| 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 the light about 2" ahead of the bulb, reducing light loss when used in deep baffle downlights. |
| Fill Light |
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| Illumination added to reduce shadows or contrast range. |
| Fixture |
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| Luminaries, as distinguished from a portable lamp, in that it is permanently wired into the building wiring system. |
| Flange |
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| Overlapping metal portion of a recessed luminaires at the ceiling line. It serves to cover the ceiling opening around the luminaries. |
| Floodlighting |
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| A system designed for lighting a scene or object to a luminance greater than its surroundings. It may be for utility, advertising or decorative purpose |
| Fluorescent Lamp |
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| A low-pressure mercury electric-discharge lamp in which a phosphor coating transforms some of the ultraviolet energy generated by the discharge into light |
| Footcandle (fc) |
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| The unit of measurement of the illumination of a surface. One footcandle is equal to one lumen per square foot. It is the illumination produced by a standard candle at a distance of one foot. |
| Footlambert (fl) |
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| The unit of measurement of brightness. A footlambert equals a candela per square feet. The brightness of a reflecting surface in the footlamberts is equal to the incident illumination in footcandles times the reflectance of the surface. |
| Frequency |
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| See Alternating Current. |
| Fuse |
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| A metal line of low melting point which melts when the current exceeds the prescribed limit. When placed in an electrical circuit, it will prevent fire and damage to electrical equipment on the circuit under abnormal operating conditions such as excessive voltage or short circuits. |
| Glare |
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| Brightness or brightness contrast which causes annoyance, discomfort, or reduced seeing efficiency.
Direct Glare - Glare resulting from high brightness or insufficiently shielded light sources in field of view.
Reflected glare - Glare resulting from specular reflections of high brightness sources in polished surfaces in the field of view.
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| High Intensity Discharge (HID) Lamp |
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| A discharge lamp in which the light producing arc is stabilized by wall temperature, and the arc tube has a bulb wall loading in excess of three watts per square centimeter. HID lamps include groups of lamps known as mercury, metal halide, and high pressure sodium |
| High Output Fluorescent Lamp |
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| Operates at 800 or more milliamperes for higher light output than standard fluorescent lamp (430MA). |
| High Power Factor (H.P.F.) |
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| See power factor. |
| Housing |
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| The metal body of a luminaire.
A metal socket cover – usually on portable lamp
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| Hydroforming |
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| A method of forming sheet metal in which the metal is placed on a flexible rubber diaphragm which is supported by oil under pressure. The metal is formed around a male punch as the diaphragm is raised. The resultant part is generally of uniform thickness and quite strong. |
| Icetron |
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| A lamp by Osram which is an inductively coupled electrodeless lamp using magnetic induction technology instead of an electrode at each end of the fluorescent tube to generate light. The absence of electrodes allows much longer lamp life. |
| Instant Start Fluorescent Lamp |
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| A fluorescent lamp designed for starting by a high voltage without preheating of the electrodes. |
| Inverse Square Law |
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| The law stating that the illuminance at a point on a surface varies directly with the intensity of a point source, and inversely as the square of the distance between the source and the point. If the surface at the point is normal to the direction of the incident light, the law is expressed by fc=cp/d2. |
| Junction box |
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| A metal housing, commonly 3” or 4” square or octagonal with removable cover. Building wire is brought into the junction box so that splices can be made leading to other points in the circuit or to the lighting fixtures. Also used frequently to support a lighting fixture from ceiling (up to 50 lbs). |
| Kelvin |
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| Unit of measurement for color temperature. The Kelvin scale starts from absolute zero, which is -273° Celsius |
| Kilowatt |
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| Unit of electrical power consumed over a period of time. KWH = watts/1000 x hours used.
1000 watts (see watt)
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| Kilowatt-hour (KWH) |
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| A unit for measuring the consumption of electrical energy. Electric power is sold by the “kilowatt-hour” (KWH). |
| Knockout |
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| A portion of a metal enclosure which has been partially cut out be remains in place. It can be easily removed to permit an electrician to attach switches, convenience outlets, conduit connectors, etc. Often referred as a KO. |
| Lamp |
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| An artificial source of light. also a portable luminaries equipped with cord and plug. lamps are divided into the following major classifications:
• Incandescent Lamp (also know as a Filament Lamp or “bulb”) to incandescence by the flow of electric current through it. The filament is usually of tungsten wire and operates in the range for 4000 degrees F. Incandescent lamps come in many sizes, wattages and shapes, in clear, frosted or white coated bulbs, and are available in many special types for particular applications such as reflectorized lamps (R and PAR types), or solved bowl lamps (SB).
• The tungsten-halogen lamp is a special type of incandescent lamp that has its filament in a quartz enclosure which is filled with halogen gas. Due to the regenerative cycle the evaporated tungsten is removed from the bulb wall and redeposit on the filament. As a result lamp blackening is eliminated and lamp life is roughly doubled compared to standard incandescent lamps.
• Fluorescent Lamp - A lamp generally in tubular form in which light is produced by the excitation of phosphors which emit light (fluoresce) when subjected to ultra-violet radiation. The ultra-violet radiation results from an electric discharge, i.e. the flow of current through a metallic vapour or gas (usually a combination of mercury and argon). The phosphors form a coating on the inside of the fluorescent tube, surrounding the electric discharge within. Fluorescent lamps come in varying colours, diameters, lengths and wattages in are made for various starting and ballasting systems.
• High Intensity Discharge (HID) Lamp - A lamp usually in a bulb shape in which light is produced by the flow of electric current (electric discharge) through vaporized metal, exciting it and causing it to give off light. Three types of HID lamps are available: mercury, metal halide and high-pressure sodium. In the current types of HID lamps the bulb wall is coated with a phosphor to improve the colour characteristics.
• LED – Light Emitting Diode – Compound semiconductors that convert electric current directly to light. LED is a very small light source ( less than 1mm Sq), usually with optics added to shape the radiation pattern and assist in reflection. The colour of the emitted light depends on the composition of semi-conducting material used.
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| Lamp Efficacy |
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| The ratio of lumens produced by a lamp to the watts consumed. Expressed as lumens per watt (LPW |
| Lamp Lumen Depreciation (LLD) |
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| Multiplier factor in illumination calculations for reduction in the light output of a lamp over a period of time |
| Lens |
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| A glass or plastic element used in incandescent and fluorescent luminaries to change the direction of and control the distribution of light rays. A fresnel lens, commonly used with incandescent luminaries, has concentric rings, each of prism section. |
| Louver |
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| A series of vertical baffles designed to cut off light traveling in undesirable directions. |
| Low Voltage Lamps |
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| Incandescent lamps that operate at 6 to 12 volts |
| Lower power factor (L.P.F.) |
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| See power factor |
| Lumen (lm) |
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| The unit of luminous flux; a measure of light output; equal to the flux emitted through a unit solid angle (one steradian) from a uniform point source one candle. |
| Luminaire |
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| A complete lighting unit comprising bare lamp and means of controlling, its light output; a lighting fixture, wall bracket, portable lamp. |
| Luminaire Direct Depreciation (LDD) |
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| The multiplier to be used in illuminance provided by clean, new luminaires to the reduced illuminance that they will provide due to direct collection on the luminaires at the time at which it is anticipated that cleaning procedures will be instituted. |
| Luminaire Efficiency |
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| Total lumen output of luminaries, (as determined by photometric tests) divided by the total lumen output of bare lamps, expressed in percent. |
| Luminaire Spacing Criteria |
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| A classification parameter for indoor luminaries relating to the distribution of the direct illuminance component produced on the work plane |
| Luminance |
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| The amount of light reflected or transmitted by an object. |
| Luminous Panel |
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| Technically, any plane of brightness; usually a translucent glass or plastic sheet used to diffuse light from an array of lamps. |
| Lux |
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| The metric unit of illuminance. One lux is one lumen per square meter (lm/m2). |
| Maintenance Factor |
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| A numerical value which provides a depreciation allowance for design purposes, relating the initial illumination to the illumination at the time at which it is anticipated that maintenance procedures will be instituted. |
| Matte Surface |
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| A non-glossy dull surface, as opposed to a shiny (specular)surface. Light reflected from a matte surface is diffused. |
| Metal Halide Lamp |
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| A high intensity discharge (HID) lamp in which the major portion of the light is produced by radiation of metal halides and their products of dissociation-possible in combination with metallic vapors such as mercury. Includes clear and phosphor coated lamps |
| Nadir |
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| Vertically downward directly below the luminaire or lamp; designated as 0° |
| PAR Lamps |
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| Parabolic aluminized reflector lamps which offer excellent beam control, come in a variety of beam patterns from very narrow spot to wide flood and can be used outdoors unprotected because they are made of "hard" glass that can withstand adverse weather. |
| Parabolic Reflector |
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| A reflector shaped, in cross-section, like a parabola. A small light source at the focal point of the parabola produces an essentially parallel ray beam.
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| Photometry |
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| The measurement of light quantities. |
| Plaster Frame |
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| A metal frame attached to the lathing or furring in a plaster ceiling to support a recessed luminaire to provide a definite stop for the plasterer to work to. Normally the luminaire trim overlaps the plaster frame. |
| Point Method Lighting Calculation |
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| A lighting design procedure for predetermining the illuminance, at various locations in lighting installations, by use of luminaire photometric data. |
| Power Factor ratio of watts / volts x amperes. |
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| P.F. is primarily applicable to ballasts. Since volts and watts are usually fixed, amperes (or current) will go up as power factor goes down. This necessitates the use of larger wire sizes to carry the increased amount of current needed with Lower Power Factor (L.P.F.) ballasts. The internal addition of a capacitor to a L.P.F. ballast converts into a H.P.F. ballast. |
| Programmed Rapid Start (PS) |
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| A method of starting fluorescent lamps where the cathode heat is applied prior to lamp ignition, then removed or reduced once the lamp has ignited. |
| R" Lamps |
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| Reflectorized lamps available in spot (clear face) and flood (frosted face). |
| Rapid Start |
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| Type of fluorescent ballast circuit not using a separate starter, which permits a rapid start fluorescent lamp to start almost instantaneously. Used on 30W and 40W lamps. Requires use of lamps marked “RAPID START” or “PRE-HEAT REAPID START”. This is the most popular type of fluorescent circuit. |
| Recessed Luminaire |
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| A luminaire installed complete above the ceiling line so that only the shielding element (and trim flanges) are visible. |
| Reflectance |
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| Sometimes called reflectance factor. The ratio of incident light (light falling on a surface) to reflected light (see reflection). Reflectance is generally expressed in percent. |
| Reflected Glare |
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| Glare resulting from specular reflections of high luminances in polished or glossy surfaces in the field of view. It usually is associated with reflections from within a visual task or areas in close proximity to the region being viewed. |
| Reflection |
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| Light bouncing off a surface. In specular reflection the light strikes and leaves a surface at the same angle. Diffuse reflected light leaves a surface in all directions |
| Reflector |
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| A surface which redirects the light striking it. |
| Refraction |
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| The change of direction a ray of light undergoes in passing obliquely from one medium to another in which its velocity is different. For example, light is refracted when it passes through a piece of glass at an oblique angle, also when it passes through water. |
| Refractor |
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| A device used to redirect the light from a light source. |
| Regressed Luminaire |
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| A luminaire mounted above the ceiling with its opening above the ceiling line. |
| Room Cavity Ration (RCR) |
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| A number indicating room cavity proportions calculated from length, width and height. |
| Rough Service Lamps |
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| Incandescent lamps designed with extra filament supports to withstand bumps, shocks and vibrations with some loss in lumen output. |
| Shielding |
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| A general term including all elements used to block, diffuse or redirect light rays. This includes baffles, louvers, shades, diffusers and lenses. Also “Light shield”. |
| Shielding Angle |
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| The angle from the horizontal at which a light source first becomes visible. It is the complementary angle of the cut-off angle. |
| Spacing Ratio |
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| The ratio of the distance, between fixtures, to the height above the work plane. The maximum spacing ratio for a particular fixture is determined from the candlepower distribution curve for that fixture and when multiple by the mounting height above the work plane, gives the maximum spacing of fixtures at which even illumination will be provided. |
| Spectral Energy Distribution (SED) Curves |
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| A plot of the level of energy at each wavelength of a light source |
| Spectral Power Distribution (SPD) |
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| The output of a light source can be characterized by its relative power at each wavelength. The output is measured and is placed on a graph which shows power vs. wavelength, which then shows which wavelengths a particular light source is stronger or weaker in possessing. |
| Specular Surface |
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| A shiny, highly polished surface which reflects light at an angle equal to that of the incident light. See reflection. |
| Task Lighting |
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| Lighting directed to a specific surface or area that provides illumination for visual tasks |
| Transformer |
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| A device to raise or lower electric voltage |
| Transmission |
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| The passage of light through a material. |
| Trim |
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| The outer frame of a recessed luminaire, which engages the ceiling. Lay-in trim lays over exposed ceiling runners. Fit-in trim butts up against ceiling tile or panels. Overlap trim extends past bottom edge of ceiling tile or ceiling opening (see “Flange”). |
| Troffer |
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| A recessed fluorescent luminaire (see “Recessed Luminaire”) generally designed to fit into modules of suspended mechanical ceilings. Many troffers are designed to be installed in continuous runs. |
| Tungsten-Halogen Lamp |
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| A gas filled tungsten incandescent lamp containing a certain proportion of halogens |
| Valance Lighting |
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| A system comprising light sources shielded by a panel parallel to the wall at the top of a window; both down and up light. |
| Veiling Reflections |
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| Regular reflections superimposed upon diffuse reflections from an object that partially or totally obscure the details to be seen by reducing the contrast. This is sometimes called reflected glare |
| Visual Comfort Probability (VCP) |
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| The rating of a lighting system expressed as a percent of people who, when viewing from the specified location and in a specified direction, will be expected to find it acceptable in terms of discomfort glare. |
| Visual Edge |
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| The line on a isolux chart which has a value equal to 10% of the maximum illumination |
| Visual Field |
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| The field of view that can be perceived when the head and eyes are kept fixed. |
| Volt (V) |
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| The unit for measuring electric potential. It defines the force or pressure of electricity which is required for satisfactory operation of an electrical devise. |
| Wall Wash Lighting |
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| Smooth even distribution of light over a wall |
| Watt (W) |
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| The unit for measuring electric power. It defines the power or energy consumed by an electrical device. The cost of operating an electrical device is determined by the watts it consumes times the hours or use. It is related to volts and amps by the following formula: Watts = Volts x Amps. |
| Watt (W) |
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| The unit for measuring electric power. It defies the power or energy consumed by an electrical device with it is in operation. The cost of operating an electrical device is determined by the watts it consumes times the hours of use. It is related to volts and amps by the following formula: watts – volts X amps. |
| Work Plane |
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| The plane at which work is done, and at which illumination is specified and measured. Unless otherwise indicated, this is assumed to be horizontal plane 20 inches above the floor. |
| Yoke |
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| A “U” shaped metal channel used to support a recessed luminaire. A yoke clamps to supporting structure of mechanical ceiling system or is fastened to plaster frame, and spans the opening where a recessed luminaire is to be installed.
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| Zonal Cavity Method Lighting Calculation |
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| A lighting design procedure used for predetermining the relation between the number and types of lamps or luminaires, the room |