FR2465287A1 - MEANS IMPROVING THE ILLUMINANCE OF A LIQUID CRYSTAL DISPLAY CELL AND DISPLAY DEVICES THUS OBTAINED - Google Patents

Abstract

MEANS ALLOWING MAXIMUM USE OF INCIDENT AMBIENT LIGHT. THEY INCLUDE: A. OPTICAL MEANS 24 ADJACENT TO THE MENTIONED REAR FACE OF THE CELL, REFLECTING AND PARTIALLY TRANSMITTING THE INCIDENT LIGHT WHICH FALLS ON THIS CELL AND EXIT; AND B. REFLECTOR MEANS 26, PLACED PARALLEL WITH THE, AND AT A CERTAIN DISTANCE FROM THE OPTICAL MEANS SO AS TO BE IN AGREEMENT WITH THESE LAST MEANS, THESE REFLECTOR MEANS REFLECTING TOWARDS THE OPTICAL MEANS THE LIGHT THAT THEY TRANSMIT ON THE SAME, SENSITIVE PATHS THAT THOSE TAKE BY THE LIGHT THAT THEY RECEIVE, SO THAT THE OPTICAL MEANS DIFFUSE LIGHT INTO THE LIQUID CRYSTAL DISPLAY CELL ON A LARGE CONE OF VISION CENTERED ON THE ENTERING RAYS OF THE LIGHT FALLING ON THE FACE OF THIS CELL. APPLICATION TO REFLECTION LIQUID CRYSTAL DISPLAYS.

Description

The invention relates, in general, to the

  liquid crystal display devices and, more particularly,

  in particular, relates to a display device whose

  Illuminance properties are improved.

  For the safe and efficient operation of certain aircraft, including large multi-engine transport aircraft and military aircraft, it is necessary for the pilot and other crew members to be constantly aware of

  various information concerning the conditions of

  and attitude, engine speed, oil pressure, remaining fuel, just to name a few. These navigation and operating conditions are generally provided from electronic or electromechanical detectors, the corresponding information being processed in associated and visualized detection circuits.

  using electro-optical and electronic display means

  combined mechanical, mounted in the cockpit in the

  field of vision of the pilot and the crew.

  Electro-optical and electronic display means

  Mechanical mounts are generally mounted in the cockpit so as to be seen at an angle, to the right, left or down from the normal direction of vision. With the only illumination which, in the cockpit, is given by the light passing through the windshield of the airplane, the only part illuminated to a certain extent with the display means is in a quarter of an upper and lateral sphere to these means. Since the level of ambient lighting is generally low in the cockpit, especially at night, it is extremely important that the display means be as bright as possible so that the information displayed is

  readable for the pilot and the crew.

  The electro-optical devices currently used for displaying alphanumeric information concerning the navigation and operating conditions of an aircraft use the reflective and transmitting properties of liquid crystal display devices and display devices. with light emitting diodes. Liquid crystal display devices are of construction

  less expensive and of lower consumption than the

  light emitting diode displays; but they

  require external lighting for the information to be displayed

  are visible to the crew. In the case of transmitter-type liquid crystal display devices, an external light source is placed behind the

  crystal display cell xliquides, so that this cell

  lule is illuminated by the light that runs through it. When it comes to liquid crystal display devices of the type

  reflector, the ambient light falling on the cell of

  liquid crystal display makes this light cell. Since the operation of this latter type of cell is based on incident ambient light, it is desirable, especially when

  the levels of ambient lighting are low, making it

  the light reflected by the cell so that information

  displayed are as bright as possible. The inventors

  The aim of this is therefore to maximize the illumination of a

  reflective type liquid crystal display device.

  According to a preferred embodiment according to the invention, it is established means improving the illumination of liquid crystal display devices by maximizing

  the light reflected by the LCD display cell

  these means consisting of a partially reflective and partially transmitting diffuser, composed of an opaline glass layer or the like, which is fixed on the rear face of the cell. Reflector means, whose configuration is defined so that they reflect light on the same

  than those followed by the incident light they receive.

  wind, are placed parallel to a certain distance from the

  fuser so as to be in optical correspondence with this diffe-

  meltagun. Ambient light falling on the display cell

  cristaix liquidsand is transmitted by the diffuser is

  the reflector towards the diffuser following the same incidence and return paths, which avoids any loss of light. The diffuser diffuses the light that is sent back to it

  by the reflector inside a large cone of central vision

  the direction of incident rays of ambient light falling on the liquid crystal display cell, thus maximizing the use of ambient light, as well as the brightness of the liquid crystal display device.

  The object of the invention is therefore to provide a

  LCD display system making it possible to

  male the use of incident ambient light so that

  this device is as bright as possible.

  The invention also aims at a device

  liquid crystal display which is sufficiently luminous

  for correct display, including information on navigation and operating conditions

on board an airplane.

  The rest of the description refers to the drawings

annexed which represent:

  - Figure 1, a side view of a display device with crys-

  liquid levels of the reflector type, known,

  FIG. 2, a side view of a crisper display device

  liquid levels according to the invention.

  The known device illustrated in FIG.

  liquid crystal display cell 12 of the reflector type.

  The cell 12 consists of two transparent plates 14 and 16, parallel and placed at a distance from each other, each formed by a layer of glass, of plastic

  or the like. References 14a and 14b, respectively, were given

  the opposite front and rear faces of the plate 14. Similarly, references 16a and 16b, respectively, have been given

  opposite front and rear faces of the plate 16.

  Two transparent electrodes 18a and 18b are

  The electrodes 18a and 18b are each formed by deposition of a thin layer of oxide, and are fixed to the rear face 14b of the plate 14 and to the front face 16a of the plate.

  of indium-tin, or the like, on the faces 14b and 16a, respectively

  plates. One of the electrodes 18a and 18b has gen-

  the shape of a character, a symbol or any other

  indication, while the surface of the other electrode is full.

  A layer 20 is placed between the electrodes 18a and 18b; it consists of a material constituting the liquid crystals, such as cyanobiphenyl, contained in appropriate means

  (not shown) which are arranged between the electrodes.

  Each of the two electrical conductors 22a and 22b is

  electrically connected to one of the electrodes 18a and 18b.

  When a potential is applied between the conductors 22a and 22b, an electric field is created between the electrodes 18a and 18b, modifying the molecular alignment of the liquid crystals which constitutes the layer 20 and allowing the transmission of the ambient light through this layer. The light that

  through the layer 20 of liquid crystals, as well as

  trode 18b and the plate 16, is reflected by a rough reflector, slightly diffuser, 23, generally consisting of a thin layer of reflective material such as aluminum or silver, this layer being deposited on the face 16b of the plate 16 which is slightly frosted, at the rear of the display cell, the central lobe of the light diffused by this reflector 23 being centered on the spectral reflection angle B defined from the normal N to the reflector, this angle B being equal to the angle θ of incidence that the incoming rays of ambient light make with this normal. The reflected light thus forms a cone of incidence of the scattered light whose angle at the apex, of the order of 20 to 30o, is centered on the spectral reflection angle B. The use of the display devices to reflector-type liquid crystals, to visualize information concerning the navigation and operating conditions of an aircraft, has the disadvantage of leading to a reflection of a small part of the ambient light in the quarter of the spheres which is top and sides of the device, either

  exactly where ambient lighting is the largest

  these devices fixed in the cockpit.

  FIG. 2 illustrates a new display device

  reflector-type liquid crystal display, whose illumination is improved and which comprises a cell 12 of conventional type

  identical in configuration to that of the display cell.

  chage 12 illustrated Figure 1. A diffuser 24, partially reflective and partially transmitting, is juxtaposed on the face 16b of the plate 16 of the cell. A retroreflector 26, which returns the incident light on the same paths as those

  borrowed by this light, is placed parallel to the diffusion

  24, at a distance from this diffuser.

  The diffuser 24 may have the configuration of a different

  surface fuser or that of a full diffuser. In this preferred embodiment, where the diffuser 24 has the configuration of a solid diffuser and is formed by a layer of opal glass or the like, the retroreflector 26 is composed of a microarray of tapered retroreflectors with cubic base. Each retroreflector of the microretwork has the shape of a prism and substantially reflects all the incident light even if this light is substantially offset from the central axis of the retroreflector considered. Reference is made to the RCA Electro-Optical Handbook, published by the RCA Corporation,

  for a more in-depth explanation of the retro-

  tapered reflectors with cubic base (1974 edition, pages

217-224).

  Since the configuration of the retroreflector 26 is that of a microarray of tapered retroreflectors with a cubic base, it is desirable to fill the voids formed between this microarray and the diffuser 24 with a layer 28 of transparent material, such as glass. or plastic, whose refractive index

  is approximately equal to that of the retroreflective material

  to adapt the surfaces facing each other and to avoid

  formation of internal light traps. He is also

  desirable to provide a layer of reflective material 29 on the surface of the microarray of retroreflectors, to increase

  the angle at which each microarray retroreflector

see the light.

  In operation, when the molecular alignment of the liquid crystal layer 20 is changed by applying an electrical potential between the leads 22a and 22b, the ambient light is transmitted through this layer 20, the electrode 18b, and the plate 16, and is broadcast by the

  diffuser 24. The scattered light falling on the retroreflec-

  26 is returned to broadcaster 24, on the same

  throws than those followed by the scattered light incident. Thus, the reflected light, which has been previously diffused by the diffuser 24, is again re-diffused by this diffuser, on a wider diffusion cone centered on the direction of the incoming rays of ambient light which fall on the display cell. As a result, the diffuser 24 and the retroreflector 26 advantageously utilize, to a maximum extent, the available ambient light, making the display

as bright as possible.

  The goniophotometric reflection and transmission characteristics of the diffuser 24, namely its directional characteristics of light distribution by reflection and

  transmission, are chosen to lead to the desired angle.

  of the cone of vision, is generally an angle of the order of 300. The thickness of the diffuser is generally of the order

from 0.025 mm to 0.50 mm.

  We have just described a device comprising a diffuser and a retroreflector which improves the illumination of liquid crystal display devices and gives them the greatest possible brightness, by backscattering in the liquid crystal cell of the light that has passed through this cell. and forming a wide vision cone centered on the direction of incoming ambient light rays falling on said cell. The diffuser and the retroreflector can be added to the liquid crystal cell without the cost being substantially increased, and the device according to the invention is therefore an inexpensive way to improve

  the illumination of liquid crystal display devices.

Claims (10)

R E V E N D I C A T IO N S   1. Means for improving the illumination of a liquid crystal display cell (12), to make this cell as bright as possible, the cell having a front face (14a) visible to the user staff, and a face opposite rear (16b) ,. characterized in that they comprise:   (a) optical means (24) adjacent to the rear face   of the cell, reflecting and transmitting   the incident light that falls on this cell and leaves it, and (b) reflector means (26), placed parallel to and at a certain distance from the optical means so as to be in agreement with these latter means, these means   reflecting reflectors towards the optical means   they transmit, substantially on the same   jets than those borrowed.by the light they receive, so that the optical means diffuse the light in the LCD cell on a large cone of vision centered on the incoming rays of light that   falls on the front of this cell, which makes it   the reflection of ambient light falling on this   front of the cell and makes the latter as possible.   2. Means according to claim 1, characterized in that   that the optical means (24) consist of a diffuser.   3. Means according to claim 2, characterized in that the diffuser consists of a thin layer of opal glass. 4. Means according to claim 1, characterized in that the reflector means (26) consist of a micro-array of tapered reflectors with cubic base, the microarray having a first face and a second opposite face, the first face being opposite the optical means.   5. Means according to claim 4, characterized in that they comprise, in addition:   a layer of transparent material (28) whose index of   fraction is equal to that of the material constituting the   reflectors of the microarray, which layer is placed between the optical means and this microarray, and a layer of reflective material (29) placed on the second face of the microarray, to increase the angle on which this   Microarray of retroreflectors returns the light.   6. A liquid crystal display device   improved sity, characterized in that it comprises (a) a liquid crystal display cell (12) - before a front face (14a) visible to the user staff and an opposite rear face (16b),   (b) optical means (24) adjacent to the oppo-   of the cell, for partial transmission and reflection of the light transmitted by this cell, and (c) reflector means (26) placed parallel to and at a distance from the optical means so as to be   concordance with these last means, these means reflect   reflectors towards the optical means the light they transmit, substantially on the same paths as those borrowed by the light they receive, so   optical means diffuse light into the cell   the LCD on a wide cone of vision centered on the incoming rays of the light that falls on the front face of this cell, which maximizes the reflection of the ambient light falling on that front face of cell and renders the latter as bright as possible. 7. Device according to claim 6, characterized in   the optical means (24) consist of a diffuser.   8. Device according to claim 7, characterized in that the diffuser consists of a thin layer of opal glass. 9. Device according to claim 6, characterized in that the reflector means (26) consist of a micro-array of tapered retroreflectors with a cubic base, this microarray having a first face and a second opposite face, the first face. being opposite the broadcaster.   10. Device according to claim 9, characterized in that it comprises, in addition:   a layer of transparent material (28) whose index of   fraction is equal to that of the material constituting the   reflectors of the microarray, which layer is placed between the diffuser and this microarray, and a layer of reflective material (29) placed on the second face of the microarray, to increase the angle on which this   Microarray of retroreflectors returns the light.