Light Reflection
Light reflection is the phenomenon in which a light ray bounces off a surface and changes direction, obeying the law of reflection: the angle of incidence equals the angle of reflection, both measured from the normal to the surface. It is fundamental to how we see non-luminous objects, as surfaces reflect light into our eyes. Applications range from mirrors in optical instruments to reflective coatings on road signs and safety gear.
Types of Reflection and Their Characteristics
| Type | Surface | Image Formed | Example |
|---|---|---|---|
| Specular | Smooth/polished | Clear, defined | Plane mirror |
| Diffuse | Rough/matte | No clear image | Paper, walls |
| Mixed | Partially smooth | Faint image | Glossy paint |
| Total Internal | Denser medium boundary | Internal image | Optical fibre |
| Retroreflection | Corner reflectors | Back to source | Road signs |
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Related Terms
Light Refraction
Light refraction is the bending of a light ray as it passes from one transparent medium into another of different optical density, caused by a change in the wave's speed. The greater the difference in refractive indices between the two media, the more the ray bends toward or away from the normal. Refraction is responsible for phenomena such as the apparent bending of a straw in water, the formation of rainbows, and the focusing action of lenses.
Plane Mirror
A plane mirror is a flat, highly polished reflective surface that forms a virtual, upright, and laterally inverted image of an object, with the image appearing to be the same distance behind the mirror as the object is in front of it. The image is the same size as the object (magnification = 1) and cannot be projected on a screen because it is virtual. Plane mirrors are used in everyday mirrors, periscopes, kaleidoscopes, and laser beam steering.
Total Internal Reflection
Total Internal Reflection (TIR) occurs when a light ray travelling through a denser medium strikes the boundary with a less dense medium at an angle greater than the critical angle, causing the ray to be completely reflected back into the denser medium rather than refracted out. The critical angle θ_c is defined as sin θ_c = n₂/n₁, where n₁ > n₂. TIR is the operating principle behind optical fibres, diamonds' brilliance, and binocular prisms.
From Latin "reflectere" meaning "to bend back" (re- = back, flectere = to bend). The term entered scientific English in the 14th century; the precise law of reflection was formalised by Ibn al-Haytham (Alhazen) around 1021 CE in his Kitab al-Manazir.