Actinic light

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Actinic light is either light that affects photographic film,[1] or will facilitate photosynthesis or stimulate light sensitive species.


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 (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 is 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 used to describe medical conditions that are triggered by exposure to light, especially UV light.

Aquarium industry[edit]

Actinic lights are also common in the reef aquarium industry. They are used to promote coral and invertebrate growth.[2][3] They are also used to accentuate the fluorescence of fluorescent fish.

Actinic lighting is also used to limit algae growth in the aquarium.[4] Since algae (like many other plants), flourish in shallower warm water, algae cannot effectively photosynthesize from blue and violet light, thus actinic light minimizes its photosynthetic benefit.

Actinic lighting is also a great alternative to black lights as it provides a "night environment" for the fish, while still allowing enough light for coral and other marine life to grow.


  1. ^ Dictionary of Photography, 1890
  2. ^ Aquarium Lighting information
  3. ^ The Correct Lighting for Your Aquarium
  4. ^ [1] What is Actinic Lighting


  • Wall, E.J. (1890). Dictionary of Photography. London: Hassel, Watson and Viney Ltd.