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Optical Radiation Terminology and Units

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Optical Radiation Terminology and Units

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There are many systems of units for optical radiation. In this tutorial, we try to adhere to the internationally agreed CIE system. The CIE system fits well with the SI system of units. We work mostly with the units familiar to those working in the UV to near IR. We have limited the first part of this discussion to steady state conditions, essentially neglecting dependence on time. We explicitly discuss time dependence at the end of the technical note.Radiometric, Photometric and Photon Quantities The emphasis is on radiometric quantities. These are purely physical. How the human eye records optical radiation is often more relevant than the absolute physical values. This evaluation is described in photometric units and is limited to the small part of the spectrum called the visible. Photon quantities are important for many physical processes. Table 1 lists radiometric, photometric and photon quantities.

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