A lens with a focal length of 100mm and a diameter of 25mm would have an aperture of f/4.Ī device which reduces the amount of energy reaching a sensor. The f/# is the ratio of the focal length of the lens to its diameter. The aperture of a lens is often expressed in terms of an f/#. Angular aperture is the angle through which the most divergent rays can pass through a hole or lens. To make valid measurements, the contribution from the ambient light or background must be subtracted from each measurement.Ī hole through which radiant energy can pass. This light contributes to the signal measured from the source. See the Optical Radiation Hazard applications page for a listing of ILT light measurement systems used to determine the actinic hazard of a light source.Īmbient light is the light diffused in the environment surrounding a detector measuring the optical radiation from another source. The color or optical density of the strip changes with the exposure. Actinic strips are used in UV processing to monitor the intensity of sources. In our industry the term is usually used with reference to UV radiation and its effects on biological systems. The characteristic of radiation that indicates its capability to produce chemical change. If the %transmission of a certain wavelength is 70% then the material has a 30% Absorptance. Absorptance can also be inferred from the transmission through a medium. The standard unit of absorptance is percent (%) or a factor between 0 an 1. The ratio of the total absorbed radiant or luminous flux to the incident flux is called absorptance. The absorption is the "missing piece", when comparing the total reflected and transmitted energy with the incident energy. The dissipation of light (radiation) within a surface or medium, caused by the conversion of radiant (luminous) energy to a different form of energy, usually heat, by interaction with matter.
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