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  T&D > T&D Pubs > Fluorescent Lamp Retrofits: Savings or Fantasy? > Summary > Glossary of Lighting Terminology T&D Publications Header

Fluorescent Lamp Retrofits: Savings or Fantasy?

Glossary of Lighting Terminology

Ambient Lighting Lighting used to provide general illumination and security.

Baffle An opaque or translucent component used to shield a light source from direct view.

Ballast A device containing the electrical components used with a discharge lamp to achieve the necessary voltage, current, and waveform for starting and operating the lamp.

Ballast Factor A measure of the actual lumen output of a lamp and ballast compared to the rated output of the lamp on an American National Standards Institute reference ballast. In other words, fluorescent light output is directly proportional to ballast factor. If the ballast factor is 0.8, the lamp will produce 80 percent of its rated output. Ballast factor also affects the lamp's power consumption and life. With a ballast factor of 1, an F40T12 lamp will use 40 watts, an F40T12ES (Energy Saving) lamp will use 34 watts, and an F32T8 lamp will use 32 watts. If a 32–watt lamp is operated with a 0.75 ballast factor, its power consumption will be roughly (0.75)(32) = 24 watts, or 27 watts including the ballast. Lamp life will be roughly 1/.75 or 1.33 times rated life. To obtain desired light output, lamp life, and power consumption, it is important to specify ballast factor.

Candela (cd) The International System of Units (ISU) base unit for luminous intensity.

Correlated Color Temperature (CCT) A measure in degrees Kelvin (°K) of light's warmness or coolness. Lamps with a CCT of less than 3,200 °K are pinkish and considered warm. Lamps with a CCT greater than 4,000 °K are bluish–white and considered cool.

Color Rendering A measure of a light source's ability to render the color appearance of an object in comparison to its color appearance under daylight.

Color Rendering Index (CRI) A measure of the accuracy with which a light source of a particular CCT renders different colors in comparison to a reference light source with the same CCT. A high CRI provides better illumination with the same or lower lighting levels. It is important not to mix lamps with different CCTs and CRIs. Specify both the CCT and CRI when purchasing lamps.

Color Temperature A measure of the color of light emitted by a bulb in comparison to black, described in degrees Kelvin. A color temperature of 5,000 °K is cool or blue, 3,500 °K is white, and 3,000 °K is warm or pink.

Constant-Wattage Autotransformer (CWA) Used to supply constant power (wattage) to high–intensity discharge lamps even when the input voltage fluctuates.

Diffuser A device used to distribute light from a source.

Dimmers Dimmers can reduce the input power requirements and the rated lumen output levels of incandescent and fluorescent lights. Fluorescent lights need special dimming ballasts. Dimming incandescent lights reduces their efficiency.

Efficacy The ratio of light output to its consumption of power, measured in lumens per watt (LPW), or the ability of a lighting system to produce the desired result.

Efficiency A measure of the effective or useful output of a system compared to the input.

Fixture The assembly that holds the lamp in a lighting system. It includes elements designed to control light output, such as a reflector (mirror) or refractor (lens), the ballast, housing, and attachment parts (baffle).

Fixture Lumens The fixture's light output.

Fixture Watts The total power consumed by a fixture. This includes the power consumed by the lamp(s) and ballast(s).

Footcandle (lumens/square foot) A measurement of light received on a surface (equal to the intensity of 1 candle at a distance of 1 foot).

Glare Excessive brightness from a light source. The most common types of glare are: direct (light straight into your eyes) and reflected (light reflected from a surface into your eyes).

    Direct Glare Light that shines straight into your eyes.

    Disability Glare Light that is relatively bright in comparison to the background. The vision effect of an oncoming car with its "brights" on is an example.

    Discomfort Glare Relativity bright light in the peripheral vision of the person. A bright table lamp with no shade off to the corner is an example of this type of glare.

    Reflected Glare Light that is reflected off a surface into your eyes.

    Illumination The density of light (luminous flux) on a horizontal surface. llumination is measured in footcandle or lux.

Incandescent Lamp A lamp in which light is produced by an electrical heating of a filament.

Instant-Start Ballast A type of ballast that uses high voltage, typically twice that of normal fluorescent ballasts, to induce the electrical arc across the lamp's electrodes. Normal ballasts heat the electrodes before applying the voltage.

Kilowatt-Hour (kWh) The work performed by one kilowatt of electric power in 1 hour. The kilowatt–hour is used to measure the amount of energy used by a facility.

Lamp Life The average life span for a specific type of lamp. Half of lamps will perform longer than the average; the others will fail before the average.

Lamp Lumen Depreciation (LLD) The measured reduction of lumen output of a lamp over its expected life.

Light Color Lamps are assigned a color temperature according to the kind of light they produce. A "cool light" is at the blue-green end of the spectrum. A "warm light" is at the red end of the spectrum. Visual tasks are easier in "cool light," which provides higher contrast than warm light.

Light Quality A measurement of a person's comfort and perception based on the lighting.

Lighting Controls Devices used for either turning lights on and off or for dimming.

    Photocells Sensors that turn lights on and off in response to natural light levels. Some advanced models can slowly dim or increase the lighting.

    Snap Switch A standard light switch.

    Time Clocks Lighting control devices that automatically turn lights on and off. Time clocks are typically used for security and safety.

    Timers Lighting control devices that turn the lights off after short intervals.

    Louver A series of baffles used to absorb unwanted light or to shield a lamp from view at selected angles.

Lumen The metric unit for the measurement of light output. A lumen is approximately the amount of light that falls on a 1–square–foot surface 1 foot away from a candle.

Luminaire A complete lighting unit that usually includes the fixture, ballasts, and lamps.

Luminaire Efficiency The ratio of the light emitted by the luminaire compared to the light emitted by the enclosed lamps.

Luminance A unit of measurement closely associated with perceived brightness, often expressed in candela per square meter. Luminance is a measure of the photometric flux density per unit solid angle.

Lux A unit of illumination that is equal to the direct illumination on a surface 1 meter from a uniform point source of 1 candle intensity (equal to 1 lumen per square meter).

Occupancy Sensors

    Passive Infrared A lighting control system that uses infrared beams to sense motion. When beams of infrared light are interrupted by movement, the sensor turns on the lighting system. If no movement is sensed after a predetermined period, the system turns the lights off.

    Ultrasonic A lighting control system using high–frequency sound waves pulsed through a space to detect movement by depth perception. When the frequency of the sound waves change, the sensor turns on the lighting system. After a predetermined time with no movement, the system turns the lights off.

Open–Circuit Voltage The voltage applied by ballast to a lamp during startup. The voltage quickly decreases to operating voltage once the lamp ignites.

Preheat One method of striking (starting) fluorescent lights. Less starting voltage is needed because the lamp's electrodes are heated before the voltage is applied.

Power Factor An attribute of ballast describing how effectively it converts current and voltage into usble power. High–power factor ballasts have a rating of 0.9 or more. See ballast factor.

Rapid–Start Ballasts A type of ballast that starts more quickly than preheat ballasts but not as quickly as instant–start ballasts. The ballast supplies voltage to a lamp's electrodes before applying the starting voltage. The lamp does not flash when it starts, as is typical of preheat ballasts.

Reflector A device used to reflect light.

Refractor A device used to redirect the light flow from a source, primarily by bending the wave light (refraction).

Restrike Time The time required for a lamp to relight. Fluorescent lamps usually only need a second or two before relighting.

Striking Starting a fluorescent lamp.

Task Lighting Task lighting is used to provide direct light for specific activities without illuminating the entire area.