Accent Lighting:
Directional lighting used to accent, emphasize or draw attention to a part of the landscape.
Ambient Lighting:
Lighting throughout an environment that produces general illumination.
Amperage (AMP):
Unit used to measure strength of electrical current.
Arc Discharge:
An electrical discharge characterized by high cathode current densities and a low voltage drop at the cathode.
Area Lighting:
The lighting of large landscape areas, usually with floodlights.
Average Luminance (of a luminaire):
The luminous intensity at a given angle divided by the projected area of the luminaire at that angle.
Axis:
The primary line of sight through a landscape design.
Background Lighting:
Lighting of walls, trees and other vertical elements to form an illuminated background for other lighting techniques.
Backlight:
Illumination from behind a subject directed substantially parallel to a vertical plane through the optical axis of the design.
Ballast:
Electrical device used with H.I.D. lamps to provide power to start the lamp and regulate the flow of electricity while it is operating.
Ballast-Factor:
The fractional loss of task illuminance due to use of a ballast other than the standard one.
Base, Lamp:
That part of the lamp (light bulb) that fits into the lamp holder (socket).
Beam Spread (in any plane):
The angle between the two directions in the plane in which the intensity is equal to a stated percentage of the maximum beam intensity. The percentage typically is 10% for floodlights and 50% for photographic lights.
Brightness:
see Illuminance.
Candela (CD):
The unit of measurement of luminous intensity of a light source in a given direction.
Candlepower:
Luminous intensity expressed in standard candles (candelas).
Candlepower (intensity) Distribution Curve:
A curve, generally polar, representing the variation of luminous intensity of a lamp or luminaire in a plane through the light center.
Capacitor:
A device consisting of two electrodes (metal or metalized surfaces) separated by a dielectric (insulator) to store electrical energy. Capacitors both “correct” the power factor of a ballast from normal to high, and in some ballast circuits work with the core-and-coil to set the operating wattage of the lamp. Capacitors today incorporate two interleaved layers of metalized poly film wound in a compact roll and then assembled into a plastic or metal housing. Depending on the capacitor’s construction, the roll is left dry or immersed in oil as a finishing process.
Color:
The characteristics of light by which a human observer may distinguish between two structure-free patches of light of the same size and shape.
Color Comparison or Color Grading (CIE, object color inspection):
The judgment of equality, or of the amount and character of difference, of the color of two objects viewed under identical illumination.
Color Discrimination:
The perception of differences between two or more colors.
Color Rendering:
The effect of a light source on the perceived color appearance of objects.
Color Rendering Index (CRI):
Measure of the degree of color shift objects undergo when illuminated by a light source as compared to the color of the same object when illuminated by a reference source of comparable color temperature. The higher the CRI, the more “true” the color rendition.
Color Temperature:
A measure of light source “whiteness,” expressed in degrees Kelvin, to indicate the warmth (toward yellow) or coolness (toward blue) of the light. Warmer light has a lower color temperature and cooler light has a higher color temperature.
Color Temperature of a Light Source:
The absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source.
Core:
Component of electromagnetic ballast or transformer that is surrounded by the coil. Core is comprised of steel laminations or solid ferrite material.
Core and Coil Ballast:
Another term for an electromagnetic ballast.
Cross Lighting:
Illumination of an area or object from two or more points to create softer shadows and/or a more pleasing effect for all-around viewing.
Directional Lighting:
Lighting provided on the work plane or on an object predominantly from preferred direction.
Direct Lighting:
Lighting by luminaries distributing 90 to 100% of the emitted light in the general direction of the surface to be illuminated. The term usually refers to light emitted in downward direction.
Distribution Temperature (of a light source):
The absolute temperature of a blackbody which has a relative special distribution that is the same (or nearly so) in the visible region of the spectrum as that of the light source.
Downlighting:
Lighting of an area, object or surface from above.
Efficacy:
A measure of a lamp’s performance to determine how much light (in lumens) is produced for each watt of electricity supplied.
Fill Lighting:
Soft lighting of background or adjacent areas to provide contrast to other lighting techniques.
Floodlighting:
The lighting of large areas or objects to a level of illumination greater than the surroundings usually for utilitarian purposes.
Fluorescence:
The emission of light (luminescence) as the result of, and only during, the absorption of light energy of other (mostly shorter) wavelengths.
Fluorescent Lamp:
A low pressure mercury, electric discharge lamp in which a fluorescing coating (phosphor) transforms some of the ultraviolet energy generated by the discharge into light.
Flush Mounted or Recessed:
A luminaire which is mounted above the ceiling (or behind a wall or other surface) with the opening of the luminaire level with the surface.
Footcandle (FC):
A unit of measurement of illuminance, the amount of light striking a surface. One footcandle is the illumination falling on a surface of one square foot from a standard candle located one foot away.
Footlambert (fL):
A unit of luminance equal to 1/p candela per square foot, to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square foot, or to the average luminance of any surface emitting or reflecting light at that rate. NOTE: The average luminance of any reflecting surface in footlamberts is, therefore, the product of the illumination in footcandles and the luminous reflectance of the surface.
General Lighting:
Lighting designed to provide a substantially uniform level of illumination throughout an area, exclusive of any provision for special local requirements.
General Purpose Floodlight (GPF):
A weatherproof unit constructed in such a way that the housing forms the reflecting surface. The assembly is enclosed by a glass cover.
Frequency:
Rate of alteration in an AC current. Expressed in cycles per second or Hertz (Hz).
Glare:
Bright light that distracts the viewer and /or interferes with seeing all elements in an environment in a comfortable manner.
Grade-Mounted:
A luminaire which is normally recessed in the soil or installed in the hardscape so the top surface is flush with the surrounding surfaces.
Grazing Light:
Lighting from an angle that accentuates the texture or surface dimension of walls, paving stones or architectural detail.
Halogen Lamp:
See Tungsten-Halogen Lamp.
High Intensity Discharge (H.I.D.) Lamp:
A lamp that produces light when electricity excites specific gases within a pressurized bulb. H.I.D. lamps include mercury vapor, metal halide and high pressure sodium types, and each requires special fixtures and ballasts.
High Pressure Sodium Lamp:
An H.I.D. lamp that illuminates by radiation from sodium vapor, producing a distinctly yellowish color rendering. Available in clear or coated types.
Illuminance:
The amount of light striking a surface or object measured in footcandles.
Illuminance (lux or footcandle) Meter:
An instrument for measuring illuminance on a plane. Instruments which accurately respond to more than one spectral distribution are color corrected. Instruments which accurately respond to more than one spatial distribution of incident flux are cosine corrected; for example, the response to a source of unit luminous intensity, illuminating the detector from a fixed distance.
Illumination:
The act of illuminating or the state of being illuminated. Often confused with “illuminance.”
Incandescent Lamp:
A lamp that produces light when electricity heats a metal filament to incandescence.
Indirect Lighting:
Lighting by luminaries distributing 90 to 100% of the emitted light upward.
Input Voltage:
The voltage from the incoming power line to the ballast or fixture.
Isocandela Line:
A line plotted on any appropriate set of coordinates to show directions in space, about a source of light, in which the intensity is the same. A series of such curves, usually for equal increments of intensity, is called an isocandela diagram.
Isofootcandle (isolux) Line:
A line plotted on any appropriate set of coordinates to show all the points on a surface where the illuminance is the same. A series of lines for various illuminance values is known as an isofootcandle (or isolux) diagram.
Isolux (isofootcandle) Line:
A line plotted on any appropriate set of coordinates to show all the points on a surface where the illuminance is the same. A series of such lines for various illuminance values is called an isolux (isofootcandle) diagram.
Lamp:
A generic term for a man-made source of light. The lighting industry term for lightbulb. It refers to the complete assembly including the internal parts as well as the outer bulb or tube and base(s).
Lamp Current:
The current delivered to the lamp by the ballast to generate light.
Lamp Watts:
The power consumed by the lamp to generate light.
(LED) Light Emitting Diode:
A semiconductor device that emits incoherent narrow-spectrum light when electrically biased in the forward direction. An LED is a diode that is chip-mounted in a reflector cup and held in place by a milled steel frames connected to a pair of electrical wires. When current flows across the junction of the two different materials, light is produced from within the solid crystal chip.
[Average Rated] Life:
The median time it takes for a lamp to burn out. For example, a typical incandescent lamp is expected, on average, to burn for 1,000 hours. Based upon continuous testing of lamps in laboratories, the 1,000-hour rating is that point when 50% of the test samples have burned out and 50% are still burning. Unless otherwise noted, fluorescent (linear and compact) rated life assumes three (3) hours average operating time per start, H.I.D. rated life assumes ten (10) hours average operating time per start.
Lighting System:
The complete system of fixtures, lamps, wiring switches and power source to supply light to an environment. Auxiliary equipment can include transformers, photocells and accessories.
Light Output:
The amount of light emitted by a lamp, measured in lumens.
Light Center (of a lamp):
The center of the smallest sphere that would completely contain the light-emitting element of the lamp.
Light Center Length (of a lamp):
The distance from the light center to a specified reference point on the lamp.
Lighting Effectiveness Factor (LEFv):
The equivalent sphere illumination to ordinary measured or calculated illumination.
Light Loss Factor (LLF):
A factor used in calculating illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation on luminaire and room surfaces, lamp depreciation, maintenance procedures, and atmosphere conditions. Formerly called maintenance factor.
Low-voltage Lighting System:
A lighting system that operates on 12-volt current instead of the standard 120 volts or higher.
Lumen:
The unit of measurement for the amount of light emitted by a lamp. One lumen per square foot is one footcandle.
[Initial] Lumens:
Initial light output of a new lamp. For H.I.D. lamps the initial lumen rating is based on the light output of the lamp after it has been seasoned (burned or “aged”) for 100 hours.
[Mean] Lumens:
Lamp light output (lumens) measured at 40% of rated lamp life for fluorescent, compact fluorescent and metal halide lamps, and 50% of rated life for mercury and HPS lamps.
Luminaire:
A complete lighting unit, consisting of a housing to position and protect the lamp, and parts to connect the lamp to the power supply.
Luminaire Efficiency:
The ratio of luminous flux (lumens) emitted by a luminaire to that emitted by the lamp or lamps used therein.
Luminance:
The degree of apparent lightness of a surface: its brilliancy. Luminance is measured in footlamberts or candelas.
Mercury Vapor Lamp:
An H.I.D. lamp that produces light by radiation from mercury vapor, when supplied with electricity. Available in clear or phosphor-coated types, mercury lamps have a distinct blue-green color rendering that complements most foliage.
Metal Halide Lamps:
An H.I.D. lamp that produces light by radiation from certain metallic vapors. Known for producing accurate color rendition, metal halide lamps are available in clear or phosphor-coated types.
Mirror Lighting:
Lighting that utilizes water (from a pond, pool, etc.) to serve as a reflecting surface for landscape and architectural elements.
PAR Lamp:
Parabolic aluminized reflector lamp, a type of lamp suitable for exposed outdoor applications.
Quartz Lamp:
See Tungsten-Halogen Lamp.
Quality of Lighting:
Characteristics of the illumination of an environment that contribute favorably to visual performance, visual comfort, ease of seeing, safety and aesthetics.
R Lamp:
Reflector lamp.
Reflectance:
A measure of the amount of light that strikes a surface and is reflected. Higher reflectance occurs with lighter-colored objects or surfaces.
Reflection:
A general term for the process by which the incident flux leaves a surface or medium from the incident side, without change in frequency. NOTE: Reflection is usually a combination of regular and diffuse reflection.
Reflector:
A device used to redirect light from a lamp by the process of reflection.
Security Lighting:
Lighting to protect people and property from criminal activity. When properly employed, security lighting eliminates shadows near buildings and provides even landscape illumination for pedestrian safety.
Shadowing:
Lighting that projects shadows of foliage on a wall or other vertical surface.
Spacing:
For roadway lighting, the distance between successive lighting units, measured along the center line of the street.
Tungsten-Halogen Lamp:
A type of incandescent lamp containing a tungsten filament within a pressurized fused-quartz bulb filled with halogen gas. Also referred to as quartz or halogen lamp. Generally smaller, higher in output, with more neutral color rendering and longer lamp life than incandescent lamps of the same wattage.
Transformer:
A device used to convert 120-volt current into 12-volt current for low-voltage lighting systems.
Uplighting:
Lighting of an object or surface from below.
Voltage:
A measurement of the electromotive force (electrical pressure) in an electrical circuit or device expressed in volts. Voltage can be thought of as being analogous to the pressure in a waterline.
Voltage to Luminaire Factor:
The fractional loss of task illuminance due to improper voltage at the luminaire.
Watt:
The unit of measurement of electrical power. Electrical power is the product of the voltage to a device: ballast, lamp, lighting fixture, etc., times the current through that device, times the power factor of that device. |