Replacing the Fluorescent Lamp with Linear LED Luminaires

The drive for energy efficiency and new componentry delivers viable LED solutions
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Sponsored by Selux
James Brigagliano, LC, IESNA
Glossary and Lighting Metrics

CCT (correlated color temperature): a measure of the color appearance of a white light source. CCT is measured on the Kelvin absolute temperature scale (K). White lighting products are most commonly available from 2,700K (warm white) to 5,000K (cool white). Cool light is preferred for visual tasks because it produces higher contrast than warm light. Warm light is preferred for living spaces because it is more flattering to skin tones and clothing. A color temperature of 2,700–3,600K is generally recommended for most indoor general and task lighting applications.

CRI (color rendering index): a measure of how a light source renders colors of objects, compared to a “perfect” reference light source. Color rendition is generally considered to be a more important lighting quality than color temperature. Most objects are not a single color, but a combination of many colors. Light sources that are deficient in certain colors may change the apparent color of an object. The Color Rendering Index (CRI) is a 1–100 scale that measures a light source’s ability to render colors the same way sunlight does. The top value of the CRI scale (100) is based on illumination by a 100-watt incandescent light bulb.

Electroluminescence: Light is generated directly when electrons recombine with holes, in the process of emitting photons.

LED: light-emitting diode. LEDs are small light sources that become illuminated by the movement of electrons through a semiconductor material. LEDs can be integrated into light fixtures to provide white and colored light.

LED light engine: comprises the driver (powers and regulates the power supply and other electronics), LEDs, optics, and heat sink/mounting.

Life performance curve: a curve that presents the variation of a particular characteristic of a light source (such as luminous flux, intensity, etc.) throughout the life of the source. Also called lumen maintenance curve.

Lumen: The International System of Units (SI) unit of luminous flux is a measurement of light. The total amount of light emitted by a light source, without regard to directionality, is given in lumens (lm). As reference, a 100-watt incandescent lamp emits about 1,600 lumens.

Lumen depreciation: the decrease in lumen output that occurs as a lamp is operated. LED useful life is typically based on the number of operating hours until the LED is emitting 70 percent of its initial light output (L70).

Lumen maintenance: the percentage of initial light output produced by a light source at some percentage of rated useful life.

Luminaire: the complete lighting unit (LED light engine and housing) ready to plug in.

Luminous efficacy: or efficacy of energy consumption is the total luminous flux emitted by the light source divided by the lamp wattage; expressed in lumens per watt (lm/W). DOE long-term research and development goals calls for white-light LEDs producing 160 lumens per watt in cost-effective, market-ready systems by 2025. If a luminaire efficacy value is not included in a manufacturer’s data sheet, it may be calculated by dividing the product’s total light output (lumens) by the input power (watts) from the same photometric test. The result is the product’s efficacy in lm/W.

Efficiency vs. efficacy: The term “efficacy” is normally used where the input and output units differ (lumens and watts). The term “efficiency” usually is dimensionless. For example, lighting fixture efficiency is the ratio of the total lumens exiting the fixture to the total lumens produced by the light source.

SSL: solid-state lighting; umbrella term for semiconductors used to convert electricity into light.

 

Fluorescent lamps use about 25 percent of the energy used by incandescent lamps to provide the same amount of illumination (efficacy of 30–110 lumens per watt). They also last about 10 times longer (7,000–24,000 hours). Lower energy costs typically offset the higher initial cost of the lamp that requires the additional cost of a ballast. Because they contain mercury, many fluorescent lamps are classified as hazardous waste. The United States Environmental Protection Agency recommends that fluorescent lamps are segregated from general waste for recycling or safe disposal.

There are two general types of fluorescent lamps: compact fluorescent lamps (CFLs) and fluorescent tubes.

CFLs

CFLs combine the energy efficiency of fluorescent lighting with the convenience and popularity of the incandescent lamp shape. They can replace incandescent lamps that are roughly 3–4 times their wattage, saving up to 75 percent of the initial lighting energy. Although CFLs cost 3–10 times more than comparable incandescent lamps, they last about 10 times as long (10,000 hours).

 

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Originally published in Architectural Record
Originally published in November 2012

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