Have you ever wondered why, on a cold winter day, you feel a distinct chill when approaching a large window, even if the room is well heated?
The so-called radiant cold sensation is often interpreted as cold returning from a surface. This perception is a sensory illusion, because cold does not spread. In reality, the phenomenon is based on a measurable energy exchange involving thermal radiation. When the human body is facing a colder surface, it loses energy in the form of infrared radiation.
N.B.:
In physics, cold does not spread. There is no cold flow. Only heat, i.e. thermal energy, is transferred from a body at a higher temperature to a body at a lower temperature, by conduction, convection, or radiation. The sensation of cold corresponds to a loss of energy from the body, not the arrival of a cold agent.
Any body whose temperature is above absolute zero emits electromagnetic radiation. For human skin, this radiation is mainly in the far infrared. If the ambient temperature is lower than that of the body, the net radiative flux is directed outward, causing continuous energy loss.
The power radiated by a body is given by the Stefan-Boltzmann law: \( P = \varepsilon \sigma S T^4 \). The parameter T is the absolute temperature of the skin (in kelvins). Since it is raised to the fourth power, even small temperature differences between the body and a cold surface result in a much greater energy loss than one might expect. The other parameters are:
- P: radiated power (in watts, W)
- \(\varepsilon\): emissivity of the skin (~0.97)
- \(\sigma\): Stefan-Boltzmann constant, \(5.67 \times 10^{-8} \, \text{W·m}^{-2}\text{·K}^{-4}\)
- S: exposed skin area (in m²)
The net radiative flux depends on the difference between the skin temperature and that of the environment. For example, facing a very cold wall, the body can lose several hundred watts instantly on exposed areas, which explains the intense feeling of cold, even though the overall body temperature drops very slowly due to metabolism.
The feeling of cold is stronger when the body is exposed to surfaces at different temperatures. A wall or window can be materially homogeneous, but they are often colder than the ambient air. This is explained by their contact with the outside and their ability to store or release heat more slowly than air.
These cold surfaces absorb some of the infrared radiation emitted by the body. They change the way the body's heat escapes around the person. Instead of the energy being evenly distributed in all directions, a large part of the heat is captured by these cold walls. The body then perceives this imbalance as a more intense cold coming from these surfaces.
Imagine your body as a heat lamp placed in the center of a room. The heat it emits spreads in all directions, but the cold walls absorb more of this energy. The heat flux will naturally "follow" these surfaces, because the thermal gradients are stronger where it is colder. It's a bit like if the body's heat were water on a slope. Cold surfaces are like deeper holes. Conversely, in directions toward warmer surfaces or those close to your temperature, the body loses less heat (the heat flux is "slower").
Even without drafts, this imbalance in heat flux gives the sensation that the cold is coming mainly from the cold surfaces in front of you, such as the wall or window.
Thermal conduction was formalized in the early 19th century by Joseph Fourier (1768-1830). He laid the mathematical foundations for heat transfer by direct contact between materials.
Blackbody radiation was described by Max Planck (1858-1947) in 1900 CE, paving the way for a quantitative understanding of radiative exchanges. The work of Albert Einstein (1879-1955) reinforced the statistical interpretation of energy transfers between matter and radiation.
N.B.:
Air temperature is not the only factor that influences thermal comfort. Even if two environments have the same temperature, one can feel very different cold or comfort depending on how heat is distributed around the body. This is called the radiative field: the set of surfaces and objects that absorb or reflect heat toward you. An imbalance in this field, for example cold walls or windows, can amplify the feeling of cold, even without drafts.
| Mechanism | Physical Description | Effect on the Body | Reference |
|---|---|---|---|
| Radiation | Infrared emission proportional to \(T^4\), quantified by blackbody physics | Overall energy loss | Max Planck, 1900 CE and Albert Einstein (1905 CE) |
| Conduction | Heat transfer by contact | Localized cooling | Joseph Fourier, 1822 CE |
| Convection | Heat transport by fluid | Secondary effect without drafts | Isaac Newton, 1701 CE |
Sources: NIST, Thermophysical Properties, ISO 7730, Ergonomics of the thermal environment.
The Perception of Radiant Cold Explained by Physics 
Sprites and Cosmic Rays: The Ghostly Lightning of the Atmosphere 
Principle of
absorption and emission of a photon 
The Femtosecond Laser: From Ultra-Short Time to Extreme Power 
The World of Color 
The colors of the rainbow 
The Nature of Light 
Plasma Lamp and Field Concept 
What is Vantablack? 
Michelson-Morley Experiment 
Redshift calculation (z) 
Spectacular airglow in France 
All the Light of the Electromagnetic Spectrum 
Solar Pillars: Celestial Mirages and Light Phenomena 
The Speed of Light: A Universal Constant 
The incredible precision of the second 
Effects of light aberration 
Why do elementary particles have no mass? 
Polar Auroras: Lights of the Solar Wind 
Blue Moon or Ice Moon: Understanding These Lunar Phenomena 
Gravitational Lenses: When Spacetime Becomes a Mirage 
Optical Illusions: Deceptions and Mysteries of Visual Perception 
Traveling Light: How a Photon Leaves the Sun to Reach Earth? 
Bioluminescence of living organisms 
Laser light 
We do not see with our eyes but with our brain 
Differences between heat and temperature 
Zodiacal Light: Reflection of Interplanetary Dust 
Explanation of the 8 of the analemma 
The Antitwilight Arch: Earth's Shadow 
How many photons to heat a cup of coffee? 
Spectroscopy: A Key to Analyzing the Invisible World 
The Cherenkov light 
The lights of the Sun 
What is a Wave? 
Planck's equation and black body light 
Energy Conservation