Light source blackbodies

Real or gray bodies deviate from these ideal blackbody values by the A-dependent emissivity, but the color sequence remains essentially the same. This mechanism explains the color of incandescent light sources such as flames in a candle, tungsten filament light bulb, flash bulb, carbon arc, limelight, lightning in part, and the incandescent part of pyrotechnics (qv). 

Figure 24-21 Blackbody radiation curves for various light sources. Note the shift in the peaks as the temperature of the sources changes.

The color of a light source is typacally characterized in terms of its color temperature. If the x,y coordinates of an illumination source do not exactly sit on the blackbody locus, the color of a light source is characterized in terms of its CCT. The CCT is the temperature of a blackbody radiator that has a colour that most closely matches the emission from a non-blackbody radiator. For high quality white light illumination the CCT should between 2500K and 6500 K. There is an accepted method (Wyszelki et al 1982) to determine lines of constant correlated color temperature in x, y space. CIE, CCT and CRI for common white light sources are given in Table 1 for comparison purpose (Misra et al 2006). 

Thermal plasma light sources are effective radiation devices in generating short-wavelength (UV and VUV) radiation (Protasov, 2000). The emission spectram of the absolute blackbody with temperatme T has a radiation maximum at the frequency max ... 

T. Thermal plasma radiation cannot exceed that of the absolute blackbody at the plasma temperature. Therefore, fixing the required spectral emission interval determines the required values of the thermal plasma temperature. Specifically, for effective emission in UV and VUV spectral ranges, the thermal plasma temperature should be in the interval from 2 to 15 eV Plasma in high-brightness light sources is usually characterized by volume... 

Photoacoustic spectra can be observed with a simple microphone and optical apparatus. A diagram of a modern piece of equipment is given in Figure 42, in which there is a blackbody sample at the second input of a look-in amplifier. Corrected photoacoustic spectra can be recorded with this type of monochromator equipment. Frequency-modulated xenon lamps are used as white light sources, so that a chopper is not needed for modulation. 

Pyrometers measuring the spectral intensity of the radiation emitted by hot surfaces allow the determination of their temperatures, provided the emissivities of the surfaces are known. At low temperatures (approximately —100 to 400 °C), where the intensity of the radiation is small, the total emitted radiation is measured. The measurement uncertainty is on the order of 1% of the total temperature. At higher temperatures, the radiation is measured in one or two narrow wavelength bands, and sometimes the signal is directly compared with the radiation of a blackbody radiator or a calibrated tungsten light source of the same temperature. 

Color temperature Absolute temperature of a blackbody radiator having a chromaticity closest to that of a light source being specified. 

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