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Apparent temperature is the temperature equivalent perceived by humans, caused by the combined effects of airtemperature, relative humidity and wind speed. The measures are most commonly applied to perceived outdoor temperatures, but also apply to indoors, especially to saunas or when homes or workplaces are not sufficiently heated or cooled or insulated to provide comfortable or healthy conditions.
The heat index and humidex measure the effect of humidity on the perception of temperatures above 27 °C (80 °F). In humid conditions, the air feels much hotter, because of the reduction in evaporation of perspiration.
The wind chill factor measures the effect of wind speed on cooling of the human body below 10 °C (50 °F). As airflow increases over the skin, more heat will be removed. Standard models and conditions are used.
The wet-bulb globe temperature (WBGT) combines the effects of radiation, humidity, temperature and wind speed on the perception of temperature. It is not often used as the resulting figure is very location specific (e.g. cloud cover and/or wind shielding).