Actinic

Actinism (/ˈæktᵻnᵻzəm/) is the property of solar radiation that leads to the production of and photobiological effects.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 (/ækˈtɪnᵻk/) chemicals include silver salts used in photography and other light sensitive chemicals.

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, 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. Actinic is also used to describe medical conditions that are triggered by exposure to light, especially UV light (see actinic keratosis).

...
Wikipedia