Spectral distribution light source

Warnings are often given that acceleration factors for relating artificial light sources with service are meaningless, because of both the variation in solar irradiation and the variation in spectral distribution. Regardless of this, acceleration factors are estimated, and indeed have to be if any extrapolation from accelerated tests is to be made. 

Some important examples of real radiation sources with spectral distributions close to the Planck distribntion are the sun (which shows a spectrum consistent with T = 6000 K) and the bright tnngsten wire of a light bulb T = 2800 K). 

Clearly, such experiments can be used to examine the relationship between primary emissions and the formation of a host of secondary pollutants. For example, runs can be carried out at varying initial concentrations of hydrocarbon and NO, and the effects on the formation of secondary pollutants such as 03 studied. The reactivity of various hydrocarbons can be examined by studying them singly or in combination. In addition, such parameters as temperature, relative humidity and total pressure, presence of copollutants, and spectral distribution of the light source can be systematically varied. 

Since in industrial photochemistry mostly polychromatic light sources are used, photon quantities are relatively difficult to calculate and require knowledge of the spectral distribution of the radiometric quantity measured. Assuming on the other hand that the radiometric measurements do not need to be corrected for the spectral response of the probe, the photon irradiance at a given point within the reactor volume would then be given by Eqs. (39) and (40), respectively. 

A color correction may also be achieved by using filters. Table 3.1 shows the type of filter used by professional photographers to achieve accurate color reproduction. The required filter depends on the type of illuminant and also on the type of film. The type of light source can be described using the temperature of a black-body radiator. A black-body radiator is a light source whose spectral power distribution depends only on its temperature (Jacobsen et al. 2000). The color temperature of a fight source is the temperature of a black-body radiator, which essentially has the same spectral distribution in the visible region. The concept of a black-body radiator is formally introduced in Section 3.5. 

Source compensation Pulse-to-pulse intensity variations and intensity fluctuations in the spectrometric excitation source are often the dominant noise source affecting the performance of the detection system. However, since OIDs are parallel multichannel detectors, these intensityvariations do equally and simultaneously affect the entire spectral distribution as a whole. Thus, with the aid of a single-channel reference detector, monitoring a portion of the source s light flux, it is possible to accurately normalize for spectrum-to-spectrum variations and practically eliminate these and any other source flicker noise related effects. 

Coherent light sources are characterized by a spectral intensity distribution E(oj) and a frequency-dependent phase 0(w). According to first-order perturbation theory, linear absorption probabilities are given by the overlap between the spectrum of the light source E(w) and the optical transition, and are independent of the phase function In non-linear processes (2nd... 

The spectral energy distribution of CIE light sources A and C is shown in Figure 6-2. CIE illuminant A is an incandescent light operated at 2854°K, and illuminant C is the same light modified by filters to result in a... 

Figure 6-2 Spectral Energy Distribution of Light Sources A and C, the CIE, and Relative Luminosity Function y for the CIE Standard Observer...

Light sources can be described by their spectral power or energy distribution. This simply plots the amount of light (relative power) as a function of wavelength. Figures 2.1-2.5 are examples of standard light sources (Billmeyer and Saltzman, 1981). 

For artificial light sources, two values are important the color temperature in degrees Kelvin and the relative spectral distribution of the light source S(k), where X shows that the radiant energy is dependent on wavelength. 

The CIE (Commission Internationale de l Eclairage) has selected a number of light sources from the wide range available with different spectral distribution and color temperature. The use of these standard illuminants is recommended and those used most commonly are listed here ... 

Figure 2. Spectral power distribution for some standard light sources used in describing color (Wyszecki, 1967,1970 Billmeyer and Saltzman, 1981).

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