| Absorption |
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| The dissipation of light within a surface or medium. |
| Accent Lighting |
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| Directional lighting to emphasize a particular object or draw attention to a part of the field of view. |
| Accommodation |
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| The process by which the eye changes focus, from one distance to another. |
| Adaptation |
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| The process by which the visual system becomes accustomed to more or less light than it was exposed to during an immediately preceding period. It results in a change in the sensitivity of the eye to light.8 |
| Alternating Current |
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| Flow of electricity which cycles alternates direction many times per second. The number of cycles per second is referred to as frequency. Most common frequency used in this country today is 60 Hertz (cycles per second). |
| Alzak |
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| A finish produced by electro-chemically brightening and anodizing a special high purity aluminium alloy. It is used to provide reflectors with a high permanent reflectivity as well as corrosion and abrasion resistance. Alzak is a registered trademark of the Aluminium Company of America. |
| Ambient Lighting |
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| Background or fill light in a space. |
| Ampere (Amp) |
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| The unit for measuring electric current. It defines the rate of flow or quantity of electricity. The ampere rating gives the requirement for the satisfactory operation of an electrical device. |
| Baffle |
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| An opaque shield of metal, wood, or plastic used to shield the view of a light source. |
| Ballast |
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| An auxiliary device consisting of starter and induction windings and sometimes a capacitor for power correction. It is used in fluorescent and HID luminaries to provide the necessary starting voltage and to limit the current during operation. (see also “Power Factor”). Dimmer ballasts are special ballasts which have used together with a dimmer control (supplied by others) will vary the light output of a lamp. |
| Ballast Factor |
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| The measured ability of a ballast to produce light from the lamp(s) it powers. Ballast Factor is derived by dividing the lumen output of a particular lamp/ ballast combination by the lumen output of the same lamp(s) on a reference ballast. |
| Ballast Loss |
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| Power consumed by a ballast that dissipates as heat instead of being converted into light. Electronic ballast operate more efficiently than magnetic or hybrid ballasts. I typical ballast loss for a standard two lamp magnetic ballast is 20 watts, where an electronic equivalent would only be 7 watts. |
| Batwing Distribution |
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| Candlepower and distribution which serves to reduce glare and veiling reflections by having its maximum output in the 30° to 60° zone. |
| Blown Glass |
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| Glass formed by exerting outward pressure on the inside of a mass of molten glass at the end of a blow pipe, this forcing the glass into contact with a metal mold. Hand tools are sometimes used to form the glass before or after it comes out of the mold. |
| Borosilicate Glass |
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| A glass with high resistance to thermal shock often used where concentrated high temperatures are encountered and for outdoor applications |
| Branch Circuits |
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| That part of the building wiring system to which a luminaire is connected for electrical power supply. |
| Brightness (Luminance) |
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| The degree of apparent lightness of a surface; its brilliancy; concentration of candlepower. Brightness is produced by either a self-luminous object, by light energy transmitted through objects, or by reflection. Unit of measurement of brightness is a footlambert (f1). |
| Candela |
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| The unit of measurement of luminous intensity of a light source in a given direction. |
| Candlepower |
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| Luminous intensity expresses in candelas. |
| Candlepower Distribution Curve |
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| A graphic presentation of the distribution of light intensity in a given plane of a lamp or luminaire. It is determined by photometric tests. |
| Canopy |
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| A covering, usually metal or wood, used to conceal that junction box and wiring at the ceiling line. |
| Capacitor |
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| An electric energy storage which when built into or wired to a ballast changes it from low to high power factor. It decreases the current required per ballast, permitting more fixtures to be installed on a given electrical circuit. (See also Power Factor). |
| Cavity Ratio |
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| A number indicating cavity proportions calculated from length, width and height. |
| Centre Beam Candle Power (CBCP) |
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| The intensity of light produced at the center of a reflector lamp beam, expressed in candelas. |
| Circuit |
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| The closed path of an electric current including the electric source, the wiring and the electric load. |
| Class "P" Ballast |
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| Contains a thermal protective device which deactivates the ballast when the case reaches a certain critical temperature. The device resets automatically when the case temperature drops to a lower temperature. |
| Coefficient of Utilization (CU) |
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| The ratio of the luminous flux (lumens) from a luminaire calculated as received on the work-plane to the luminous flux emitted by the luminaires lamps alone. |
| Color Rendering Index (CRI) |
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| Measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same objects when illuminated by a reference source of comparable color temperature. |
| Color Temperature |
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| The absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source |
| Conduit |
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| Tube or pipe, often used in an enclosure to protect electrical wires. |
| Contrast |
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| Generally used to refer to Task Contrast. The difference between the luminance (brightness) of the detail in a visual task and the luminance of its immediate background (e.g between the print and the paper). |
| Convenience Outlet |
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| Electrical outlet provided on some fixtures (e.g. bathroom lighting) for plugging in an electric shaver or other electrical device. A grounded convenience outlet accommodates 3-prong cord plugs. |
| Cool Beam Lamps |
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| Incandescent PAR lamps that use a special coating (dichroic interference filter) on the reflectorized potion of the bulb to allow heat to pass out the back while reflecting only visible energy to the task, thereby providing a "cool beam" of light. |
| Cornice Lighting |
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| A system comprising light sources shielded by a panel parallel to the wall and attached to the ceiling and distributing light over the wall; down light only. |
| Cover Lighting |
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| A system comprising light sources shielded by a ledge or horizontal recess, and distributing light over the ceiling and upper wall; up light only. |
| Cut-off Angle |
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| The angle from the vertical at which a reflector, louver, or other shielding devices cuts off direct visibility of a light source. It is the complementary angle of the shielding angle. |
| Cut-off Luminaires |
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| Outdoor luminaires that restrict all light output to below 85° from vertical. |
| Diffuser |
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| A translucent glass or plastic that shields the light source and spreads light evenly in all directions. |
| Diffusion |
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| The scattering of light rays so that they are emitted or reflected from all directions. Light that comes from a larger source of uniform brightness is more diffused because it is coming from more directions. |
| Dimming Ballasts |
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| See ballast. |
| Direct Current (DC) |
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| Flow of electricity continuously in one direction from positive to negative. Rarely used in today’s lighting circuits. |
| Discharge Lamp |
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| A lamp in which light (or radiant energy near the visible spectrum) is produced by the passage of an electric current through a vapor or a gas. |
| Distribution of light |
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| Luminaries may be classified according to the percentage of light emitted above and below the horizontal.
Classifications include the following:
1. Direct: 0 to 10% up’ 90 to 100% down.
2. Semi-direct: 10 to 40% up; 60 to 90% down.
3. General diffuse: 40 to 60% up; 40 to 60% down.
4. Semi-indirect: 60 to 90% up; 10 to 40% down.
5. Indirect: 90 to 100% up; 0 to 10% down.
Distribution of light may also be defined in terms of angular array or distribution of the individual rays:
• Directional – If all rays of light are aligned essentially parallel with each other, a definite beam is determined and a directional distribution of light is obtained.
• Spread - Actually all light distributions fall between two idealized limits of directional and diffuse. Those of high directional quality are those characterized by the beams from automobile headlights, floodlighting projectors, and high=bay industrial units. Distribution of a more diffused character are those from indirect lighting systems. Between these idealized and practical limits are the spread types of distribution. There are no sharp lines of demarcation between directionally, spread and diffuse classifications.
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| Efficacy |
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| The rate at which a lamp is able to convert power (watts) into light (lumens), expressed in lumens per watt (LPW). |
| Efficiency |
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| The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein. |
| Ellipsoidal Reflector |
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| A reflector shaped, in cross section, like an ellipse. The reflected rays of light from a light source at one focal point will converge at the other focal point, making it possible to send a large amount of light through a small opening. |
| ER (Elliptical Reflector) |
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| Lamp whose reflector focuses t |