Actinism () is the property of

solar radiation Solar irradiance is the power per unit area ( surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre ...

that leads to the production of

photochemical Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 nm), visible light (400–7 ...

and photobiological effects. ''Actinism'' is derived from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

ἀκτίς, ἀκτῖνος ("ray, beam"). The word ''actinism'' is found, for example, in the terminology of imaging technology (esp. photography), medicine (concerning sunburn), and

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a natural science that covers the elements that make up matter to the compounds made of atoms, molecules and ions: their composition, structure, proper ...

(concerning containers that protect from photo-degradation), and the concept of actinism is applied, for example, in chemical photography and

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

imaging. Actinic () chemicals include silver salts used in photography and other light sensitive chemicals.

In chemistry

In chemical terms, actinism is the property of radiation that lets it be absorbed by a molecule and cause a photochemical reaction as a result.

Albert Einstein Albert Einstein ( ; ; 14 March 1879 – 18 April 1955) was a German-born theoretical physicist, widely acknowledged to be one of the greatest and most influential physicists of all time. Einstein is best known for developing the theor ...

was the first to correctly theorize that each photon would be able to cause only one molecular reaction. This distinction separates photochemical reactions from exothermic reduction reactions triggered by radiation. For general purposes, ''photochemistry'' is the commonly used vernacular rather than ''actinic'' or ''actino-chemistry'', which are again more commonly seen used for photography or imaging.

In medicine

In medicine, actinic effects are generally described in terms of the dermis or outer layers of the body, such as eyes (see:

Actinic conjunctivitis Actinic conjunctivitis is an inflammation of the eye contracted from prolonged exposure to actinic (ultraviolet) rays. Symptoms are redness and swelling of the eyes. Most often the condition is caused by prolonged exposure to Klieg lights, ther ...

) and upper tissues that the sun would normally affect, rather than deeper tissues that higher-energy shorter-wavelength radiation such as x-ray and gamma might affect. Actinic is also used to describe medical conditions that are triggered by exposure to light, especially UV light (see

actinic keratosis Actinic keratosis (AK), sometimes called solar keratosis or senile keratosis, is a pre-cancerous area of thick, scaly, or crusty skin.Freedberg, et al. (2003). ''Fitzpatrick's Dermatology in General Medicine''. (6th ed.). McGraw-Hill. . Actinic k ...

). The term ''actinic rays'' is used to refer to this phenomenon.

In biology

In biology, "actinic light" denotes light from solar or other sources that can cause photochemical reactions such as

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...

in a species.

In photography

''Actinic light'' was first commonly used in early

photography Photography is the art, application, and practice of creating durable images by recording light, either electronically by means of an image sensor, or chemically by means of a light-sensitive material such as photographic film. It is emplo ...

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 A darkroom is used to process photographic film, to make prints and to carry out other associated tasks. It is a room that can be made completely dark to allow the processing of the light-sensitive photographic materials, including film and ph ...

without risk of exposing (fogging) light-sensitive

films A film also called a movie, motion picture, moving picture, picture, photoplay or (slang) flick is a work of visual art that simulates experiences and otherwise communicates ideas, stories, perceptions, feelings, beauty, or atmospher ...

, plates or papers. Early "non colour-sensitive" (NCS) films, plates and papers were only sensitive to the high-energy end of the

visible spectrum The visible spectrum is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called '' visible light'' or simply light. A typical human eye will respond to ...

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 In chemistry, orthochromasia is the property of a staining, dye or stain to not change color on binding to a target, as opposed to Metachromasia, metachromatic stains, which change color. The word is derived from the Greek ''wikt:ortho-, orthos'' ...

and

panchromatic Panchromatic emulsion is a type of black-and-white photographic emulsion that is sensitive to all wavelengths of visible light. Description A panchromatic emulsion renders a realistic reproduction of a scene as it appears to the human eye, altho ...

, and extended that through to near

infra-red Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...

light. These gave a truer reproduction of human perception of

lightness Lightness is a visual perception of the luminance (L) of an object. It is often judged relative to a similarly lit object. In colorimetry and color appearance models, lightness is a prediction of how an illuminated color will appear to a stan ...

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

In manufacturing

Actinic inspection of masks in computer chip manufacture refers to inspecting the mask with the same wavelength of light that the lithography system will use.

In aquaculture

Actinic lights are also common in the

reef aquarium A reef aquarium or reef tank is a marine aquarium that prominently displays live corals and other marine invertebrates as well as fish that play a role in maintaining the tropical coral reef environment. A reef aquarium requires appropriatel ...

industry. They are used to promote coral and invertebrate growth. They are also used to accentuate the fluorescence of fluorescent fish. Actinic lighting is also used to limit algae growth in the aquarium. What is Actinic Lighting 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. Aesthetically, they make fluorescent coral "pop" to the eye, but in some cases also to promote the growth of deeper-water coral adapted to photosynthesis in regions of the ocean dominated by blue light.

In artificial lighting

"Actinic" lights are a high-color-temperature blue light. They are also used in electric fly killers to attract flies.

References

* {{Radiation-related disorders Electromagnetic radiation Physical chemistry Radiation Science of photography Lighting