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Broadband Global Irradiance
Published in Frank Vignola, Joseph Michalsky, Thomas Stoffel, Solar and Infrared Radiation Measurements, 2019
Frank Vignola, Joseph Michalsky, Thomas Stoffel
Ideally, the responsivity of a pyranometer to the solar radiation from any direction within its hemispherical field of view, 2π steradians, depends exactly on the cosine of incidence angle. Lambert’s cosine law states that the irradiance received at a surface should be proportional to the cosine of the incident angle. Therefore, a pyranometer with an ideal angular response, or Lambertian response, would respond to incident radiation in accordance with Lambert’s cosine law. When the pyranometer measurements are not Lambertian, the instrument’s responsivity is said to vary with incident angle. It is difficult, if not impossible, to produce a pyranometer with a perfect angular response, especially for a pyranometer with a relatively large receiver that is covered by glass domes. In most literature and in this book, angular response is referred to as cosine response and a perfect or Lambertian angular response is called a true angular or cosine response. When describing an instrument’s angular response, the comparison is normalized against a true cosine response. By making the comparison against an ideal Lambertian response, deviations of a few percent become easier to detect. Optical leveling of the receiving disk is very important, especially at large solar zenith angles where small differences in the angle of incidence can translate into large errors in angular response. The spirit levels used to orient a pyranometer are not always consistent with the optical plane defined by the detector surface. Imperfections in the glass domes and even refraction of light as it passes through the domes can cause some deviations from true cosine (Lambertian) response. For solar irradiance measurements, the sun is considered an idealized point source with the collimated light coming from a given direction.
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Published in Carl W. Hall, Laws and Models, 2018
W=h– where W = maximum kinetic energy given off by electrons h = Planck constant = frequency = minimum energy to remove an electron from a solid (can also be applied to a gas) Keywords: energy, frequency, light, photoelectron BROGLIE, Louis Victor de, 1892-1987, French physicist; Nobel prize, 1929, physics DIRAC, Paul Adrien Maurice, 1902-1984, English physicist; Nobel prize, 1933, physics (shared) Sources: Bothamley, J. 1993; Gamow, G. 1961. 1988. See also EINSTEIN PHOTOELECTRIC PROPORTIONALITY LAW As long as there is no change in the "spectral quality of the light causing emission of photoelectrons, the photoelectric current is directly proportional to the illumination on the emitting surface." Keywords: current, emission, illumination, light Source: Thewlis, J. 1961-1964. PHOTOGRAPHIC LAW--SEE BUNSEN-ROSCOE PHOTOMETRIC LAWS Many photometric measurements are based on the inverse square law and on Lambert cosine laws of incidence and emission. Inverse-Square Law Illumination (E) is proportional to intensity of the source (I) divided by the square of the distance from the source perpendicular to the surface (D2): E = I/D2 Lambert Cosine Law of Incidence E = 1/D2 cos where = the angle of incidence between the normal to the surface and the incident ray Lambert Cosine Law of Emission The intensity of illumination from a point source in a given direction, radiated or reflected from a perfectly radiating surface, varies as the cosine of the angle between the direction and the normal to the surface. Keywords: angle, illumination, incidence, intensity, radiating LAMBERT, Johann Heinrich, 1728-1777, German mathematician Sources: Parker, S. 1971. 1987. 1994. See also BEER; LAMBERT PHOTOMETRY, LAWS OF The time rate at which energy is transported in a beam of radiant energy is the ratio of the unabsorbed and absorbed energy passing through a material: T = P/Po
Colorimetric and photometric characterisation of clear and coloured pavements for urban spaces
Published in Road Materials and Pavement Design, 2021
Federico Autelitano, Giulio Maternini, Felice Giuliani
A detailed analysis of the luminance recorded for each of the three viewing angles identified an almost perfect overlap of these values. This quasi-isotropic diffusion of luminance allowed to schematically model, to a first approximation, the slurry seals as uniform reflecting diffusers (Lambertian surfaces), i.e. surfaces which appear equally bright from all viewing directions. For these surfaces, which obey Lambert’s cosine law, the luminance (L) of the surface element in a given direction is dependent on the illuminance (E) on the medium according to the relation ρ = (L·π)/E, where ρ is called reflectance factor. Thus, the reflectance ρ of the unaged and aged slurry seals were calculated, considering as luminance the average value related to the three observation angles .