Spectral radiant power

The term intensity is commonly used but is imprecise. According to IUPAC recommendations (see Pure 6[ Appl. Chem. 68, 2223-2286 (1996)), this term should be replaced by the spectral radiant power Ph i.e. the radiant power at wavelength X per unit wavelength... 

The emitted spectral radiant power (or exitance) or the emitted spectral photon trradiance (or exitance) plotted as a function of the frequency, wavenumber, or wavelength. The corrected emission spectrum has been cor-... 

Figure 8.3 Spectral radiant power (per unit time per unit area) distribution of a blackbody at various temperatures. Note that the maximum intensity, even at 3500 K, is still in the infrared region of the spectrum. The displacement of the maximum of the radiant energy shifts linearly with absolute temperature (dotted lines) in accordance with Wein s displacement law.

Quantitatively, absorption is often expressed as absorbance (A), which is the logarithm to the base 10 of the ratio of the spectral radiant power of incident, essentially monochromatic (of A wavelength), radiation (P°) to the radiant power of transmitted radiation (P.y. 

Example 3-6 a) Calculate the photon flow Op in mol h- at X = 253.7 nm of a low-pressure mercury lamp (type NN 50/81, Heraeus) that has an electric input power Pel of 50 W and a radiant power efficiency ri = Px/P x 100 = 40% at this wavelength Px- spectral radiant power in W nm- ) b) compare this value with Op at X = 253.7 nm of a medium-pressure mercury lamp with a spectral radiant power 253.7 nm of 1.035 kW (refers to a 20 kW lamp). 

Aio is the (decadic) absorbance of a beam of collimated monochromatic radiation in a homogeneous isotropic medium (Verhoeven, 1996) is the incident spectral radiant power ... 

The transmittance T is the ratio of transmitted spectral radiant power to... 

Especially, for AOPs it is essential to note that the absorbance A is an additive property (cf. Braun et al, 1991), with the consequence that the individual compounds of a wastewater or a gas mixture may compete for the absorption of the incident spectral radiant power. Hence, the concentrations C of any radiation absorbing species i present in water or air must be considered as well as their individual molar absorption coefficients Therefore, the Beer-Lambert law changes to Eq. 3-8, which describes the absorbance A of a multi-component mixture at a specified wavelength X. 

According to Pfoertner (1998) the absorbed spectral radiant power P f of a specific component i is related to the spectral radiant power P absorbed by all other components of a mixture according to the relationships of Eqs. 3-9 and 3-10. 

Depth of penetration (of light) The inverse of the absorption coefficient. The SI unit is m. If the decadic absorption coefficient, a, is used, the depth of penetration (1/a) is the distance at which the spectral radiant power, Px decreases to one tenth of its incident value, P . If the Napierian absorption coefficient, a, is used, the depth of penetration (1/a = p in this case) is the distance at which the spectral radiant power decreases to 1 /e of its incident value. 

Emission spectrum Plot of the emitted spectral radiant power (spectral radiant exi-tance) or of the emitted spectral photon irradiance (spectral photon exitance) against a quantity related to photon energy, such as frequency, v, wavenumber, a, or wavelength, X. When corrected for wavelength dependent variations in the equipment response, it is called a corrected emission spectrum. 

Lambert law The fraction of hght absorbed by a system is independent of the incident spectral radiant power (f ). This law holds only if is small, scattering is negligible, and multiphoton processes, excited state populations, and photochemical reactions are negligible. 

Spectral radiant flux Same as spectral radiant power. 

Spectral radiant power (Px) The radiant power at wavelength X per unit wavelength interval. The SI unit is W m , but a commonly used unit is W nm . ... 

Transmittance (7) The ratio of the transmitted spectral radiant power (Px) to that incident on the sample (f ) ... 

For monochromatic light, the molar photon flux q =nv/t, the amount (in moles or einsteins) of photons incident on a sample cell per unit time, is proportional to the incident spectral radiant power Px° (Equation 3.16). The unit of q n p (Equation 2.3) is mols... 

The fluorescence spectral radiant power that an optical system will collect from the laser interaction volume to a detector is, to a good approximation, given by... 

Fig. 10.2. Spectral radiant power distribution of the mercury vapour high-pressure lamp HPR-125 W [2345].

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