Actinic light

From Wikipedia, the free encyclopedia

Actinic light is that light that causes change to be recorded on photographic medium. I.e that films or papers are sensitive to. An early definition from 1890 records it as ^[1]:

"...that portion of light that effects chemical changes. In photography the actinic portion of the spectrum may be said to be confined to the ultra-violet, violet, indigo, blue and green.... But the division is entirely arbitrary as it depends on the substance exposed as to whether the rays are actinic or not actinic."

Contents 1 Photography Use 2 Medical Use 3 Aquarium Use 4 Notes 5 References

[edit] Photography Use

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. This would render a print of the 'red' areas as a very dark tone. Such light was actinic light. Yellow and red light was non-actinic. Xenon flash lamps are generally highly actinic, as is daylight.

In the first half of the 20th century, developments in film technology produced films (orthochromatic and panchromatic) sensitive to red and yellow light and extended that through to near infra-red light. These gave a truer equivalent rendering of colour (hue) as a light, medium or dark tone, according to how we believe the human eye experiences it.

In photography, therefore, actinic light must now be referenced to the photographic material in question.

[edit] Medical Use

Actinic is also applied to medical conditions triggered off by exposure, or excessive exposure to light, especially UV light.

[edit] Aquarium Use

Actinic lights are also common in the reef aquarium industry. They are used to promote coral and invertebrate growth.^[2][3]

[edit] Notes

[edit] References

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