Sorry, no. If you are thinking magnifying glass then what you are doing is directing light from a wide area to a smaller one which concentrates the energy. In terms of heat a glass tube that should not happen, the radiation is still going of at a right angle from the bulb and glass tube. The heat off the bulb surface heats the air and the tube confines it stopping it from moving into the tent. The air going through the tube cools the tube and bulb by conduction. Because we have lowered the temperature of both glass surfaces and we took that heat out of the tent there is a net loss of energy in the tent as compared to without the tube. I worked in industrial heating and in large building HVAC, the best way to keep an area cool is to collect the heat at the source and remove it.
