Illuminance - The luminous flux density at a surface, i.e. the luminous flux incident per unit area. This quantity was formerly known as the illumination value or illumination level.

Illumination - The process of lighting.

Incandescent Lamp - A lamp in which light is produced by a filament heated to incandescence by the passage of an electric current.

Indirect Lighting - Lighting in which the greater part of the flux reaches the surface (usually the working plane) only after reflection at other surfaces, usually a roof or ceiling.

Initial Illuminance - Average illuminance for a new installation when lamps, luminaires and room surfaces are clean.

Initial Light Output- The luminous flux from a new lamp. In the case of discharge lamps this is usually the output after 100 hours of operation.

Installed Efficacy - A factor which quantifies the effectiveness of a lighting installation in converting electrical power to light. Specifically, it is the product of the lamp circuit luminous efficacy and the utilisation factor. This term is now replaced by Installed Power Density.

Installed Power Density -The installed power density per 100 lux is the power needed per square metre of floor area to achieve 100 lux on a horizontal plane with general lighting.

Irradiance - The radiant flux density at a surface, i.e. the radiant flux incident per unit area of the surface.

Isolux Diagram - A diagram showing contours of equal illuminance.

Lumen -The unit of luminous flux, used to describe a quantity of light emitted by a source or received by a surface.

Luminaire - An apparatus which controls the distribution of light given by a lamp or lamps and which includes all the components necessary for fixing and protecting the lamps and for connecting them to the power supply. Colloquially a ‘lighting fitting’.

Luminaire Maintenance Factor - The proportion of the initial light output from a luminaire that occurs after a set time due to dirt deposition on and in the luminaire.

Luminance - A measure of the stimulus which produces a sensation of brightness measured by the luminous intensity of the light emitted or reflected in a given direction from a surface element, divided by the projected area of the element in the same direction.

Luminous Efficacy - The ratio of the luminous flux emitted by a lamp to the power consumed by it. When the power consumed by the control gear is taken into account this term is sometimes known as lamp circuit luminous efficacy and is expressed in lumens per circuit watt.

Luminous Intensity - The power of a source or illuminated surface to emit light in a given direction.

Lux (lux) - unit of illuminance, equal to one lumen per square metre (lm/m2).

Maintained Illuminance - The average illuminance over the reference surface at the time of replacing lamps and/or cleaning the equipment and room surfaces.

Maintenance Factor -The ratio of the illuminance provided by an installation at some stated time (eg. 100 hours of operation) to the initial illuminance. It is the product of the lamp lumen maintenance factor, the lamp survival factor, the luminaire maintenance factor and the room surface maintenance factor.

Reflectance - The ratio of the luminous flux reflected from a surface to that incident on it. Except for matt surfaces, reflectance depends on how the surface is illuminated, especially the direction and spectral distribution of the incident light. The value is always less than one.

Room Surface Maintenance Factor - The proportion of the illuminance provided by a lighting installation after a set time compared with when the room was clean. Depreciation in lumen output of lamps and the effect of dirt deposition on luminaires is not included.

Skylight - The diffuse light from the sky vault, excluding direct sunlight.

Sunlight - The direct light from the sun, after diffusion in the atmosphere.

Transmittance - The ratio of luminous flux transmitted by a material, such as a window, to the incident luminous flux.

Uplighter - Luminaires which direct most of the light upwards onto the ceiling or upper walls in order to illuminate the working plane by reflection.

Utilisation Factor - The proportion of the luminous flux emitted by a lamp which reaches the working plane.

Working Plane - The plane in which the visual task lies. If no information is available, the working plane may be considered to be horizontal and in the case of sports halls at floor level.

Understanding Daylighting of Sports Halls

Glossary of Terms

A selective glossary has been included to assist readers in the understanding of the technical lighting terms used throughout this report.

Adaptation - The process which takes place as the visual system adjusts itself to the brightness or the colour of the visual field. Also used to denote the final state of this process. For example ‘dark adaptation’ when the visual system has become adapted to very low illuminance.

Average Daylight Factor - The average of daylight factors over a reference plane or planes. In the case of this report, it is the average over the floor surface level.

Average Illuminance -The mean illuminance over the specified surface.

Brightness - The subjective response to luminance in the field of view dependent upon the adaptation of the eye.

Colour Rendering - The appearance of surface colours when illuminated by light from a given source compared, consciously or unconsciously, with their appearance under light from some reference source. ‘Good colour rendering’ implies similarity of appearance to that under an acceptable light source, such as daylight.

Colour Rendering Index (CRI) - A measure of the degree to which the colours of surfaces illuminated by a given light source conform to those of the same surfaces under a reference illuminant, suitable allowance having been made for the state of chromatic adaptation.

Colour Temperature - The temperature of a ‘full radiator’ which emits radiation of the same chromaticity as the radiator being considered.

Contrast - Subjectively the difference in appearance (brightness or colour or both) of two parts of a visual field seen simultaneously or successively. Objectively, the luminance difference between the two parts of the field.

Correlated Colour Temperature (CCT) -The temperature of a full radiator which emits radiation having a chromaticity nearest to that of a light source being considered, eg., the colour of a full radiator at 3500 K is the nearest match to a white tubular fluorescent lamp.

Daylight -The combined effect of sunlight and skylight. In this document, the word daylight is used as a general description for natural lighting in a sports hall, and refers to the skylight.

Daylight Factor (D) -The illuminance received at a point indoors, from a sky of known or assumed luminance distribution expressed as a percentage of the horizontal illuminance outdoors from an unobstructed hemisphere of the same sky. Direct sunlight is excluded.

Daylight Factor - Externally Reflected Component (De) -The illuminance received directly at a point indoors from a sky of known or assumed illuminance distribution after reflection from an external surface.

Daylight Factor - Internally Reflected Component (Di) -The illuminance received at a point indoors from a sky of known or assumed luminance distribution after reflection within the interior.

Daylight Factor - Sky Component (Dc) - The illuminance received directly at a point indoors from a sky of known or assumed luminance distribution.

Diffuse Reflection - Reflection in which the reflected light is diffused and there is no significant specular reflection, as from a matt paint.

Diffuse Lighting - Lighting in which the luminous flux comes from many directions, none of which predominates.

Disability Glare - Glare produced directly or by reflection that impairs the vision of objects without necessarily causing discomfort.

Discharge Lamp - A lamp which produces light either directly or by the excitation of phosphors by an electric discharge through a gas, a metal vapour or a mixture of gases and vapours.

Discomfort Glare - Glare which causes visual discomfort.

Downlighter - Direct lighting luminaire from which light is emitted only within relatively small angles to the downward vertical.

Efficacy - See luminous efficacy.

Energy Management Systems (EMS) - Computer based systems for controlling the energy use of a site, a single building or a section of a building. The signals which initiate the controls may be related to time of year, month, week or day, maximum demand or power factor, daylight availability, occupancy, etc.

Glare - The discomfort or impairment of vision experienced when parts of the visual field are excessively bright in relation to the general surroundings.

Glare Index System - A system which enables the discomfort glare from lighting installations to be ranked in order of severity and the permissible limit of discomfort glare from an installation to be prescribed quantitatively. Information usually provided by manufacturers but can be calculated for pre-prepared tables for a particular luminaire.

Group Lamp Replacement - A maintenance procedure where all lamps are replaced at one time. The lumen maintenance characteristics and probability of lamp failure dictate the period after which bulk replacement, usually linked with luminaire cleaning, will take place. It has visual, electrical and financial advantages over the alternative of ‘spot replacement’.

Heliodon -A multi-axis turntable on which a building or room model is mounted. It is then adjusted, in relation to an artificial sun (bright, parallel beam spot light) or the real sun, according to the time of day, season, orientation and position on the planet that is desired, to simulate sunpaths in the model.


						Illuminance - The luminous flux density at a surface, i.e. the luminous flux incident per unit area. This quantity was formerly known as the illumination value or illumination level. Illumination - The process of lighting. Incandescent Lamp - A lamp in which light is produced by a filament heated to incandescence by the passage of an electric current. Indirect Lighting - Lighting in which the greater part of the flux reaches the surface (usually the working plane) only after reflection at other surfaces, usually a roof or ceiling. Initial Illuminance - Average illuminance for a new installation when lamps, luminaires and room surfaces are clean. Initial Light Output- The luminous flux from a new lamp. In the case of discharge lamps this is usually the output after 100 hours of operation. Installed Efficacy - A factor which quantifies the effectiveness of a lighting installation in converting electrical power to light. Specifically, it is the product of the lamp circuit luminous efficacy and the utilisation factor. This term is now replaced by Installed Power Density. Installed Power Density -The installed power density per 100 lux is the power needed per square metre of floor area to achieve 100 lux on a horizontal plane with general lighting. Irradiance - The radiant flux density at a surface, i.e. the radiant flux incident per unit area of the surface. Isolux Diagram - A diagram showing contours of equal illuminance. Lumen -The unit of luminous flux, used to describe a quantity of light emitted by a source or received by a surface. Luminaire - An apparatus which controls the distribution of light given by a lamp or lamps and which includes all the components necessary for fixing and protecting the lamps and for connecting them to the power supply. Colloquially a ‘lighting fitting’. Luminaire Maintenance Factor - The proportion of the initial light output from a luminaire that occurs after a set time due to dirt deposition on and in the luminaire. Luminance - A measure of the stimulus which produces a sensation of brightness measured by the luminous intensity of the light emitted or reflected in a given direction from a surface element, divided by the projected area of the element in the same direction. Luminous Efficacy - The ratio of the luminous flux emitted by a lamp to the power consumed by it. When the power consumed by the control gear is taken into account this term is sometimes known as lamp circuit luminous efficacy and is expressed in lumens per circuit watt. Luminous Intensity - The power of a source or illuminated surface to emit light in a given direction. Lux (lux) - unit of illuminance, equal to one lumen per square metre (lm/m2). Maintained Illuminance - The average illuminance over the reference surface at the time of replacing lamps and/or cleaning the equipment and room surfaces. Maintenance Factor -The ratio of the illuminance provided by an installation at some stated time (eg. 100 hours of operation) to the initial illuminance. It is the product of the lamp lumen maintenance factor, the lamp survival factor, the luminaire maintenance factor and the room surface maintenance factor. Reflectance - The ratio of the luminous flux reflected from a surface to that incident on it. Except for matt surfaces, reflectance depends on how the surface is illuminated, especially the direction and spectral distribution of the incident light. The value is always less than one. Room Surface Maintenance Factor - The proportion of the illuminance provided by a lighting installation after a set time compared with when the room was clean. Depreciation in lumen output of lamps and the effect of dirt deposition on luminaires is not included. Skylight - The diffuse light from the sky vault, excluding direct sunlight. Sunlight - The direct light from the sun, after diffusion in the atmosphere. Transmittance - The ratio of luminous flux transmitted by a material, such as a window, to the incident luminous flux. Uplighter - Luminaires which direct most of the light upwards onto the ceiling or upper walls in order to illuminate the working plane by reflection. Utilisation Factor - The proportion of the luminous flux emitted by a lamp which reaches the working plane. Working Plane - The plane in which the visual task lies. If no information is available, the working plane may be considered to be horizontal and in the case of sports halls at floor level.

	Back to Top ^