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Case study 2.1 Quantum theory and black-body radiation. In 1899 Liimmer and Pringsheim investigated how the energy from a black-body radiator was distributed. The shape of the resulting spectral lines (Figure 2.9) was not easy to explain. According to the prevailing classical theory, which argued that radiation was emitted continuously, the energy radiated at each wavelength (EA) should vary with wavelength (X) (Figure 2.10).