highreflectance

High reflectance is the property of a surface or material that reflects a large portion of incident electromagnetic radiation. It is commonly quantified as reflectance R, the ratio of reflected to incident radiant flux, or expressed as a percentage. Reflectance can be specular, with light reflected in a single direction, or diffuse, with reflection scattered in many directions. Hemispherical reflectance measures the fraction of light reflected into the upper hemisphere, integrating over exit angles.

Measurement and spectral behavior: In practice, high reflectance is often designed for specific wavelength ranges. Measurements use spectrophotometers with integrating spheres for diffuse reflectance or gonioreflectometers for angular dependence. Materials may exhibit high reflectance in the visible, the near-infrared, or across broader bands. Performance depends on surface roughness, coatings, oxide layers, and aging, which can cause spectral shifts or degradation over time.

Materials and approaches: Metals such as silver and aluminum inherently offer high reflectance in the visible and near-infrared, though they may tarnish or oxidize. Dielectric coatings—stacks of alternating high and low refractive index materials—can achieve very high reflectance over selected bands or across broad spectra, as in dielectric mirrors. White pigments, including titanium dioxide-based materials, provide high diffuse reflectance in the visible. Multilayer coatings and engineered surfaces enable tailored spectral and angular reflectance for specific applications.

Applications and considerations: High reflectance is important for solar mirrors, telescope and laser optics, architectural design for daylighting and thermal management, and optical sensors. Trade-offs include angle dependence, glare, spectral selectivity, durability, and cost. Environmental exposure can degrade reflectance, making protective coatings and maintenance important for longevity.