Useful Heat Radiation Is Generated by High Temperatures

Because all molecules are vibrating to some extent, everything around us is emitting at least some infrared radiation all the time. The hotter an object gets, the more energy it radiates in higher regions of the spectrum. So it is that glowing metal is hotter than metal that does not radiate visible light, and that yellow-hot metal is hotter than red-hot. It turns out that the rate of infrared radiation is relatively low below about 1,800°F/980°C, or the point at which objects begin to glow visibly red. Cooking by radiation is thus a slow process except at very high cooking temperatures, those characteristic of grilling and broiling near glowing coals, electrical elements, or gas flames. At typical baking and frying temperatures, conduction and convection tend to be more significant than infrared radiation. But as the oven temperature goes up, the proportion of heat contributed by the radiating oven walls goes up with it. The cook can control this contribution by moving the food close to the walls or ceiling to increase it, or shielding the food with reflective foil, which reduces it.