We present temperature measurements made at skylights in the active flow field of Kilauea Volcano between 1995 and 2000. Spot temperature measurements of the lava stream within the lava tube revealed surface temperatures of 1017--1132¿C. This compared with lava core temperatures of 1161 ¿ 3¿C. The difference is the result of surface cooling due to radiation at the skylights. A FLIR thermal imager recorded a down-tube lava surface temperature decrease followed by a surface temperature recovery due to entrainment of the crust down flow of the skylight. The temperature of hot air expelled from skylights reached a maximum of 600¿C. From these field data, we place constraints on heat loss from the skylight and lava tube. Heat losses due to conduction and circulation of air in wall rocks around the tube are 103--104 and 104--106 W m-1 down tube, respectively. At skylights, heat losses due to radiation and forced convection are 1.5 ¿ 105 W m-1 over the skylight length and 5 ¿ 105 W per skylight, respectively. For a 10-km-long tube, the total heat loss is between 5 ¿ 108 and 1 ¿ 1010 W for a fully roofed tube with an additional 1.1 ¿ 106 W lost per 4 m ¿ 1 m skylight. In terms of cooling rates, 1.2¿C km-1 is a minimum resulting from heat losses at fully roofed tubes with no skylights. Heat loss and cooling rate will, however, increase with skylight area.