The world we perceive is defined by how objects interact with light. Seeing an object depends entirely on reflection, where light strikes a surface and bounces back toward our eyes. Every material, from a window to a shirt, constantly reflects light in a distinct way. This interaction between light and a material’s surface structure determines its appearance, color, and texture.
The Core Concept of Light Reflection
Reflection occurs when light waves, traveling through a medium like air, encounter a boundary and are redirected back. This interaction is governed by the Law of Reflection, which states that the angle at which an incoming light ray strikes a surface is exactly equal to the angle at which it leaves the surface. To measure these angles, a hypothetical line called the “normal” is drawn perpendicular to the surface where the light hits. The angle of incidence (between the incoming ray and the normal) must match the angle of reflection. This principle holds true for every single light ray, regardless of the object’s material or texture.
Specular Reflection and Highly Polished Surfaces
Specular reflection occurs when light rays strike a smooth, polished surface and reflect in a single, concentrated direction. Because the surface is flat microscopically, all incoming parallel light rays remain parallel after bouncing off. This uniform reflection allows us to see clear, undistorted mirror images. Examples include a plane mirror, polished chrome, or the still surface of a lake. Surfaces exhibiting specular reflection are typically metals or materials with a smooth coating, and this concentrated light often results in glare.
Diffuse Reflection and Everyday Materials
The majority of everyday objects, such as clothing, paper, and painted walls, are seen due to diffuse reflection. This occurs when light strikes a surface that is rough or uneven microscopically, causing the light rays to scatter in many directions. Even surfaces appearing smooth, like paper, have microscopic irregularities caused by wood pulp fibers. When parallel light rays hit these uneven surfaces, they obey the Law of Reflection, but the surface angle changes for every point. This causes the light rays to bounce off at widely varying angles, scattering the light broadly and allowing the object to be seen from almost any viewing angle without glare.
How Reflection Determines Color
Reflection involves both the direction light travels and which specific wavelengths an object returns to the eye. White light, such as sunlight, contains all visible wavelengths, which the brain interprets as a spectrum of colors. When light strikes an object, the material’s atomic structure determines which wavelengths are absorbed and which are reflected. The color we perceive is the combination of wavelengths reflected back to our eyes. For example, a red apple absorbs most blue, green, and yellow wavelengths, but reflects red. Conversely, a black shirt absorbs almost all visible light, reflecting very little back, while white objects reflect almost all wavelengths equally.