Abstract

Contrast ratio is an important measure of the performance of an electrooptic display. From measurements of film brightness and transmittance, we determined contrast ratios of thin polymer films containing microdroplets of liquid crystalline material. Contrast ratios based on brightness were typically ~3 for all samples studied, whereas contrast ratios based on transmittance varied from ~20 to 200 depending on the sample. We explain these differences by analyzing the relations between the illumination geometries in the two measurements and the voltage-dependent multiple scattering of light which controls the electrooptic performance of the films. Effects of the spectral content of the light source and the response of the human eye on contrast ratio were also determined. The results presented here demonstrate the importance of standardizing procedures for measuring contrast ratios of these new liquid crystal films.

© 1987 Optical Society of America

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References

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  1. H. G. Craighead, J. Cheng, S. Hackwood, “New Display Based on Electrically Induced Index Matching in an Inhomogeneous Medium,” Appl. Phys. Lett. 40, 22 (1982).
    [Crossref]
  2. J. L. Fergason, “Polymer Encapsulated Liquid Crystals for Display and Light Control Applications,” SID Dig. Tech. Pap. 16, 68 (1985).
  3. J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
    [Crossref]
  4. N. A. Vaz, G. W. Smith, G. P. Montgomery “A Light-Control Film Composed of Liquid Crystal Droplets Dispersed in an Epoxy Matrix,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).
  5. N. A. Vaz, G. W. Smith, G. P. Montgomery “An Electro-Optic Film Composed of Liquid Crystal Droplets Dispersed in a UV-Curable Polymer,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).
  6. L. Goodman, “Passive Liquid Displays: Liquid Crystals, Electrophoretics and Electrochromics,” Proc. SID 17, 30 (1976).
  7. R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
    [Crossref]
  8. W. Kaye, “Sensitive Measurement of Twist in LCD’s,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 143.
  9. T. J. Scheffer, J. Nehring, “Guest-Host Displays,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 173.
  10. J. I. Pankove, “Introduction,” in Display Devices, J. I. Pankove, Ed. (Springer-Verlag, Berlin, 1980), p. 1.
    [Crossref]
  11. B. Bahadur, “Liquid Crystal Displays,” Mol. Cryst. Liq. Cryst. 109, 3 (1984).
    [Crossref]
  12. L. E. Tannas, Ed. Flat Panel Displays and CRTs (Van Nostrand Reinhold, New York, 1985).
    [Crossref]
  13. J. Duclos, Perkin-Elmer Corp.; private communication.
  14. W. G. Driscoll, Ed. Handbook of Optics (McGraw-Hill, New York, 1978), Chaps. 1 and 9.
  15. P. Moon, “Proposed Standard Solar-Radiation Curves for Engineering Use,” J. Franklin Inst. 230, 583 (1940).
    [Crossref]
  16. N. A. Vaz, G. P. Montgomery, unpublished results.
  17. G. P. Montgomery, N. A. Vaz, unpublished results.

1986 (1)

J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
[Crossref]

1985 (1)

J. L. Fergason, “Polymer Encapsulated Liquid Crystals for Display and Light Control Applications,” SID Dig. Tech. Pap. 16, 68 (1985).

1984 (1)

B. Bahadur, “Liquid Crystal Displays,” Mol. Cryst. Liq. Cryst. 109, 3 (1984).
[Crossref]

1982 (1)

H. G. Craighead, J. Cheng, S. Hackwood, “New Display Based on Electrically Induced Index Matching in an Inhomogeneous Medium,” Appl. Phys. Lett. 40, 22 (1982).
[Crossref]

1979 (1)

R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
[Crossref]

1976 (1)

L. Goodman, “Passive Liquid Displays: Liquid Crystals, Electrophoretics and Electrochromics,” Proc. SID 17, 30 (1976).

1940 (1)

P. Moon, “Proposed Standard Solar-Radiation Curves for Engineering Use,” J. Franklin Inst. 230, 583 (1940).
[Crossref]

Bahadur, B.

B. Bahadur, “Liquid Crystal Displays,” Mol. Cryst. Liq. Cryst. 109, 3 (1984).
[Crossref]

Cheng, J.

H. G. Craighead, J. Cheng, S. Hackwood, “New Display Based on Electrically Induced Index Matching in an Inhomogeneous Medium,” Appl. Phys. Lett. 40, 22 (1982).
[Crossref]

Craighead, H. G.

H. G. Craighead, J. Cheng, S. Hackwood, “New Display Based on Electrically Induced Index Matching in an Inhomogeneous Medium,” Appl. Phys. Lett. 40, 22 (1982).
[Crossref]

Cremers, R. A.

R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
[Crossref]

Doane, J. W.

J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
[Crossref]

Duclos, J.

J. Duclos, Perkin-Elmer Corp.; private communication.

Fahrenschon, K.

R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
[Crossref]

Fergason, J. L.

J. L. Fergason, “Polymer Encapsulated Liquid Crystals for Display and Light Control Applications,” SID Dig. Tech. Pap. 16, 68 (1985).

Goodman, L.

L. Goodman, “Passive Liquid Displays: Liquid Crystals, Electrophoretics and Electrochromics,” Proc. SID 17, 30 (1976).

Hackwood, S.

H. G. Craighead, J. Cheng, S. Hackwood, “New Display Based on Electrically Induced Index Matching in an Inhomogeneous Medium,” Appl. Phys. Lett. 40, 22 (1982).
[Crossref]

Kaye, W.

W. Kaye, “Sensitive Measurement of Twist in LCD’s,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 143.

Knoll, P. M.

R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
[Crossref]

Mlynski, D. A.

R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
[Crossref]

Montgomery, G. P.

N. A. Vaz, G. W. Smith, G. P. Montgomery “An Electro-Optic Film Composed of Liquid Crystal Droplets Dispersed in a UV-Curable Polymer,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

N. A. Vaz, G. W. Smith, G. P. Montgomery “A Light-Control Film Composed of Liquid Crystal Droplets Dispersed in an Epoxy Matrix,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

N. A. Vaz, G. P. Montgomery, unpublished results.

G. P. Montgomery, N. A. Vaz, unpublished results.

Moon, P.

P. Moon, “Proposed Standard Solar-Radiation Curves for Engineering Use,” J. Franklin Inst. 230, 583 (1940).
[Crossref]

Nehring, J.

T. J. Scheffer, J. Nehring, “Guest-Host Displays,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 173.

Pankove, J. I.

J. I. Pankove, “Introduction,” in Display Devices, J. I. Pankove, Ed. (Springer-Verlag, Berlin, 1980), p. 1.
[Crossref]

Scheffer, T. J.

T. J. Scheffer, J. Nehring, “Guest-Host Displays,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 173.

Smith, G. W.

N. A. Vaz, G. W. Smith, G. P. Montgomery “A Light-Control Film Composed of Liquid Crystal Droplets Dispersed in an Epoxy Matrix,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

N. A. Vaz, G. W. Smith, G. P. Montgomery “An Electro-Optic Film Composed of Liquid Crystal Droplets Dispersed in a UV-Curable Polymer,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

Vaz, N. A.

J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
[Crossref]

N. A. Vaz, G. W. Smith, G. P. Montgomery “A Light-Control Film Composed of Liquid Crystal Droplets Dispersed in an Epoxy Matrix,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

N. A. Vaz, G. W. Smith, G. P. Montgomery “An Electro-Optic Film Composed of Liquid Crystal Droplets Dispersed in a UV-Curable Polymer,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

N. A. Vaz, G. P. Montgomery, unpublished results.

G. P. Montgomery, N. A. Vaz, unpublished results.

Wu, B.-G.

J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
[Crossref]

Žumer, S.

J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
[Crossref]

Appl. Phys. Lett. (2)

H. G. Craighead, J. Cheng, S. Hackwood, “New Display Based on Electrically Induced Index Matching in an Inhomogeneous Medium,” Appl. Phys. Lett. 40, 22 (1982).
[Crossref]

J. W. Doane, N. A. Vaz, B.-G. Wu, S. Žumer, “Field Controlled Light Scattering from Nematic Microdroplets,” Appl. Phys. Lett. 48, 269 (1986).
[Crossref]

Displays (1)

R. A. Cremers, P. M. Knoll, D. A. Mlynski, K. Fahrenschon, “A New Method for the Characterization and Evaluation of the Optical Appearance of Reflective TN-LCD’s,” Displays 1, 12 (1979).
[Crossref]

J. Franklin Inst. (1)

P. Moon, “Proposed Standard Solar-Radiation Curves for Engineering Use,” J. Franklin Inst. 230, 583 (1940).
[Crossref]

Mol. Cryst. Liq. Cryst. (1)

B. Bahadur, “Liquid Crystal Displays,” Mol. Cryst. Liq. Cryst. 109, 3 (1984).
[Crossref]

Proc. SID (1)

L. Goodman, “Passive Liquid Displays: Liquid Crystals, Electrophoretics and Electrochromics,” Proc. SID 17, 30 (1976).

SID Dig. Tech. Pap. (1)

J. L. Fergason, “Polymer Encapsulated Liquid Crystals for Display and Light Control Applications,” SID Dig. Tech. Pap. 16, 68 (1985).

Other (10)

N. A. Vaz, G. W. Smith, G. P. Montgomery “A Light-Control Film Composed of Liquid Crystal Droplets Dispersed in an Epoxy Matrix,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

N. A. Vaz, G. W. Smith, G. P. Montgomery “An Electro-Optic Film Composed of Liquid Crystal Droplets Dispersed in a UV-Curable Polymer,” at Eleventh International Liquid Crystal Conference, Berkeley, CA (June 1986).

W. Kaye, “Sensitive Measurement of Twist in LCD’s,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 143.

T. J. Scheffer, J. Nehring, “Guest-Host Displays,” in The Physics and Chemistry of Liquid Crystal Devices, G. J. Sprokel, Ed. (Plenum, New York, 1980), p. 173.

J. I. Pankove, “Introduction,” in Display Devices, J. I. Pankove, Ed. (Springer-Verlag, Berlin, 1980), p. 1.
[Crossref]

N. A. Vaz, G. P. Montgomery, unpublished results.

G. P. Montgomery, N. A. Vaz, unpublished results.

L. E. Tannas, Ed. Flat Panel Displays and CRTs (Van Nostrand Reinhold, New York, 1985).
[Crossref]

J. Duclos, Perkin-Elmer Corp.; private communication.

W. G. Driscoll, Ed. Handbook of Optics (McGraw-Hill, New York, 1978), Chaps. 1 and 9.

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Figures (2)

Fig. 1
Fig. 1

Schematic diagram of the experimental arrangement used for brightness measurements.

Fig. 2
Fig. 2

Transmittance spectra of some PDLC fims. The sample numbers in each figure correspond to those in Table I. For each sample, the upper trace corresponds to the on-state and the lower trace to the off-state.

Tables (1)

Tables Icon

Table I Transmittances and Contrast Ratios of PDLC Samples

Equations (5)

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

CR = L v on / L v 0 L v off / L v 0 .
T radiometric = λ 1 λ 2 S ( λ ) T ( λ ) d λ λ 1 λ 2 S ( λ ) d λ × 100 % ,
T photopic = λ 1 λ 2 S ( λ ) T ( λ ) y ¯ ( λ ) d λ λ 1 λ 2 S ( λ ) y ¯ ( λ ) d λ × 100 % ,
CR = T on T off ,
n eff = n o · n e n o 2 sin 2 θ p + n e 2 cos 2 θ p .

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