BaffleAn opaque or translucent element to shield a light source from direct view. BrightnessThe strength of the sensation that results from the eye viewing the surfaces which the light comes from. Bulb or lampThe source of electric light. To be distinguished from the whole assembly (see luminaire). Candela (cd)Unit of luminous intensity. One candela is one lumen per steradian. Formerly called the candle. CIECommission Internationale de lEclairage. The International Commission on Illumination. Colour renderingThe effect of a light source on the colour appearance of objects in comparison with their colour appearance under a reference source at the same colour temperature. Cut-off angle of a luminaireThe angle measured between the line straight down and the line of sight at which all surfaces of high luminance (of lamps and of the luminaire) just cease to be visible. Cut-off LuminaireA luminaire that provides a cut-off (shielding) of the emitted light so that no light is emitted above the horizontal. This applies to all lateral angles around the luminaire. This kind of luminaire is often referred to as Full Cut Off (FCO) or Fully Shielded. Fully ShieldedSee definition for Cut-off Luminaire. If a luminaire is to be used which does not comply with this requirement then some form of permanent physical opaque material must be used to provide the cut-off requirement. This can be a cover or part of a building. Care must be taken to ensure that adjacent surfaces, especially if they are light coloured, are also shielded to prevent excessive reflected light from adding to unwanted sky glow or glare The shielding should be constructed to minimise emission in the 10 degrees below horizontal. 10 GlareIntense and blinding light. Never helps visibility. This is further described as either discomfort glare which, while causing discomfort, does not necessarily diminish visual performance, or disability glare which results in reduced visual performance and visibility. HID lampIn a discharge lamp, the emitted energy (light) is produced by the passage of an electric current through a gas. High-intensity discharge (HID) includes mercury, metal halide, and high pressure sodium lamps. Other discharge lamps are low pressure sodium and fluorescent. HIDHID Illuminance - horizontalThe density of luminous flux incident on a horizontal surface. The unit is lux (lumens/meter2). / Illuminance verticalThe density of luminous flux incident on a vertical surface. The unit is lux (lumens/metre). / IESNA - Illuminating Engineering Society of North AmericaThe US professional society of lighting engineers, including those from manufacturing companies and others professionally involved in lighting. It is the major standardising body for illuminating engineering in the US. IESNA formatOne of the recognised electronic formats used to store and present the photometric information which describes the light technical characteristics of luminaires. IESNA.ies Incandescent lampLight is produced by a filament heated to a high temperature by electric current. IntensityThe degree or amount of energy or light in a given direction(s). The unit is candela (cd). Light pollutionAny adverse effect of artificial light. Often used to denote urban sky glow, but also includes glare, light trespass, visual clutter, and other adverse effects of lighting. Light trespassLight falling where it is not wanted or needed. The terms Stray Light, Spill Light and Obtrusive Light can also be used to describe this. LumenThe unit of luminous flux which is the light emitted by a lamp. LuminaireThe complete lighting unit, including the lamp, the fixture, and other parts. LuminanceThe amount of light emitted in a given direction from a surface by the light source or by reflection from a surface. The unit is candela per square metre. LuxOne lumen per square metre. The unit of illuminance. Mounting heightThe height of the fixture or lamp above the ground. PhotometryThe quantitative measurement of light level and distribution. Strict International and National Standards apply to ensure accuracy. Photometric RequirementsPhotometric measurements for describing the light technical characteristics of a luminaire, so that they can be used to assess its performance and to enable accurate design calculations to be made. International Standards apply to ensure accurate presentation. Reflected LightNot all light which causes sky glow is emitted directly from the luminaire. Reflected light from surfaces illuminated by the luminaire can cause varying amounts of sky glow. Light colours reflect more light than darker colours. When floodlights aimed at a grazing angle illuminate a vertical surface which has a specular (shiny) finish (such as windows), up to 70 percent of the light reaching that surface can be directed into the night sky at an equivalent angle. 70% SpotlightA fixture or lamp designed to light only a small area. / SteradianLight radiates in a sphere from a single bulb or lamp unless it is modified by a luminaire or baffle. A steradian is the angle, measured at the centre of a sphere, which cuts off an area on the surface of the sphere, that is equal to a square with sides the same length as the radius of the sphere. Sky glowThe brightening of the night sky due to artificial lighting. VisibilityBeing perceived by the eye. Seeing effectively. The goal of night lighting.