Variable reflectance automobile mirror

• US 5,751,467 A
• Filed: 04/23/1992
• Issued: 05/12/1998
• Est. Priority Date: 03/31/1986
• Status: Expired due to Fees

• Current Assignee: Gentex Corporation
• Original Assignee: Gentex Corporation
• Inventors: Byker, Harlan J.
• Primary Examiner(s): Epps, Georgia Y.
• Assistant Examiner(s): Lester, Evelyn A.
• Application Number:
  US07/874,175
• Time in Patent Office: 2,210 Days
• Field of Search: 359/265, 359/267, 359/269, 359/270, 359/272, 359/274, 359/321
• US Class Current: 359/272
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: C07D 498/04 Ortho-condensed systems
• CPC Class Codes: C09K 9/02 Organic tenebrescent materials
• CPC Class Codes: G01R 13/40 using modulation of a light beam otherwise than by mechanical displacement, e.g. by Kerr effect visual indication of correct tuning H03J3/14
• CPC Class Codes: G02F 1/1503 caused by oxidation-reduction reactions in organic liquid solutions, e.g. viologen solutions
• CPC Class Codes: G02F 1/1533 structural features not otherwise provided for
• CPC Class Codes: G02F 1/157 Structural association of cells with optical devices, e.g. reflectors or illuminating devices
• CPC Class Codes: G02F 2001/1502 complementary cell
• CPC Class Codes: G02F 2001/15145 the electrochromic layer comprises a mixture of anodic and cathodic compounds

Abstract

The present invention provides variable reflectance automobile mirrors wherein the component of variable transmittance is a single-compartment, self-erasing, solution-phase electrochromic device.

Claims

1. A variable reflectance rearview mirror for a motor vehicle, (A) wherein the variable reflectance is provided by a component of reversibly variable transmittance which is a single-compartment, self-erasing, solution-phase electrochromic device, wherein the solution of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, at least one of which is transparent and each of which, on the side in contact with said solution, is coated with an electrode layer of electrically conductive material, wherein the separation between the electrode layers is between about 0.0025 cm and about 0.050 cm, provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said solution and the transparent wall, light which reaches said reflecting layer after entering the solution through the transparent wall, and wherein the solution of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said solution, and which hold apart said walls and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the solution of the electrochromic device, light which reaches said reflecting layer after passing through said solution.

2. A mirror according to claim 1 wherein the component of reversibly variable transmittance provides continuously variable reflectance and is gray-scale controllable.

3. A mirror according to claim 2 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

4. A mirror according to claim 1 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

5. A mirror according to any one of claims 2, 3 and 4 wherein, in the one electrochromic device, the solution of variable transmittance comprises:

(A) a solvent;

(B) a cathodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible reduction waves, with the first of said reductions accompanied by a increase in molar extinction coefficient at at least one wavelength in the visible range;

(C) an anodic electrochromic compound which, in a voltammogram done in the solvent at room temperature, displays at least two chemically reversible oxidation waves, with the first of said oxidations accompanied by an increase in molar extinction coefficient at at least one wavelength in the visible range; and

(D) if all cathodic and anodic compounds in their zero potential equilibrium states are not ionic, an inert current-carrying electrolyte.

6. A mirror according to claim 5 wherein, in the solution of reversibly variable transmittance, the solvent is propylene carbonate.

26. A mirror according to any one of claims 1, 7, 9-11, 15-17, 19-21, 29 and 25 wherein, in the solution of reversibly variable transmittance, the solvent is propylene carbonate.

7. A variable reflectance rearview mirror for a motor vehicle, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a single-compartment, self-erasing, solution-phase electrochromic device, wherein the solution of reversibly variable transmittance comprises:

(A) a non-aqueous solvent;

(B) a cathodic electrochromic compound;

(C) 5,10-dihydro-5,10-dimethylphenazine; and

(D) if all cathodic compounds in their zero-potential equilibrium states are not ionic, an inert, current-carrying electrolyte.

8. A mirror according to claim 7 wherein, in the electrochromic device, the solution of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, at least one of which is transparent and each of which, on the side in contact with said solution, is coated with an electrode layer of electrically conductive material, provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said solution and the transparent wall, light which reaches said reflecting layer after entering the solution through the transparent wall and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the solution of the electrochromic device, light which reaches said reflecting layer after passing through said solution.

9. A mirror according to claim 8 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

10. A mirror according to claim 8 wherein the separation between the electrode layers is between 0.0025 and 0.050 cm.

11. A mirror according to claim 10 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

12. A mirror according to claim 8 wherein, in the electrochromic device, the solution of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said solution, and which hold apart said walls.

13. A mirror according to claim 12 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

14. A mirror according to claim 12 wherein the separation between the electrode layers is between 0.0025 and 0.050 cm.

15. A mirror according to claim 14 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

16. A mirror according to claim 7 wherein the component of reversibly variable transmittance provides continuously variable reflectance and is gray-scale controllable.

17. A mirror according to claim 16 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

18. A mirror according to claim 16 (A) wherein, in the electrochromic device, the solution of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, at least one of which it transparent and each of which, on the side in contact with said solution, is coated with an electrode layer of electrically conductive material, provided that, it one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said solution and the transparent wall, light which reaches said reflecting layer after entering the solution through the transparent wall and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the solution of the electrochromic device, light which reaches said reflecting layer after passing through said solution.

19. A mirror according to claim 18 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

20. A mirror according to claim 18 wherein the separation between the electrode layers is between 0.0025 and 0.050 cm.

21. A mirror according to claim 20 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

22. A mirror according to claim 18 wherein, in the electrochromic device, the solution of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said solution, and which hold apart said walls.

23. A mirror according to claim 22 wherein the separation between the electrode layers is between 0.0025 and 0.050 cm.

24. A mirror according to claim 23 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

25. A mirror according to claim 12 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

27. A mirror according to any one of claims 7-25 wherein, in the solution of reversibly variable transmittance in its zero-potential equilibrium state, all of the cathodic electrochromic compounds are salts of viologen dications.

28. A mirror according to claim 27 wherein, in the solution of reversibly variable transmittance, the solvent is propylene carbonate.

29. A mirror according to claim 27 wherein, in the solution of reversibly variable transmittance in its zero-potential equilibrium state, the concentration at room temperature of 5,10-dihydro-5,10-dimethylphenazine is between 0.01 and 0.1 molar and the total concentration at room temperature of all of the viologen dications together is between 0.01 and 0.1 molar.

30. A mirror according to claim 29 wherein the viologen dications are selected from the group consisting of 1,1'"'"'-dimethyl-4,4'"'"'-bipyridinium and 1,1'"'"'-dibenzyl-4,4'"'"'-bipyridinium.

31. A mirror according to claim 30 the solvent is propylene carbonate.

32. A mirror according to claim 31 wherein the viologen salts are the difluoroborate salts.

33. A variable reflectance rearview mirror for a motor vehicle, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a single-compartment, self-erasing, solution-phase electrochromic device, wherein the solution of reversibly variable transmittance comprises:

(A) a non-aqueous solvent;

(B) a viologen salt; and

(C) an anodic electrochromic compound which is neutral in its zero-potential equilibrium state.

34. A mirror according to claim 33 wherein the component of reversibly variable transmittance provides continuously variable reflectance and is gray-scale controllable.

35. A mirror according to claim 34 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

36. A mirror according to claim 34 (A) wherein, in the electrochromic device, the solution of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, at least one of which said transparent and each of which on the side in contact with said solution, is coated with an electrode layer of electrically conductive material, provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said solution and the transparent wall, light which reaches said reflecting layer after entering the solution through the transparent wall and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the solution of the electrochromic device, light which reaches said reflecting layer after passing through said solution.

37. A mirror according to claim 36 wherein the separation between the electrode layers is between 0.0025 cm and 0.050 cm.

38. A mirror according to claim 37 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

39. A mirror according to claim 36 wherein, in the electrochromic device, the solution of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said solution, and which hold apart said walls.

40. A mirror according to claim 39 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

41. A mirror according to claim 39 wherein the separation between the electrode layers is between 0.025 and 0.050 cm.

42. A mirror according to claim 41 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

43. A mirror according to claim 33 (A) wherein, in the electrochromic device, the solution of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, at least one of which is transparent and each of which, on the side in contact with said solution, is coated with an electrode layer of electrically conductive material, provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reaches through said solution and the transparent wall, light which reaches said reflecting layer after entering the solution through the transparent wall and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the solution of the electrochromic device, light which reaches said reflecting layer after passing through said solution.

44. A mirror according to claim 43 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

45. A mirror according to claim 43 the separation between the electrode layers is between 0.0025 cm and 0.050 cm.

46. A mirror according to claim 45 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

47. A mirror according to claim 43 wherein, in the electrochromic device, the solution of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said solution, and which hold apart said walls.

48. A mirror according to claim 47 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

49. A mirror according to claim 47 wherein the separation between the electrode layers is between 0.0025 and 0.050 cm.

50. A mirror according to claim 49 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

51. A mirror according to claim 36 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

52. A mirror according to any one of claims 33-51 wherein, in the solution of reversibly variable transmittance, the viologen salts are selected from the group consisting of salts of 1,1'"'"'-dimethyl-4,4'"'"'-bipyridinium and 1,1'"'"'-dibenzyl-4,4'"'"'-bipyridinium.

53. A mirror according to claim 52 wherein, in the solution of reversibly variable transmittance in its zero-potential equilibrium state, the solvent is propylene carbonate, the concentration at room temperature of the anodic electrochromic compound is between 0.01 and 0.1 molar and the total concentration at room temperature of all of the viologen dications together is between 0.01 and 0.1 molar.

54. A mirror according to any one of claims 33-51 wherein, in the solution of reversibly variable transmittance, the solvent is propylene carbonate.

55. A variable reflectance rearview mirror for a motor vehicle, (A) wherein the variable reflectance is provided by a component of reversibly variable transmittance which is a self-erasing electrochromic device, wherein the medium of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, at least one of which is transparent and each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall, and wherein the medium of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said medium, and which hold apart said walls and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the medium of the electrochromic device, light which reaches said reflecting layer after passing through said mediums and wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

56. A mirror according to claim 55 wherein the component of reversibly variable transmittance provides continuously variable reflectance and is gray-scale controllable.

57. A variable reflectance rearview mirror for a motor vehicle, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a self-erasing electrochromic device having a layer of reflective material which reflects, through said reversibly variable transmittance component of said electrochromic device, light which reaches said reflecting layer after passing through said component, wherein the medium of reversibly variable transmittance comprises:

(A) a non-aqueous solvent;

(B) a viologen salt; and

(C) an anodic electrochromic compound which is neutral in its zero-potential equilibrium state.

58. A mirror according to claim 57 wherein the component of reversibly variable transmittance provides continuously variable reflectance and is gray-scale controllable.

59. A mirror according to claim 58 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

60. A mirror according to claim 58 (A) wherein, it the electrochromic device, the medium of reversibly variable transmittance is between and In contact with two planar, parallel, spaced-apart walls, at least one of which is transparent and each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the medium of the electrochromic device, light which reaches said reflecting layer after passing through said medium.

61. A mirror according to claim 60 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

62. A mirror according to claim 60 wherein, in the electrochromic device, the medium of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said medium, and which hold apart said walls.

63. A mirror according to claim 62 wherein the reflectance is capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less than 1.4 volts between the electrode layers of the electrochromic device.

64. A mirror according to claim 57 (A) wherein, in the electrochromic device, the medium of reversibly variable transmittance is between and in contact with two planar, parallel spaced-apart walls, at least one of which is transparent and each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material provided that, if one of said walls is not transparent, said non-transparent wall comprises a reflecting layer of high reflectance material which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall and (B) wherein, if both of said walls are transparent, the mirror comprises a reflecting layer of high reflectance material which reflects, through the medium of the electrochromic device, light which reaches said reflecting layer after passing through said medium.

65. A mirror according to claim 64 wherein, in the electrochromic device, the medium of reversibly variable transmittance is held in a space defined by said two planar, parallel, spaced-apart walls, and a periphery defined by an epoxy seal in which are embedded glass beads, which are in contact with the sides of said walls, which are in contact with said medium, and which hold apart said walls.

66. A mirror according to any one of claims 57-65 wherein, in the medium of reversibly variable transmittance, the viologen salt is selected from the group consisting of salts of 1,1'"'"'-dimethyl-4,4'"'"'-bipyridinium and 1,1'"'"'-dibenzyl-4,4'"'"'-bipyridinium.

67. A variable reflectance rearview mirror for a motor vehicle, which has a range of reflectance from greater than 70% to less than lot and wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a self-erasing electrochromic device.

68. A mirror according to claim 67, wherein in the electrochromic device the medium of reversibly variable transmittance comprises propylene carbonate.

69. A mirror according to claim 67 wherein the reflectance is continuously variable.

70. A mirror according to claim 67 wherein, in electrochromic device, there is a medium of reversibly variable transmittance which comprises an electrochromic compound in solution.

71. A mirror according to claim 67 which is gray-scale controllable.

72. A mirror according to claim 71 wherein the reflectance is continuously variable.

73. A mirror according to claim 67 wherein, in the electrochromic device, there is a medium of reversibly variable transmittance which is between and in contact with two planar, parallel, spaced-apart walls, each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, one of which is transparent, and the other of which has as its electrode layer in contact with said medium a reflecting layer of high reflectance material, which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall.

74. A mirror according to claim 73 wherein said high reflectance material is selected from the group consisting of rhodium, silver and inconel.

75. A mirror according to claim 74 wherein the medium of reversibly variable transmittance comprises an electrochromic compound in solution.

76. A variable reflectance rearview mirror for a motor vehicle, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a self-erasing electrochromic device, wherein the sheet resistance of a transparent electrode layer is 40 ohms per square or less.

77. A mirror according to claim 76 which is gray-scale controllable.

78. A mirror according to claim 76 wherein the reflectance is continuously variable.

79. A mirror according to claim 76 wherein, in the electrochromic device, there Is a medium of reversibly variable transmittance which comprises an electrochromic compound in solution.

80. A mirror according to claim 76, wherein in the electrochromic device the medium of reversibly variable transmittance comprises propylene carbonate.

81. A mirror according to claim 80 which has a range of reflectance from greater than 70% to less than 10%.

82. A mirror according to claim 76 wherein, in the electrochromic device, there is a medium of reversibly variable transmittance which is between and in contact with two planar, parallel, spaced-apart walls, each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, one of which is transparent, and the other of which has as its electrode layer in contact with said medium a reflecting layer of high reflectance material, which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall.

83. A mirror according to claim 82 wherein said high reflectance material is selected from the group consisting of rhodium, silver and inconel.

84. A mirror according to claim 83 wherein the medium of reversibly variable transmittance comprises an electrochromic compound in solution.

85. A mirror according to claim 76 which has a range of reflectance from greater than 70% to less than 10%.

86. A mirror according to claim 85 whereon the reflectance is continuously variable.

87. A mirror according to claim 85 which is gray-scale controllable.

88. A mirror according to claim 85 wherein, in the electrochromic device, there is a medium of reversibly variable transmittance which comprises an electrochromic compound in solution.

89. A mirror according to claim 88 wherein in the electrochromic device, the medium of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, each of which, an the side in contact with said medium, is coated with an electrode layer of electrically conductive material, one of which is transparent, and the other of which has as its electrode layer in contact with said medium a reflecting layer of high reflectance material, which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall, and which reflectance material is selected from the group consisting of rhodium, silver and inconel.

90. A variable reflectance rearview mirror for an automobile, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a self-erasing electrochromic device wherein the medium of reversibly variable transmittance comprises a gel.

91. A mirror according to claim 90 which has a range of reflectance from greater than 70% to less than 10%.

92. A mirror according to claim 90 wherein a transparent electrode layer of the electrochromic device has a sheet resistance of 40 ohms per square or less.

93. A mirror according to claim 90 wherein the medium of reversibly variable transmittance comprises an electrochromic compound in solution.

94. A mirror according to claim 90 wherein, in the electrochromic device, the medium of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart walls, each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, one of which is transparent, and the other of which has as its electrode layer in contact with aid medium a reflecting layer of high reflectance material, which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall.

95. A mirror according to claim 94 wherein said high reflectance material is selected from the group consisting of rhodium, silver and inconel.

96. A mirror according to claim 95 wherein the medium of reversibly variable transmittance comprises an electrochromic compound in solution.

97. A variable reflectance rearview mirror for an automobile, wherein the variable reflectance is provided by a component of reversibly variable transmittances which is a self-erasing electrochromic device wherein the medium of reversibly variable transmittance comprises an acrylic material.

99. A mirror according to claim 97 wherein a transparent electrode layer of the electrochromic device has a sheet resistance of 40 ohms per square or less.

100. A mirror according to claim 97 wherein the medium of reversibly variable transmittance comprises an electrochromic compound in solution.

101. A mirror according to claim 97 wherein, in the electrochromic device, the medium of reversibly variable transmittance is between and in contact with two planar, parallel, spaced-apart wails, each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, one of which is transparent, and the other of which has as its electrode layer in contact with said medium a reflecting layer of high reflectance material, which reflects, through said medium and the transparent wall, light which reaches said reflecting layer after entering the medium through the transparent wall.

102. A mirror according to claim 101 wherein said high reflectance material is selected from the group consisting of rhodium, silver and inconel.

103. A mirror according to claim 102 wherein the medium of reversibly variable transmittance comprises an electrochromic compound in solution.

98. A mirror according to claim 98 which has a range of reflectance from greater than 70% to less than 10%.

104. A variable reflectance rearview mirror for a motor vehicle, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a self-erasing electrochromic device, and wherein, in said electrochromic device, there is a medium of reversibly variable transmittance which is between and in contact with two planar parallel, spaced-apart walls, each of which, on the side in contact with said medium, is coated with an electrode layer of electrically conductive material, one of which is transparent and the other of which has as its electrode layer in contact with said medium a reflecting layer of high reflectance material, which layer reflects, through said medium and the transparent wall, light which reaches said layer after entering the medium through the transparent wall and which reflectance material is selected from the group consisting of rhodium and inconel.

105. A variable reflectance rearview mirror for a motor vehicle, wherein the variable reflectance is provided by a component of reversibly variable transmittance, which is a self-erasing electrochromic device, wherein the medium of reversibly variable transmittance comprises:

(A) a non-aqueous solvent;

(B) a cathodic electrochromic compound;

(C) 5,10-dihydro-5,10-dimethylphenazine; and

(D) if all cathodic compounds in their zero-potential equilibrium states are not ionic, an inert, current-carrying electrolyte.

106. A mirror according to claim 105 wherein the component of reversibly variable transmittance provides continuously variable reflectance and is gray-scale controllable.

107. A mirror according to claim 106 wherein the reflectance in capable of being reduced from greater than 70% to less than 20% in less than 10 seconds with a potential difference of less then 1.4 volts between the electrode layers of the electrochromic device.

108. A mirror according to any one of claims 105-107 wherein the cathodic electrochromic compounds are salts of viologen dications.

109. A mirror according to claim 108 wherein the viologen dications are selected from the group consisting of 1,1'"'"'-dimethyl-4,4'"'"'-bipyridinium and 1,1'"'"'-dibenzyl-4,4'"'"'-bipyridinium.