Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 104

An ideal blackbody is an object that absorbs all incident radiation. A blackbody reradiates energy with an emitted spectral distribution that depends only on the temperature of the blackbody in accordance with Planck's equation:

(9)

where M_λ is the spectral radiant exitance, k is Boltzmann's constant, and T is the absolute temperature. The emission spectra for blackbodies at various temperatures are shown in Figure 4. As the temperature increases, the peak of the blackbody emission spectrum shifts to shorter wavelengths, and the power emitted at any wavelength increases. A blackbody at room temperature (300 K) emits nearly all of its radiation in the IR region. A blackbody at 3000 K, the temperature of the filament in a tungsten–halogen lamp, has its emission peak in the near IR but emits radiation throughout the visible region and well into the UV. Though no real object is a perfect blackbody emitter, the theoretical blackbody spectral emission curve is a useful approximation of the emission spectra of many optical radiation sources, including the sun, incandescent lamp filaments, quartz tungsten halogen lamps, electrical heating elements, furnaces, molten metals, and other hot objects.

FIGURE 4 Spectral radiant exitance (W m⁻² μm⁻¹) in the optical radiation region (100 nm–1000 μm) calculated using Planck's formula for blackbody radiance at different absolute temperatures: 300 K ∼room temperature, 1000 K ∼red‐hot object, 3000 K ∼incandescent lamp filament, 5780 K ∼effective temperature of the sun. The visible radiation band (0.4–0.78 μm) lies between the vertical dotted lines.