xt79gh9b7064 https://exploreuk.uky.edu/dips/xt79gh9b7064/data/mets.xml   Kentucky Agricultural Experiment Station. 1965 journals 154 English Lexington : Agricultural Experiment Station, University of Kentucky Contact the Special Collections Research Center for information regarding rights and use of this collection. Kentucky Agricultural Experiment Station Progress report (Kentucky Agricultural Experiment Station) n.154 text Progress report (Kentucky Agricultural Experiment Station) n.154 1965 2014 true xt79gh9b7064 section xt79gh9b7064 RBGDIIIIIIBIIIIZIIDIIS
Fur Grading Tuhaccu
Light Source
By Carl M. Clay-k and Gerald M. Whale rnocnzss nsvonr 154

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Leaf Grading on the Farm Stick Sorting for Basket Federal Grading for Auction Sale _
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Auction Selling of Baskets Sale Purchase Regrading for Sample Grading of Hogsheads in Storage
Redrying and Storage
Tobacco leaf is graded at several points and at different times in a _, A
the market flow. This is a part of the complexity of achieving a i   2*  U
uniformity of light conditions throughout the market channel.       ''''   V L1 ‘
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Cover Picture—Floor of burley ready for auction sale under the *5 W A  
first electric lamp officially approved for selling purposes.  y  ’·  
(Photo - Lexington, Ky. , Herald-Leader)     li   l ud; 
Leaf Preparation for Processing
(Photos on this page furnished by Louisville, Ky. , Courier-journal Consumer Product:
and Lexington, Ky. , Herald—Leader. )

The authors express appreciation to these electrical firms for their
cooperation in the study; Macbeth Corporation, Newburg, N. Y. ; Verd—a—Ray
Corporation, Toledo, Ohio; Sylvania Electric Products, Inc., Salem, Mass.;
‘ General Electric Company, Cleveland, Ohio; and Certified Electric Division,
` El-Tronics, Inc. , Warren, Pa. Their generous assistance in providing much
electrical equipment and counselling on the technical aspects of light energy made
possible the extensive research completed under the project.
Appreciation is also extended to the Tobacco Division, Agricultural Market-
ing Service, U. S. Department of Agriculture, for supplying graders and tobacco
samples and for scoring grader performance under the different light sources.
The authors are especially indebted to Mr. R. N. Lowe and Mr. A. R. Waits, of
the Lexington office of the Tobacco Division, for guidance in designing the experi-
mental tests.
Thanks go to hundreds of individual farmers, buyers, and F. F.A. members I
for their participation in the numerous experimental grading tests. Appreciation is
due, also, to the Winchester Tobacco Warehouse and Winn Avenue Tobacco Ware-
house of Winchester, Ky. and the Farmers Tobacco Warehouse for assistance in
giving the results of the study a practical test experience in the auction selling of

INTRODUCTION ................................ 5
QUALITY OF ILLUMINATION ........................ 6
Progress in Lamp Development ................... 8 `
Color Rendition of Light Sources ................... 9 _
Experimental Research Procedures ................. 10
Results of Experimental Tests .................... 11 ·
Light Quality Recommendations ................... 13
QUANTITY OF ILLUMINATION ........................ 14
Level of Light Illumination ...................... 14 v
Uniformity of Illumination ....................... 14
Maintenance of Light Equipment ................... 17
Light Quantity Recommendations ................... 18 °
COLOR OF BACKGROUND .......................... 18 _
Neutrality of Background Color .................... 18
Tone of Background Color ....................... 18
Color of Background Recommended .................. 18
SUMMARY ................................... 18
LITERATURE CITED ............................. 20 _

By Carl M. Clark and Gerald M. White
Tobacco lighting research work of the Kentucky Agricultural Experiment
Station stems from a study made of basket price variation in the auction selling of
burley tobacco. The wide variation in daylight conditions occurring during the
auction sale has been generally recognized throughout trade channels as one of the
possible causal factors for the price risks of buying and selling (1) .1 This was the
basis for initiating research on the character and influence of light in grading
tobacco. The first step was to study daylight conditions existing in the looseleaf
auction sale. Light quantity or intensity was found to vary from day to day through
the sale season, from hour to hour through the sale day, from warehouse to ware-
house, and from basket to basket on the sale floor (2). ‘
The next phase was to survey progress made by different industries toward
adapting the electric lamp as a substitute for northsky daylight in product evaluation.
Much progress has been made in some areas toward dependence on the electric lamp
as a source of light. Over the past 30 years, considerable research on light require-
ments for product evaluation has been done by the United States Department of
( Agriculture and others. Much of this research has concerned the light quality of the
electric lamp, and, as such, has been directed largely toward bringing the color
composition of the electric lamp more in line with that of normal northsky daylight.
Until substantial teclmical progress was made in improving the electric lamp, com-
merce and industry depended, as a base point, on northsky daylight at high noon for
product evaluation and standardization. Some industries—for example, the cotton
- and textile——have progressed to an extensive dependence on the electric lamp for - A
product evaluation and color standardization.
. The next step in the research of the Kentucky Station was an experimental
phase, testing the various electric lamps designed for grading and color evaluation
as to their suitability for use in grading tobacco. The lamp developed for the grading
of cotton was the first and most important lamp used. It became the base lamp in
the experimental research work for tobacco and was put through much testing for its
suitability and adaptability. Other lamps were included in comparative testing as to
usefulness and economy of application. During the 10 years or more that the experi- '
mental phase has been under way, considerable technical progress has been made by
the lamp industry in improving the color composition of the electric lamp—mainly
that of bringing the color composition of the output of the fluorescent lamp more in
line with the color balance as found in northsky daylight. /
At least three major factors stand out in past research as essential to achiev-
ing optimum light conditions in all—product evaluation. Much of the research in this
study has been that of establishing the dimensions or specifications for each of these
three factors to assure the most satisfactory light for grading tobacco. The factors
are (a) quality or color balance of light source, (b) quantity of light, and (c) color of
backgrotmd. The first factor has been by far the most difficult one for which to
establish technical specifications.
1Nu.mbers in parentheses refer to "Literature Cited, " page 20.
` 5

 The objective of this publication is to report on the progress made in
establishing the conditions essential to a good uniform light for grading tobacco.
The specifications are given in terms of the three major factors recognized above.
The full, comprehensive report on the light research program, to be published
later, will present the research methods, the results of the experimental tests,
and the problems and advantages of establishing a uniform light throughout the
tobacco market channel.
To understand and describe the quality characteristics of light energy, it ,
is necessary for one to be familiar with certain concepts and terminology used by
lighting engineers. These concepts include the use of spectral energy distribution
curves, chromaticity values, and chromaticity diagrams, and color temperature
designations. Each is useful in evaluating the possible application of different _
light sources for tobacco grading.
The spectral energy distribution of a light source indicates the relative  
amount of radiant energy provided by that light source at all wavelengths through- ‘
out the visible spectrum. It can be displayed graphically (as in Fig. 1) or in tabu-
lar form. Knowing the spectral energy distribution of a light source enables one
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 to determine the color of the light source by using standard colorimetric techniques
(3) to establish its location on a C.I. E. chromaticity chart (Fig. 2). Each position
on this diagram corresponds to a specific color. This allows one to specify the
color which the light source itself will exhibit when viewed by an observer having
average or normal color vision.
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rio. 2.- cn: cHRoMAT1c1TY DIAGRAM wma Locus Fon PLANCKLAN 1>.A01AToR.
The foregoing procedure is very useful in making it possible for the color .
of a light source or that of any object to be specified by only two numbers—the x
and y coordinates on the chromaticity diagram. This does not imply, however,
that all light sources located at the same point on the chromaticity diagram will
have the same spectral energy distribution. This difference in spectral distribution
can cause a wide variation in the color—rendering abilities of two or more light /
sources having the same chromaticity coordinates (x, y values).
Another concept employed by engineers in describing light sources is color
temperature. This refers to the color exhibited by a Planckian (or so—called black
body) radiator when heated to different absolute temperatures (degrees Kelvin).
When such a body is heated, it emits a continuous spectrum of radiation according
to Planck's Law (4). At low temperatures this radiation is invisible, but as the
temperature of the body is increased the radiation emitted shifts more toward the
visible region of the spectrum. The color exhibited by this visible radiation is
7 .

 precisely related to its absolute temperature, and this effect has resulted in the
use of the term "color temperature" to describe the color of light sources. The
chromaticity of the radiation emitted by a Planckian radiator at various tempera-
tures can easily be determined; the locus of these chromaticities is presented
on the chart in Fig. 2.
Although there is no such thing as a perfect black body radiator, many
objects behave so much like one that the concept of color temperature can be re-
liably applied to describe their radiant energy output at high temperatures. The
filament in an incandescent lamp is one such body; thus, color temperature (as
well as chromaticity values) can be used in specifying the color of the light from
an incandescent lamp. For light sources not supplying radiant energy with the
same spectral distribution as that produced by a black body, the term "color
temperature" cannot be strictly applied. For such lights the term "correlated color
temperature" is used to indicate the color temperature of the point on the Planckian ‘
locus which affords the nearest color match for the light source being described.
Thus, correlated color temperature can be used to represent the color of any light
source, although it does not give any specific information about the spectral energy
distribution of the light source itself.
Research (5) has indicated that, when there is sufficient light intensity,
warehousemen and tobacco graders prefer to grade under natural light from "north"
skylights with a high overcast sky. Similar studies (6, 7) with other products have
yielded similar results. Measurements (7) have shown that north skylight conditions
classed as "very good" by textile color matchers required a minimum color temp-
erature close to 75000K for a minimum of 100 footcandles light intensity. On the .
basis of such research, several industries (8, 9) have taken as a standard for pre-
ferred north skylighting the 74000K Abbot-Gibson spectral distribution (10). This
distribution represents a combination of 85 percent Abbot sunlight plus 15 percent _
blue skylight. It was also adopted for use in this investigation as a reference
standard against which to compare the color and spectral distribution of the differ-
ent light sources.
Proggess in Lamp Development
From the facts just stated, it would appear that for tobacco lighting, one ”
would need only to specify an illuminant with the same color temperature and spectral ·
distribution as the "standard" illuminant and then to install a sufficient number of  
these fixtures in a certain designated manner so as to meet all other specifications
for proper lighting. However, no commercially available illuminant duplicates the
spectral distribution of the established standard light source. Fluorescent light
tubes are available over a wide range of color temperatures, some of which are
near that of the established standard; however, the spectral distribution of most of
these lamps deviates considerably from that of the standard and, therefore, results
in poor color rendition.
One company has developed a lighting fixture employing both fluorescent and ‘
incandescent lights. This unit approaches the spectral distribution of the Abbot-
Gibson source and provides a high degree of daylight color rendering. However,
it is relatively expensive in comparison with standard fluorescent fixtures and has,
therefore, been limited in its use to installations much smaller than those which
would normally be required for lighting tobacco auction sales areas or long pro-
duction lines in processing.

 In some of the work done at the Kentucky Station, a combination of several
different fluorescent tubes was employed in a single fixture to produce a light source
_ with more desirable color-rendering properties than those available with one type
e of tube. While a certain degree of success was obtained with this approach, the
‘ authors felt that it would be more desirable from an application standpoint if an
_ _ acceptable illuminant could be produced using only one type of fluorescent tube. Lamp
manufacturers have indicated that it is now possible to achieve the desired color
balance by using a particular mixture of fluorescent chemicals. A research grading
I experiment in which a number of experimental lamps supplied by different lamp
manufacturers were evaluated as to their ability to do a satisfactory job of tobacco
‘ lighting will be discussed later in this report.
Color Rendition of Light Sources
The perceived color of a tobacco sample placed under any given illuminant
’ depends on the illuminant, the nature of the tobacco sample and its surroundings,
and the response of the observer's eye—brain mechanism. The intensity, color
temperature and the spectral distribution of the light source are important in that
these factors have a major influence on the nature of the light energy seen by the
observer in looking at the tobacco sample. The tobacco sample affects its perceived p
color by the manner in which it modifies light energy falling on it from the illumin-
The response of the human eye-brain mechanism in perceiving the color of
a tobacco sample or any other object is complex and sometimes relatively unstable.
 , The perceived color depends not only on the physical nature of the radiation received
by the eye from the sa.mple being viewed, but also on the adaptation of the eye, the
intensity of radiant energy and the degree of "normalcy" of the viewer's color vision.
The sensitivity of the human eye to any given color in the spectrum increases or
decreases, depending on whether the light received by the eye is lacking or is rich
in energy in that portion of the spectrum. Thus, the sensitivity of the eye to the
different colors of the spectrum is inversely related to the spectral distribution of
the light energy received by the eye. This type of eye adaptation tends to make the
color of objects viewed under different illuminants appear similar and is referred
to as "color constancy." This effect does not result in precisely the same color
being perceived under different illuminants; but it does result in approximately the
. same color perception as long as illuminants with extreme color temperatures and/or
unusual spectral distributions are not employed. Thus, eye sensitivity and adapta— f
tion become very important factors in evaluating the color-rendering ability of a
light source.
In selecting a light source for grading tobacco, one needs to be concerned
with the quality of the illuminant, its luminous efficiency, its ease of installation
and maintenance, its expected life, and its overall installation and operating costs.
All other things being comparable, lamp selection must be made on the basis of
light quality as denoted by the illuminant's spectral energy distribution. This, in
turn, must be related to the ability of the light to render tobacco colors the same
as they would appear under an accepted standard light source. One method of
specifying the color-rendering ability of light sources is the I. E.S. color—rendering
index (ll, I2). This method is based on determining the relative amount of colori-
metric shift on a chromaticity diagram for a number of standardized color samples
when viewed under a test light source as compared with the same samples when
viewed under a standard reference source of approximately the same correlated

 color temperature. For light sources with correlated color temperatures below .
60000K, the reference standard is a Planckian radiator at the nearest color temp- -
erature Q 500K); above 6000OK, the Abbot-Gibson series of spectral energy dis-
tributions is used, with the selected reference standard being that distribution
having the nearest correlated color temperature Q 250OK) to that of the test source.
While the method described above does a satisfactory job of specifying the relative .
color-rendering abilities of light sources which vary in spectral quality but not in
correlated color temperature, it is still limited in that it cannot take into account
the influence of chromatic adaptation. For this reason, it cannot be used for com-
paring the color-rendering abilities of lamps which vary widely in their color
temperatures as well as in their spectral energy distribution. Therefore, the ’
method rates illuminants only in terms of how well their color-rendering abilities
approach that of natural daylight of the same correlated color temperature.
Experimental Research Procedures _
At Kentucky work was conducted in the spring of 1964 to show which of
several experimental fluorescent tubes supplied by lamp manufacturers would be
most satisfactory for use in grading leaf tobacco. There was also a need for some
definite means of specifying and rating different illuminants as to their acceptability
or relative merit for use in such an application. Correlated color temperature and V
the I. E. S. color-rendering index were used to specify the different light sources.
For the experimental work, eight grading booths were constructed. The
walls of each booth were covered with neutral gray paper of about Munsell value 8,
and the tops of the grading tables were covered with brown tobacco—colored paper · ·
to conform with the current operating procedures of the Federal Tobacco Grading
Laboratory (13). Conventional four-tube lamp fixtures were installed in seven of
the booths with a commercial fluorescent-incandescent daylighting fixture in the .
eighth booth. This combination fixture was the same as that employed in Federal .
Tobacco Grading Laboratories and widely accepted for use in other industries where `
accurate daylight color-rendering is considered important. It was, therefore, used
as the light source for the base booth against which to compare the grading perform-
ance in the other seven booths. The seven conventional fixtures were equipped with
commercially available and experimental fluorescent tubes ranging in color tempera- D
ture from 42000K to 84000K. The I. E.S. color-rendering indexes of these lights V p
varied from 85 to 92. Each of the light sources was randomly assigned to the differ-
ent booths and adjusted so that the light intensity on the table top in each booth was ' ,
100 footcandles. `
The Tobacco Division, Agricultural Marketing Service, USDA, cooperated in
this study by supplying tobacco samples and graders for the experimental work and
by scoring the performance of the graders under each of the illuminants. Four sets
of burley tobacco samples were used, with each set containing 60 samples boxed
into three lots of 20 samples each. The base grade of each sample was established
by the Federal Grading Service under the light source approved for use in Federal
Tobacco Grading Laboratories. Twelve Federal tobacco graders participated in the
grading experiments, and the Federal tobacco grading score system was used for
evaluating performance under each of the illuminants. Each grader graded a
complete set of 60 tobacco samples under each light source in a random sequence.
The set of samples graded in each booth consisted of three 20-sample boxes drawn
at random from the four available sets with the restriction that no grader would grade l

 any box of samples more than twice in completing the eight—booth grading sequence.
This restriction was introduced to reduce the effect of memory bias in the grading
Results of Experimental Tests
. Data obtained from the experimental grading procedures described in the
above section are summarized in Table 1. The average number of points deducted
. per box of samples for errors made in establishing the group, quality and color
designation of the tobacco samples is presented along with the average net grading
. index of the graders under each light source. These results indicate that there is
no pronoimced difference in overall grading performance under the various light
sources. This result, while somewhat unexpected, probably indicates the extent to
which eye adaptation can compensate for variations in the color and spectral distri-
bution of different light sources.
Examination of the number of points deducted under different lights owing to
‘ errors made in establishing color grades indicates very little variation between
booths. No apparent effect of lamp correlated color temperature on a grader's
ability to designate color grades is indicated. There is some indication that overall
color grading accuracy is improved with an increase in lamp color-rendering index;
however, no definite conclusion can be drawn from the composite color grading .
TABLE 1. — Results of Experimental Tobacco Grading Tests Under Various Light
Sources (Error Points Deducted and Average Net Rating of Graders)
Correlated I. E. S. Color Average Number of Grade Points Deducted Net Rating
Booth Color Rendering Group Quality Color Average
No. Temp. Index Factor Factor Factor Total of Grading
1 4200OK 85 2.9 10.7 4.8 18.4 81.6
2 5125OK — 2.9 9.9 3.7 16.5 83.5
3 84000K 88 3.6 9.3 4.2 17.1 82.9
4 6570OK 90 2.4 9.3 4.2 15.9 84.1
` 5 589OOK 92 3.0 10.7 4.1 17.8 82.2
6 6900OK — 3.6 10.8 3.7 18.1 81.9
7 7300OK 92 3.1 10.4 3.5 17.0 83.0
8 7050OK 89 2.9 9.7 4.5 17.1 82.9 I
Average 3.0 10.1 4.1 17.2 82.8
Further consideration of grading performance for specific grades indicated a
variation in grading accuracy for different color grades. The grading of well-defined
colors such as tan (F), red (R), and green (G) was more accurate and less variable
between booths than was the grading of combination colors such as tannish-red (FR),
green-tan (GF), and green-red (GR). An analysis of the percentage of color grades
graded differently from their established base grade for several well—defined and
several combination colors indicated an apparent improvement in grading perform-
ance for combination color grades with an increase in the color-rendering index of
the light source. A summary of these data is shown in Table 2 for those light
sources on which color-rendering indexes were available. A very definite improve-

 ment in the over-all grading accuracy for FG, GF, and GR color grades can be noted ·
with an increase in the color-rendering index of the light sources. No such effect
can be detected in relation to correlated lamp color temperatures.
TABLE 2. -— Percentage of Color Grades Unchanged from Base Grades—Arra.nged
in Order of I. E.S. Color-rendering Index
Percentage Unchanged
I. E. S. Color- Booth FR, GF and GR F, G, R, D and K
Rendering Index Number Color Grades Color Grades
85 1 71 . 6 87 . 4
88 3 72. 8 84. 4
89 8 73 . 9 82.0
90 4 73. 8 85 . 4
92 5 82. 3 84. 3 .
92 7 79. 2 87. 2
Another phenomenon noted in analyzing the results of this study was that the
graders tended to raise the color grade of tobacco samples above the base grade
more often than they tended to lower it. This was equally true for all light sources
and cannot be fully explained by the authors. One possible explanation for such a
tendency might be that the graders were not accustomed to grading under the foot-
candle light intensity which was established in each booth. Light intensities on ware-
house floors vary considerably and probably average closer to 60 footcandles than to ,
100 footcandles. The light intensity used in test booths may have "washed out" or
made less perceptible to the grader certain secondary colors in the tobacco samples,
thereby raising their designation of those color grades in which such color factors · _
were important.
After completing the entire sequence of grading operation, as described in
the experimental procedure, each grader was asked to make a visual appraisal of ·
the different light sources—indicating which sources he preferred for grading pur-
poses and also those that he considered least desirable. Ten graders gave the rela-
tive ranking of enough lights to establish a complete preference order. By adding
up the number corresponding to the ranking (1 for best, 2 for second choice, etc.)
TABLE 3.- Color Temperature, I. E.S. Color-rendering Index and Grader Prefer- -4
ence Index for Light Sources Used in Grading Experiment
Correlated Lamp Color Rendering Preference
Booth Temperature gK°2 Index Index
1 4200 85 80 . 0
2 51 25 —— 46 . 5
3 8400 88 48.0
4 6570 90 51. 0 .
5 5890 92 32. 0
6 6900 — 30.0
7 7300 92 30 . 5
8 7050 89 42. 0

 given each light by these 10 graders, a numerical preference index was obtained,
as shown in Table 3. A high degree of preference by the graders resulted in a low
index, while a low ranking resulted in a high index. The tabular values show that
all graders listed the light source in the first booth as being the least desirable.
_ ‘ Booths 5, 6, and 7 received ratings well above those of the other five booths. In
general, the values in Table 3 indicate that grader preference for the different light
sources is much more closely related to a light's color—rendering index than to its
correlated color temperature.
Light Quality Recommendations
Based on the research of the Kentucky Station reported in this study and on
lighting practices currently being employed where daylight color rendering is
important, the following specifications are recommended for providing acceptable
and standardized light quality when tobacco is graded under electric fluorescent
l lamps.
Color guality specifications. —The standard for color quality of illumination
is the color and spectral distribution of a moderately overcast northern sky as
represented by the 74000K Abbot-Gibson daylight. Acceptable illuminants for
general tobacco grading and sorting should have a correlated color temperature
between 65000K and 75000K. .
Color—rendering index. —Acceptable light sources should provide an I. E.S.
color—rendering index of not less than 90. 2 For establishing standards and for more
critical grading operations, the color—rendering index should be 92 or higher.
As noted earlier in this report, the results of experimental grading tests
under various light sources ranging well below the foregoing recommended color
temperature range showed no significant difference in the grader's ability to evaluate
grade factors under the different lights. It was deemed advisable, however, to
narrow the recommended tolerance for color quality to the specified limits as set
forth. This is because the long—established objective of the lamp industry has been
to create a light source which would provide a spectral energy distribution or exhibit
a color quality equal to or comparable with northsky daylight at high noon. Techno-
logical progress in the electrical industry has arrived at the stage where color
energy of the level of northsky daylight can be provided in a single, standard fluor-
escent tube at an economical cost to the user. Another reason for specifying a
specific narrow range of tolerance is for the sake of achieving uniform light quality. V
Uniformity of light, not only over a given work area but also throughout the many
points of product evaluation in the tobacco market channel, is more important than
V any one specific level or quality of light energy. Experimental grading tests at the
Kentucky Station substantiate the point that the human eye has the capacity for con-
siderable adjustment to various levels of color energy without losing grading accuracy.
But this condition for product evaluation need not exist now since the electrical
industry has the capacity to manufacture an economical lamp reproducing a color
. energy approximating northsky daylight. A uniform light over all points of grade
evaluation of the market channel means a more efficient, coordinated flow where
grading is essential to price and use determination.
2Fluo1·escent light sources which meet these specifications have been shown in grading experiments to
be acceptable illuminants for tobacco grading. The reference or standard light source used to compute the
‘ color-rendering index of different light sources should be the Abbot-Gibson spectral distribution having the
nearest correlated color temperature Q 250°K) to that of the test source. Standard I. E. S. procedures (4)