GB2283103A

GB2283103A - Anti-glare device

Info

Publication number: GB2283103A
Application number: GB9321836A
Authority: GB
Inventors: Nicholas Andrew Donald Gribble
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-10-22
Filing date: 1993-10-22
Publication date: 1995-04-26
Also published as: GB9321836D0

Abstract

Anti-glare viewing frames which contain at least one lens 2 comprising a liquid crystal cell having a plurality of addressable light transmitting elements, characterised in that the frame includes scene evaluation means 5 adopted to provide a series of signals relating to elements of scene brightness across the field of view and control means arranged to lower the transparency of each light transmitting element in response to the brightness of the element of the scene observed throught it. <IMAGE>

Description

VARIABLE TRANSPARENCY VIEWING FRAMES This invention relates to a variable transparency viewing frames and more particularly to such frames with spacially located areas of transparency variation to avoid the effects of glare.

Antiglare spectacles having a continuously variable controlled transparency using lenses comprising liquid crystal cells are described in GB-A-2 083 649. The overall transparency of the lenses is controlled by signals applied to the cells in accordance with the ambient illumination as sensed by a frame mounted photocell.

Antiglare spectacles capable of having an adjustable pattern of transparency across the visual field have been proposed in GB-A-2 149 136. The lenses of these spectacles comprise liquid crytal cells divided into a plurality of spacial elements by rows and columns of electrode strips on each inner surface of the cell wall.

The application of an appropriate pattern of potentials to the electrode strips the transparency of the liquid crystal within each cell is used to provide the transparency pattern across the visual field. It is proposed that the spacial variation should be controlled by connection to external light sensitive members, of a type not specified, which sense the position of a viewer's head relative to a source of scene illumination. The system provides a graded transparency pattern across each of the lenses.

The present invention provides antiglare viewing frames which provide a continuously variable transparency pattern across the visual field in accordance with the luminance of a scene being viewed. The viewing frames allow the wearer to observe scenes at a substantially uniform overall brightness while retaining small area brightness variations. Use of the frames enables fine detail in a scene to be discerned regardless of major brightness variations across the scene so that visual acuity of fine detail is enhanced.

According to the present invention there are provided antiglare viewing frames which contain at least one lens comprising a liquid crystal cell having a plurality of addressable light transmitting elements, characterised in that the frame includes scene evaluation means adapted to provide a series of signals relating to elements of scene brightness across the field of view and control means arranged to lower the transparency of each light transmitting element in response to the brightness of the element of the scene observed through it.

The scene evaluation means may comprise any scene analysis device such as a combination of a lens with a video pick-up tube, a charge coupled device or an array of photosensors.

The device may supply continously information relating to the brightness of each scene element or successively such information by scanning the scene area, for instance with a rater scan. The brightness information may be supplied to the liquid crystal cell elements continuously or successively. In a preferred embodiment the scene is focussed on to a charge coupled device sensor so that the field of view covered by the device is substantially the same as that of the user of the spectacles. The charge coupled device is scanned in conventional manner and the output from one or more elements of the device is used to control the transmission of the element of the lens associated with the same scene area.

For the purposes of macro scene brightness control the number of scene elements, pixels, scanned may be considerably lower than that used for image formation. Scanning arrays and liquid crystal lenses having a range of 5 X 10 to 50 X 100 elements provide adequate brightness control for enhancing visual acuity at an aspect ratio of 2 to 1.

The aspect ratio of of the scanned scene may vary from 1 to 1 to 1 to 10 according to the layout of the frame and whether a single lens or a pair of lenses is used.

The necessary power supplies for the operation of the scene sensor, associated circuitry and the liquid crystal cells may be obtained from batteries integral with the farme or carried externally. In one embodiment the batteries may be maintained in a charged state by means of a series of photovoltaic cells.

In one alternative embodiment the viewing frame may take the form of a visor on a helmet and the scene evaluation means may be located on the helmet. In a further embodiment the scene evaluation means may be located behind the visor in a feedback system so that the inner surface of the liquid crystal lens or lenses is scanned. The associated control circuitry adjusts the transparency of each lens element to ensure that the intensity of light falling upon each element of the scanned scene is constant.

In order that the invention may be clearly understood it will now be described with reference to the accompanying drawings in which: Figure 1 is a schematic front view of a variable transparency viewing frame according to the invention, and Figure 2 is a rear view of the frame shown in Figure 1 when in operational use.

A variable transparency viewing frame, see Figure 1, consists of a frame 1 carrying a pair of lenses 2 and 3.

A first arm 4 of the frame 1 carries a scene evaluation means 5 and a second arm 6 carries control circuitry in an attachment 7. The lenses 2 and 3 consist of a pair of liquid crystal cells. Each cell consists of a pair of transparent walls carrying a set of linear electrodes on their inner surfaces and enclosing a liquid crystal composition. The electrodes on the two walls are oriented orthogonally. Application of a suitable potential between any pair of electrodes will alter the orientation of the liquid crystal molecules and in consequence the transparency of the associated cell element in known manner.

The scene evalution means 5 consists of a lens and a charge coupled device (CCD) brightness sensing element. The lens focal length is selected so that the area of the scene focussed on the sensitive surface of the CCD corresponds with the angle of view of the user wearing the frame. The CCD element is raster scanned in known manner to provide a series of signals related to scene brightness which are passed to the circuitry in the attachment 7. The cell elements are scanned successively by the circuitry in the attachment 7 in synchronism with the CCD raster scan to provide a transparency pattern on the lenses 2 and 3 corresponding to a negative image of the scene.

A scene observed by the driver of a car, see Figure 2a, is observed in the lenses 2 and 3 as a shown in Figure 2b.

Due to the low resolution of the scanned scene image and the location of the lenses 2 and 3 with respect to the eye the overall effect will be that of an unsharp negative mask enabling fine detail in a scene to be observed at a substantially constant brightness level regardless of the actual scene brightness.

Claims

1. Anti-glare viewing frames which contain at least one lens comprising a liquid crystal cell having a plurality of addressable light transmitting elements, characterised in that the frame includes scene evaluation means adapted to provide a series of signals relating to elements of scene brightness across the field of view and control means arranged to lower the transparency of each light transmitting element in response to the brightness of the element of the scene observed through it.

2. Anti-glare viewing frames as claimed in claim 1, characterised in that the scene evaluation means comprises a scene analysis device consisting of a combination of a lens with a video pick-up tube, a charge coupled device or an array of photosensors.

3. Anti-glare viewing frames as claimed in claim 2, characterised in that the scene is focussed on a charge coupled device sensor so that the field of view covered by the device is substantially the same as that of the user of the frames.

4. Anti-glare viewing frames as claimed in claims 1 or 2, characterised in that the scene analysis device supplies information relating to the brightness of each scene element continuously.

5. Anti-glare viewing frames as claimed in claims 1 or 2, characterised in that the scene analysis device supplies information relating to the brightness of each scene element successively by scanning the scene area.

6. Anti-glare viewing frames as claimed in claims 4 or 5, characterised in that a charge coupled device is scanned in conventional manner and the output from one or more elements of the device is used to control the transmission of an element of the lens associated with the same scene area.

7. Anti-glare viewing frames as claimed in 6, characterised in that the charge coupled device provides a scanning array having a range of 5 X 10 to 50 X 100 elements.

8. Anti-glare viewing frames as claimed in 6, characterised in that the liquid crystal lenses have an array of from 5 X 10 to 50 X 100 addressable light transmitting elements.

9. Anti-glare viewing frames as claimed in any of the preceding claims, characterised in that the liquid crystal lenses have an aspect ratio in the range from 1 to 1 to 1 to 10.

10. Anti-glare viewing frames as claimed in any of the preceding claims, characterised in that the power supplies for the operation of the scene evaluation means and the control means is provided by batteries integral with the frame.

11. Anti-glare viewing frames as claimed in 10, characterised in that the batteries are maintained in a charged state by means of a series of photovoltaic cells.

12. Anti-glare viewing frames as claimed in any of the preceding claims, characterised in that the viewing frame forms a visor on a helmet.

13. Anti-glare viewing frames as claimed in claim 12, characterised in that the the scene evaluation means is located on the helmet.

14. Anti-glare viewing frames as claimed in claim 12, characterised in that the the scene evaluation means is means is located behind the visor in a feedback system, and associated control circuitry adjusts the transparency of each lens element to ensure that the intensity of light falling upon each element of the scanned scene is constant.

15. Anti-glare viewing frames as claimed in claim 1 and as herein described.

16. Anti-glare viewing frames as herein described with reference to the accompanying drawings.