Glossary of Commercial Lighting Terms

AC Current vs. DC Current - AC Current (Alternating Current) is electrical current in which the direction is reversed at regular intervals or cycles; in the U.S. the standard is 120 reversals or 60 cycles per second. DC Current (Direct Current) is a type of electrical current and distribution by which electricity flows in one direction the conductor. Battery operated systems are typical DC applications.

Ampere (amp) - A unit of measure of electric current. It is proportional to the quantity of electrons flowing through a conductor past a given point in one second. It is analogous to cubic feet of water flowing per second. It is the unit current produced in a circuit by one volt acting across a resistance of one ohm.

Atom - The smallest particle of an element that cannot be divided or broken up by chemical means. It consists of a central core called a nucleus, which contains protons and neutrons. Electrons revolve in orbits in the region surrounding the nucleus.

ANSI (American National Standards Institute) - The Organization that develops voluntary guidelines and product performance standards for the electrical and other industries.
Arc Tube - completely sealed quartz or ceramic tube where the electrical discharge (arc) occurs and generates light.
Average Rated Life - An average rating, in hours, indicating when 50% of a group of lamps have failed when operated at nominal lamp voltage and current. Manufacturers use 3 hours per start for fluorescent lamps and 10 hours per start for HID (High Intensity Discharge) lamps when performing lamp life testing procedures. Every lamp type has a unique mortality curve that depicts its average rated life.
Average Lamp Life - Average lamp life is a value for life expectancy based on laboratory tests using controlled system characteristics measured in hours where 50% are still operating.

 

 

Baffles (Fixture) - A mechanism that regulates the flow of light in a fixture.
Ballast - A device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current, and waveform) for starting and operating; all fluorescent and HID light sources require a ballast for proper operation.
Ballast Factor - The percentage of rated lumens from the same lamp using commercial ballast as compared to ANSI reference ballast. A ballast factor of .96 means the commercial ballast produces 96% of light produced by ANSI reference ballast operating the same lamp. The ballast factor can be referred to in the catalogs from fluorescent or HID ballast manufacturers.

Ballast Hum - A sound generated by the vibration of laminations in the electromagnetic field that transforms the current for discharge lamp use.
British Thermal Unit (Btu) - The standard unit for measuring quantity of heat energy, such as the heat content of fuel. It is the amount of heat energy necessary to raise the temperature of one pound of water one degree Fahrenheit.

Brightness - The luminance in terms of subjective sensation as experienced by an individual person. Brightness is a psychological response to luminous and not synchronous with it.

Burning Position - The position in which a lamp is designed to operate for maximum performance & safety. These include:

• BD - Base Down (bulb is vertically positioned with the metal base at the bottom, glass up)
• BU - Base Up (bulb is vertically positioned with the metal base at the top, glass hanging down)
• HBU - Base Up +/- 90° (bulb can be operated in a base up or horizontal position)
• HOR - Horizontal Burn (bulb is positioned with the metal base parallel to the ground)
• U - Universal Burn (bulb can be operated in any position.

 

 

Candela - The unit of measure for the intensity of light at the source roughly equal to the amount of light in any direction from the flame of a candle.

Capacitor - An electrical device that maintains or increases voltage in power lines and improves the efficiency of the electrical system by compensating for inductive losses which produce wasted energy.

Circuit Breaker - A protective device located on an electric circuit to interrupt the flow of current at that particular point. If a transmission or distribution line or transformer experiences an electrical fault or short circuit, it can be disconnected from the rest of the system by means of a circuit breaker. The interrupting medium can be air, oil or gas.
Color Rendering Index (CRI) - This is a scientific measurement of the balance between the wavelengths making up any “white” light. This is an index from 0-100 measuring a light source’s ability to render color accurately. The lower the color temperature, the warmer or more yellow is the appearance. The higher the color temperature, the cooler or bluer is the appearance. Typical color temperatures are 2800K for incandescent, 3000K for halogen, 4100K for cool white, and 5000K for metal halide and daylight fluorescent lamps. Sodium lamps can have a CRI as low as 22, while tungsten halogen lamps can have a CRI as high as 100. Any lamp rated above 80 CRI tend to be good color rendering.
Color Temperature - Originally, a term used to describe the "whiteness" of incandescent lamp light. Color temperature is directly related to the physical temperature of the filament in incandescent lamps, so the Kelvin (K) (absolute) temperature scale is used to describe it. Although it may not seem sensible, a higher color temperature (K) describes a visually cooler, bluer light source. More recently, the term "chromaticity" has been used in place of color temperature.

Conductor - A substance or body that allows an electric current to pass continuously along it.

Cool White - Reference to the color tone or appearance of light produced by a lamp for a specific color temperature. Cool White is the least expensive and most widely used fluorescent lamp color in lighting today. Its name comes from the cool, airy atmosphere it creates wherever it is used. Modern, efficient and business-like, it is popular in stores, classrooms, offices, corridors and factories.
Correlated Color Temperature (CCT) - A term used for discharge lamps, where no hot filament is involved, to indicate that the light appears "as if" the discharge lamp is operating at a given color temperature. CCT generally measures the "warmth" or "coolness" of light source appearance using Kelvin (K) temperature scale.
Compact Fluorescent Lamp (CFL) - A fluorescent type bulb that has the ability to be utilized in an incandescent fixture, and still maintain the efficiency and qualities of a standard fluorescent bulb. These bulbs generally offer 75% savings in electricity while maintaining comparable light levels. Compact Fluorescent bulbs require a special adapter/ballast or may have one built in. Average life span is 10,000 hours.

Cutoff - A means of defining the distribution of a luminaire based on candela per 1000 lamp lumens. Luminaries are rated as Full Cutoff, Cutoff, Semi-cutoff, or Non-cutoff.

 

• Cutoff Full - A luminaire light distribution is designated as full cutoff where zero candela intensity occurs at an angle of 90o above nadir, and all greater angles from nadir. Additionally the candela per 1000 lamp lumens does not numerically exceed 100 (10%) at an angle 80o above nadir. This applies to all lateral angles around the luminaire.

 

• Cutoff - A luminaire light distribution is designated as cutoff when the candlepower per 1000 lamp lumens does not numerically exceed 25 (2.5 percent) at an angle of 90o above nadir, and 100 (10%) at a vertical angle of 80o above nadir. This applies to all lateral angles around the luminaire.

 

• Cutoff-Semi - A luminaire light distribution is designated as semi cutoff when the candlepower per 1000 lamp lumens does not numerically exceed 50 (5%) at an angle of 90o above nadir, and 200 (20%) at a vertical angle of 80o above nadir. This applies to all lateral angles around the luminaire.

 

• Cutoff-Non - A luminaire is designated as non-cutoff where there is no intensity (candela) limitation in the zone above maximum intensity.

Cycle - In one cycle of alternating electric current, the current goes from zero potential or voltage to a maximum in one direction, back to zero, then to a maximum in the other direction and then back again to zero. The number of such complete cycles made each second determines the frequency of the current. (Direct current does not fluctuate from positive to negative and hence cycles or frequency can apply only to alternating current).

 

 

Daylight - Reference to the color tone or appearance of light produced by a lamp for a specific color temperature. The bluish white appearance of this lamp is similar to natural daylight. It makes rooms very cool and often gives a store or office a blue-white radiance. It is often used over white goods.
Direct Glare - Glare resulting from high luminance or insufficiently shielded light sources in the field of view or from reflecting areas of high luminance. It usually is associated with bright areas, such as luminaires, that are outside the visual task or region being viewed. A direct glare source may also affect performance by distracting attention.

Disability Glare - The effect of stray lighting on the eye whereby visibility and visual performance are greatly reduced. A direct glare source that produces discomfort may also produce disability glare by introducing a measurable amount of stray light in the eye.

Discomfort Glare - The sensation experienced by an observer when brightness relationships in the field or view because discomfort but do not necessarily interfere with visual performance.

 

 

Economic Life - The number of hours a group of lamps will burn before it is economically and aesthetically advisable to group re-lamp (typically 60% to 75% of rated life).
Efficacy - Efficacy is an industry term for the amount of light produced per watt of electricity (comparable to efficiency). It is the rate at which a light bulb is able to convert electrical power (watts) into light (lumens), expressed in terms of lumens per watt (LPW). For example, a 100 watt lamp producing 1750 lumens gives 17.5 lumens per watt.
Enclosed Fixtures - Fixtures which have a lens that protects the bulb from the elements.
Energy - A measure of work done by an electrical system over a given period of time, often expressed in kilowatt-hours (kWh).
Environmental Protection Agency (EPA) - A federal agency created in 1970 to permit coordinated and effective governmental action for protection of the environment by the systematic abatement and control of pollution through integration of research monitoring, standard setting, and enforcement activities.

 

 

Filament - Tungsten wire positioned inside a bulb which generates light when heated.
Fluorescent Lamp - A high efficiency lamp utilizing an electric discharge through low pressure mercury vapor to produce ultra-violet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube which makes up the structure of the lamp. The phosphors transform the UV to visible light.
Footcandle or (fc) - A footcandle is a unit of luminance. One footcandle is equal to one lumen per square foot (lmft2). A lighting designer would use a measure of footcandles at the work surface to determine the proper illumination level for home or office lighting.
Frost - The glass of the lamp has a slightly opaque white appearance.
Four-Pin Compact Fluorescent Lamps - Type of lamps that do not have any starter built into the base of the lamp. Therefore, the ballast has the starting circuit. Traditionally, 4-pin lamps are designed to work with electronic ballasts.
Full Spectrum - A bulb that reproduces the full color spectrum of natural outdoor light.

 

 

Glare - The sensation produced by luminance’s within the visual field that are sufficiently greater than the luminance to which the eyes are adapted. Which cause annoyance, discomfort, or loss in visual performance and visibility.

 

 

Halogen Lamp - A short name for a tungsten-halogen lamp or quartz halogen lamp. Halogen lamps are high pressure incandescent lamps containing halogen gases such as iodine or bromine which allow the filaments to be operated at higher temperatures and higher efficacies. A high-temperature chemical reaction, involving tungsten and the halogen gas, recycles evaporated particles of tungsten back onto the filament surface.
Harmonic - An integral multiple of the fundamental frequency (60HZ) that becomes a component of the current.
Hertz (Hz) - A unit of frequency equal to one cycle per second.

High Intensity Discharge (HID) Lamp - An electric 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 vapor, metal halide and high-pressure sodium.
High Pressure Sodium - These HID bulbs contain a sodium gas and produce a yellow/orange light. They are very bright, and last up to 24,000 hours.

High Power Factor - This is a measurement of the effectiveness of which an electrical device converts amperages to watts. Power factors can range from 0 to 1.0. A high power factor means that the electrical system is utilizing the power efficiently. Devises with power factors of greater than .90 are considered “high power factor.”

 

 

Illumination - The result of the use of light.

Incandescent - Incandescent light bulbs are perhaps the most commonly found bulb in your home. The incandescent bulb contains a filament, which glows to an incandescent level when electricity flows into the bulb.
Infrared Radiation - Electromagnetic energy radiated in the wavelength range of about 770 to 1106 nanometers. Energy in this range cannot be seen by the human eye, but can be sensed as heat by the skin.

Initial Lumens - This is the quantity of light output measured after the first 100 hours of operation using controlled system characteristics.

Instant Start - A fluorescent lamp starting method in which the lamp is started by high voltage input.  No preheating of lamp filaments is necessary. Some rapid start lamps are designed so that they may be instantly started.
Instant Start Lamp - A fluorescent lamp which has a single pin at each end of the light bulb. The lamp is ignited by a high voltage without any filament heating.

 

Kelvin Temperature - See Color Temperature
Kilowatt or (kw) - A kilowatt is a measure of electrical power equal to 1000 watts.