Radiation (Thermal)
Heat transfer through electromagnetic waves — the mechanism behind infrared grilling and broiling.
Thermal radiation is the emission of electromagnetic energy (primarily infrared light) from a hot surface. Unlike conduction and convection, radiation doesn't require any physical medium — it travels through empty space at the speed of light. Every object above absolute zero emits thermal radiation, but the intensity increases dramatically with temperature (following the Stefan-Boltzmann law, which states radiation is proportional to the fourth power of absolute temperature).
In cooking, thermal radiation is significant when you're near very hot surfaces: glowing charcoal (1,200°F+), broiler elements (1,000°F+), or dedicated infrared searing units (1,500°F+). At these temperatures, infrared emission is intense enough to heat the steak's surface rapidly without requiring contact or moving air.
Radiation in grilling: On a charcoal grill, the steak receives heat through three mechanisms simultaneously: radiation from the coals below, convection from hot air currents, and conduction at the grate contact points. Radiation is the dominant mechanism for the parts of the steak between the grate lines — it's how the surface browns even where it doesn't touch metal.
The inverse square law: Radiation intensity decreases with the square of the distance from the source. A steak 2 inches from the coals receives 4 times more radiant heat than one 4 inches away. This is why raising or lowering the grate height on a grill has such a dramatic effect on cooking speed.
Practical tip: When broiling, keep the steak as close to the broiler element as possible (3–4 inches). The inverse square law means those extra inches significantly reduce heat delivery.