GB2225647A

GB2225647A - Mirrors

Info

Publication number: GB2225647A
Application number: GB8925974A
Authority: GB
Inventors: Andrew Alexander Robertso Meek
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-11-25
Filing date: 1989-11-16
Publication date: 1990-06-06
Also published as: GB8925974D0; GB8827603D0

Abstract

A vehicle rear-view mirror which is intended to obviate the nuisance of dazzle from headlights of following vehicles at night comprises a transparent front layer (2) and a reflective rear layer (6), which may be the vehicle's own rear-view minor if convenient. Between these layers is sandwiched a liquid crystal assembly (4) adapted to darken under high levels of illumination. Alternatively the transparent layer itself may be capable of darkening. <IMAGE>

Description

MIRRORS The invention relates to mirrors having variable light reflection characteristics.

It is sometimes necessary, for example to avoid dazzle, to reduce the ratio of the amount of light reflected by a mirror to that falling on it. This may be done in a permanent manner by a number of techniques, for example, the use of darkened, i.e. so-called smoked, glass in the manufacture of the mirror. However, in certain circumstances, for example in a vehicle rear-view mirror, it is not desirable to reduce the reflection levels under all light conditions.

The invention provides a mirror device comprising a multi-layer reflecting member comprising a transparent component and a light-reflective backing layer, wherein there is provided means responsive to changes in the intensity of light falling thereupon, to change the visible colour of at least a portion of the transparent layer so as to vary the amount of light effectively reflected by said backing layer.

Advantageously, the colour change may involve the rapid darkening of the transparent layer when the intensity of light increases and reversal of the darkening effect when the intensity returns to an initial level.

In one example of the invention, the transparent component may be of glass or glass-substitute material, such as a suitable plastics material, containing a photo chromic material capable of temporary darkening in bright light.

In another example of the invention, the transparent component may include a layer comprising a liquid crystal substance, and a light-responsive electrical signal generating device adapted to produce an electrical field to cause molecular re-alignment of the crystal.

There will now be described an example of a mirror device according to the invention. It will be understood that the description which is to be read with reference to the accompanying drawings is given by way of example only and not by way of limitation.

In the drawings: Fig. 1 shows diagrammatically an exploded perspective view of the device, and Fig. 2 is a block diagram indicating circuitry components.

The device comprises a transparent component 2 comprising a sheet of glass. Bonded to the rear of the glass is a liquid crystal assembly 4, to the rear surface of which is applied a reflective layer 6. The assembly 4 includes two photo-electric cells 8. If preferred, the assembly may be interposed between two sheets of glass, the rear one of which is conventionally "silvered".

In the present example, the liquid crystal assembly 4 comprises two thin transparent plastic layers 10 each having a thin transparent conductive coating which thus provide two electrodes. Laminated between the two electrode layers 10 is a polymer film layer 12 throughout which is dispersed a pleochroic liquid crystal material in the form of small droplets.

When an electric current is applied across the assembly the molecules of the liquid crystal assembly are aligned with the field lines allowing light to pass through the assembly relatively unhindered. However, when the current ceases the molecules take up a random distribution. The incoming light is then strongly absorbed and scattered so that the film layer 12 appears dark and thus reduces the reflecting characteristics of the layer 6.

In use in a road vehicle, the electric field normally maintains the mirror device in its fully reflective condition until an excessive level of light from headlamps of a following vehicle are detected by the photoelectric cells 8 controlling a pre-set switch device 16 connected to the electrodes 10 which removes the electric field from the assembly 4.

The circuitry associated with the above arrangement is shown in Figure 2. A liquid crystal drive unit 14 is used to apply the electrical field in the assembly 4. The switch 16 is operated by the photoelectric cells 8 and the power to the drive unit (c. 80v) is derived from the battery (12v) through a voltage transformer 18.

Various modifications may be made within the scope of the invention as defined by the following claims.

Claims

CLAIMS:

1. A mirror device comprising a multi-layer reflecting member comprising a transparent component and a light-reflective backing layer, wherein there is provided means responsive to changes in the intensity of light falling thereupon, to change the visible colour of at least a portion of the transparent layer so as to vary the amount of light effectively reflected by said backing layer.

2. A mirror device as claimed in claim 1, wherein the transparent layer includes photochromic material capable of temporary darkening in bright light.

3. A mirror device as claimed in claim 1, wherein the transparent layer includes pleochroic liquid crystal material, capable of absorbing or scattering bright light.

4. A mirror device as claimed in claim 3, wherein the liquid crystal material, molecular re-alignment of the crystals being controlled by a light-responsive electric signal generating device arranged to apply or remove an electric field produced between electrodes provided adjacent said crystal material.

5. A mirror device as claimed in claim 4, comprising a first transparent layer, and a second, liquid crystal material containing layer, at least one photo-electric cell being received between the first and second layers.

6. A mirror device as claimed in claim 5, wherein a third reflecting, layer is secured to the surface of the second layer remote from the first layer.

7. A mirror device as claimed in claim 5, wherein the device, in use, is fixed to a vehicle rear-view mirror which comprises a third, reflecting, layer.

8. A mirror device as claimed in either one of claims 6 and 7, wherein said second layer comprises two thin film sub-layers between which is received an intermediate layer throughout which is dispersed said pleochroic liquid crystal material in droplets said thin film sub-layers being coated with electro-conductive material to comprise said electrodes.

9. A mirror device as claimed in any one of claims 4 to 8, wherein the electric filed produced between said electrodes is controlled by a photocell-operated switch, the arrangement being that the photo-cell operates at a predetermined level of illumination falling thereon.

10. A mirror device constructed and arranged substantially as hereinbefore described with reference to and as shown in the drawings.