Fundamental law of thermal radiation: Planck's law. The black body
Thermal radiation from opaque materials
Article REF: BE8210 V1
Fundamental law of thermal radiation: Planck's law. The black body
Thermal radiation from opaque materials

Author : Simone MATTEÏ

Publication date: January 10, 2005 | Lire en français

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1. Fundamental law of thermal radiation: Planck's law. The black body

1.1 Definition of luminance

Consider an elementary surface of area dS around a point O (figure 1 ) a straight line Δ passing through O making an angle θ with the normal ON to the surface, and the elementary solid angle dΩ (in sr) of axis Δ. The radiative flux d Φ (in W) in the wavelength interval between λ and λ + d λ, propagating to or from dS, within d Ω is written :

d Φ (O, Δ, λ ) = L λ (O, Δ, λ ) dS cos θ d Ω d λ ( 1 )

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