1The Laboratory of Physiological Hygiene, University of Minnesota, Minneapolis, Minnesota
**With the assistance of W. J. Bushard and H. G. Peterson of the Division of Ophthalmology, University of Minnesota, School of Medicine, J. C. Franklin, and A. Butler.
There is a large but inconclusive amount of literature on the effects of the color of light on single visual functions, such as visual acuity. The amount of dependable information on the effects of the spectral quality of illumination on work performance is negligible. It was the purpose of the present study to investigate this problem. The work test involved recognition of very fine details (letters) and was designed to reproduce the essential features of conveyor inspection. The standard duration of work was 2 hours. Output, results of a large array of tests of visual functions, subjective reactions (complaints), and subjective preferences were considered as criteria in judging the relative superiority or inferiority of the three illuminants compared (ordinary inside frosted lamps; “natural white” lamps with a white, slightly bluish coating; and Verd-A-Ray lamps having a greenish coating). The illumination intensity (5 ft.-c, 100 ft.-c, and 300 ft.-c) on the work place was made identical for all three lamps. Statistically significant differences between the illuminants were established with reference to a number of criteria of performance and fatigue. The differences were, in general, in favor of the illuminant with greenish coating. The present study used commercially available illuminants. Further systematic studies designed to determine the optimal spectral characteristics of light are needed.
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Emission of spectral energy for the frosted (Fr), “natural white” (NW), and Verd-A-Ray (VR) lamps, in terms of utilizable spectral energy, and emission of NW and VR lamps in percentage of Fr lamps.
Wave-length angstrom units
Relative average light sensitivity of human retina
Utilizable energy
Percent of Fr
Fr
NW
VR
NW
VR
4300
0.01
0.02
0.02
0.01
111
43
4400
0.02
0.04
0.05
0.03
112
88
4600
0.07
0.19
0.21
0.19
109
98
4800
0.14
0.50
0.53
0.45
107
90
5000
0.32
1.42
1.45
1.51
106
106
5200
0.70
3.72
3.92
4.05
105
109
5400
0.95
5.85
6.12
6.12
105
105
5500
1.00
6.58
6.90
6.64
105
101
5600
0.99
7.08
7.24
6.80
102
96
5700
0.95
7.12
7.12
6.53
100
92
5800
0.87
6.96
6.70
6.18
96
89
6000
0.63
5.61
5.22
4.85
93
87
6200
0.37
3.62
3.35
3.13
92
86
6300
0.25
2.56
2.35
2.20
92
86
6400
0.17
1.81
1.67
1.55
92
86
6600
0.06
0.70
0.64
0.60
92
85
Table II
Effect of three different illuminants (Fr, NW, VR) on visual performance, blinking rate, and questionnaire score during visual work at three levels of illumination. Mean values of 12 determinations. Negative values indicate deterioration.
Level of illumination
5 ft.-c
100 ft.-c
300 ft.-c
Function
Fr
NW
VR
Fr
NW
VR
Fr
NW
VR
Units
Questionnaire score
10.3
7.0
8.1
7.8
7.3
8.0
9.7
7.9
7.2
Total score
Performance average
164.8
166.1
171.3
187.8
190.1
189.9
187.8
189.4
186.7
Number of correct letters
Performance drop
−13.2
−15.2
−13.8
−8.6
−5.8
−6.0
−9.7
−8.6
−14.3
Number of correct letters
Performance range
25.9
24.9
16.8
10.9
9.1
7.5
11.8
11.3
15.8
Number of correct letters
Blinking rate average
9.76
9.95
9.59
5.39
6.26
5.75
8.09
8.48
8.39
Blinks per minute
Blinking rate difference
−2.19
−1.92
1.63
0.13
0.08
−1.64
−1.96
0.94
−1.15
Blinks per minute
Table III
Effect of three different illuminants (Fr, NW, VR) on the change (
) of retinal functions during visual work at three levels of illumination. Mean values of 12 determinations. Negative values indicate deterioration.
Level of illumination
5 ft.-c
100 ft.-c
300 ft.-c
Function
Fr
NW
VR
Fr
NW
VR
Fr
NW
VR
Units
Recognition time
−3.50
−6.04
−1.54
−2.29
−2.29
1.29
−0.9
−1.8
2.3
Seconds
Flicker fusion frequency
−1.00
−1.42
−0.36
−1.33
−1.52
0.13
−1.46
−1.93
−0.07
Flashes per second
Brightness discrimination—green
−0.24
0.26
0.14
−0.16
−0.07
−0.16
−0.15
−0.03
−0.09
Arbitrary Units
Brightness discrimination—red
−0.37
0.03
−0.28
−0.17
−0.03
0.11
−0.06
−0.13
0.32
Arbitrary Units
Table IV
Effect of three different illuminants (Fr, NW, VR) on the change (
) of several ophthalmological routine tests during visual work at three levels of illumination. Mean values of 12 determinations. Negative values indicate deterioration.
Level of illumination
5 ft.-c
100 ft.-c
300 ft.-c
Function
Fr
NW
VR
Fr
NW
VR
Fr
NW
VR
Units
Abduction power
−0.35
0.11
−0.09
−0.14
−0.32
−0.21
0.26
−0.03
0.06
Diopters
Adduction power
1.10
2.48
0.47
−0.48
1.66
1.47
−0.08
0.76
1.78
Diopters
Vertical divergence
0.08
0.04
−0.10
−0.02
0.11
−0.20
0.03
−0.11
0.03
Diopters
Accommodation near point
0.11
−0.03
−0.51
0.41
0.58
−0.07
−0.10
−0.09
0.15
Centimeters
Convergence near point
0.18
0.05
−0.48
−0.23
−0.12
−0.17
−0.08
−0.08
−0.29
Centimeters
Table V
Effect of three different illuminants (Fr, NW, VR) on the changes (
) of ophthalmographic functions during visual work at 5 foot-candles. Mean values of 12 determinations. Negative values indicate deterioration.
Function
Fr
NW
VR
Movement phase, in 1/100 sec.
0.14
−0.73
−0.87
Angular velocity, arbitrary units
0.24
−0.58
−0.52
No. of movements, cycles per sec.
−0.26
−0.10
−0.19
Fixation phase, in 1/100 sec.
−1.64
−0.67
−1.09
Extent of movement during fixation phase, arbitrary units
−0.22
−0.62
−0.52
Discrepancy between fixation point and target, arbitrary units
0.26
−1.47
−0.15
Table VI
Average change of recognition time, flicker fusion frequency, and adduction power resulting from visual work under each illuminant (Fr, NW, VR), all illumination levels combined.
=the mean difference between 36 pairs of measurements made before and after visual work under the illuminant indicated. Negative
’s express deterioration. F expresses the statistical significance of the mean changes (
). F at 5 percent of significance is 4.13. F at 1 percent of significance is 7.44.
Table VII
Mean differences (
) between three illuminants (Fr, NW, VR) at three levels of illumination, and their statistical significance.
Negative
’s indicate the relative inferiority, the positive Δ’s a relative superiority of the first of the two illuminants compared. F expresses the statistical significance of the mean differences (
) between the two compared illuminants. F at 5 percent of significance is 4.84. F at 1 percent of significance is 9.65.
Table VIII
Mean differences in flicker fusion frequency and questionnaire score between illuminants (Fr, NW, VR), all illumination levels combined, and their statistical significance (F-test).
Negative
’s indicate greater deterioration at the first of the two compared illuminants. F expresses the statistical significance of the mean difference (
) between the two compared illuminants. F at 5 percent of significance is 4.13. F at 1 percent of significance is 7.44.
Table IX
Subjective preference scores (average values of 6 subjects).
Illumination level, in ft.-c
VR
Fr
NW
5
1.17
2.50
2.33
50
1.33
2.33
2.33
100
1.25
2.33
2.42
300
1.42
2.17
2.42
Mean of all illumination levels
1.29
2.33
2.37
Tables (9)
Table I
Emission of spectral energy for the frosted (Fr), “natural white” (NW), and Verd-A-Ray (VR) lamps, in terms of utilizable spectral energy, and emission of NW and VR lamps in percentage of Fr lamps.
Wave-length angstrom units
Relative average light sensitivity of human retina
Utilizable energy
Percent of Fr
Fr
NW
VR
NW
VR
4300
0.01
0.02
0.02
0.01
111
43
4400
0.02
0.04
0.05
0.03
112
88
4600
0.07
0.19
0.21
0.19
109
98
4800
0.14
0.50
0.53
0.45
107
90
5000
0.32
1.42
1.45
1.51
106
106
5200
0.70
3.72
3.92
4.05
105
109
5400
0.95
5.85
6.12
6.12
105
105
5500
1.00
6.58
6.90
6.64
105
101
5600
0.99
7.08
7.24
6.80
102
96
5700
0.95
7.12
7.12
6.53
100
92
5800
0.87
6.96
6.70
6.18
96
89
6000
0.63
5.61
5.22
4.85
93
87
6200
0.37
3.62
3.35
3.13
92
86
6300
0.25
2.56
2.35
2.20
92
86
6400
0.17
1.81
1.67
1.55
92
86
6600
0.06
0.70
0.64
0.60
92
85
Table II
Effect of three different illuminants (Fr, NW, VR) on visual performance, blinking rate, and questionnaire score during visual work at three levels of illumination. Mean values of 12 determinations. Negative values indicate deterioration.
Level of illumination
5 ft.-c
100 ft.-c
300 ft.-c
Function
Fr
NW
VR
Fr
NW
VR
Fr
NW
VR
Units
Questionnaire score
10.3
7.0
8.1
7.8
7.3
8.0
9.7
7.9
7.2
Total score
Performance average
164.8
166.1
171.3
187.8
190.1
189.9
187.8
189.4
186.7
Number of correct letters
Performance drop
−13.2
−15.2
−13.8
−8.6
−5.8
−6.0
−9.7
−8.6
−14.3
Number of correct letters
Performance range
25.9
24.9
16.8
10.9
9.1
7.5
11.8
11.3
15.8
Number of correct letters
Blinking rate average
9.76
9.95
9.59
5.39
6.26
5.75
8.09
8.48
8.39
Blinks per minute
Blinking rate difference
−2.19
−1.92
1.63
0.13
0.08
−1.64
−1.96
0.94
−1.15
Blinks per minute
Table III
Effect of three different illuminants (Fr, NW, VR) on the change (
) of retinal functions during visual work at three levels of illumination. Mean values of 12 determinations. Negative values indicate deterioration.
Level of illumination
5 ft.-c
100 ft.-c
300 ft.-c
Function
Fr
NW
VR
Fr
NW
VR
Fr
NW
VR
Units
Recognition time
−3.50
−6.04
−1.54
−2.29
−2.29
1.29
−0.9
−1.8
2.3
Seconds
Flicker fusion frequency
−1.00
−1.42
−0.36
−1.33
−1.52
0.13
−1.46
−1.93
−0.07
Flashes per second
Brightness discrimination—green
−0.24
0.26
0.14
−0.16
−0.07
−0.16
−0.15
−0.03
−0.09
Arbitrary Units
Brightness discrimination—red
−0.37
0.03
−0.28
−0.17
−0.03
0.11
−0.06
−0.13
0.32
Arbitrary Units
Table IV
Effect of three different illuminants (Fr, NW, VR) on the change (
) of several ophthalmological routine tests during visual work at three levels of illumination. Mean values of 12 determinations. Negative values indicate deterioration.
Level of illumination
5 ft.-c
100 ft.-c
300 ft.-c
Function
Fr
NW
VR
Fr
NW
VR
Fr
NW
VR
Units
Abduction power
−0.35
0.11
−0.09
−0.14
−0.32
−0.21
0.26
−0.03
0.06
Diopters
Adduction power
1.10
2.48
0.47
−0.48
1.66
1.47
−0.08
0.76
1.78
Diopters
Vertical divergence
0.08
0.04
−0.10
−0.02
0.11
−0.20
0.03
−0.11
0.03
Diopters
Accommodation near point
0.11
−0.03
−0.51
0.41
0.58
−0.07
−0.10
−0.09
0.15
Centimeters
Convergence near point
0.18
0.05
−0.48
−0.23
−0.12
−0.17
−0.08
−0.08
−0.29
Centimeters
Table V
Effect of three different illuminants (Fr, NW, VR) on the changes (
) of ophthalmographic functions during visual work at 5 foot-candles. Mean values of 12 determinations. Negative values indicate deterioration.
Function
Fr
NW
VR
Movement phase, in 1/100 sec.
0.14
−0.73
−0.87
Angular velocity, arbitrary units
0.24
−0.58
−0.52
No. of movements, cycles per sec.
−0.26
−0.10
−0.19
Fixation phase, in 1/100 sec.
−1.64
−0.67
−1.09
Extent of movement during fixation phase, arbitrary units
−0.22
−0.62
−0.52
Discrepancy between fixation point and target, arbitrary units
0.26
−1.47
−0.15
Table VI
Average change of recognition time, flicker fusion frequency, and adduction power resulting from visual work under each illuminant (Fr, NW, VR), all illumination levels combined.
=the mean difference between 36 pairs of measurements made before and after visual work under the illuminant indicated. Negative
’s express deterioration. F expresses the statistical significance of the mean changes (
). F at 5 percent of significance is 4.13. F at 1 percent of significance is 7.44.
Table VII
Mean differences (
) between three illuminants (Fr, NW, VR) at three levels of illumination, and their statistical significance.
Negative
’s indicate the relative inferiority, the positive Δ’s a relative superiority of the first of the two illuminants compared. F expresses the statistical significance of the mean differences (
) between the two compared illuminants. F at 5 percent of significance is 4.84. F at 1 percent of significance is 9.65.
Table VIII
Mean differences in flicker fusion frequency and questionnaire score between illuminants (Fr, NW, VR), all illumination levels combined, and their statistical significance (F-test).
Negative
’s indicate greater deterioration at the first of the two compared illuminants. F expresses the statistical significance of the mean difference (
) between the two compared illuminants. F at 5 percent of significance is 4.13. F at 1 percent of significance is 7.44.
Table IX
Subjective preference scores (average values of 6 subjects).