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Schneider, Homer J. (ed.) / The Wisconsin engineer
Volume 46, Number 4 (January 1942)

Hornberg, Kenneth; Lindsley, Warren
Observations on fluorescent lighting,   pp. 10-11


Page 11


the fluorescent installation being $11,779, of which $9,341
was spent for custom built troffers and installation, $1,598
for glass, and $840 for the lamps. A total floor area of
11,730 square feet was lighted by the fluorescent system,
amounting to a unit cost of $1.00 per square foot.
  The original design called for a typical semi-indirect
and indirect incandescent lighting system with a 25 foot-
candle average, using 500 watt lamps in the offices. This
part of the installation with incandescent lighting would
have cost $1,584, or roughly $0.135 per square foot, for a
connected load of 52,900 watts.
  The fluorescent lighting load amounts to an average of
3.35 watts per square foot, based on the total load at 120
volts.
  The incandescent installation in the area actually
equipped with fluorescent units would have been 4.5 watts
per square foot.
                     Operating Costs
  The connected load consists of 39,330 watts of fluores-
cent lighting (at 120 volts) including auxiliary losses, and
about 14,000 watts of incandescent lighting, with about 8
horse-power in motors for auxiliary services and distribut-
ing cooled or warmed air. The maximum metered de-
mand and energy consumption data for the period from
July 1, 1941, to December 31, 1941, are as follows:
        Month, 1941        Kw Demand KWH Consumption
           July                            5280
           August             29.2         5440
           September          34.4         5760
           October            33.2         6160
           November           32.0         5760
           December           32.8         6160
   It is interesting to observe the relatively constant
monthly demand and energy use. This is explained by
the fact that the artificial lighting is so effective that it is
used nearly as much in the summer as during the dark
days of autumn and winter.
   At this point, if not before, an engineer will inquire as
 to how the operating costs of this installation compare
 with those of the incandescent system originally specified.
 Unfortunately, for purposes of this comparison, the exact
 hours of operation of the lighting equipment are not
 known. Consequently, to compare the operating cost of
 the two types of lighting, it will be simpler to consider
 one or two typical offices such as that of the President on
 the north corner of the first floor and a general office on
 the southeast end of the same floor. For the sake of com-
 pleteness, an incandescent installation providing approxi-
 mately the same amount of light as the fluorescent instal-
 lation will also be considered.
   A table of the pertinent data for making these com-
 parisons follows:
            DATA FOR COST COMPARISON
       COMPARATIVE COSTS FOR TWO R
       At 4 Hrs. Use per Day for 300 Days At
                    President's Office     C
                         Incandescent
                         Origi-  Hypo-
                 Fluor.  nal  thetical  Fluor.
KWH   per Year    1560   1200  3000    3180
Lamp Cost
  per Year*     $14.26  $2.16  $5.40  $27.98
Fixed Costs
At 10% of Inv. 32.20    4.35  10.88  92.60
($1.00 per sq. ft. for fluorescent;
    .135 per sq. ft. original incandescent.)
Energy plus Lamp Cost per Year:
  0.8c per KWH $26.74 $11.76 $29.40  $53.42
  lOc per KWH    29.86  14.16  35.40  59.78
  2.Oc per KWH   45.46  26.16  65.40  91.58
  3.Oc per KWH   61.06  38.16  95.40  123.38
Total Cost per Year:
  0.8c per KWH   58.94  16.11  40.28  146.02
  1.0c per KWH   62.06  18.51  46.28  152.38
  2.Oc per KWH   77.66  30.51  76.28  184.18
  3.Oc per KWH   93.26  42.51 106.28  215.98
.OOMS
inually
General Office
  Incandescent
  Origi-  Hypo-
  nal  thetical
  5400   6600
  $9.72  $11.88
  12.50  15.30
$52.92
63.72
117.72
171.72
65.42
76.22
130.22
184.22
$64.88
77.88
143.88
209.88
79.98
93.18
159.18
225.18
*40 watt fluorescent lamps at $1.10, 2500 hr. life.
500 watt incandescent lamps at $.90, 1000 hr. life.
No labor charge for replacement. Lamp costs are 20% less than retail
price.
  It is evident from the tabulated energy and lamp costs
that, because the incandescent lamp renewals are less
expensive, the greater efficiency of fluorescent lamps will
not compensate for their higher cost if energy is cheap
enough.
  It is also evident (although not tabulated) that with
longer hours of use per year, the energy savings with
fluorescent lights will balance the higher fixed costs at
lower rates per KWH of energy. In other words, the
more a fluorescent lighting installation is used, the lower
is the unit cost of energy at which it is more economical
than a corresponding incandescent lamp installation.
                       Performance
  A study of lighting conditions was made in rooms which
required different seeing tasks such as executive work,
general office work, and filing. Illumination values were
taken corresponding to actual working conditions such
as night and day to show the influence of natural light.
Dimensions
Ceiling Height
Area, Square Feet
Fluorescent Lamp Installation:
    Rated Lamp Watts
    Total Fixture Watts
Originally Specified Installation:
    Incandescent Lamp Watts
Hypothetical Incandescent Lamp Load
    for 50 Foot-Candles
,resident's
Office
14' x 23'
9'-10"
  322
1080
1350
1000
2500
General
  Office
28.5' x 32.5'
  9'-10"
  926
  2120
  2650
  4500
  5500
             T  LWO AI.' U/,vr  S| v/NL, LAnP 4}NIT7
         Fig. 1-Fluorescent installation plan in the
                     president's office.
  The main executive office of the president, Mr. George
Boissard, offers a fine example of uniform and pleasant
                  (continued on page 22)
JANUARY, 1942
Page 1 1


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