GB669554A - Prismatic rear view mirror device - Google Patents

Abstract

669,554. Optical rettectors. LIBBEYOWENS-FORD GLASS CO. July 1, 1948 [Nov. 26, 1947], No. 17759/48. Class 97 (i). [Also in Group XXXII] A rear view mirror -comprises a support of prism form having front and rear supporting surfaces at an angle to each other, the portion of said support between said surfaces being transparent, semi - transparent substantially non-light absorptive mirror reflecting means on said front supporting surface forming a front mirror providing a first image for normal day or night driving, and other mirror reflecting means on said rear surface forming a rear mirror providing a second image by reflection through said front mirror reflecting means for normal day or night driving, the rear mirror reflecting means further co-operating with said front reflecting means to produce by internal reflection within the prism form and by reflection through said front mirror reflecting means a further image useful for night driving under abnormal glare conditions having an intensity of between 2.5 and 12 per cent of the incident light. The mirror comprises either a transparent prism C, Fig. 5, or two transparent plates, Fig. 15, positioned at an angle to each other in which the front face a is coated with a metallic oxide reflective coating such as titanium dioxide which has over 30 per cent reflectivity and is transparent and of substantially no light absorption and the rear face b is coated with a material such as silver or aluminium having a specular reflectivity of 50 to 90 per cent or coloured reflectors such as gold or copper or semi-transparent layers which are coloured by light interference effects. Alternatively, coloured prisms or plates may be used. The mirror, which is pivotally mounted, can be set to bring within the driver's focus the first; second and third or further images as shown by the lines R, S and T, I being the incident light and R the reflection from the face a having a reflectivity of over 30 per cent and in the reflections S and T the reflectivity is reduced by internal reflection to between 10 to 30 per cent and 4.5 to 12 per cent respectively. To reduce the effect of disturbing reflections occurring at the plain uncoated surfaces X, Fig. 15, such surfaces may be given a thin coating of calcium or magnesium fluoride. Various arrangements are described in which reflective coatings are applied to all or some of the faces of the angularly positioned plates and it may be arranged that the first image S produced by internal reflection from the surface b is of greater intensity than the intensity of the image R produced by the surface a. Specifications 632,5 7 0, 650,173, 652,851, 652,858 and 652,859 are referred to.