Thermal Emittance
Thermal emittance is a number between 0 and 1 describing how well a surface radiates heat. A high-emittance surface sheds heat quickly; a low-emittance one holds onto it.
Scientific detail
Thermal emittance ε is the ratio of a surface's emissive power to that of a black body at the same temperature, typically integrated over 3–50 μm or specifically over the 8–13 μm atmospheric window for PDRC applications. Together with solar reflectance, ε governs both the daytime equilibrium temperature of passive cooling materials and their radiative coupling to the sky.
Related terms
Radiative Cooling
Heat loss from any object by emitting thermal infrared radiation.
Passive Daytime Radiative Cooling
A material that stays cooler than the air even under direct sunlight by radiating heat to the cold sky.
Atmospheric Window
A range of infrared wavelengths (roughly 8–13 μm) where the atmosphere absorbs relatively little of Earth's outgoing thermal radiation.
Solar Reflectance
The fraction of incoming solar energy a surface reflects across the sun's spectrum.
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Passive Cooling
Everything MEER publishes on passive cooling — reflective roofs, PDRC materials, canopies, reservoir systems, projects, publications and stories, gathered in one place.
Radiative Cooling & PDRC
PDRC materials, the atmospheric window, thermal emittance and the practical engineering of surfaces that radiate heat directly to deep space.