Lighting Research Center Lighting Research Center
    Volume 9 Issue 1
June 2006    
average rated life - The number of hours at which half of a large group of product samples fail under standard test conditions. Rated life is a median value; any lamp or group of lamps may vary from the published rated life. ballast factor (BF) - The ratio of the light output of a fluorescent lamp or lamps operated on a ballast to the light output of the lamp(s) operated on a standard (reference) ballast. Ballast factor depends on both the ballast and the lamp type; a single ballast can have several ballast factors depending on lamp type. color rendering index (CRI) - A rating index commonly used to represent how well a light source renders the colors of objects that it illuminates. For a CRI value of 100, the maximum value, the colors of objects can be expected to be seen as they would appear under an incandescent or daylight spectrum of the same correlated color temperature (CCT). Sources with CRI values less than 50 are generally regarded as rendering colors poorly, that is, colors may appear unnatural. rapid start - A method of starting fluorescent lamps in which the electrodes are heated prior to starting, using a starter that is an integral part of the ballast. Heating the electrodes before starting the lamps reduces the voltage required to strike the electric arc between the electrodes. A rapid-start system starts smoothly, without flashing. initial light output - A lamp's light output, in lumens, after 100 hours of seasoning. instant start - A method of starting fluorescent lamps in which the voltage that is applied across the electrodes to strike the electric arc is up to twice as high as it is with other starting methods. The higher voltage is necessary because the electrodes are not heated prior to starting. This method starts the lamps without flashing. It is more energy efficient than rapid or preheat starting, but results in greater wear on the electrodes during starting. The life of instant-start lamps that are switched on and off frequently may be reduced by as much as 25 percent relative to rapid-start operation. However, for longer burning cycles (such as 12 hours per start), there may be no difference in lamp life for different starting methods. correlated color temperature (CCT) - A specification for white light sources used to describe the dominant color tone along the dimension from warm (yellows and reds) to cool (blue). Lamps with a CCT rating below 3200 K are usually considered warm sources, whereas those with a CCT above 4000 K usually considered cool in appearance. Temperatures in between are considered neutral in appearance. Technically, CCT extends the practice of using temperature, in kelvins (K), for specifying the spectrum of light sources other than blackbody radiators. Incandescent lamps and daylight closely approximate the spectra of black body radiators at different temperatures and can be designated by the corresponding temperature of a blackbody radiator. The spectra of fluorescent and LED sources, however, differ substantially from black body radiators yet they can have a color appearance similar to a blackbody radiator of a particular temperature as given by CCT. mean light output - Light output typically evaluated at 40% of rated lamp life. In combination with initial light output, mean light output may be used to estimate lamp lumen depreciation. lamp efficacy - The ratio of the light output of a lamp (lumens) to its active power (watts), expressed as lumens per watt (LPW). color rendering - A general expression for the effect of a light source on the color appearance of objects in conscious or subconscious comparison with their color appearance under a reference light source. system efficacy - Also referred to as relative system efficacy, system efficacy is a measurement of a system'’s ability to convert electricity into light. Measured in lumens per watt (LPW), system efficacy is the ratio of the light output (in lumens) to the active power (in watts). lumen maintenance - The ability of a lamp to retain its light output over time. Greater lumen maintenance means a lamp will remain brighter longer. The opposite of lumen maintenance is lumen depreciation, which represents the reduction of lumen output over time. Lamp lumen depreciation factor (LLD) is commonly used as a multiplier to the initial lumen rating in illuminance calculations to compensate for the lumen depreciation. The LLD factor is a dimensionless value between 0 and 1. spectral power distribution (SPD) - A representation of the radiant power emitted by a light source as a function of wavelength. chromaticity - The dominant or complementary wavelength and purity aspects of the color taken together, or of the aspects specified by the chromaticity coordinates of the color taken together. It describes the properties of light related to hue and saturation, but not luminance (brightness). full-spectrum color index (FSCI) - A mathematical transformation of full-spectrum index into a zero to 100 scale, where the resulting values are directly comparable to color rendering index. An equal energy spectrum is defined as having an FSCI value of 100, a “standard warm white” fluorescent lamp has an FSCI value of 50, and a monochromatic light source (e.g., low pressure sodium) has an FSCI value of 0. gamut area - A measure of color rendering based upon volume in color space. It is the range of colors achievable on a given color reproduction medium (or present in an image on that medium) under a given set of viewing conditions. CIE - Abbreviated as CIE from its French title Commission Internationale de l'Eclairage, the International Commission on Illumination is a technical, scientific, and cultural organization devoted to international cooperation and exchange of information among its member countries on matters relating to the science and art of lighting. standard deviation - A measure of the average distance of a set of data points from their mean. A set of data points that are all close to their mean will have a smaller standard deviation than a set of points that are further from their mean. RE90 - Designation referring to lamps that use rare-earth phosphors and have color-rendering index values equal to or greater than 90. RE80 HLO, LL - An RE80 lamp with additional enhancements of high light output (HLO) and/or long life (LL). RE80 - Designation referring to lamps that use rare-earth phosphors and have color-rendering index values of 80-89. MacAdam ellipse - Researcher David L. MacAdam showed that a just noticeable difference (JND) in the colors of two lights placed side-by-side was about three times the standard deviation associated with making color matches between a reference light and a test light (MacAdam 1942, Wyszecki and Stiles 1982). These JNDs form an elliptical pattern of "constant discriminability" in a chromaticity space, centered on the chromaticity of a reference light, known as MacAdam ellipse. RE70 - Designation referring to lamps that use rare-earth phosphors and have color-rendering index values of 70-79. combined uncertainty - Combined uncertainty is calculated by finding the sum of the squares of sample random variability (standard deviation) and laboratory measurement uncertainty and taking the square root of that sum.

Appendix A: Test methods

The purpose of the limited testing in this study was to compare T8 fluorescent lamp models offering substantially different performance characteristics. While many manufacturers offer both RE70 and RE80 lamps, there exists a greater variety of RE80 lamps with claims of enhanced performance characteristics, such as high light output (HLO) and long life (LL). Two lamp types were chosen from the RE80 category and tested to compare the measured characteristics with each other and against those reported in manufacturers' catalogs. RE80 HLO, LL lamps were compared with RE80 lamps that did not offer those enhancements. Table App-1 lists the trade names and catalog numbers of the lamps that NLPIP tested for this study. NLPIP purchased most of the T8 lamps it tested at local electrical supply stores. Lamps that were not available locally were received from normal production runs directly from the manufacturers.

Table App-1. Trade names and catalog numbers of tested lamps

Manufacturer Trade Name Catalog Number

RE80

General Electric ECOLUX® F32T8/SPX35/ECO
F32T8/SPX41/ECO

OSRAM Sylvania OCTRON® 800 FO32/835/ECO
FO32/841/ECO

Philips Lighting ALTO® Universal F32T8/TL835/ALTO
F32T8/TL841/ALTO

RE80 HLO, LL

General Electric ECOLUX® High Lumen F32T8/XL/SPX35/HL/ECO
F32T8/XL/SPX41/HL/ECO

OSRAM Sylvania OCTRON® 800 XPS® FO32/835/XPS/ECO
FO32/841/XPS/ECO

Philips Lighting ALTO Advantage F32T8/ADV835/ALTO
F32T8/ADV841/ALTO

The test group consisted of RE80 and RE80 HLO, LL lamps from three manufacturers, in two different correlated color temperatures (CCT), with a sample size of three lamps of each type. This yielded 18 RE80 and 18 RE80 HLO, LL lamps, for a total of 36 lamps. The lamps were seasoned using electronic instant-start ballasts for 100 operating hours using the 3-hour-on, 20-minute-off cycle specified in the IESNA Guide to Lamp Seasoning (IESNA LM-54-99). The lamps were placed in an integrating sphere at the Lighting Research Center in Troy, New York, and operated using a standard reference ballast circuit as specified by the American National Standard for Lamp Ballasts-Reference Ballasts for Fluorescent Lamps (ANSI C82.3-2002). Electrical measurements were obtained from the reference circuit in the manner specified by the American National Standards Institute (ANSI), while the integrating sphere and an Optronic Laboratories OL 750 spectroradiometer were used to measure the spectral power distribution (SPD) of each lamp.

The light output values of three of the T8 lamps tested for this publication were measured by the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, for comparison with the data obtained from the integrating sphere at the Lighting Research Center. The NIST data provided a scaling factor that was applied to all light output values for tested lamps reported in this publication.

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