Lighting Research Center Lighting Research Center
    Volume 7 Issue 4
June 2003    
ballast - A device required by electric-discharge light sources such as fluorescent or HID lamps to regulate voltage and current supplied to the lamp during start and throughout operation. 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. compact fluorescent lamp (CFL) - A family of single-ended fluorescent-discharge light sources with small-diameter [16-millimeter (5/8-inch) or less] tubes. electrodes - The structure that serves as the electric terminals at each end of electric discharge lamps. high-intensity discharge (HID) - An electric lamp that produces light directly from an arc discharge under high pressure. Metal halide, high-pressure sodium, and mercury vapor are types of HID lamps. luminaire - A complete lighting unit consisting of a lamp or lamps and the parts designed to distribute the light, to position and protect the lamp(s), and to connect the lamp(s) to the power supply. (Also referred to as fixture.) load shedding - The practice of turning off electrical devices during peak energy demand hours to reduce building energy use. rated lamp life - The number of hours at which half of a group of product samples fail. The rated life is a median value of life expectancy; any lamp or group of lamps may vary from the published rated life. Rated life is based on standard test conditions. rated light output - The sum of the initial rated lamp lumens of the lamp(s) that were supplied with the luminaire.
How well do adaptable ballasts perform?

Table 2 shows the results of the NLPIP’s independent testing of one manufacturer’s adaptable ballast, which was capable of operating either one or two of several types of compact fluorescent lamps. As expected, the input power and light output vary depending on lamp type. Note that the lamp current remains fairly constant, and that the ballast typically provides less lamp power than the lamp manufacturer recommends.

Table 2: NLPIP’s test results for a sample adaptable ballast
Lamp Lamp current
(ma)
Lamp input
power
(W)
Ballast input
power (W)*
Light output
(lm)
System
efficacy
(lm/W)
Mfr. NLPIP Mfr. NLPIP NLPIP NLPIP NLPIP
F282D/827/4P 320 277.9 28.0 27.5 31.0 1851 59.7
F382D/827/4P 430 277.4 38.0 27.1 33.6 2162 64.4
FT24DL/835 340 276.3 24.7 21.6 25.4 1619 63.6
FC 22W/840 300 275.4 22.3 21.1 24.2 1630 67.3
FC 40W/840 320 273.6 39.9 33.7 37.3 2573 68.9
F26DBXT4SPX27/4P 325 281.6 26.0 23.8 26.5 1509 56.9
F26TBX/SPX30/A/4 325 282.3 26.0 25.3 29.4 1613 54.8
F32TBX/SPX30A/4P   320 276.7 32.0 28.9 33.5 1902 56.8
PL-T42W/35/4P/ALTO  320 273.8 42.0 39.8 43.8 2817 64.3
2 x FT24DL/835  340 261.8 49.4 41.3 48.7 3165 65.0
2 x F26DBXT4SPX27/4P 325 260.1 52.0 44.3 51.4 3003 58.4
2 x F26TBX/SPX30/A/4 325 259.7 52.0 47.7 55.4 3102 56.0
* Ballast input power includes lamp power.
For lamp current and lamp input power, both the manufacturer-reported value and NLPIP's test results are shown for comparison.
Value reflects the individual lamp power multiplied by the lamp quantity.

Table 2 also indicates that the lamp/ballast system’s efficacy is relatively stable over all lamp types, increasing slightly for two-lamp operation compared to one-lamp operation, due to ballast power that is fairly constant regardless of lamp quantity. See Figure 3 for a comparison of system efficacy for one-lamp vs. two-lamp operation.

Figure 3. Comparison of an adaptable ballast’s system efficacy for one-lamp vs. two-lamp operation
Lamp-ballast system efficacy is higher when the ballast is operating two lamps than when operating one. The difference is attributable to ballast power that remains fairly constant regardless of lamp quantity.

Although system efficacy remains fairly constant, adaptable ballasts may exhibit different ballast factors depending especially on the lamp type operated. For example, the ratio of actual light output to the lamp’s rated light output varied from 0.75 to 1.0 for Ace Compact Electronics’ CSD-UV42PS. Table 3 shows the manufacturer-reported ballast factor for this ballast with several lamp-type/lamp-quantity combinations. Note that for a specific lamp type, the ballast factor remains fairly constant as the voltage or quantity of lamps changes.

Table 3: Manufacturer’s reported ballast factors for an adaptable ballast
Lamp power
(W)
Voltage
(V)
Lamp quantity Ballast factor>
26 120 2 1.00
277 2 0.95
32 120 1 1.00
2 0.95
277 1 0.95
2 0.90
36 120 1 0.85
2 0.85
277 1 0.85
2 0.88
38 120 1 0.83
277 1 0.85
39 120 1 0.85
2 0.85
277 1 0.85
2 0.80
40 120 1 0.90
2 1.00
277 1 0.90
2 1.00
42 120 1 0.95
2 0.90
277 1 0.95
2 0.95
50 120 1 0.75
277 1 0.75
55 120 1 0.75
277 1 0.76
Summarized from product literature for Ace Compact Electronics CSD-UV42PS.


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