Light Corporation glossary of lighting terms: fluorescent, industrial, high bay, lamps, ballasts, and more

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Ambient lighting
Lighting throughout an area that provides general illuminations.

Ballast
A device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current, and wave form) for starting and operating. See electronic ballast, magnetic ballast.

Batwing distribution
A symmetrical light distribution producing light pattern angles to the right and left of the observer with comparatively little direct downward illumination. The shape is thus similar to that of a batwing.

Batwing lens (linear prismatic)
A lens, usually of molded or extruded acrylic, consisting of a series of prisms that cause a batwing distribution of light.

Candela
The unit of measure indicating the luminous intensity (candlepower) of a light source in a specific direction; any given light source will have many different intensities, depending upon the direction considered.

Color rendering index (CRI)
A method for describing the effect of a light source on the color appearance of objects being illuminated, with a CRI of 100 representing the reference condition (and thus the maximum CRI possible). In general, a lower CRI indicates that some colors may appear unnatural when illuminated by the lamp.

Color temperature (chromaticity)
The degree of warmth or coolness of a light source, measured in degrees Kelvin (K). The higher the degree K, the more blue, or cooler the lamp appears. The lower the degree K, the more red, or warmer the lamp appears.

Compact fluorescent lamps
Small diameter tubes that are bent so they begin and end in a sing base. This allows them to be produced in a wide variety of configurations, greatly extending the applications for fluorescent lighting.

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).

Diffuser
A device to redirect or scatter the light from a source, primarily by the process or diffuse transmission.

Direct glare
Glare resulting from the excessive brightness or insufficiently shielded light sources in the field of view.

Electric-discharge lamp
A lamp in which light is produced by passing an electric current through a gas. These lamps may be named after the gas they contain, as in mercury lamps, sodium lamps, neon lamps; or they may be named for their operating parameters or dimensions, as in short arc lamps, high pressure lamps, etc.

Electronic ballast
A ballast that uses solid state electronic components and operates lamps (typically fluorescent) at frequencies in the range of 25-35 kHz. See ballast, magnetic ballast.

Emergency fluorescent ballast
A fixture that operates one or two lamps for a set period of time in the event of a power failure. Emergency ballasts are also used for normal, day to day operation.

Fluorescent lamp
A low pressure mercury, electric-discharge lamp in which phosphor coating transforms ultraviolet energy (created by electric discharge) into visible light.

Fixture
A complete lighting unit consisting of a lamp or lamps together with parts designed to distribute the light, to position and protect the lamps, and to connect the lamps to the power supply. Also called Luminaire.

Footcandle (fc)
A unit of measurement indicating how much illumination is reaching a surface. It is equal to one lumen striking an area of one square foot.

General lighting
Lighting designed to provide a substantially uniform level of illumination throughout an area, exclusive of any provision for special local requirements.

Glare
A sensation caused by light within the visual field that is brighter than the level of light to which the eyes are adapted, causing annoyance, discomfort or loss in visual performance.

Halogen lamps
High pressure tungsten filament lamps containing halogen gases. The halogen gases allow the filaments to operate at higher efficacies than incandescent lamps.

High bay lighting, high bay fixtures
Lighting designed for locations (typically industrial) with a ceiling height of 25 feet and above.

High-Intensity Discharge (HID) lamps
Lamps in which an arc passing between two electrodes in a pressurized tube causes various metallic additives to vaporize and release large amounts of light.

High-Pressure Sodium (HPS) lamps
High-intensity discharge light sources that produce light by an electrical discharge through sodium vapor operating at relatively high pressures and temperatures.

Illuminance
The amount of light that reaches a surface. Illuminance is measured in footcandles (lumens/square foot) or lux (lumens/square meter). One footcandle equals 10.76 lux, although for convenience the IESNA uses 10 lux as the equivalent.

Indirect lighting
Lighting by luminaires distributing 90 to 100 percent of the emitted light upward.

Instant start
A method of starting fluorescent lamps by applying high voltage, without heating the electrodes (as in rapid start systems). Higher starting voltage places greater stress on the electrodes, slightly shortening lamp life. However, the elimination of electrode heating reduces system energy consumption, which more than offsets the slightly shorter lamp life. See rapid start.

Intelligent lighting
Fluorescent high-bay lighting that is forward-thinking in its design, accommodating occupancy and daylight harvesting systems, security applications, and programmable control systems.

Lamp
A generic term for a man-made source of light.

Lamp flicker
Cyclic variation in output of a light source. High frequency electronic ballasts provide a minimal level of lamp flicker.

Lamp Lumen Depreciation Factor (LLDF)
The multiplier to be used in illumination calculations to relate the initial rated output of light sources to the anticipated minimum rated output based on the relamping program.

Lens
A glass or plastic shield that covers the bottom of a luminaire to control the direction and brightness of the light it emits.

Light
Radiant energy that is capable of exciting the retina and producing a visual sensation.

Louver
A series of baffles used to shield a light source from view at certain angles or to absorb unwanted light. The baffles are usually arranged in a geometric pattern.

Low bay lighting, low bay fixtures
Lighting designed for use when the bottom of the luminaire is less than 20 feet above the floor. Fixtures are usually 22–28" in diameter in order to spread the light evenly.

Lumen
The unit of measurement defining the output of a lamp. Could be said to measure a volume of light.

Lumen depreciation
The decrease in lumen output of a light source over time; every lamp type has a unique lumen depreciation curve. (Sometimes called Lumen maintenance curve)

Luminaire
A complete lighting unit consisting of a lamp or lamps together with parts designed to distribute the light, position and protect the lamps, and connect the lamps to the power supply.

Luminaire efficiency
The ratio of the light emitted by a luminaire to the light emitted by the lamp or lamps within it. Components of a luminaire such as reflectors and diffusers absorb some of the light from the lamp(s). A highly efficient luminaire emits most of the light that the lamp(s) emits.

Luminance
Light reflected in a particular direction; the photometric quantity most closely associated with brightness perception, measured in units of luminous intensity (candelas) per unit area (square feet or square meters).

Luminance contrast
The relationship between the luminances of an object and its immediate background.

Luminance ratio
The ratio between the luminances of any two areas in the visual field.

Luminous flux
The time rate of flow of light.

Lux (lx)
A unit of illuminance. One lux is one lumen per square meter.

Magnetic ballast
A ballast that uses "core & coil" assembly to transform electrical current to start an arc between electrodes. See ballast, electronic ballast.

Matte surface
A surface from which the reflection is predominately diffuse, with or without a negligible specular component.

Mean lumens
Lumen output of a light source after the source has been used.

Mercury vapor lighting
A high-intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapor. Phosphor coatings on some lamp types add additional light and improve color rendering.

Modular reflector
A device used to redirect the luminous flux from a source by the process of reflection.

Offending zone
A lighting location that produces maximum veiling reflections.

Open plan office
An office space, divided by screened or panels that do not reach the ceiling, with desk layouts designed through a system planning process to produce a flexible office environment.

Portable lighting
Lighting from a fixture designed for manually portability.

Power factor
A measure of how effectively a ballast converts current and voltage into usable power to operate the lamps. A power factor of 0.9 or greater indicates a high power factor ballast.

Preheat
A method of starting fluorescent lamps in which the electrodes are heated before a switch opens to allow a starting voltage to be applied across the lamp. With preheat starting, the lamp flashes on and off for a few seconds before staying lit, because several starting attempts may be necessary to establish the electric arc across the lamp electrodes. Often, the luminaire's start button must be held down until the lamp lights. Preheat ballasts are less energy efficient than rapid-start or instant-start ballasts.

Prismatic lens
An optical component of a luminaire that is used to distribute the emitted light. It is usually a sheet of plastic with a pattern of pyramid-shaped refracting prisms on one side. Most ceiling-mounted luminaires in commercial buildings use prismatic lenses.

Programmed rapid start
A new, "smart" method of starting fluorescent lamps by heating electrodes to their optimum operating temperature before voltage is applied. Programmed rapid start greatly reduces stress on electrodes and increases the number of lamp switching cycles without adversely effecting lamp life—a critical issue in occupancy sensor applications. The level of maintained electrode heat can also be optimized for a balance between lamp life and energy efficiency. Initial system costs, maintenance considerations, and the increasing use of dimming and occupancy sensor controls all factor into the selection of lamp starting and operating methods. See rapid start.

Quality of lighting
Pertains to the distribution of luminance in a visual environment. The term is used in a positive sense and implies that all luminances contribute favorably to visual performance, visual comfort, ease of seeing, safety, and aesthetics for the specific visual tasks involved.

Rapid start
A method of starting fluorescent lamps in which the ballast simultaneously applies starting voltage across the lamp while heating the electrodes. The electrode heating reduces the voltage needed to start the lamp but remains constant after starting, consuming additional power. While rapid start (RS) systems consume more energy than instant start (IS) systems, they also place less stress on electrodes and deliver longer lamp life in typical operating cycles. See programmed rapid start, instant start.

Reflected glare
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
A general term for the process by which the incident flux leaves a surface or medium from the incident side, without change in frequency.

Reflector
A device used to redirect the luminous flux from a source by the process of reflection.

Seismic design or seismic-rated
Design which enables a fixture to withstand vibrations and physical contact without falling from the ceiling.

Slip-Fit
A proprietary mounting and hanging system designed specifically for the Semaphore product line from Light Corporation. Slip-Fit is designed to become a physical extension of the fluorescent fixture, enabling the fixture to withstand vibrations while staying in place (see seismic design). Designed in a "Y" configuration, Slip-Fit allows the fixture to self-level without time-consuming manual adjustment. Made of high-density aircraft cable, Slip-Fit makes the fixture look as if it's floating in the air, for a clean, aesthetic appearance. Slip-Fit enables end-users and installers to hang more fixtures faster, reducing installation time by 15% compared to other mounting systems.

Smart lighting
Fluorescent high-bay lighting that provides increased worker productivity, reduced fatigue, and enhanced and brightened work environments. Lighting that provides the ultimate control over peripherals and energy usage.

Specular reflector
A mirrorlike surface for which the angle of reflection equals the angle of incidence; contrast with a diffuser.

Task lighting
Lighting directed to a specific surface or area that provides illumination for visual tasks.

Task-ambient lighting
A combination of task lighting and ambient lighting within an area such that the general level of ambient lighting is lower than and complementary to the task lighting.

Total harmonic distortion (THD)
A measure of the degree to which a sinusoidal wave shape is distorted by harmonic wave forms, with higher values of THD indicating greater distortion. Electrical devices, such as computers and fluorescent lighting systems, can send harmonic wave forms at many frequencies back onto the power supply line, thereby distorting the current wave shape. For 4-foot lamps, the American National Standards Institute (ANSI) recommends a THD limit of 32 percent, but some electric utilities only provide financial incentives for ballasts that produce less than 20 percent THD. Ballasts that produce less than 10 percent THD are available for installations with critical power requirements.

Veiling luminance
A luminance superimposed on the retinal image which reduces its contrast. It is the veiling effect produced by bright sources or areas in the visual field that results in decreased visual performance and visibility.

Veiling reflection
A reflection of a light source that obscures task details by reducing the contrast between them and their background. Also known as reflected glare.

Visual performance
The quantitative assessment of the performance of the visual task, taking into consideration speed and accuracy.

Visual task
Conventionally designates those details and objects that must be seen for the performance of a given activity and includes the immediate background of the details or objects.

Watt
A unit of electrical power equal to 1 joule per second. Lamps are rated in watts to indicate power consumption.

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