Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
The present invention rela-tes to optical display arrange-
men-ts comprising a light ~ralve (i.e. a display having at least one
display element which is switchable between an opaque or diffusecl
state and a transparent state), in particular a liquid crystal cell;
a light trap in the form of a body (hereinafter referred to as a
"fluorescent body") which is made of a material having a refractive
index greater than 1, which contains fluorescent particles and which
is provided with one or more light-emergence windows; and finally
an auxiliary illuminating means.
Such displays have already been proposed, for example, in
U.S. Patents 4,142,781 issued March 6, 1979 and 4,167,307 issued
September 11, 1979. The fluorescent body used in these displays
increases the contrast of the display, since it traps incident ambient
light by fluorescent scattering and subsequent total reflection, and
finally emits it again at a higher level of intensity through the
light-emergence windows specifically provided for this purpose.
Since this light trap merely intensifies the image displayed but
does not itself generate any light, an auxiliary means of illumin-
ation is still required for use when the ambient light is not
sufficiently bright, for example, under night conditions.
In such a display, the auxiliary light source provided,
; if it is to be suitable for use with battery-powered devices, should
consume as little power as possible and preferably should be operable
(for example, in wrist-watches) without any need for manual opera-
~ tion, and it is an object of the present invention to provide an
`~ optical display arrangement incorporating such an auxiliary light
source.
According to the invention, there is provided an optical
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display arranclement comprising a light valve, a liyht -trap in the
form of a fluorescent body made of a material having a refractive
index greater than 1, which contains fluorescent particles and which
is provided with at leas-t one light-emergence window, and an
auxiliary illumination means comprlsing a radio-ac-tive substance
and a luminous material which is activated by the radiation Erom
said substance. A weak ~-ray emitter, such as tritium, for
example, is particularly suitable for use as the radio-active
substance.
- 10 The light source provided in the arrangement of the
invention emits light con-tinuously without any need to press
a button to activate it and without requiring any supply of
energy, for example, from a battery. In addition, it does not
require replacement or regeneration during the normal service
life of the display, since its illuminating power, depending
only on the half-life of the radio-active material, only declines
to an appreciable extent after a relatively long period.
Liquid crystal displays with luminous colours excited
by weak ~-emitters are already known per se (see, for example,
German Patent Specification No. 2,232,632 of Charrier, laid open
January 24, 1974). Moreover, liquid crystal displays are already
on the market having miniature bulbs filled with tritium gas. The
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arrangement of the invention offers considerable advan-
tages over these known arrangements~ however, since in
the arrangement of th~ invention the light onLy ha~ to
be available at the emergence windows and consequently
S the radio-activity level which must be ~olerated can be
made substantially lower.
In the arrangements of the invention, the fluorescent
body is generally plate-shaped and located behind the light
valve ~n the viewing direction. With such an arrangement,
the auxiliary means of lllumination, such as a mi~iature
tritium bulb, ~ay conveniently be disposed either along one
or more o~ the side edyes of the fluorescent plate or behind
this plate; in the latter case, it should totally cover the
face of tbe plate ad~acent to ito ~lternatively~ o cour~e,
the light so~rce may be incorporated in the fluorescent
plate itself, for example by casking it in when the plate
is made.
If a par~icularly space-savins design is r~quired,
~ with uniform illumination of all the elements of the dis-
; 20 play, the radio-active substance should be directly
incorporated in the fluorescent body in as homogeneously
distr~buted a manner as possible~ In this case, it may be
worth binding the radio-activ~ substance chemically, for
; example~ to the fluorescent particles. Finally, it may
be possibLe to add phosphorescent particIes that can be
made to gLow by the radiating substance.
;~ With the arrangement of the lnvent~on, a particularly
small amount ot radio-act~ve substance can suffice; i~ the
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emergence windows of the fluorescent: plate are constltuted
b~ a combination of scattering areas on the front f ace of
the pl ate and indentations located at corresponding point~
in the rear face ~hereof, the radlo-act~ve substance and
the luminous material is applied to the scattering areas
only. In this case, the light yield can be made aven
higher, if lt is also ensured that the largest possible
part o~ ~he fluorescent or other l~minous radlation passes
-- through the light val~e. This can be achieve~ by locatlngj 10 the ~luorescent plate~ a~ close as possible to the ~witchable
medium and/or lf the light valve is freed from undasirably
absorbent component~O In a liquid crystal cell normally
using polarisers for its operation~ for example, it i5
particularly ad~antageous to i~plant a pleochroic dye in
the liquid crystal layer, since such an additive renders
unnecessary that polar~er which is located between the
fluorescent body anà the liquid crystal layer and which,
in practice, not only polarises but also weakPns the light
~, passing through it by absorptlon.
The invention will now be further descr~ bed with
reference to ~he drawing~ ~n which :-
Figure 1 is a schematic side sectional view o~ a
first embodiment of the invention;
Flgure 2 is a similar ~iew to that of Figure 1 of
a second embodiment of the invent~on; and
Figur.e 3 is a schematic side-sectional view of a
- fluorescent plate for use in a ~hird
. embodiment o~ the invention.
In all the Figures~ like parts are indicated by the
same refere~nce numeral. ~ 5
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he embodiment shown in Figure 1, includes a light
valve in the form of a liquid crystal cell with a single-digit
numerical display. In detail, the arrangement illustrated comprises
a front linear polariser 1, a front carrier plate 2, a rear carrier
plate 3, a rear linear polariser 4, a fluorescent plate 5 and an
absorption film 6, all disposed sequentially one behind another in
the named order in -the direction of viewing.
On their opposed faces the two carrier plates are pro-
vided with electrically conducting coatings, the rear plate 3
with an unbroken coating forming a rear electrode 8, and the front
plate 2 with a segmented electrode forming electrode segments 9.
Between the two carrier plates a spacing frame 10 is located,
defining with the two plates a sealed chamber filled with a liquid
crystal layer 11.
On its four side faces the fluorescent plate 5 carries
reflective coatings 12 and it is provided with a plurality of
light-emergence windows one disposed behind each individual elec- -
trode segment 9 (considered in the direction of viewing). Each of
~ these windows consists of an indentation 13 whlch may be silvered,
20 in the rear face of the plate 5 and of a co-operating scattering
area 14 on the front face of the plate and constituted, for example,
by a pigment or a roughened flat area of the plate surface. This
form of window gives a wide angle viewing zone with relatively
high light intensity and provides a practically parallax-free
~` display.
An auxiliary illuminating means in the form of a small
lamp 15 filled with tritium gas is attached to one of the four
side faces of the plate. On this side the reflective coating is
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so cons-ti-tuted that the -tritium light can pass in-to the interior of
-the plate but -the fluorescent light is reflected back, -the reflective
coating being in the form of a dichroic mirror 16. Naturally, other
kinds of optical linking between the small lamp and the pla-te can
equally be used.
The liquid crystal cell works on the principle of the so-
called "rotary cell". For further details, reference should be made
to German Patent Specifica-tion No. 2,158,563 of Wuesthoff et al,
laid open June 29, 1972. In the embodiment of Figure 1, the axes of
polarisation of the two linear polarisers are arranged at right
angles to one another so that the light valve is transparent in the
inoperative state and opaque in the activated sta-te. At the same
time the activating means (not shown) is so designed that it is
always only those electrode segments not required to form the image
to be displayed that are supplied with a voltage. This is known
as the "principle of complementary activation". These measures give
a particularly bright image on a dark background; the part of the
display screen not covered by the electrode segments appears almost
black since only a very small part of the trapped light leaves the
fluorescent plate outside the windows and moreover the light from
the background is collected by the absorption film 6. The activated
display elements are black since there the valve blocks the passage
of light. Finally, the image is particularly intense, since the
front face of the fluorescent plate 5 which is covered by the liquid
crystal cell can also absorb light.
The embodiment illustrated in Figure 2 differs from the
first embodiment in the following ways. The light source is placed,
not as in the embodiment of Figure 1, to the side, but behind the
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~luorescent plate 5 and without any optical con-tact -therewith; all
-the side faces of -the pla-te 5 are completely silvered; the absorp-
tion film 6 is replaced by a filter providecl with a highly reflec-
tive coating on its rear face and which only admits light for the
excitation of the fluorescent particles (this measure increases
the length of the absorption path for the incident and excitation
light and thus generally makes it possible to use a lower concen-
tration of fluorescent material with a consequent greater ultimate
brilliance); complementary activation is not used; the rear linear
polariser is eliminated and in its stead, the liquid crystal layer
contains a pleochroic dye. In its inoperative state, the li~uid
crystal layer exhibits a planar texture wi-th a bias parallel to the
axis of polarisation of the linear polariser, whilst in its activated
state, it exhibits a homotropic orientation. A focal-conical in-
active texture could alternatively be used.
The radio-active substance used need not be present in the
gaseous state, it can alternatively be present in chemically bound
form in the fluorescent plate, in a film disposed behind the plate
or in a layer which fills the indentations in the rear face of the
plate, for example. It is, moreover, possible to implant scattering
particles of luminous material in the front face of the plate and
to surround these particles with a compound containing the radio-
active substance. This possibility is illustrated in Figure 3.
Here, the scattering layer 1~ of the fluorescent plate 5 is coated
with a tritium lacquer 18. With this form of light source, the
light yield from the luminous material is particularly high.
If necessary, for example, in order to keep within a
prescribed radiation tolerance level, the radio-active substance
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can be embedded in a ma-terial that absorbs the undesired radio~
active energy, and is also acid and alkali-resistant, and in
particular, is not decomposed by stomach acid.
The inven-tion is not, oi- course, limited to -the embodi-
ments illustra-ted, for example, radio-active substances other than
tritium can be used, and the light valve, i-luorescen-t body and
radio-active adcditional lighting can be combined in other ways.
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