| Absorption |
Transformation of radiant energy to a different form of energy by the intervention of matter. |
| Adaptation |
The process by which the state of the human visual system is modified by previous and present exposure to stimuli that may have various luminances, spectral distributions, and angular subtenses. |
| Altitude |
The angular distance of the sun measured upward from the horizon on the vertical plane that passes through the sun. Altitude is measured positively from horizon to zenith from 0° to 90°. |
| Angle of Incidence |
The angle between a ray of light falling on a surface and a line perpendicular to the surface. |
| Atrium |
An interior light space enclosed laterally by the walls of a building and covered with transparent or translucent material that permits light to enter interior spaces through pass-through components. |
| Azimuth |
The azimuth of the sun is the angle between the vertical plane containing the sun and the vertical plane oriented to the north (direction of origin). |
| Blinds |
Blinds are solar shadings used to control the solar incident radiation and protect against glare. Blinds are build-up of lamellas blocking and/or redirecting the direct sunshine, in function of their slope. The dimensions, colour and gloss of the lamellas determine the properties of blinds. Blinds perform best when they are placed on the exterior of the façade. Due to their limited resistance to wind, blinds are best applied on low height buildings. |
| Brightness |
The visual sensation by which an observer registers the degree to which a surface appears to emit or reflect more or less light. This subjective sensation cannot be measured in absolute units; it describes the appearance of a source or object. |
| Candela |
The unit of luminous intensity. The luminance of a full radiator at the temperature of solidification of platinum is 60 candelas / cm2. |
| Candela Per Square Meter |
A unit of luminance in a particular direction recommended by the Commission Internationale de L’Éclairage (CIE). |
| CIE Standard Clear Sky |
Cloudless sky for which the relative luminance distribution is described in Publication CIE No. 22 (TC 4.2) 1973 Commission Internationale de L’Éclairage (CIE). |
| CIE Standard Overcast Sky |
A completely overcast sky for the luminance (cd/m2) of any point in the sky at an angle of elevation g above the horizon, is assumed to be given by the relation: Lg = Lz (1+2sing ) / 3 where Lz is the luminance at the zenith. |
| Clerestory |
Daylight opening in the uppermost part of an exterior wall. |
| Colour rendering |
Effect of a light source on the colour appearance of objects by conscious or
subconscious comparison with their colour appearance under a reference light source. |
| Colour rendering index |
Measure of the degree to which the psychophysical colour of an object illuminated by the test light source conforms to that of the same object illuminated by the reference light source, suitable allowance having been made for the state of the chromatic adaptation. |
| Colour temperature: |
Temperature of a Planckian radiator whose radiation has the same chromaticity as that of a given stimulus; unit: K. |
| Contrast |
The subjective assessment of the difference in appearance of two parts of a field of view seen simultaneously or successively. It can be defined objectively as: (L1–L2) /L1 where L1 and L2 are the luminances of the background and object, respectively. |
| Correlated colour temperature |
The temperature of the Planckian radiator whose perceived colour most closely resembles that of a given stimulus at the same brightness and under specified viewing conditions; unit: K. |
| Daylight |
Visible global radiation. Daylight is the sum of sunlight and skylight. |
| Daylight Factor |
Ratio, at a point on a given plane, of the illuminance that results from the light received directly or indirectly from a sky of assumed or known luminance distribution to the illuminance on a horizontal plane that results from an unobstructed hemisphere of this sky. The contribution of direct sunlight to both illuminances is excluded. |
| Daylight Opening |
Area, glazed or unglazed, that is capable of admitting daylight to an interior. |
| Diffuse Illuminance from the Sky |
Illuminance from the sky received on a horizontal plane from the whole hemisphere, excluding direct sunlight. |
| Diffuse Reflection |
The process by which incident flux is redirected over a range of angles. |
| Diffuse Transmission |
The process by which the incident flux passing through a surface or medium is scattered. |
| Diffuse Transmittance |
The ratio of the diffusely transmitted luminous flux leaving a surface or medium to the total incident flux. |
| Diffuser |
A device object or surface used to alter the spatial distribution of light. |
| Diffusion |
The scattering of light rays so that they travel in many directions rather than in parallel or radiating lines. |
| Disability Glare |
Excessive contrast, especially to the extent that visibility of one part of the visual field is obscured by the eye’s attempt to adapt to the brightness of the other portion of the field of view; visibility of objects is impaired. |
| Discomfort Glare |
Glare that causes annoyance without physically impairing a viewer’s ability to see objects. |
| Electrochromic glazing |
In an electrochromic (EC) window, a coating on the inside surface of the outer pane allows the glass to change transmittance in response to a small applied voltage (±3-5V). Electrochromic coatings are switchable thin-film coatings applied to glass or plastic that can change appearance reversibly from a clear to a dark Prussian Blue tint. Electrochromic glazing is to be applied when solar heat gains need to be reduced, while allowing a view out and daylight contribution. |
| Emission |
Release of radiant energy. |
| Fenestration |
Any opening or arrangement of openings in a building for the admission of daylight or air. |
| Fluorescent lamp |
A discharge lamp of the low pressure mercury type in which most of the light is emitted by one or several layers of phosphors excited by the ultraviolet radiation from the discharge. |
| Glare |
A visual condition which results in discomfort, annoyance, interference with visual efficiency, or eye fatigue because of the brightness of a portion of the field of view (lamps, luminaires, or other surfaces or windows that are markedly brighter than the rest of the field). Direct glare is related to high luminances in the field of view. Reflected glare is related to reflections of high luminances. |
| Goniophotometer |
Photometer for measuring the directional light distribution characteristics of sources, luminaires, media, or surfaces. |
| Illuminance |
The luminous flux incident on a surface per unit area. The unit is lux, or lumens per square foot. |
| Indirect Lighting |
Illumination achieved by reflection, usually from wall and/or ceiling surfaces. |
| Integrating Sphere |
Hollow sphere whose internal surface is a diffuse reflector that is as non-selective as possible. |
| Light |
Radiant energy evaluated according to its capacity to produce visual sensation. |
| Light Duct |
An element of a building that carries natural light to interior zones. Duct surfaces are finished with highly reflective materials. |
| Light emitting diode (LED) |
Solid state device embodying a p-n junction, emitting optical radiation when excited by an electric current. |
| Light shelves |
Light shelves are horizontal or nearly horizontal baffles in the façade to simultaneously shade and reflect daylight. They enhance user comfort by providing more uniformly distributed daylight in rooms. Light shelves affect a buildings architecture and need high rooms to function effectively. |
| Louvres |
Louvres are applied to shade the heat of the sun and its glare in order to enhance user visual and thermal comfort and reduce energy consumption. They are situating mainly in the exterior in front of the façade with a wide variety in their designs. Louvres affect the architectural appearance of a building. They can be used in any locality on sun facing façades. The maintenance of louver slats should be frequent in polluted locales. |
| Lumen |
The unit of luminous flux. It is equal to the flux through a unit of solid angle (steradian) from a uniform point source of one candela or the flux on a unit surface all points of which are at a unit distance from a uniform point of one candela. |
| Luminaire |
A complete lighting unit (fixed or portable) that distributes, filters, or transforms the light given by a lamp or lamps and that includes all the components necessary for mounting and protecting the lamps and connecting them to the supply circuit. |
| Luminance |
The luminous intensity of any surface in a given direction per unit or projected area of the surface as viewed from that direction. |
| Lux |
The International System (SI) unit of illumination. It is the illumination on a surface one square metre in area on which there is a uniformly distributed flux of 1 lumen. |
| Microstructured glazing |
Microstructured glazing uses microscopic structures as a film to the surface of a window or inside the insulated glass unit to enhance the daylight provision and/or to reduce glare caused by direct sunlight. The seasonal thermal gains can potentially be optimized. Microstructured glazing is to be used when a simple retrofit of façade is required and parameters as low maintenance and daylight usage are important. |
| Obstruction |
Surfaces outside the building that obstruct direct view of the sky from a reference point. |
| Overcast Sky |
Sky completely covered by clouds with no sun visible. |
| Radiation |
Energy in the form of electromagnetic waves or particles. |
| Redirecting blinds |
Redirecting blinds reflect daylight from sun and sky to the ceiling to provide improved daylight illumination even in the depth of the adjacent rooms. For optimal functionality, the upper surfaces are highly specular leading to somewhat increased maintenance costs. A retrofit solution for enhanced daylighting and improved visual comfort, especially suitable for deep rooms. |
| Reflectance |
The ratio of light reflected to incident light. |
| Reflection |
Process by which radiation is returned by a surface or a medium without change of frequency of its monochromatic components. |
| Reflector |
A device that returns incident visible radiation; used to alter the spatial distribution of light. |
| Refraction |
Change in direction of propagation of radiation determined by change in the velocity of propagation as radiation passes through an optically non-homogeneous medium or from one medium to another. |
| Relative Sunshine Duration |
Ratio of actual time to possible time when the sun is not obscured by clouds. |
| Shading |
Use of fixed or movable devices to block, absorb, or redirect incoming light for purposes of controlling unwanted heat gains and glare. |
| Shading Coefficient |
The dimensionless ratio of the total solar heat gain from a particular glazing system to that for one sheet of clear, 3-mm, double-strength glass. |
| Shading Device |
Device used to obstruct, reduce, or diffuse the penetration of direct sunlight. |
| Shutters |
Shutters are elements which dynamically solve fundamental functions of the façade: solar shading, daylight control, dynamic façade U-value, natural ventilation, and noise reduction. The shutters can be moved horizontally or vertically in front of the window. Shutters cannot be used on fully glazed façades. |
| Skylight |
An opening situated in a horizontal or tilted roof. |
| Sunscreens |
Sunscreens are textile solar shadings used to control the solar incident radiation. The threads of the fabrics are mainly made of glass fibre, polyester or acrylic weft. The fabric and the colour of the determine the properties of the sunscreen. Sunscreens perform best when they are placed on the exterior of the façade. Due to their limited resistance to wind, sunscreens are best applied on low height buildings. |
| Toplighting |
Daylight that enters through the upper portion of an interior space such as a clerestory or skylight. |
| Translucent Glass |
A glass with the property of transmitting light diffusely. |
| Transmission |
Passage of radiation through a medium without change of frequency of its monochromatic components. |
| Transmittance |
Ratio of the transmitted radiant or luminous flux to the incident flux in the given conditions. |
| Veiling Reflections |
Reflections that reduce the contrast between the task/object and the background when extremely bright reflections of light sources appear on the task object itself. |
| Visual comfort |
Subjective condition of visual well-being induced by the visual environment. |
| Visual performance |
Performance of the visual system as measured for instance by the speed and accuracy with which a visual task is performed. |
| Visual task |
Visual elements of the work being done. |
| Window |
Daylight opening on a vertical or nearly vertical area of a room envelope. |