GB2048506A - Liquid crystal optical filter system - Google Patents
Liquid crystal optical filter system Download PDFInfo
- Publication number
- GB2048506A GB2048506A GB7914477A GB7914477A GB2048506A GB 2048506 A GB2048506 A GB 2048506A GB 7914477 A GB7914477 A GB 7914477A GB 7914477 A GB7914477 A GB 7914477A GB 2048506 A GB2048506 A GB 2048506A
- Authority
- GB
- United Kingdom
- Prior art keywords
- plane
- filter
- light
- polarising
- polarisation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133528—Polarisers
- G02F1/133533—Colour selective polarisers
Abstract
A switchable colour light source, e.g. for traffic signals where reliability is important, comprises in sequence an electroluminescent panel 20 (or other white light source), a neutral linear polariser 21, a liquid crystal twist cell 22 (allowing the polarisation direction to be changed by 90 DEG ), a magenta dichroic polarising filter 23, an isotropic yellow filter 24 and a blue dichroic polarising filter 25 crossed relative to filter 23 and polariser 21. Depending on the state of cell 22 either red or green light is transmitted. <IMAGE>
Description
SPECIFICATION
Optical filters
This invention concerns optical filters. It relates more particularly to devices that emit light and involve the switching of the emitted light from one wavelength (or group of wavelengths) to another, and concerned especially light signal devices involving the switching of the emitted light from one colour to another.
There are many signal devices which involve the switching of the signal from one form in one colour to the same or another form in another colour.
Typical examples of such devices are traffic lights or railway signals (switching a signal of the same form from red through amber to green, and vice versa) and the sort of motorway warning light signals which can indicate, in white, amber or red, warning of lane or speed restrictions. Devices of these general types tend to operate-to cause the signal to be switched from form to form and/or colour to colour-either by means of separate light sources each behind its own shaped and/or coloured filter or by means of a single light source behind a movable shaped and/or coloured filter. In the former case the signal generated by the device is switched by changing from one light source to another, while in the latter case the generated signal is switched by changing the filter.
These devices are simple and straightforward, but nevertheless suffer from a number of serious disadvantages. In particular, the former variety (changing the light source) is prone to problems caused by the severe aging effect, on the source itself and on the electrical switch contacts, of the repetitive switching of quite large currents, while the latter variety (displacing the filter) is prone to faults developing in the electro-mechanical systems employed to effect filter displacement.
The present invention seeks to provide novel forms of signalling device some of which avoid these disadvantages.
In one aspect, therefore, this invention provides apparatus for selecting the perceived wavelength or wavelengths of light emitted from a source thereof, which apparatus comprises, in operative association;a) polarising means adapted to polarise the light emitted by a source thereof; b) control means adapted to change the mode of polarisation of the emitted light; and c) filter means adapted to select the wavelength of the light transmitted thereby according to the light's mode of polarisation.
The prime intended purpose of the device of the invention is for use in connection with sources of visible light, to alter the perceived light transmitted by the source from one colour (or mixture of colours) to another. The light source may be of any type used or suggested for use as such. It may, therefore, be one or a set of incandescent or fluorescent bulbs.
Preferably, however, it is one or more of the relatively new electroluminescent panels of the zinc sulphide type. the source may be of any colour or combination of colours provided that its output does include the colour or colours to be selected and transmitted by the filter means (in this contect the term "colour or combination of colours" is intended to include white light).
The first integer of the apparatus of the invention is the polarising means adapted to polarise the source's emitted output, these polarising means being operatively associated with the second integer, namely the control means adapted to change the mode of polarisation. Most conveniently, the mode chosen is that of plane polarisation in a particular direction, the change of mode being a change from plane polarisation in one direction to plane polerisation in another (preferably substantially at right angles to the first). The polarising means is therefore desirably a plane polariser (advantageously of neutral density or colour), such as a Nicol prism our a sheet of type H or type K linear polarising polymericfilm material of the same general sort as that available under the name POLAROID (POLAR
OID is a Registered Trade Mark).The control means, effecting the change in the plane of polarisation, can be a simple mechanical linkage effecting physical rotation of the polarising means, but very preferably it is such a device as a liquid crystal twist cell which is so designed as to twist through the requisite angle the plane of the plane-polarised light passing therethrough when the cell is in the relaxed state but to allow the light to pass plane unchanged when the cell is in its activated (driven) state. Such a cell can switch the plane of plane-polarised light passing therethrough from one direction to another without the involvement of any moving parts.A typical twist cell employs indium/tin oxide electrodes upon glass substrate plates the inner surfaces of which are suitably oriented and spaced between 5 and 50 microns apart; the liquid crystal substance is one or more compounds - such as a mixture of alkyl-cyanobiphenyls - displaying positive dielectric anisotropy.
The third integer of the apparatus of the invention is the filter means adapted to select for trnasmission from the source's light output a particular colour (or colours) according to the mode (plane direction) of that light's polarisation. Preferably the apparatus is intended for the transmission of one or the other of two colours extractable from the source's output, and in that case the filter means will comprise two such means each adapted to select one of the required colours. The most convenient such filter means is a dichroic plane-polarising filter of an appropriate colour - that is, passing only that colour when receiving light polarised with its plane substantially crossed as regards the dichroic filter's polarising plane.Advantageously the dichroic filter is an appropriately-coloured sheet of type DT linear polarising polymeric film material of the same general sort as that available under the name
POLAROID.
A preferred form of the invention as so far described will be seen to be definable in the folowing terms:
Apparatus for switching the perceived output of a light source between two colours present in or derivable from the source's output, which apparatus comprises: a) means for plane polarising the light source's output so that the polarisation plane is changeable at will between two positions substantially at right angles to each other; and, operatively associated therewith, b) two dichroic plane-polarising filters characterising the two chosen colours and having their polarisation planes aligned with the two extreme positions adoptable by the polarisation plane of the light source's output.
Moreover, a more preferred form of the invention is definable, when in cooperation with a light source, as follows:
Apparatus adapted to provide alight output in both of two colours, the output at any one time being of one of the two colours only, which device comprises:a) a light source the output of which includes in combined or derivable form at least the two chosen colours; b) a neutral plane-polarising filter, through which passes the output of the light source to emerge in plane-polarised form; c) a liquid crystal twist cell, capable of being switched between a first state (in which it rotates the plane of plane-polarised light passing therethrough from a first plane to a second plane disposed substantially at right angles to the first plane) and a second state (in which it causes no such rotation), through which cell passes the output from the neutral plane polariser; and d) in the pathway of the light output from the neutral polariser, two dichroic plane-polarising filters, arranged so that the plane of polarisation of one is substantially aligned with the plane of polarisation of the netural plane-polarising filter while the plane of the other is substantially at right angles thereto, the light wavelength selectivity of the two filters being so chosen as to enable one filter to pass one of the two chosen colours, and to enable the otherfilter to pass the other of the two chosen colours.
As explained above, the light source may be any suitable such source but is preferably an electroluminescent panel, while the neutral planepolarising filter may likewise be of any suitable sort but is preferably of the POLAROID type, and the liquid crystal twist cell is as described hereinbefore.
The dichroic plane-polarising filters will also be as briefly described hereinbefore (and so preferably of the POLAROID type), with the important proviso that each filter may consist of a set of filters (not all of which need be dichroic plane-polarising filters) the effect of which is to cause selection of the desired colour. by way of example, if it is desired to select, from a white light source, the two colours red and green, and because (to date) it has not proven possible to achieve a satisfactory green dichroic plane-polarising filter, the two colours may be obtained by using (for green) a blue dichroic planepolarising filter combined with an isotropic yellow filter (that is to say, non-dichroic, a/non-polarising filter) and (for red) a magenta dichroic planepolarising filter combined with a (the same) isotropic yellow filter.
A particular embodiment of the invention will now be described, though by way of illustration only, with referenceto the accompaying drawings, in which:
Figure la and lb show very diagrammatically the principle behind the invention (for clarity, the identifying numerals are shown only on Figure la);
Fogures 2a and 2b show, in diagrammatic form, one embodiment of the invention (for clarity, the identifying numerals are shown only on Figure 2a); and
Figure 3 shows, in graphical form, the output of the Figure 2 source and the transmissivity of the
Figure 2 filters as a function of the percentage of the total dependent upon the wavelength of the light concerned.
In Figures la and ib there is shown a light source 10 emitting both red and green light, the light path from this source being through a neutral planepolarising filter 11 followed by a green dichoric plane-polarising filter 12.
The light source 10 emits both red and green light which is randomly polarised -that is, which shows no preferential polarisation plane, and so may be regarded as being an even mixture of light polarised in all possible directions. For the purpose of this discussion, however, this light may be regarded as though it were an even mixture of light polarised in a vertical direction (as viewed) in the plane of the paper (arrow 10pv) and light polarised normal to the plane of the paper (represented by arrow lops).
The neutral plane-polarising filter 11 passes, colour unchanged, only light which is plane-polarised with the polarisation direction being that of the filter 11 (ds shown by arrow 11 p), while the green dichroic plane-polarising filter 12 will pass green light no matter what the light's mode of polarisation, but will only pass ay other colour of light red, say - if that light is plane-polarised with the polarisation direction being that of the dichroic filter 12 (as shown by arrow l2p). As will now be explained, the colour light passed by the green dichroic plane-polarising filter 12 depends upon the direction of polarisation (lip) of the neutral plane-polarising filter 11.
In Figure la both the neutral plane-polarising filter 11 and the green dichroic plane-polarising filter 12 have their polarisation direction (1 1, and 12p) vertical (as viewed) in the plane of the paper. Red and green randomly-polarised light emitted by the source 10 meets the neutral filter 11, and only the component plane-polarised aong arrow 11p is allowed to pass. Thus, both red and green light, plane-polarised along arrow 11,, travel to the green dichroic plane-polarising filter 12. This filter 12, because it has its polarising direction 12, the same as that (1 p) of the neutral plane-polarising filter 11, because it will pass any colour light provided that light is plane-polarised in the filter's own polarisation direction (1 2p), and because the red/green light reaching itis so polarised,allows both the red and the green light to pass through. In this case, therefore, the light source's output, as perceived from a position down path of the two filters 11 and 12, will be a mixture of red and green (seen, in fact, as yellow).
In Figure, however, the neutral plane-polarising filter 11 has been moved so that its polarisation direction lip is normal to the plane of the paper. As a result, randomly polarised red/green light emitted from the source 10 is "converted" by the filter 11 to plane-polarised light having its polarisation direction in the plane of the paper - and thus across (at right angles to) the polarisation direction 12p of the green cidhroic plane-polarising filter 12.So, because this green filter 12 will only pass light polarised cross the filter's own polarisation direction 12p if that light is the filter's own colour (in this example, green), the green light is passed through the filter 12 but the red light is blocked. thus, in this particular case, therefore, the light source's output, as perceived from a position down path of the two filters 11 and 12, will be green.
The embodiment of the invention shown diagrammatically in Figures 2a and 2b is more complicated than the apparatus of Figure 1, but operates essentially in the same way. A light source 20 emits white randomly-polarised light, and in the path of this emitted light are placed, successively: a neutural plane-polarising filter 21; a liquid crystal twist cell 22; a magenta dichroic plane-polarising filter 23 having its polarisation direction 23p vertical (as viewed) in the plane of the paper; an ordinary - that is, isotropic - yellow filter 24; and a blue dichroic plane-polarising filter 25 having its polarisation direction 25p normal to the plane of the paper.
The light source 20 is a zinc sulphide electroluminescent panel having a broad-band, yellowish output with a spectral distribution as shown by the dashdot line in Figure 3. The neutral plane-polarising filter 21 has its polarisation direction 21 p fixed vertically - as viewed - in the plane of the paper. The twist cell 22 is so arranged that in its relaxed (or undriven) state - Figure 2b - it will reotate the polarisation direction of plane-polarised light passing therethrough from a direction which is vertical (as viewed) in the plane of the paper to a direction normal to the plane of the paper, while in its driven state (Figure 2a) it will not change the polarisation direction of any plane-polarised light passing therethrough.The magenta, yellow and blue filters 23, 24 and 25 have transmission spectral distributions as shwon by the dash, dot and solid lines respectively in Figure 3. the combination of magenta and yellow filters acts as a red filter, while the combination of yellow and blue filters acts as a green filter.
The embodiment of the invention shown in Figure 2 operates as follows.
With reference to Figure 2a, white light from the source 20 is plane-polarised (as 21p) by the neutral plane-polarising filter 21 and passes through the twist cell 22 unchanged to the series of colourfilters 23,24 and 25. The magenta dichroic plane-polarising filter 23 (polarisation direction 23p, the same as that of the light) passes all colours; the ordinary yellow filter passes only yellow (which may conveniently be regarded as a mixture of red and green); finally, the blue dichroic plane-polarising filter 25 (polarisation direction 25p, across the polarisation direction of the light), which passes blues and greens but blocks reds, allows through only the green component.
Hence, the white light source is caused to appear green.
Figure 2b is the same as Figure 2a except that the twist cell 22 now rotates the light's polarisation direction through 90". White light from the source 20
is plane-polarised (as 2lip), and the twist cell then
rotates the polarisation direction by 90 . The magenta dichroic plane-polarising filter 23 (polarisation direction 23p, now across the light's polarisation direction) passes only magenta (which may conveniently be regarded as a mixture of blue and red); the yellow filter (which passes reds and greens but blocks blues) allows through the red component;.
and the blue dichroic plane-polarising filter (polarisation directon 25p - aligned with the light so it will pass all of the light regardless of colour) allows through the red light. Hence, the white light is caused to appear red.
It will be observed that the particular arrangement of polarisation directions in Figure 2 is "fail-safe" that is, if the driving voltage to the twist cell 22 fails, so that the cell is stuck in its relaxed state, the perceived colour output of the whole set-up is red for danger.
Claims (10)
1. Apparatus for selecting the perceived wavelength or wavelengths of light emitted from a source thereof, which apparatus comprises, in operative association:
a) polarising means adapted to polarise the light emitted buy a source thereof;
b) control means adapted to change the mode of polarisation of the emitted light; and
c) filter means adapted to select the wavelength of the light transmitted thereby according to the light's mode of polarisation.
2. Selection apparatus as claimed in claim 1, wherein the polarising means is a neutral plane polariser.
3. Selection apparatus as claimed in claim 2, wherein the neutral plane polariser is a sheet of type
H ortype K linear polarising polymeric film material.
4. Selection apparatus as claimed in any of the preceding claims, wherein the control means, effecting the change in the plane of polarisation, is a liquid crystal twist cell.
5. Selection apparatus, as claimed in any of the preceding claims, which is intended for the transmission of one or the other of two colours extractable from the source's output, wherein the filter means adapted to select for transmission from the source's lightoutputa particularwavelength (or wavelengths) according to the mode of that light's polarisation comprises two such means each adapted to select one of the required colours.
6. Selection apparatus as claimed in claim 5, wherein the or each filter means is a dichroic plane-polarising filter of an appropriate colour.
7. Selection apparatus as claimed in claim 6, wherein the dichroic filter is an appropriatelycoloured sheet of type DT linear polarising polermic film material.
8. Selection apparatus, as claimed in any of the preceding claims, for switching the perceived output of a light source between two colours present in or derivable from the source's output, which apparatus comprises:
a) means for plane polarising the light source's output so that the polarisation plane is changeable at will between two positions substantially at right angles to each other, and, operatively associated therewith,
b) two dichroic plane-polarising filters characterising the two chosen colours and having their polarisation planes aligned with the two extreme positions adoptable by the polarisation plane of the light source's output.
9. Selection apparatus as claimed in any of the preceding claims and substantially as described hereinbefore with reference to the accompanying drawings.
10. Signal apparatus as claimed in any of claims 7 to 9 and substantially as described hereinbefore with reference to the accompanying drawings.
10. Signal apparatus adapted to provide a light output in both of two colours, the output at any one time being of one of the two colours only, which device comprises:
a) a light source the output of which includes in combined or derivable form at least the two chosen colours;
b) a neutral plane-polarising filter, through which passes the output of the light source to emerge in plane-polarised form;
c) a liquid crystal twist cell, capable of being switched between a first state (in which it rotates the plane of plane-polarised light passing therethrough from a first plane to a second plane disposed substantially at right angles to the first plane) and a second state (in which it causes no such rotation), through which cell passes the output from the neutral plane- polariser; and
d) in the pathway of the light output from the netural polariser, two dichroic plane-polarising filters, arranged so that the plane of polarisation of one is substantially aligned with the plane of polarisation of the neutral plane-polarising filter while the plane of the other is substantialy at right angles thereto, the light wavelength selectivity of the two filters being so chosen as to enable one filter to pass oneof the two chosen colours, and to enable the other filter to pass the other of the two chosen colours.
11. Signal apparatus as claimed in claim 10, wherein the light source is an electroluminescent panel.
12. Signal apparatus as claimed in either of claims 10 and 11, wherein each dichroic planepolarising filter consists of a set of filters the effect of which is to cause selection of the desired colour.
13. Signal apparatus as claimed in claim 12, wherein selection, from a white light source, of the two colours red and green is achieved by using (for green) a blue dichroic plane-polarising filter combined with an isotrpoic yellow filter, and (for red) a magenta dichroic plane-polarising filter combined with a (the samet isotrpoic yellow filter.
14. Signal apparatus as claimed in any of claims 10 to 13 and substantially as described hereinbefore with reference to the accompanying drawings.
New claims or amendments to claims filed on
Superseded claims: 1-14
New or amended claims:
CLAIMS
1. Apparatus for selecting the colour green from the light emitted from a source thereof, which apparatus comprises, in operative association:
a) a netural plane polariser adapted to polarise the light emitted by the source;
b) a liquid crystal twist cell adapted to change the plane of polarisation of the light after transmission by the plane polariser so that the polarisation plane is changeble at will between two positions substantialy at right angles to each other; and
c) filter means adapted to select the wavelength of the light transmitted thereby according to the light's plane of polarisation, which filter means comprises two filters one of which is in isotropic yellow filter and the other of which is a blue dichroic plane-polarising filter having its polarisation plane aligned with one or other of the two extreme positions adoptable by the polarisation plane of the light source's output.
2. Selection apparatus as claimed in claim 1, wherein the neutral plane polariser is a sheet of type
H or type K linear polarising polymeric film material.
3. Selection apparatus, as claimed in either of the preceding claims, which is intended for the transmission of one or the other of two colours extractable from the source's output, wherein in association with the filter means for green there is a second filter means adapted to selectfortransmission from the source's light output a second colour according to the plane of that light's polarisation.
4. Selection apparatus as claimed in claim 3, wherein each filter means is an isotropic yellow filter combined with a dichroic plane-polarising filter of an appropriate colour having its polarisaton plane aligned with one or the other of the two extreme positions adoptable by the polarisation plane of the light source's output.
5. Selection apparatus as claimed in either of claims 3 and 4, wherein each dichroic filter is an appropriately-coloured sheet of type DT linear polarising polymeric film material.
6. Selection apparatus as claimed in any of the preceding claims and substantially as described herein before with reference to the accompanying drawings.
7. Signal apparatus adapted to provide alight output in both of two colours one of which is green, the output at any one time being of one of the two colours only, which device comprises:
a) a light source the output of which includes in combined or derivable form at least the two chosen colours;
b) a neutral plane-polarising filter, through which passes the output of the light source to emerge in plane-polarised form;
c) a liquid crystal twist cell, capable of being switched between a first state (in which it rotates the plane of plane-polarised light passing therethrough from a first plane to a second plane disposed substantially at right angles to the first plane) and a second state (in which it causes no such rotation) through which cell passes the output from the neutral plane-polariser; and, in the pathway of the light output from the neutral polariser,
d) an isotropic yellow filter and two dichroic plane-polarising filters one of which is a blue dichroic filter, the two dichroic filters being arranged so that the plane of polarisation of one is substantially aligned with the plane of polarisation of the neutral plane polarising filter while the plane of the other is substantially at right angles thereto, the light wavelength selectivity of the two filters being so chosen as to enable one dichroic filter and the isotropic filter to pass one of the two chosen colours, and to enable the other dichroic filter and the isotropic filter to pass the other of the chosen colours.
8. Signal apparatus as claimed in claim 7, wherein the light source is an electroluminescent panel.
9. Signal apparatus as claimed in either of claims 7 and 8, wherein selection, from a white light source, of the two colours red and green is achieved by using (for green) a blue dichroic plane-polarising filter combined with an isotropic yellow filter, and (for red) a magenta dichroic plane-polarising filter combined with a (the same) isotropic yellow filter.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/142,961 US4353493A (en) | 1979-04-25 | 1980-04-23 | Advance mechanism |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB4786978 | 1978-04-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2048506A true GB2048506A (en) | 1980-12-10 |
Family
ID=10446536
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7914477A Withdrawn GB2048506A (en) | 1978-04-25 | 1979-04-25 | Liquid crystal optical filter system |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2048506A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2139778A (en) * | 1983-05-09 | 1984-11-14 | Tektronix Inc | Color display system |
| US4611889A (en) * | 1984-04-04 | 1986-09-16 | Tektronix, Inc. | Field sequential liquid crystal display with enhanced brightness |
| GB2272318A (en) * | 1992-10-26 | 1994-05-11 | Tokyo Seimitsu Co Ltd | Traffic signals |
| WO1994028445A2 (en) * | 1993-05-22 | 1994-12-08 | Andreas Biedermann | Variable colour filter |
| USRE36654E (en) | 1989-03-28 | 2000-04-11 | In Focus Systems, Inc. | Stacked LCD color display |
| EP1209513A2 (en) * | 2000-11-22 | 2002-05-29 | Seiko Epson Corporation | Liquid crystal display device and electronic apparatus provided with the same |
-
1979
- 1979-04-25 GB GB7914477A patent/GB2048506A/en not_active Withdrawn
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2139778A (en) * | 1983-05-09 | 1984-11-14 | Tektronix Inc | Color display system |
| US4582396A (en) * | 1983-05-09 | 1986-04-15 | Tektronix, Inc. | Field sequential color display system using optical retardation |
| GB2184860A (en) * | 1983-05-09 | 1987-07-01 | Tektronix Inc | Liquid-crystal variable optical retarder |
| US4611889A (en) * | 1984-04-04 | 1986-09-16 | Tektronix, Inc. | Field sequential liquid crystal display with enhanced brightness |
| USRE36654E (en) | 1989-03-28 | 2000-04-11 | In Focus Systems, Inc. | Stacked LCD color display |
| GB2272318A (en) * | 1992-10-26 | 1994-05-11 | Tokyo Seimitsu Co Ltd | Traffic signals |
| GB2272318B (en) * | 1992-10-26 | 1996-09-04 | Tokyo Seimitsu Co Ltd | Traffic signals |
| CN1037297C (en) * | 1992-10-26 | 1998-02-04 | 株式会社东京精密 | A traffic signal, a display system therefor and a hood for a lamp thereof |
| WO1994028445A2 (en) * | 1993-05-22 | 1994-12-08 | Andreas Biedermann | Variable colour filter |
| WO1994028445A3 (en) * | 1993-05-22 | 1995-01-26 | Andreas Biedermann | Variable colour filter |
| EP1209513A2 (en) * | 2000-11-22 | 2002-05-29 | Seiko Epson Corporation | Liquid crystal display device and electronic apparatus provided with the same |
| EP1209513A3 (en) * | 2000-11-22 | 2003-07-30 | Seiko Epson Corporation | Liquid crystal display device and electronic apparatus provided with the same |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |