Lambertische

Lambertische describes a model of diffuse reflection known in English as Lambertian reflectance. The term honors Johann Heinrich Lambert, who formulated the related law in the 18th century. It remains a foundational concept in optics, computer graphics, and vision for representing matte or non-glossy surfaces.

In a Lambertian surface, the brightness seen by an observer is independent of the viewing direction, following Lambert’s cosine law: the intensity of reflected light toward a direction is proportional to the cosine of the angle between that direction and the surface normal. In formal terms, the bidirectional reflectance distribution function (BRDF) for a Lambertian surface is constant, f_r(ω_i, ω_r) = ρ/π, where ρ is the surface albedo. This means the radiance leaving the surface toward any observer is a constant multiple of the incident irradiance, determined by the albedo.

Lambertische surfaces are widely used because they provide a simple, computationally efficient approximation for dull, non-metallic materials. They are a common baseline in rendering algorithms, photometric analysis, and material estimation, particularly when the goal is to model diffuse appearance without strong specular highlights. The model is typically combined with a separate, angle-dependent specular component to capture glossy behavior.

Limitations include real-world deviations from perfect Lambertian behavior. Many materials exhibit anisotropy, microfacet-based reflections, or color shifts with viewing angle. Consequently, more complex BRDF models are employed when higher physical accuracy is required, though the Lambertian term often remains a useful first approximation.