across the color spectrum. In photography, therefore, actinic light must now be referenced to the photographic material in question.
Actinic is also applied to medical conditions triggered off by exposure, or excessive exposure to light, especially UV light.
Not only is Actinic Lighting used to accentuate the colors of the deepest marine life that is in an aquarium, it also limits the amount of algae growth. Since Algae like many other plants flourish in shallower warm water, algae cannot effectively photosynthesize from blue and violet lights. Although it does benefit from actinic lights, the effect is minimal.
Actinic lighting is also a great alternative to black lights as it does provide a "night environment" for the fish, while allowing enough light for coral and marine life to grow.
- Wall, E.J. (1890). Dictionary of Photography. London: Hassel, Watson and Viney Ltd.
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