Energy-saving lamps such as LEDs (Light Emitting Diodes) have potential to provide energy saving in business-related buildings. Installation of these lightings has been accelerated due to their high cost effectiveness and long operating life in comparison to other lighting. Because of low power consumption of energy-saving lamps, the air-conditioning load in the building can be influenced if conventional lamps are replaced by energy-saving lamps. In this paper, we investigate thermal and luminous characteristics of energy-saving and conventional lamps experimentally, and the rate of heat emitted downward from a lamp to its power consumption is discussed. Next, based on these experimental results, we calculate air-conditioning loads in a model building. Changes of air-conditioning load by replacing the conventional fluorescent lamps with LEDs in the buildings are also discussed.