Grilling and broiling are the modern, controlled versions of the oldest culinary technique, roasting over an open fire or glowing coals. In grilling, the heat source is below the food; in broiling, above. Though air convection contributes some heat, especially as the distance between heat source and food is increased, broiling is largely a matter of infrared radiation. The heat sources used in these techniques all emit visible light and so are also intense radiators of infrared energy. Glowing coals or the nickel-chrome alloys used in electrical appliances reach about 2,000°F/1,100°C, and a gas flame is closer to 3,000°F/1,600°C. The walls of an oven, by contrast, rarely exceed 500°F/ 250°C. The total amount of energy radiated by a hot object is proportional to the fourth power of the absolute temperature, so that a coal or metal rod at 2,000°F is radiating more than 40 times as much energy as the equivalent area of oven wall at 500°F.