Thermal infrared measurements indoors and under gray or blue skies

This paper describes a series of student lab experiences that use an infrared (IR) thermometer to measure heat flows by thermal IR radiation indoors and outside. The conversion from the temperature readings to the power from thermal IR radiation uses the Stefan–Boltzmann equation from the theory of blackbodies. Indoor experiences commence by recording the thermometer readings at differing angles relative to the floor and ceiling. The readings are compared with the predictions from blackbody theory. They are also used to compare the upward flow of heat from the floor with the downward flow from the ceiling—and hence to check how well the room is insulated. Outdoor measurements determine the thermal IR flow up from Earth’s surface and down from the atmosphere. The balance of these flows is a key element of climate calculations. Measurements under cloudy skies are similar to indoor measurements. However, there is a noticeable difference between up...