Abstract

Switchable windows are being installed into modern buildings. We report on how the variable transmittance of gasochromic and electrochromic switchable windows changes the color rendering properties of the daylight passing through these windows. We present a series of color rendering examples. Correlated color temperature and color rendering indices are insufficient to describe the color properties of this filtered light, as these indices are beyond the applicability limits. We obtain more reliable results using the color shifts (ΔE) of different objects. We find that as the transmittance of the window changes, each surface color moves along a path of the CIELAB space in the same direction for both switchable units. The direction and distance moved differs among test-color samples. The appearance of an array of colored objects is strongly distorted at higher coloration states of the windows.

© 2005 Optical Society of America

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References

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  1. C. G. Granqvist, Handbook of Inorganic Electrochromic Materials (Elsevier, Amsterdam, 1995).
  2. P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism (Wiley-VCH, Weinheim, Germany, 1995).
  3. W. J. Platzer, ed., Handbook for the Use of Switchable Façade Technology: Architectural and Technical Guidelines (European Project SWIFT, Contract ENK6-CT1999-SWIFT), http://www.eu-swift.de .
  4. Colorimetry, 2nd ed., (CIE, Vienna, Austria, 1986).
  5. K. H. Bäuml, “Simultaneous color constancy: how surface color perception varies with the illuminant,” Vision Res. 39, 1531–1550 (1999).
    [CrossRef] [PubMed]
  6. J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
    [CrossRef]
  7. J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
    [CrossRef]
  8. A. Hurlbert, “Is color constancy real?” Curr. Biol. 9, R558–R561 (1999).
    [CrossRef] [PubMed]
  9. S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
    [CrossRef]
  10. “Method of measuring and specifying color rendering properties of light sources,” (CIE, Vienna, Austria, 1995).
  11. C. Chain, D. Dumortier, M. Fontoynont, “Consideration of daylight’s color,” Energy Build. 33, 193–198 (2001).
    [CrossRef]
  12. H. Xu, “Color-rendering capacity of light,” Color Res. Appl. 18, 267–269 (1993).
    [CrossRef]
  13. C. van Trigt, “Color rendering, a reassessment,” Color Res. Appl. 24, 197–206 (1999).
    [CrossRef]
  14. H. Xu, “Sample-independent color rendering index,” Color Res. Appl. 20, 251–254 (1995).
    [CrossRef]
  15. J. A. Worthey, “Color rendering: asking the question,” Color Res. Appl. 28, 403–412 (2003).
    [CrossRef]
  16. J. A. Worthey, “Color rendering: a calculation that estimates colorimetric shifts,” Color Res. Appl. 29, 43–56 (2004).
    [CrossRef]
  17. U. Opara Krašovec, A. Šurca, B. Orel, “Comparative studies of ‘all sol-gel’ electrochromic windows employing various counter electrodes,” Sol. Energy Mater. Sol. Cells 73, 21–37 (2002).
    [CrossRef]
  18. A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
    [CrossRef]
  19. B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
    [CrossRef]
  20. U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
    [CrossRef]
  21. “Color rendering index (CRI),” Lighting Design Knowledge database, http://www.schorsch.com/kbase/glossary/cri.html .
  22. “Farbtoleranzen für Automobillackierungen, Teil 1: Unilackierungen,” (1986).
  23. “Graphic technology—process control for the manufacture of half-tone color separations, proof and production paints. Part 2: processes in offset printing,” (1997).

2004 (1)

J. A. Worthey, “Color rendering: a calculation that estimates colorimetric shifts,” Color Res. Appl. 29, 43–56 (2004).
[CrossRef]

2003 (2)

J. A. Worthey, “Color rendering: asking the question,” Color Res. Appl. 28, 403–412 (2003).
[CrossRef]

J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
[CrossRef]

2002 (2)

J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
[CrossRef]

U. Opara Krašovec, A. Šurca, B. Orel, “Comparative studies of ‘all sol-gel’ electrochromic windows employing various counter electrodes,” Sol. Energy Mater. Sol. Cells 73, 21–37 (2002).
[CrossRef]

2001 (1)

C. Chain, D. Dumortier, M. Fontoynont, “Consideration of daylight’s color,” Energy Build. 33, 193–198 (2001).
[CrossRef]

2000 (1)

U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
[CrossRef]

1999 (4)

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

C. van Trigt, “Color rendering, a reassessment,” Color Res. Appl. 24, 197–206 (1999).
[CrossRef]

K. H. Bäuml, “Simultaneous color constancy: how surface color perception varies with the illuminant,” Vision Res. 39, 1531–1550 (1999).
[CrossRef] [PubMed]

A. Hurlbert, “Is color constancy real?” Curr. Biol. 9, R558–R561 (1999).
[CrossRef] [PubMed]

1998 (1)

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

1996 (1)

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

1995 (1)

H. Xu, “Sample-independent color rendering index,” Color Res. Appl. 20, 251–254 (1995).
[CrossRef]

1993 (1)

H. Xu, “Color-rendering capacity of light,” Color Res. Appl. 18, 267–269 (1993).
[CrossRef]

Bäuml, K. H.

K. H. Bäuml, “Simultaneous color constancy: how surface color perception varies with the illuminant,” Vision Res. 39, 1531–1550 (1999).
[CrossRef] [PubMed]

Benson, B.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Berman, S. M.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Bullimore, M. A.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Chain, C.

C. Chain, D. Dumortier, M. Fontoynont, “Consideration of daylight’s color,” Energy Build. 33, 193–198 (2001).
[CrossRef]

Dražic, G.

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Dumortier, D.

C. Chain, D. Dumortier, M. Fontoynont, “Consideration of daylight’s color,” Energy Build. 33, 193–198 (2001).
[CrossRef]

Fein, G.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Fontoynont, M.

C. Chain, D. Dumortier, M. Fontoynont, “Consideration of daylight’s color,” Energy Build. 33, 193–198 (2001).
[CrossRef]

Georg, A.

U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
[CrossRef]

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Geusenbroek, J. M.

J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
[CrossRef]

Gevers, T.

J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
[CrossRef]

Graf, W.

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Granqvist, C. G.

C. G. Granqvist, Handbook of Inorganic Electrochromic Materials (Elsevier, Amsterdam, 1995).

Grošelj, N.

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Hernández-Andrés, J.

J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
[CrossRef]

Hurlbert, A.

A. Hurlbert, “Is color constancy real?” Curr. Biol. 9, R558–R561 (1999).
[CrossRef] [PubMed]

Jewett, D. L.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Kosec, M.

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Law, T.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Monk, P. M. S.

P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism (Wiley-VCH, Weinheim, Germany, 1995).

Mortimer, R. J.

P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism (Wiley-VCH, Weinheim, Germany, 1995).

Myers, A.

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

Nieves, J. L.

J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
[CrossRef]

Nitz, P.

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Opara Krašovec, U.

U. Opara Krašovec, A. Šurca, B. Orel, “Comparative studies of ‘all sol-gel’ electrochromic windows employing various counter electrodes,” Sol. Energy Mater. Sol. Cells 73, 21–37 (2002).
[CrossRef]

U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
[CrossRef]

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Orel, B.

U. Opara Krašovec, A. Šurca, B. Orel, “Comparative studies of ‘all sol-gel’ electrochromic windows employing various counter electrodes,” Sol. Energy Mater. Sol. Cells 73, 21–37 (2002).
[CrossRef]

U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
[CrossRef]

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Pérez-Ocón, F.

J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
[CrossRef]

Reisfeld, R.

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Romero, J.

J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
[CrossRef]

Rosseinsky, D. R.

P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism (Wiley-VCH, Weinheim, Germany, 1995).

Schweiger, D.

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Smeulders, A. W. M.

J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
[CrossRef]

Šurca, A.

U. Opara Krašovec, A. Šurca, B. Orel, “Comparative studies of ‘all sol-gel’ electrochromic windows employing various counter electrodes,” Sol. Energy Mater. Sol. Cells 73, 21–37 (2002).
[CrossRef]

van den Boomgaard, R.

J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
[CrossRef]

van Trigt, C.

C. van Trigt, “Color rendering, a reassessment,” Color Res. Appl. 24, 197–206 (1999).
[CrossRef]

Wilson, H. R.

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Wittwer, V.

U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
[CrossRef]

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Worthey, J. A.

J. A. Worthey, “Color rendering: a calculation that estimates colorimetric shifts,” Color Res. Appl. 29, 43–56 (2004).
[CrossRef]

J. A. Worthey, “Color rendering: asking the question,” Color Res. Appl. 28, 403–412 (2003).
[CrossRef]

Xu, H.

H. Xu, “Sample-independent color rendering index,” Color Res. Appl. 20, 251–254 (1995).
[CrossRef]

H. Xu, “Color-rendering capacity of light,” Color Res. Appl. 18, 267–269 (1993).
[CrossRef]

Color Res. Appl. (5)

H. Xu, “Color-rendering capacity of light,” Color Res. Appl. 18, 267–269 (1993).
[CrossRef]

C. van Trigt, “Color rendering, a reassessment,” Color Res. Appl. 24, 197–206 (1999).
[CrossRef]

H. Xu, “Sample-independent color rendering index,” Color Res. Appl. 20, 251–254 (1995).
[CrossRef]

J. A. Worthey, “Color rendering: asking the question,” Color Res. Appl. 28, 403–412 (2003).
[CrossRef]

J. A. Worthey, “Color rendering: a calculation that estimates colorimetric shifts,” Color Res. Appl. 29, 43–56 (2004).
[CrossRef]

Curr. Biol. (1)

A. Hurlbert, “Is color constancy real?” Curr. Biol. 9, R558–R561 (1999).
[CrossRef] [PubMed]

Displays (1)

J. L. Nieves, F. Pérez-Ocón, J. Hernández-Andrés, J. Romero, “Spectral-reflectance function recovery for improved color-constancy experiments,” Displays 23, 213–222 (2002).
[CrossRef]

Energy Build. (1)

C. Chain, D. Dumortier, M. Fontoynont, “Consideration of daylight’s color,” Energy Build. 33, 193–198 (2001).
[CrossRef]

J. Illumin. Eng. Soc. (1)

S. M. Berman, D. L. Jewett, G. Fein, B. Benson, T. Law, A. Myers, M. A. Bullimore, “Lighting spectral effect on Landoldt C performance is enhanced by blur and abolished by mydriasis,” J. Illumin. Eng. Soc. 25, 42–50 (1996).
[CrossRef]

J. Sol-Gel Sci. Technol. (1)

B. Orel, U. Opara Krašovec, N. Grošelj, M. Kosec, G. Dražič, R. Reisfeld, “Gasochromic behaviour of sol-gel derived Pd doped peroxopolytungstic acid (W-PTA) nano-composite films,” J. Sol-Gel Sci. Technol. 14, 291–308 (1999).
[CrossRef]

Pattern Recogn. Lett. (1)

J. M. Geusenbroek, R. van den Boomgaard, A. W. M. Smeulders, T. Gevers, “Color constancy from physical principles,” Pattern Recogn. Lett. 24, 1653–1662 (2003).
[CrossRef]

Sol. Energy (2)

U. Opara Krašovec, B. Orel, A. Georg, V. Wittwer, “The gasochromic properties of sol-gel WO3 films with sputtered Pt catalyst,” Sol. Energy 68, 541–555 (2000).
[CrossRef]

A. Georg, W. Graf, D. Schweiger, V. Wittwer, P. Nitz, H. R. Wilson, “Switchable glazing with a large dynamic range in total solar energy transmittance (TSET),” Sol. Energy 62, 215–228 (1998).
[CrossRef]

Sol. Energy Mater. Sol. Cells (1)

U. Opara Krašovec, A. Šurca, B. Orel, “Comparative studies of ‘all sol-gel’ electrochromic windows employing various counter electrodes,” Sol. Energy Mater. Sol. Cells 73, 21–37 (2002).
[CrossRef]

Vision Res. (1)

K. H. Bäuml, “Simultaneous color constancy: how surface color perception varies with the illuminant,” Vision Res. 39, 1531–1550 (1999).
[CrossRef] [PubMed]

Other (8)

“Color rendering index (CRI),” Lighting Design Knowledge database, http://www.schorsch.com/kbase/glossary/cri.html .

“Farbtoleranzen für Automobillackierungen, Teil 1: Unilackierungen,” (1986).

“Graphic technology—process control for the manufacture of half-tone color separations, proof and production paints. Part 2: processes in offset printing,” (1997).

“Method of measuring and specifying color rendering properties of light sources,” (CIE, Vienna, Austria, 1995).

C. G. Granqvist, Handbook of Inorganic Electrochromic Materials (Elsevier, Amsterdam, 1995).

P. M. S. Monk, R. J. Mortimer, D. R. Rosseinsky, Electrochromism (Wiley-VCH, Weinheim, Germany, 1995).

W. J. Platzer, ed., Handbook for the Use of Switchable Façade Technology: Architectural and Technical Guidelines (European Project SWIFT, Contract ENK6-CT1999-SWIFT), http://www.eu-swift.de .

Colorimetry, 2nd ed., (CIE, Vienna, Austria, 1986).

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Figures (11)

Fig. 1
Fig. 1

Schematic presentation of a switchable window with a low-e coating.

Fig. 2
Fig. 2

Schematic presentation of an EC active unit (coloring process is shown) together with a chemical reaction describing oxidation/reduction reaction that takes place during coloring/bleaching processes. Layer thickness is not to scale.

Fig. 3
Fig. 3

Transmittance spectra of the EC device in its bleached, colored, and some intermediate states. The amount of the charge intercalated into WO 3 layer in millicoulombs per square centimeters (mC/cm2) is given.

Fig. 4
Fig. 4

Schematic presentation of a GC active unit together with a chemical reaction describing oxidation/reduction reaction that takes place during coloring/bleaching processes. Layer thickness is not to scale.

Fig. 5
Fig. 5

Transmittance spectra of the GC device in its bleached, colored, and some intermediate states. The spectra were taken during the coloring process, i.e., during flushing of the device with 4% H 2 in a carrier gas of Ar (time intervals were 20 s).

Fig. 6
Fig. 6

Chromaticity diagram showing data for D 65 daylight when filtered through EC (triangles) and GC (open circles) switchable units. Solid curve, blackbody locus with indicated color temperatures (in K, stars); solid circle, chromaticity of nonfiltered D 65 daylight.

Fig. 7
Fig. 7

Relations between luminous transmittance ( T vis ) , CCT, and general CRI of the light filtered through EC (triangles) and GC (circles) switchable units. The CCT values for the largest three colorations of the GC unit are too large to have any meaning. Therefore the three smallest CRI values cannot be compared with CCT values.

Fig. 8
Fig. 8

Object colors of the CIE test-color samples (Table 1) illuminated by the average daylight ( D 65 ) through the EC switchable unit S i ( λ ) in the ( a * ,   b * ) (a), and ( a * ,   L * ) (b) planes. Open circles, colors of a basic set of samples (a–h). Solid circles, colors of additional samples (i–n); triangles, color caused by the bleached state of the unit.

Fig. 9
Fig. 9

Object colors of the CIE test-color samples (Table 1) illuminated by average daylight ( D 65 ) through the GC switchable unit S i ( λ ) in the ( a * ,   b * ) (a) and ( a * ,   L * ) (b) planes. Open circles, colors of a basic set of samples (a–h); solid circles, those of additional samples (i–n); triangles, color caused by the bleached state of the unit.

Fig. 10
Fig. 10

Transmittance spectra of EC (solid curve) and GC (dotted curve) units in fully colored states in the spectral range where the color rendering properties were calculated (360–830 nm). The spectral boundaries of the color calculations (400–700 nm) are indicated by a dashed curve. The reflectance spectra of the test-color samples i and j are also shown.

Fig. 11
Fig. 11

Color difference ( Δ E ) of the CIE test-color samples (Table 1) between the bleached and the fully colored state of the EC and GC switchable units. For comparison of the EC and GC devices having similar T vis , the Δ E for the partially colored state of the GC unit is also presented (Figs. 3 and 5).

Tables (1)

Tables Icon

Table 1 Description of the CIE Test-Color Samples a

Equations (3)

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

S i ( λ ) = S o ( λ ) T ( λ ) ,
Δ E = [ ( Δ L * ) 2 + ( Δ a * ) 2 + ( Δ b * ) 2 ] 1 / 2 ,
T vis = λ = 380 nm 780 nm D 65 ( λ ) T ( λ ) V ( λ ) Δ λ λ = 380 nm 780 nm D 65 ( λ ) V ( λ ) Δ λ ,

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