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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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Base Sizes
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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 spec