Title: Reading and Audio-Visual Assignments
Course: WGF 107 DEVELOPMENT > Section: Content

Image | Diffuse and specular reflection from a glossy surface.^[1] The rays represent luminous intensity, which varies according to Lambert's cosine law for an ideal diffuse reflector.

Sub-Title | Key Measurements Involving Light
Content
Diffuse reflection is the reflection of light from a surface such that an incident ray is reflected at many angles rather than at just one angle as in the case of specular reflection. An illuminated ideal diffuse reflecting surface will have equal luminance from all directions which lie in the half-space adjacent to the surface (Lambertian reflectance).

A surface built from a non-absorbing powder such as plaster, or from fibers such as paper, or from a polycrystalline material such as white marble, reflects light diffusely with great efficiency. Many common materials exhibit a mixture of specular and diffuse reflection.

The visibility of objects, excluding light-emitting ones, is primarily caused by diffuse reflection of light: it is diffusely-scattered light that forms the image of the object in the observer's eye.

In architecture, Light Reflectance Value (LRV), is a measure of the percentage^[1] of visible and usable light that is reflected from a surface when illuminated by a light source. The measurement is most commonly used by design professionals like architectural color consultants, architects, environmental graphic designers and interior designers.

LRVs are frequently reported on paint chips or paint samples. The values are used by lighting designers to calculate the number and type of light fixtures needed to provide a certain amount of light for interior spaces.

Guidance[edit]

Designers of buildings need to comply with the Building Regulations applicable to the structure under consideration. Since 2004 guidance has existed on access to and use of buildings. The guidance is particularly concerned with provisions to assist the disabled, including those who are visually impaired. The guidance highlights the need for certain surfaces and features to contrast visually with their surroundings. Areas of particular interest are:

- wall to ceiling and wall to floor junctions;
- exposed edges of sloping floors;
- seating and its surroundings;
- leading edges of doors, door opening furniture and door surfaces;
- sanitary fittings and grab bars.

This is relevant to a wide range of non-residential buildings, e.g. hospitals, schools, hotels, theatres, etc.
Images | Figure 1 – General mechanism of diffuse reflection by a solid surface (refraction phenomena not represented) Figure 2 – Diffuse reflection from an irregular surface
Content
Specular reflection is the mirror-like reflection of light (or of other kinds of wave) from a surface, in which light from a single incoming direction (a ray) is reflected into a single outgoing direction. Such behavior is described by the law of reflection, which states that the direction of incoming light (the incident ray), and the direction of outgoing light reflected (the reflected ray) make the same angle with respect to the surface normal, thus the angle of incidence equals the angle of reflection ( in the figure), and that the incident, normal, and reflected directions are coplanar. This behavior was first discovered through careful observation and measurement by Hero of Alexandria (AD c. 10–70).^[1]

Explanation[edit]

Specular reflection is distinct from diffuse reflection, where incoming light is reflected in a broad range of directions. An example of the distinction between specular and diffuse reflection would be glossy and matte paints. Matte paints have almost exclusively diffuse reflection, while glossy paints have both specular and diffuse reflection. A surface built from a non-absorbing powder, such as plaster, can be a nearly perfect diffuser, whereas polished metallic objects can specularly reflect light very efficiently. The reflecting material of mirrors is usually aluminum or silver.

Even when a surface exhibits only specular reflection with no diffuse reflection, not all of the light is necessarily reflected. Some of the light may be absorbed by the materials. Additionally, depending on the type of material behind the surface, some of the light may be transmitted through the surface. For most interfaces between materials, the fraction of the light that is reflected increases with increasing angle of incidence . If the light is propagating in a material with a higher index of refraction than the material whose surface it strikes, then total internal reflection may occur if the angle of incidence is greater than a certain critical angle. Specular reflection from a dielectric such as water can affect polarization and at Brewster's angle reflected light is completely linearly polarized parallel to the interface.
Links/Uploads
Wikipedia – The Free Internet Encyclopedia

Lighting                                   http://en.wikipedia.org/wiki/Lighting

Diffuse Reflection     http://en.wikipedia.org/wiki/Diffuse_reflection

Light Reflectance Value http://en.wikipedia.org/wiki/Light_Reflectance_Value

Light Specular Value http://en.wikipedia.org/wiki/Specular_reflection

See also[edit]

 | Computer graphics portal

- Diffuser
- Reflectivity
- Oren–Nayar reflectance model
Attributions | Images and Content courtesy of Wikipedia – The Free Internet Encyclopedia