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The SED of M51 (upper right) obtained by combining data at many different wavelengths, e.g. UV, visible, and infrared (left). A spectral energy distribution (SED) is a plot of energy versus frequency or wavelength of light (not to be confused with a 'spectrum' of flux density vs frequency or wavelength). [1]
The air mass coefficient defines the direct optical path length through the Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e. at the zenith. The air mass coefficient can be used to help characterize the solar spectrum after solar radiation has traveled through the atmosphere.
Mathematically, for the spectral power distribution of a radiant exitance or irradiance one may write: =where M(λ) is the spectral irradiance (or exitance) of the light (SI units: W/m 2 = kg·m −1 ·s −3); Φ is the radiant flux of the source (SI unit: watt, W); A is the area over which the radiant flux is integrated (SI unit: square meter, m 2); and λ is the wavelength (SI unit: meter, m).
The value of the energy spectral density at is then estimated to be () /. In this example, since the power V ( t ) 2 / Z {\displaystyle V(t)^{2}/Z} has units of V 2 Ω −1 , the energy E ( f ) {\displaystyle E(f)} has units of V 2 s Ω −1 = J , and hence the estimate E ( f ) / Δ f {\displaystyle E(f)/\Delta f} of the energy spectral density ...
The Estimated Energy Requirement, , is the estimated number of daily kilocalories, or Calories, an individual requires in order to maintain his or her current weight. For a person with a body mass of m {\displaystyle m} (kg), height of h {\displaystyle h} (m), age of a {\displaystyle a} (years) and Physical Activity PA {\displaystyle {\text{PA ...
In 1838, Claude Pouillet made the first estimate of the solar constant. Using a very simple pyrheliometer he developed, he obtained a value of 1.228 kW/m 2 , [ 6 ] close to the current estimate. In 1875, Jules Violle resumed the work of Pouillet and offered a somewhat larger estimate of 1.7 kW/m 2 based, in part, on a measurement that he made ...
Light with the same radiant intensity at other wavelengths has a lower luminous intensity. The curve which represents the response of the human eye to light is a defined standard function y (λ) or V (λ) established by the International Commission on Illumination (CIE, for Commission Internationale de l'Éclairage ) and standardized in ...
Energy density is the amount of energy per mass or volume of food. The energy density of a food can be determined from the label by dividing the energy per serving (usually in kilojoules or food calories) by the serving size (usually in grams, milliliters or fluid ounces). An energy unit commonly used in nutritional contexts within non-metric ...