The word is derived from the Greek Actinism meaning radiant force. Its use is in the context of the technological application of radiation, as in the modification of material properties, such as with the photochemical reactions of the photographic process. Actinic Inspection Tools (AIT) are important in the field of silicon wafer patterning-mask production, as mask defects have to be detected, and repaired when possible, before the costly mass production of the wafers is instigated. In this context the term refers to the inspection of the masks at the same wavelength of radiation (at wavelength) as they are to be used in the photolithographic wafer fabrication process.