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Actinism (/ˈæktnzm/) is the property of solar radiation that leads to the production of photochemical and photobiological effects.[1] Actinism is derived from the Greek ακτίς, ακτῖνος (a ray or beam). The word actinism is found, for example, in the terminology of imaging technology (esp. photography), medicine (concerning sunburn), and chemistry (concerning containers that protect from photo-degradation), and the concept of actinism is applied, for example, in chemical photography and X-ray imaging.

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

In chemistry[edit]

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. Einstein 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[edit]

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

The term actinic rays is used to refer to this phenomenon.[2]

In biology[edit]

In biology, "actinic light" denotes light from solar or other sources that can cause photochemical reactions such as photosynthesis in a species.

In manufacturing[edit]

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.

Artificial lighting[edit]

"Actinic" lights are a high-color-temperature blue light.

They are also used in electric fly killers to attract flies.

In aquaculture[edit]

Actinic lights are used in aquariums, primarily because they make fluorescent coral "pop" to the eye, but in some cases also to promote the growth of deeper-water coral that is specialized in photosynthesis using blue light.


  1. ^ Appendix 3. "Units for photochemical and photobiological quantities", pp.173-174 of The International System of Units (SI), BIPM, 2006 [1]
  2. ^ "actinic rays" at Dorland's Medical Dictionary

See also[edit]

  • Spectral sensitivity is commonly used to describe the actinic responsivity of photographic materials.