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Lighting Reference Glossary

The Bulborama lighting reference guide clearly defines and illustrates many of the most commonly used terms and phrases related to light bulbs. Learn light bulb shapes and sizes, common light bulb base sizes, lighting color temperatures including kelvin and CRI, along with a complete electrical glossary. Common lighting reference terms are explained here to assist you in making knowledgeable decisions regarding your lighting needs.

Bulb Shapes Bulb Sizes Base Sizes Color Temperature Glossary


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Color Temperature and Color Rendering (Kelvin and CRI)
There are two standard measurements for the color characteristics of light: "color rendering index" (CRI), a term used to describe the extent to which an artificial light source is able to render the true color of objects as seen by natural outdoor sunlight which has a CRI of 100, and "color temperature", which expresses the color appearance of the light itself.

Color Rendering Index (CRI): Incandescent is used as the base reference of 100 CRI. Compact fluorescent lamps are graded at 82-86 CRI, which is considered high quality color rendering. CRI is a more important consideration for retail lighting design than it is for office lighting.

Any CRI rating of 80 or above is considered high and indicates that the source has good color properties. Incandescent lamps and daylight have a CRI of 100, the highest possible CRI. The higher the CRI of the light source, the "truer" it renders color.

Color Temperature (Kelvin): Refers to the way color groups are perceived – the psychological impact of lighting. Color temperature is how cool or warm the light source appears.
The color temperature of a light source is a numerical measurement of its color appearance. This temperature is based on the principle that any object will emit light if it is heated to a high enough temperature and that the color of that light will shift in a predictable manner as the temperature is increased. This system is based on the color changes of a black metal as it is heated from a cold black to a white hot state. As the temperature increases, the color would shift gradually from red to orange to yellow to white and finally to a blue white. Color temperature is measured in degrees Kelvin (K). Colors and light sources from the red/orange/yellow side of the spectrum are described as warm (incandescents) and those toward the blue end are referred to as cool (natural daylight).

The sun, for example, rises at approximately 1800 Kelvin and changes from red to orange to yellow and to white as it rises to over 5000 Kelvin at high noon. It then goes back down the scale as it sets.

Color Temperature Chart


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Color Temperature - Common Applications
Kelvin Associated Effects & Moods Appropriate Applications
2700° Friendly, personal, intimate Homes, libraries, restaurants
3000° Soft, warm pleasing light Homes, hotel rooms and lobbies, restaurants, retail stores
3500° Friendly, inviting, non-threatening Executive offices, public reception areas, supermarkets
4100° Neat, clean, efficient Office, classrooms, mass merchandisers, showrooms
5000° Bright, alert Graphic industry, hospitals
6500° Bright, cool Jewelry stores, beauty salons, galleries, museums, printing


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Lighting and Electrical Glossary

A unit expressing the rate of flow of electric current.

(Design) Amperes
The approximate current which the lamp will draw at design volts

ANSI (American National Standards Institute)
The organization that develops voluntary guidelines and produce performance standards for the electrical and other industries.

Average Rated Life
An average rating, in hours, indicating when 50% of a large 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 lamps when performing lamp life testing procedures; every lamp type has a unique mortality curve that depicts its average rated life. For PHOTO-OPTIC lamps average rated life refers to the operating period after which on statistical average, 50% of the lamps will perform within their specified values.

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. Ballasts have two primary functions: 1) start the lamp and 2) control operation of the lamp once it has started. High frequency electronic ballasts operate lamps more efficiently (30 - 40% at equivalent light output) and eliminate the hum and visible flicker normally associated with standard magnetic ballasts. Electronic ballasts also typically have better power quality than magnetic ballasts (higher power factor and lower THD).

Ballast Efficacy Factor (BEF)
Relative light output (ballast factor) divided by input power (watts). Used to measure the level of efficiency of similar ballast models. For example, the OSRAM SYLVANIA QT2X32IS which has a ballast factor of 0.90 and input watts of 59 (BEF=1.53), is more efficient than competitors' electronic ballasts with ballast factor of 0.875 and input watts of 62 (BEF=1.41).

Ballast factor (BF)
Relative light output as compared to a reference ballast (i.e. BF of 0.90 would yield 90% of a lamp's rated lumens. The measured ability of a particular 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 life
Bulborama ballasts are designed to have a life expectancy of 60,000 hours. To maximize life, ambient temperature should be kept as low as possible. It is also important to maintain effective dissipation of heat using the lighting fixture as a heatsink for the ballast enclosure.

Ballast losses
Power consumed by a ballast that dissipates as heat instead of being converted into light. Electronic ballasts operate more efficiently than magnetic or hybrid ballasts. A typical ballast loss for a standard two lamp magnetic ballast is 20 watts, which an electronic equivalent would only be 7 watts.

Ballast types
There are three types of lighting ballasts: 1) Magnetic: an inefficient device that uses a core and coil assembly transformer to perform the minimum functions required to start and operate the lamp; 2) Hybrid or "low frequency electronic": essentially a magnetic ballast with a few electronic components that switch off voltage to the lamp coil once the lamp has started. A minimal increase in efficiency is obtained via more expensive magnetic core material and the absence of power to the lamp coils during operation; 3) High frequency electronic: a ballast that operates lamps at frequencies above 20,000 Hz. Maximum efficiency is obtained through the use of electronic circuitry and optimum lamp operating characteristics.

The lamp base mechanically holds the lamp in place in the application. The lamp base directly or indirectly (via a cable or lead-in wires) conducts electricity from the circuit to the lamp and can be designed to dissipate heat. Lamp bases should be operated within specified temperature range.

Beam angle
Also called the beam spread; the angular dimension of the cone of light from reflectorized lamps encompassing the central part of the beam out ot the angle where the intensity is 50 percent of maximum.

Hard, soft or quartz glass enclosure, which can contain a vacuum, elemental inert gas or metal and a means of light generation (filament or electrodes).

Candela (cd)
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.

Candlepower distribution
A curve that represents the variation in luminous intensity (expressed in candelas) in a plane through the light center of a lamp or luminaire; each lamp or lamp/luminaire combination has a unique set of candlepower distributions that indicate how light will be spread.

Center Beam Candlepower (CBCP)
The intensity of light produced at the center of a reflector lamp, expressed in candelas.

Compact Fluorescent Lamp or Compact Fluorescent Light Bulb.

Color rendering index (CRI)
The Color Rendering Index (CRI) measures the effect a light source has on the perceived color of objects and surfaces. High CRI lights makes virtually all colors look natural and vibrant. Low CRI causes some colors to appear washed out or even to take on a completely different hue.

Color temperature (CT)
Color temperature, which is measured in Kelvin, indicates whether a lamp has a warm, midrange or cool color appearance. "Warm" light sources have a low color temperature (2000-3000K) and feature more light in the red/orange/yellow range. Light with a higher color temperature (>4000K) features more blue light and is referred to as "cool."

Compact Fluorescent Lamps (CFL)
Compact fluorescent lamps employ small diameter tubes that are bent so they begin and end in a ceramic base. This allows them to be produced in a wide variety of configurations, greatly extending the applications for fluorescent lighting and offering innovative energy efficient lighting solutions.

Correlated Color Temperature (CCT)
A specification of the color appearance of a lamp, relating its color to that of a reference source heated to a particular temperature, measured in degrees Kelvin (K); CCT generally measures the "warmth" of "coolness" of light source appearance.

A measure of the flow of electricity, expressed in amperes (A).

Decorative lamps, such as candelabra or post lights, in a variety of shapes and bases.

See ordering abbreviation.

Lamps that have two bases opposite one another for series electrical connection, mechanical mounting and heat dissipation.

The rate at which a lamp is able to convert power (watts) into light (lumens). A watt of electricity is the amount of power in and a lumen or light is the amount of power out. Represented in lumens per watt and found by dividing the light output in lumens by the electrical power input (to the lamp). Also see LPW performance.

Electronic ballasts
The electric arc in any fluorescent system is generated by a ballast. The ballast starts the lamp, then limits its operating current and provides power factor correction. Modern electronic ballasts perform these functions with great efficiency and provide other control functions as well.

Ballasts contain circuits that limit electrical noise conducted onto the power line or radiated through the air, otherwise referred to as EMI/RFI. Bulborama ballasts comply with FCC 47 CFR Part 18, Non-Consumer limits for commercial applications.

End Foot Candles (EFC)
A measure of that portion of the total light output of a T-2 lamp that passes through a .250" orifice placed at the end of the lamp.

A measure of work done by an electrical system over a given period of time, often expressed in kilowatt-hours (kWh).

A tungsten wire purposely positioned inside a lamp bulb, that when heated electrically generates radiation in the visible, infrared and ultraviolet ranges. Tungsten material replaced carbon almost universally, as it has great tensible strength, and is very durable. However, the basic reason for its selection as the best filament material is the fact that it can be burned very near its melting point without evaporating rapidly. Lamp filaments are offered in a variety of designs optimized for specific applications.

A reflectorized lamp whose emitted beam pattern is enlarging. Also a luminaire consisting of lamp and reflector at fixed distance providing a wide field of illumination.

Fluorescent lamp
High efficiency lamp that uses 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 that makes up the structure of the lamp. The phosphors transform the UV to visible light.

Footcandle (fc)
A unit of illuminance equal to 1 lumen per square foot.

The number of times per second that an alternating current system reverses from positive to negative and back to positive, expressed in cycles per second or hertz (Hz).

All Bulborama ballasts contain inherent electrical protection. Although there is no need to externally fuse the ballast, should code or regulation require one, 3 amp slow blow fuses are recommended.

Excessive brightness that may be caused by either direct of indirect viewing of a light source.

Glow to arc transition
In order to achieve full rated lamp life, a ballast should start a lamp so that the time from when the lamp begins to glow to the time the lamp arc strikes should be as short as possible. Bulborama instant start ballasts typically accomplish this task within 50 msec.

The ballast case and fixture must always be grounded. The grounding helps assure safety, proper lamp starting, and acceptable EMI/RFI performance.

Halogen lamps
(Tungsten-halogen lamp) high pressure lamps containing halogen gases which allow the filaments to operate at higher temperatures and higher efficacies. Halogen lamps use a filament, but since it is sealed in a pressurized capsule containing halogen gas, the lamp provides brighter, whiter light with better color characteristics, longer service life and improved energy efficiency.

An electrical frequency that is an integer multiple of the fundamental frequency; for example, if 60 Hz is the fundamental frequency, then 120 Hz is the second harmonic and 180 Hz is the third harmonic; some electronic devices, such as ballasts or power supplies, can cause harmonic distortion, directly affecting power quality.

High-intensity discharge (HID) lamps
In HID lamps, an arc passing between two cathodes in a pressurized tube cause various metallic additives to vaporize and release large amounts of light. All HID lamps offer outstanding energy efficiency and service life. Metal halide lamps also offer good to excellent color rendering index (CRI).

Hot ignition
The restarting of a previously operating lamp shortly after turn-off. Hot ignition is a high performance feature in many OSRAM discharge lamp types.

Light arriving at a surface, expressed in lumens per unit area; 1 lumen per square foot equals 1 footcandle, while 1 lumen per square meter equals 1 Lux.

Incandescent lamps
A light source that generates light utilizing a think filament wire (usually tungsten) heated to white heat by an electric current passing through it. Regular incandescent lamps produce light by passing an electric current through a filament in a vacuum or gas-filled bulb. They provide low initial cost, good color rendition and excellent optical control.

Instant start (IS) vs. rapid start (RS)
Instant start (high voltage is applied across the lamp with no preheating of the cathode) is the most energy efficient starting method for fluorescent lamp ballasting. IS ballasts use 1.5 to 2 watts less per lamp than rapid start ballast (low voltage is applied to the cathodes prior to lamp ignition and is maintained throughout operation). Other IS ballast benefits typically include parallel lamp circuitry, longer remote wiring distance, easier installation due to less complicated wiring, and capability to start lamps at 0 degrees (versus 50 degrees F for rapid start).

A measurement that quantifies the effect of non-linear equipment, such as lighting ballasts, on an electrical system. Lighting systems should be designed so that the transformer rating is sufficient for the ballast used (typically K-factor <4). All Bulborama ballasts meet this specification.

Manufactured light source; synonymous with light bulb; the three broad categories of electric lamps are incandescent, fluorescent and high-intensity discharge.

Lamp Current Crest Factor (LCCF)
The ratio of peak lamp current to the RMS (average) lamp current. Lamp manufacturers require a LCCF of less than 1.70 in order to achieve full lamp life. Values less than 1.70 do not achieve higher than rated lamp life.

Lamp Disposal
When disposing of spent lamps, always consult federal, state, local and/or provincial hazardous waste disposal rules and regulations to ensure proper disposal.

Lamp flicker
High frequency electronic ballasts provide a minimal level of lamp flicker. Lamp flicker from magnetic ballasts can cause eye fatigue for some people.

Radiant energy that is capable of producing a visual sensation.

Light bulb
see Bulb

Light Center Length (LCL)
The distance from a specified reference point on a lamp base to its light center, typically expressed in inches.

Linear fluorescent lamps
In a fluorescent lamp, an electric arc passing between cathodes in a tube excites mercury vapor and other gases and produces UV radiant energy. A phosphor coating on the tube then converts this energy to visible light. Fluorescent lamps are very energy efficient and provide a wide range of color responses.

LPW performance
Lumens Per Watt. The number of lumens produced by a lightsource for each watt of electrical power supplied to the light source. Also see Efficacy.

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

A unit of luminous flux; overall light output; quantity of light, expressed in lumens. For example, a dinner candle provides about 12 lumens and a 60-watt soft white incandescent lamps provides about 840 lumens.

A light fixture; the complete lighting unit, including lamp, reflector, ballast, socket, wiring, diffuser and housing.

Luminance (L)
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).

Lux (lx)
A unit of luminance equal to 1 lumen per square meter.

Maximum Overall Length (MOL)
The total length of a lamp, from top of bulb to bottom of base, typically expressed in inches.

Mean Spherical Candela (MSCD)
The average value of the luminous intensity of a light source in all directions. To convert MSCD to Lumens, multiply by 4?(12.57).

MTBF - Mean Time Between Failures
A calculation of ballast life based on thermal conditions, component values, and circuit characteristics used to develop relative predictions of ballast life.

Medium pin
Referring to the lamp base pin diameters. Often referencing fluorescent lamps (T-8F and T-12F).

Nominal watts
Represents the rated wattage consumption period. Represents the energy used to produce light. Watts= Volts x Amperes. Also see Watt.

Operating Position
All Bulborama lamps must be operated within the specified operational positions (base, filament, electrodes).

Ordering abbreviation code
Provides a shorthand description of the lamp, using a unique code which can be used when ordering a lamp if you do not know the item number. An example would be: 50PAR20/FL 130V, which translates to a 50-watt PAR20 flood 130 volt halogen par lamp.

Parallel vs. series
Ballasts with parallel lamp circuitry have the benefit of companion lamps remaining lit, even if one of the lamps operated by the ballast should fail. Systems with series lamp wiring (magnetic ballasts and many competitors' electronic types) result in all lamps operated on the ballast going out if one should fail.

PAR lamps
Usually halogen lamps, means parabolic reflector lamps.  A lamp fixed within a parabolic reflector, a lamp system that can use incandescent, halogen and HMI lamp types. Numeric portion of PAR description indicates actual parabolic reflector diameter size in 1/8th inch units (example: PAR 64 is a lamp whose diameter is 64/8th inch or 8 inches).  Example: PAR 36, 38, 46, 56 and 64 types.

Photo-Optic lamps
Photo-Optic lamps employ a variety of technologies to meet the very precise levels of performance required by the entertainment industry, science, medicine and other high-tech fields.

The rate at which energy is taken from an electrical system or dissipated by a load, expressed in watts; power that is generated by a utility is typically expressed in volt-amperes.

Power factor
A measure of the effectiveness with which an electrical device converts volt-amperes to watts; devices with power factors (0.90) are "high power factor" devices.

Reflectance (icon)
The percentage of light reflected back from a surface, the difference having been absorbed or transmitted by the surface. See Reflection.

If a light ray strikes a mirror- life surface, it is reflected. The angle of incidence equals the angle of reflection; this is called specular reflection. When a ray strikes a mat surface, light is reflected uniformly in all directions. This is called diffuse reflection. With the reflectors the rays of light are pencilled in the proper direction. See Reflectance.

An optical device to reflect light. PHOTO-OPTIC reflector lamps utilize ellipsoidal (converging light rays) or parabolic (collimating light rays) reflectors. Dichroic coated reflectors are designed to reflect visible light and pass through unwanted infrared wavelengths.

Resistance (R)
A measure of resistance to flow of current, expressed in ohms.

Ballasts should be installed and operated in compliance with the National Electric Code (NEC), Underwriters Laboratories Inc. (UL) requirements, and all applicable codes and regulations. As it is possible to come in contact with potentially hazardous voltages, only qualified personnel should perform ballast installation. All installation, inspection, and maintenance of lighting fixtures should be done with the power to the fixture turned off.

Single pin
Single pins have a mini can or D.C. bay base whereas bi- pin lamps have a bi- pin base.

Lamps having a single lamp base or point of electrical connection.

Spectral Power Distribution (SPD)
A curve illustrating the distribution of power produced by the lamp, at each wavelength across the spectrum.

A luminaire using halogen/incandescent or a high intensity discharge (HID) lamp that produces a narrow beam angle designed to illuminate a specifically defined area.

Total harmonic distortion (THD)
Excessive THD (defined by ANSI as greater than 32%) may cause adverse effects to the electrical system. THD levels below 20% provide optimal system compatibility, but levels below 10% may not add any practical benefit. 10% THD types may also introduce excessive in-rush current unless circuitry is added that limits in-rush levels.

(Toxicity Characteristic Leaching Procedure), Federal EPA regulations (RCRA of 1990) have define a TCLP test to determine whether wastes are to be treated as hazardous or non-hazardous.

Tungsten Halogen Cycle
Halogen light sources utilizing the halogen regenerative cycle to prevent blackening of the lamp envelope during life.

Voltage (E)
A measure of electrical potential, expressed in volts (V).

A unit of electrical power. Lamps are rated in watts to indicate power consumption. Also see Nominal watts.

Wavelength (icon)
Distance between two successive points of a periodic wave; the wavelengths of light are typically expressed in nanometers (nm), or billionths of a meter.

Working Distance
As a function of an elliptical reflector, light is collected and converged into a specific area a certain distance in front of the lamp. Lamp alignment can be provided for specific illumination and color qualities at the designated area.

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Glossary courtesy of Sylvania Lighting