Abstract

The purpose of this study was to investigate the relation of the level of illumination intensity to performance and fatigue in visual work. The question of illumination requirements is of considerable importance from the point of view of physiological optics, industrial physiology, and public health. Yet a large part of the research done in the past leaves much to be desired in regard to general approach and specific testing techniques as well as experimental analysis and statistical evaluation. In the present series six illumination levels (2, 5, 15, 50, 100, and 300 footcandles) were studied in repeated experiments in six normal subjects. The work task involved recognition of fine details (letters) and reproduced the essential features of a conveyor inspection operation. In addition to the studying of various criteria of work performance and their change in the course of 2 hours of work, a large battery of visual tests was applied before and after the work so as to characterize the degree of fatigue. Varied illumination affected the performance more than the functional criteria of fatigue. Only one function, the recognition time for stimuli of threshold size, showed a decreasing degree of fatigue up to 300 ft.-c, all other variables, including performance, which changed with a changing level of illumination showed an optimum at 100 ft.-c. The demonstration of an optimum level of illumination makes highly questionable the current practice of recommending “minimum” levels of illumination for industrial jobs, since deterioration of performance and increase in fatigue may result when the optimal level is exceeded. The optimum of 100 ft.-c for the present strenuous visual task is at or below the minimum which should be recommended on the basis of the code of the Illuminating Engineering Society.

© 1948 Optical Society of America

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References

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  1. “American recommended practice of industrial lighting,” Illuminating Engineering Society (1942).
  2. J. S. Rogers, Illumination. In “Protecting Plant Manpower,” pp. 63–66, U. S. Dept. of Labor, Washington, 1941.
  3. A. D. Brandt and H. E. Seifert, “Illumination, noise and radiant energy,” Manual of Industrial Hygiene (W. M. Gafafer) (W. B. Saunders, Philadelphia, 1943), pp. 353–372.
  4. Committee on Industrial and School Lighting, “Report on lighting in the textile industry,” Trans. Illum. Eng. Soc.32, 247 (1937).
  5. Committee on Industrial and School Lighting, “Report on lighting in the shoe manufacturing company,” Trans. Illum. Eng. Soc.32, 289 (1937).
  6. Committee on Industrial and School Lighting, “Progress report on the lighting in the printing industry,” Trans. Illum. Eng. Soc.31, 277 (1936).
  7. Committee on Industrial and School Lighting, “Report on lighting in the candy manufacturing industry,” Trans. Illum. Eng. Soc.32, 483 (1937).
  8. Committee on Industrial and School Lighting, “Studies in lighting of intricate production, assembly and inspection processes,” Trans. Illum. Eng. Soc. 32, 1019 (1937).
  9. Committee on Industrial and School Lighting, “Lighting for silk and rayon throwing and wide goods weaving,” Trans. Illum. Eng. Soc. 33, 17 (1938).
  10. Committee on Industrial and School Lighting, “Lighting for the machining of small metal parts,” Trans. Illum. Eng. Soc. 34, 21 (1939).
  11. Committee on Industrial and School Lighting, “Lighting of power presses,” Trans. Illum. Eng. Soc. 34, 153 (1939).
  12. M. Luckiesh and F. M. Moss, The Science of Seeing (D. Van Nostrand Company, Inc., New York, 1938), p. 548.
  13. J. Brozek, E. Simonson, and A. Keys, “A work test for quantitative study of visual performance and fatigue,” J. App. Psychol. 31, 519 (1947).
    [CrossRef]
  14. H. C. Weston, “The relation between illumination and industrial efficiency: I. The effect of the size of work.” Joint Rep. Industr. Health Res. Board and Illum. Res. Comm. (London) (1935).
  15. F. N. Freeman, “An investigation of the illumination requirements of school buildings,” National Education Association: Report of Committee on School House Planning, 90 (1925).
  16. H. J. Ströer, “Rationalisierung der Arbeitsplatz-beleuchtung,” Industr. Psychotechnik 3, 289 (1926).
  17. J. Brozek, E. Simonson, and A. Keys, “Quantitative analysis of voluntary eye movements,” (to be published).
  18. J. Brozek, E. Simonson, W. J. Bushard, and J. H. Peterson, “Effects of practice and the consistency of repeated measurements of accommodation and vergence,” Am. J. Ophthal. (in press).
  19. J. Brozek, E. Simonson, and H. Alexander, “Statistical comparison of changes in fitness characteristics,” (in press).
  20. M. A. Tinker, “Effect of visual adaptation upon intensity of light preferred for reading,” Am. J. Psychol. 54, 559 (1941).
  21. E. Simonson, “L’adaptation au travail physique,” Le Travail Humain 4, 129 (1936).
  22. M. Luckiesh and F. M. Moss, “Fatigue of convergence induced by reading as a function of illumination intensity,” Am. J. Ophthal. 18, 319 (1935).
  23. H. Schulz, “Die Ermüdung des Auges,” Industr. Psychotechnik 2, 5 (1925).
  24. C. E. Ferree and G. Rand, “The efficiency of the eye under different conditions of lighting: the effect of varying the distribution factors and intensity,” Trans. Illum. Eng. Soc. 10, 407 (1915).
  25. M. A. Tinker, “Illumination standards,” Am. J. Pub. Health 36, 963 (1946).
  26. T. A. Ryan, “Work and effort: the psychology of efficiency,” (in press).
  27. L. R. White, R. H. Britten, J. H. Ives, and L. R. Thompson, “Studies in illumination II. Relationship of illumination to ocular efficiency and ocular fatigue among the letter separators in the Chicago post office,” , Washington (1929).
    [CrossRef]
  28. A. C. Hoffman, “Luckiesh and Moss on reading illumination,” J. App. Psychol. 31, 44 (1947).
  29. C. A. Oakley, Men at Work (University of London Press, London, 1946), p. 301.
  30. H. C. Weston and A. K. Taylor, “The relation between illumination and efficiency in fine work (typesetting by hand),” Joint Rep. Industr. Fatigue Res. Board and Illum. Res. Comm., (London) (1926).
  31. C. E. Snow, “A discussion of the relation of illumination intensity to productive efficiency,” Tech. Eng. News 8, 257 (1927).
    [CrossRef]
  32. M. A. Tinker, “Validity of frequency of blinking as a criterion of readability,” J. Exp. Psychol. 36, 453 (1937).
  33. R. A. McFarland, A. H. Holway, and L. M. Hurvich, “Studies of visual fatigue,” Harvard Univ. Graduate School of Business Administration (1942).
    [CrossRef]
  34. R. A. McFarland, C. A. Knehr, and C. Berens, “Metabolism and pulse rate as related to reading under high and low levels of illumination,” J. Exp. Psychol. 25, 65 (1939).
    [CrossRef]
  35. M. E. Bitterman, “Heart rate and frequency of blinking as indices of visual efficiency,” J. Exp. Psychol. 35, 279 (1945).
    [CrossRef]

1947 (2)

J. Brozek, E. Simonson, and A. Keys, “A work test for quantitative study of visual performance and fatigue,” J. App. Psychol. 31, 519 (1947).
[CrossRef]

A. C. Hoffman, “Luckiesh and Moss on reading illumination,” J. App. Psychol. 31, 44 (1947).

1946 (1)

M. A. Tinker, “Illumination standards,” Am. J. Pub. Health 36, 963 (1946).

1945 (1)

M. E. Bitterman, “Heart rate and frequency of blinking as indices of visual efficiency,” J. Exp. Psychol. 35, 279 (1945).
[CrossRef]

1942 (1)

“American recommended practice of industrial lighting,” Illuminating Engineering Society (1942).

1941 (1)

M. A. Tinker, “Effect of visual adaptation upon intensity of light preferred for reading,” Am. J. Psychol. 54, 559 (1941).

1939 (3)

Committee on Industrial and School Lighting, “Lighting for the machining of small metal parts,” Trans. Illum. Eng. Soc. 34, 21 (1939).

Committee on Industrial and School Lighting, “Lighting of power presses,” Trans. Illum. Eng. Soc. 34, 153 (1939).

R. A. McFarland, C. A. Knehr, and C. Berens, “Metabolism and pulse rate as related to reading under high and low levels of illumination,” J. Exp. Psychol. 25, 65 (1939).
[CrossRef]

1938 (1)

Committee on Industrial and School Lighting, “Lighting for silk and rayon throwing and wide goods weaving,” Trans. Illum. Eng. Soc. 33, 17 (1938).

1937 (2)

M. A. Tinker, “Validity of frequency of blinking as a criterion of readability,” J. Exp. Psychol. 36, 453 (1937).

Committee on Industrial and School Lighting, “Studies in lighting of intricate production, assembly and inspection processes,” Trans. Illum. Eng. Soc. 32, 1019 (1937).

1936 (1)

E. Simonson, “L’adaptation au travail physique,” Le Travail Humain 4, 129 (1936).

1935 (1)

M. Luckiesh and F. M. Moss, “Fatigue of convergence induced by reading as a function of illumination intensity,” Am. J. Ophthal. 18, 319 (1935).

1927 (1)

C. E. Snow, “A discussion of the relation of illumination intensity to productive efficiency,” Tech. Eng. News 8, 257 (1927).
[CrossRef]

1926 (1)

H. J. Ströer, “Rationalisierung der Arbeitsplatz-beleuchtung,” Industr. Psychotechnik 3, 289 (1926).

1925 (1)

H. Schulz, “Die Ermüdung des Auges,” Industr. Psychotechnik 2, 5 (1925).

1915 (1)

C. E. Ferree and G. Rand, “The efficiency of the eye under different conditions of lighting: the effect of varying the distribution factors and intensity,” Trans. Illum. Eng. Soc. 10, 407 (1915).

Alexander, H.

J. Brozek, E. Simonson, and H. Alexander, “Statistical comparison of changes in fitness characteristics,” (in press).

Berens, C.

R. A. McFarland, C. A. Knehr, and C. Berens, “Metabolism and pulse rate as related to reading under high and low levels of illumination,” J. Exp. Psychol. 25, 65 (1939).
[CrossRef]

Bitterman, M. E.

M. E. Bitterman, “Heart rate and frequency of blinking as indices of visual efficiency,” J. Exp. Psychol. 35, 279 (1945).
[CrossRef]

Brandt, A. D.

A. D. Brandt and H. E. Seifert, “Illumination, noise and radiant energy,” Manual of Industrial Hygiene (W. M. Gafafer) (W. B. Saunders, Philadelphia, 1943), pp. 353–372.

Britten, R. H.

L. R. White, R. H. Britten, J. H. Ives, and L. R. Thompson, “Studies in illumination II. Relationship of illumination to ocular efficiency and ocular fatigue among the letter separators in the Chicago post office,” , Washington (1929).
[CrossRef]

Brozek, J.

J. Brozek, E. Simonson, and A. Keys, “A work test for quantitative study of visual performance and fatigue,” J. App. Psychol. 31, 519 (1947).
[CrossRef]

J. Brozek, E. Simonson, and A. Keys, “Quantitative analysis of voluntary eye movements,” (to be published).

J. Brozek, E. Simonson, and H. Alexander, “Statistical comparison of changes in fitness characteristics,” (in press).

J. Brozek, E. Simonson, W. J. Bushard, and J. H. Peterson, “Effects of practice and the consistency of repeated measurements of accommodation and vergence,” Am. J. Ophthal. (in press).

Bushard, W. J.

J. Brozek, E. Simonson, W. J. Bushard, and J. H. Peterson, “Effects of practice and the consistency of repeated measurements of accommodation and vergence,” Am. J. Ophthal. (in press).

Ferree, C. E.

C. E. Ferree and G. Rand, “The efficiency of the eye under different conditions of lighting: the effect of varying the distribution factors and intensity,” Trans. Illum. Eng. Soc. 10, 407 (1915).

Freeman, F. N.

F. N. Freeman, “An investigation of the illumination requirements of school buildings,” National Education Association: Report of Committee on School House Planning, 90 (1925).

Gafafer, W. M.

A. D. Brandt and H. E. Seifert, “Illumination, noise and radiant energy,” Manual of Industrial Hygiene (W. M. Gafafer) (W. B. Saunders, Philadelphia, 1943), pp. 353–372.

Hoffman, A. C.

A. C. Hoffman, “Luckiesh and Moss on reading illumination,” J. App. Psychol. 31, 44 (1947).

Holway, A. H.

R. A. McFarland, A. H. Holway, and L. M. Hurvich, “Studies of visual fatigue,” Harvard Univ. Graduate School of Business Administration (1942).
[CrossRef]

Hurvich, L. M.

R. A. McFarland, A. H. Holway, and L. M. Hurvich, “Studies of visual fatigue,” Harvard Univ. Graduate School of Business Administration (1942).
[CrossRef]

Ives, J. H.

L. R. White, R. H. Britten, J. H. Ives, and L. R. Thompson, “Studies in illumination II. Relationship of illumination to ocular efficiency and ocular fatigue among the letter separators in the Chicago post office,” , Washington (1929).
[CrossRef]

Keys, A.

J. Brozek, E. Simonson, and A. Keys, “A work test for quantitative study of visual performance and fatigue,” J. App. Psychol. 31, 519 (1947).
[CrossRef]

J. Brozek, E. Simonson, and A. Keys, “Quantitative analysis of voluntary eye movements,” (to be published).

Knehr, C. A.

R. A. McFarland, C. A. Knehr, and C. Berens, “Metabolism and pulse rate as related to reading under high and low levels of illumination,” J. Exp. Psychol. 25, 65 (1939).
[CrossRef]

Luckiesh, M.

M. Luckiesh and F. M. Moss, “Fatigue of convergence induced by reading as a function of illumination intensity,” Am. J. Ophthal. 18, 319 (1935).

M. Luckiesh and F. M. Moss, The Science of Seeing (D. Van Nostrand Company, Inc., New York, 1938), p. 548.

McFarland, R. A.

R. A. McFarland, C. A. Knehr, and C. Berens, “Metabolism and pulse rate as related to reading under high and low levels of illumination,” J. Exp. Psychol. 25, 65 (1939).
[CrossRef]

R. A. McFarland, A. H. Holway, and L. M. Hurvich, “Studies of visual fatigue,” Harvard Univ. Graduate School of Business Administration (1942).
[CrossRef]

Moss, F. M.

M. Luckiesh and F. M. Moss, “Fatigue of convergence induced by reading as a function of illumination intensity,” Am. J. Ophthal. 18, 319 (1935).

M. Luckiesh and F. M. Moss, The Science of Seeing (D. Van Nostrand Company, Inc., New York, 1938), p. 548.

Oakley, C. A.

C. A. Oakley, Men at Work (University of London Press, London, 1946), p. 301.

Peterson, J. H.

J. Brozek, E. Simonson, W. J. Bushard, and J. H. Peterson, “Effects of practice and the consistency of repeated measurements of accommodation and vergence,” Am. J. Ophthal. (in press).

Rand, G.

C. E. Ferree and G. Rand, “The efficiency of the eye under different conditions of lighting: the effect of varying the distribution factors and intensity,” Trans. Illum. Eng. Soc. 10, 407 (1915).

Rogers, J. S.

J. S. Rogers, Illumination. In “Protecting Plant Manpower,” pp. 63–66, U. S. Dept. of Labor, Washington, 1941.

Ryan, T. A.

T. A. Ryan, “Work and effort: the psychology of efficiency,” (in press).

Schulz, H.

H. Schulz, “Die Ermüdung des Auges,” Industr. Psychotechnik 2, 5 (1925).

Seifert, H. E.

A. D. Brandt and H. E. Seifert, “Illumination, noise and radiant energy,” Manual of Industrial Hygiene (W. M. Gafafer) (W. B. Saunders, Philadelphia, 1943), pp. 353–372.

Simonson, E.

J. Brozek, E. Simonson, and A. Keys, “A work test for quantitative study of visual performance and fatigue,” J. App. Psychol. 31, 519 (1947).
[CrossRef]

E. Simonson, “L’adaptation au travail physique,” Le Travail Humain 4, 129 (1936).

J. Brozek, E. Simonson, and H. Alexander, “Statistical comparison of changes in fitness characteristics,” (in press).

J. Brozek, E. Simonson, W. J. Bushard, and J. H. Peterson, “Effects of practice and the consistency of repeated measurements of accommodation and vergence,” Am. J. Ophthal. (in press).

J. Brozek, E. Simonson, and A. Keys, “Quantitative analysis of voluntary eye movements,” (to be published).

Snow, C. E.

C. E. Snow, “A discussion of the relation of illumination intensity to productive efficiency,” Tech. Eng. News 8, 257 (1927).
[CrossRef]

Ströer, H. J.

H. J. Ströer, “Rationalisierung der Arbeitsplatz-beleuchtung,” Industr. Psychotechnik 3, 289 (1926).

Taylor, A. K.

H. C. Weston and A. K. Taylor, “The relation between illumination and efficiency in fine work (typesetting by hand),” Joint Rep. Industr. Fatigue Res. Board and Illum. Res. Comm., (London) (1926).

Thompson, L. R.

L. R. White, R. H. Britten, J. H. Ives, and L. R. Thompson, “Studies in illumination II. Relationship of illumination to ocular efficiency and ocular fatigue among the letter separators in the Chicago post office,” , Washington (1929).
[CrossRef]

Tinker, M. A.

M. A. Tinker, “Illumination standards,” Am. J. Pub. Health 36, 963 (1946).

M. A. Tinker, “Effect of visual adaptation upon intensity of light preferred for reading,” Am. J. Psychol. 54, 559 (1941).

M. A. Tinker, “Validity of frequency of blinking as a criterion of readability,” J. Exp. Psychol. 36, 453 (1937).

Weston, H. C.

H. C. Weston, “The relation between illumination and industrial efficiency: I. The effect of the size of work.” Joint Rep. Industr. Health Res. Board and Illum. Res. Comm. (London) (1935).

H. C. Weston and A. K. Taylor, “The relation between illumination and efficiency in fine work (typesetting by hand),” Joint Rep. Industr. Fatigue Res. Board and Illum. Res. Comm., (London) (1926).

White, L. R.

L. R. White, R. H. Britten, J. H. Ives, and L. R. Thompson, “Studies in illumination II. Relationship of illumination to ocular efficiency and ocular fatigue among the letter separators in the Chicago post office,” , Washington (1929).
[CrossRef]

Am. J. Ophthal. (1)

M. Luckiesh and F. M. Moss, “Fatigue of convergence induced by reading as a function of illumination intensity,” Am. J. Ophthal. 18, 319 (1935).

Am. J. Psychol. (1)

M. A. Tinker, “Effect of visual adaptation upon intensity of light preferred for reading,” Am. J. Psychol. 54, 559 (1941).

Am. J. Pub. Health (1)

M. A. Tinker, “Illumination standards,” Am. J. Pub. Health 36, 963 (1946).

Illuminating Engineering Society (1)

“American recommended practice of industrial lighting,” Illuminating Engineering Society (1942).

Industr. Psychotechnik (2)

H. J. Ströer, “Rationalisierung der Arbeitsplatz-beleuchtung,” Industr. Psychotechnik 3, 289 (1926).

H. Schulz, “Die Ermüdung des Auges,” Industr. Psychotechnik 2, 5 (1925).

J. App. Psychol. (2)

A. C. Hoffman, “Luckiesh and Moss on reading illumination,” J. App. Psychol. 31, 44 (1947).

J. Brozek, E. Simonson, and A. Keys, “A work test for quantitative study of visual performance and fatigue,” J. App. Psychol. 31, 519 (1947).
[CrossRef]

J. Exp. Psychol. (3)

M. A. Tinker, “Validity of frequency of blinking as a criterion of readability,” J. Exp. Psychol. 36, 453 (1937).

R. A. McFarland, C. A. Knehr, and C. Berens, “Metabolism and pulse rate as related to reading under high and low levels of illumination,” J. Exp. Psychol. 25, 65 (1939).
[CrossRef]

M. E. Bitterman, “Heart rate and frequency of blinking as indices of visual efficiency,” J. Exp. Psychol. 35, 279 (1945).
[CrossRef]

Le Travail Humain (1)

E. Simonson, “L’adaptation au travail physique,” Le Travail Humain 4, 129 (1936).

Tech. Eng. News (1)

C. E. Snow, “A discussion of the relation of illumination intensity to productive efficiency,” Tech. Eng. News 8, 257 (1927).
[CrossRef]

Trans. Illum. Eng. Soc. (5)

C. E. Ferree and G. Rand, “The efficiency of the eye under different conditions of lighting: the effect of varying the distribution factors and intensity,” Trans. Illum. Eng. Soc. 10, 407 (1915).

Committee on Industrial and School Lighting, “Studies in lighting of intricate production, assembly and inspection processes,” Trans. Illum. Eng. Soc. 32, 1019 (1937).

Committee on Industrial and School Lighting, “Lighting for silk and rayon throwing and wide goods weaving,” Trans. Illum. Eng. Soc. 33, 17 (1938).

Committee on Industrial and School Lighting, “Lighting for the machining of small metal parts,” Trans. Illum. Eng. Soc. 34, 21 (1939).

Committee on Industrial and School Lighting, “Lighting of power presses,” Trans. Illum. Eng. Soc. 34, 153 (1939).

Other (17)

M. Luckiesh and F. M. Moss, The Science of Seeing (D. Van Nostrand Company, Inc., New York, 1938), p. 548.

J. S. Rogers, Illumination. In “Protecting Plant Manpower,” pp. 63–66, U. S. Dept. of Labor, Washington, 1941.

A. D. Brandt and H. E. Seifert, “Illumination, noise and radiant energy,” Manual of Industrial Hygiene (W. M. Gafafer) (W. B. Saunders, Philadelphia, 1943), pp. 353–372.

Committee on Industrial and School Lighting, “Report on lighting in the textile industry,” Trans. Illum. Eng. Soc.32, 247 (1937).

Committee on Industrial and School Lighting, “Report on lighting in the shoe manufacturing company,” Trans. Illum. Eng. Soc.32, 289 (1937).

Committee on Industrial and School Lighting, “Progress report on the lighting in the printing industry,” Trans. Illum. Eng. Soc.31, 277 (1936).

Committee on Industrial and School Lighting, “Report on lighting in the candy manufacturing industry,” Trans. Illum. Eng. Soc.32, 483 (1937).

H. C. Weston, “The relation between illumination and industrial efficiency: I. The effect of the size of work.” Joint Rep. Industr. Health Res. Board and Illum. Res. Comm. (London) (1935).

F. N. Freeman, “An investigation of the illumination requirements of school buildings,” National Education Association: Report of Committee on School House Planning, 90 (1925).

J. Brozek, E. Simonson, and A. Keys, “Quantitative analysis of voluntary eye movements,” (to be published).

J. Brozek, E. Simonson, W. J. Bushard, and J. H. Peterson, “Effects of practice and the consistency of repeated measurements of accommodation and vergence,” Am. J. Ophthal. (in press).

J. Brozek, E. Simonson, and H. Alexander, “Statistical comparison of changes in fitness characteristics,” (in press).

T. A. Ryan, “Work and effort: the psychology of efficiency,” (in press).

L. R. White, R. H. Britten, J. H. Ives, and L. R. Thompson, “Studies in illumination II. Relationship of illumination to ocular efficiency and ocular fatigue among the letter separators in the Chicago post office,” , Washington (1929).
[CrossRef]

R. A. McFarland, A. H. Holway, and L. M. Hurvich, “Studies of visual fatigue,” Harvard Univ. Graduate School of Business Administration (1942).
[CrossRef]

C. A. Oakley, Men at Work (University of London Press, London, 1946), p. 301.

H. C. Weston and A. K. Taylor, “The relation between illumination and efficiency in fine work (typesetting by hand),” Joint Rep. Industr. Fatigue Res. Board and Illum. Res. Comm., (London) (1926).

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Figures (7)

Fig. 1
Fig. 1

Effect of the illumination level on the performance average. The values at 5, 100, and 300 ft.-c are based on 36 determinations (solid circles), the values at 2, 15, and 50 ft.-c are based on 6, 12, and 12 determinations (open circles).

Fig. 2
Fig. 2

Effect of the illumination level on the drop of performance during 2 hours of visual work.

Fig. 3
Fig. 3

Effect of the illumination level on the performance range (maximum intra-individual variation of performance during 2 hours of visual work).

Fig. 4
Fig. 4

Effect of the illumination level on the blinking rate during visual work.

Fig. 5
Fig. 5

Effect of the illumination level on subjective discomfort, scored on the basis of 10 items of a questionnaire.

Fig. 6
Fig. 6

Effect of the illumination level on the change of recognition time for threshold size stimuli, tested before and after the visual work. The grand mean was −1.64 sec.

Fig. 7
Fig. 7

Effect of the illumination level on the change in the fusion frequency of flicker, tested before and after the visual work.

Tables (7)

Tables Icon

Table I Units of functions and the “desirable” values of the scores.

Tables Icon

Table II Mean scores for performance, blinking rate, and questionnaire score at three levels of illumination, and significance of the fatigue changes taking place during 2 hours of visual work.

Tables Icon

Table III Visual functions which exhibited significant trends with variation of the illumination level.

Tables Icon

Table IV Fatigue changes in retinal functions resulting from 2 hours of visual work at three levels of illumination.

Tables Icon

Table V Change in several ophthalmological routine tests at three levels of illumination.

Tables Icon

Table VI Fatigue changes in ophthalmographic functions at three levels of illumination.

Tables Icon

Table VII Average preference scores for 5 levels of illumination intensity. The smaller the score, the more preferred the condition.

Equations (8)

Equations on this page are rendered with MathJax. Learn more.

Δ = X 1 - X 2 ,
F = ( Σ Δ ) 2 / n Σ Δ 2 - ( Σ Δ ) 2 / n n - 1 ,
t = Δ ¯ S. D. Δ ¯ .
t = Δ ¯ S.D. Δ ¯ .
Δ ¯ = X ¯ i - X ¯ .
S.D. Δ ¯ = 1 c S. D. Δ ¯ c ,
c = k ! 2 ( k - 2 ) ! .
( t ) = Δ ¯ S.D. Δ ¯ .