Plants absorb carbon dioxide by photosynthesis using solar energy and use thermal energy in the atmosphere by transpiration. Paying attention to the excellent functions that plants perform, we have measured the daily variation of the temperature and humidity on plant circumference of an individual level using Pothos (Epipremnum aureum), and have investigated the thermal conditioning effect of the plant irradiated white LED in a closed space covered with thermal insulation at the incubator adjusted temperature. The air-cooling effect of Pothos in a closed space at the incubator adjusted 23 degrees C was about 1 degrees C. High correlation between air temperature and that of soil was shown in the air-cooling effect, and long-time white light irradiation increased the air-cooling effect. (C) 2011 Elsevier B.V. All rights reserved.