Infra-red technology is quite complex; the plotting of
Planck's formula graphically indicates that, for any
given source temperature, the radiation emitted is
spread over a wide range of wavelengths with approximately
one-third of the energy at wavelengths shorter
than the peak energy wavelength (kmax) and two-thirds
at wavelengths longer than the peak energy wavelength.
Furthermore, the ability of a product to absorb this
energy depends on both the source wavelength and on
the composition of the surface of the product.