Mean radiant temperature
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Mean Radiant Temperature (MRT) is the uniform surface temperature of a black enclosure with which an individual exchanges the same heat by radiation as the actual environment considered. It describes the radiant environment for a point in space. Distance to a source affects the temperature that is felt. For instance, if the sun is setting, turning to night, you may feel coolness, although the temperature is unchanged at that moment.
You can find all about thermal comfort and related quantities here.http://dt.fme.vutbr.cz/enviro/Pohoda/thermal.htm
Some calculators for these quantities. http://www.meanradianttemperature.com/mrt_input_form.htm