A-F     G-M     N-S     T-Z

Ambient: A term given to general lighting of the visual environment.

Beam: The beam angle is the total angle of the beam where the edge of the beam is taken half the intensity of its peak value.

Brightness: Subjective experience of the brightness of an object or surface, as opposed to the objective measurement of luminance with a meter. Brightness is determined by the measured luminance of the object and the adaptation level of the viewer. Since adaptation level cannot be measured, neither can brightness.

Colour rendering: A general expression for 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 temperature: An indication of the colour of a lighting source. In thermal radiators it corresponds approximately to the temperature of the lamp filament in Kelvin (K). In discharge lamps, it indicates the nearest colour temperature. This is the temperature at which a thermal radiator emits light of a comparable colour. The majority of artificial light sources range from 2100K (warm white) to 6500K (cool white).

Control gear: A general term applied to the equipment required to operate a lamp. It consists mainly of current limiting ballasts and igniters for the operation of discharge lamps, HID and fluorescent, as well as transformers to operate low-voltage halogen lamps.

Diffuse light: Diffuse light is given off from large luminescent surfaces, producing a soft, even illumination with low modelling ability and low brilliance.

Diffusing lens: A lens used to widen and soften the distribution of light from a source, thereby increasing its diffusion.

Dimming: The variable adjustment of the luminous flux of a light source. Dimming creates a rich visual experience and adds flexibility to any room, providing the right lighting environment for a variety of activities. Save electricity and increase lamp life. Dimming saves electricity and reduces the demand on HVAC systems.

Disability glare: Light which reduces the visibility of a visual task. Any light incident on the eye is slightly scattered by the cornea, and produces a veiling luminance over the entire visual field. When the task is comparatively dark, and other areas of the visual field (such as windows) comparatively bright, the veiling luminance can be so large that the contrast and therefore the visibility of the task is reduced. This also relates to reflected images in TV or computer screens that prevent you from seeing the screen properly.

Efficacy: The ratio of the radiant flux emitted by a lamp compared to the power it consumes. Measured in lumens per Watt.

Fill light: The effect to counteract or soften strong shadows on an object discreetly without being consciously perceived by the observer. The fill light supplements the key or main light.

Fluorescent dimming: The variable adjustment of the light output of the lamp. Generally these lamps are run on electronic control gear and can be controlled in a number of ways.

Fluorescent: Fluorescence is a process by which the phosphor coating of the lamp is excited by means of UV radiation. This produces light in the visible part of the spectrum. The wavelength of the light emitted is always greater than the wavelength of the radiation used to excite the phosphor.

Flux: The total energy field generated by light source.

Glare: Collective term for the reduced ability to see, or the disruption of perception, by the intensity or contrasts in luminance in a visual environment. Physiological glare is a subjective reduction in visual performance. Whereas psychological glare is a subjective reduction in perception caused by disparity between light intensity and the information content of the area perceived. Glare can be caused by the light source itself (direct glare) or by its reflection (reflected glare).

GLS (General Service Lamp) / standard incandescent light bulb: This is the bulb that most of us grew with.  Light is created inside the bulb by heating a tungsten filament. The filament is contained in a glass bulb filled with an inert gas (nitrogen or rare gas), which prevents it from oxidising, and delays the vaporisation of the filament material. Incandescent lamps are available in many forms; the most common are GLS bulbs, commonly with pear shaped, clear or matt bulbs, R lamps with a variety of inner reflective coatings, and PAR lamps made of moulded glass with integral parabolic reflector.

Halogen lamp: The halogen lamp takes its name from the halogens included in the gas within its quartz bulb. The filament is made of tungsten hence the use of the term tungsten halogen. The halogen gas prolongs filament life and allows increased heat and subsequently light output.

Horizontal illumination: A measure of falling light on a horizontal surface.

Illuminance: A measure of visible light incident on a surface. Defined as the number of lumens falling per unit area (1 lumen/m2 = 1 lux), and measured in lux. Illuminance may be measured horizontally, vertically, or at any intermediate angle according to the task or object to be lit. Illuminance may be measured as a point value, or may be averaged over a surface.

Illumination: The process of lighting.

Indirect lighting: Illumination of a point or surface where the light arrives after reflecting from a surface onto the area being lit, for example, lighting a desk using an uplight.

Lamp life: Rated life of the lamp. For incandescent lamps, this is the time before a percentage of the lamp fail. For discharge lamps and LEDs, it's the time before the luminous flux from the lighting installation is reduced by failed lamps and reduced luminous flux.

Light output ratio: The total light output of a luminaire, divided by the number of lumens, which originally left the lamp. The result is the dimensionless quantity expressing the efficiency of the luminaire.

Luminance: A term given to the brightness of a surface that emits light, either as a light source or by transmission or reflection. Luminance is defined as the relation of luminous intensity to the surface projected vertically to the direction of observation. Different coloured surfaces with the same luminance are equally bright. Unit: Candela/m2 (cd/m2). Equally different coloured surfaces with the same illuminance will differ in luminance.

Quality CFL: A CFL that meets the requirements of AS/NZS 4847.2(INT):2008 that specifies minimum energy performance standards requirements for self-ballasted lamps sold in New Zealand and Australia for general lighting services. These standards include the requirement for the CFL to have a minimum rated life of at least 6000 hours and 3000 switching cycles and also includes a requirement to meet Standards AS/NZS60968:2001 and AS/NZS60969:2001 that cover safety and performance requirements respectively. 

Reflection: The ability of surfaces to reflect light; the ratio of the luminous flux reflected to the luminous flux incident on it. Reflection can be specular or diffuse.

Scene options: A number of scenes or moods created by the composition of the various dimming circuits in a space.

Soften: To scatter the light rays in various directions. This allows light to ease into areas, which would otherwise remain underexposed (dark) if directional light is the primary source. In effect, it reduces the impact of highlight areas while filling the shadow areas.

Specular surface: A surface that reflects light like a mirror. Specular surfaces can have very high reflectance, and produce reflected images of the light source.

Spot lighting: Light fittings with light distribution that can be directed at any desired point by turning and swivelling. Normally spotlights have narrow to medium beams; used mainly with track.

Standby scene: A scene created with the minimum amount of light to perceive and negotiate the space.

Uplight: Pendant luminaires (light fittings), wall luminaires, floor luminaires or freestanding luminaires that generally emit their light towards the ceiling. Also see indirect lighting.

Vertical illumination: A measurement of the visible light incident on a vertical surface.

Visual comfort: Conditions conducive to productivity in the workplace. Historically, the aim of lighting was to provide sufficiently bright conditions to allow error-free work; lighting design was motivated by visual performance. During the 1980s the wellbeing of workers (visual comfort) emerged as the primary aim of workplace lighting. Generally, comfort can be achieved by the use of well-controlled direct light distribution, indirect lighting, varying conditions (active lighting) and the control of reflections in screens etc.

Wall washing: Luminaires with a special reflector system or reflecting lens system for uniform lighting of walls; it is essential that they are spaced equally and parallel to the wall.

Wattage: Power requirement of the lighting device (lamp, gear control).  Wattage refers to the electricity consumed – not the light output.