A downloadable (PDF Format) “Application Note” from the Santa Barbara Infrared website. It explains the relationship between emitted thermal radiation, reflected thermal radiation, emissivity and the wavelength region used by a measuring device. It provides several informative examples with figures and graphs.

It reads in part:

“.. a 40°C blackbody in a 40°C room would require no correction. But a 40°C blackbody in a 25°C room would have a radiometric temperature of less than 40°C….
Note that this error will be wavelength dependent. …the reflected energy will be a different fraction of the total flux in the 3-5? band than in the 8-12? band.”