DE2554226B2 - Radiation collector and compressor in the form of a fluorescent plastic plate - Google Patents

Description

The invention relates to a radiation collector and -compressor in the form of a plastic plate at least partially mirrored at its end faces, in the fluorescent substance are dissolved and which is provided with at least one light exit window ("fluorescent plate"). Such a plate is from the literature "Research Disclosure", January 1975, pp. 20 and 21, known. The design described there is used for the collection and bundled emission of sunlight and for this purpose it has two front surfaces that are either pre-mirrored or adjoining photocells.

With the known liquid crystal (LC) displays, such as those in the review article »Liquid Crystals "in" VDI-Z. "115, No. 8, June 1973, p. 629 bis 638, are shown, the physical basic effect is used in various versions that light, which passes through a thin LC layer, under the action of an electric field on the latter is modulated. Extremely small electrical voltages or powers are required for the modulation itself. This? In principle, passive FK displays can do that Modulate ambient light and then have the further great advantage over the self-illuminating displays that their readability in a very wide brightness range is independent of the bypass brightness. In practice, however, it looks like that to achieve an acceptable readability glow lamp

chen behind the displays (transmission operation), which has decisive potential advantages of the passive Ads are not applicable. Or one uses the ambient light in such a way that one behind the display A mirror is placed which reflects the ambient light passing through the cell (Reflection operation). This operating mode, too, only leads to satisfactory results under restricted conditions Readability of the advertisements. Among other things, there is the annoying effect that the incident light casts a shadow caused by the display elements on the mirror surfaces. The possibilities of the newer Field effect displays that require polarizers are due to the loss of light in the polarizers and Badly affected by drop shadows

The invention has the task of finding a way how to do it in a simple way and without additional power requirement the optical qualities of passive displays, especially display contrast, Improve image brightness, readability depending on the ambient light, parallax errors and shading kanr :. According to the invention, this object is achieved proposed to passively increase the flexibility of single or multicolored display devices a fluorescent plate of the type mentioned use. There are particular advantages if the fluorescent plate is fitted with an LC display device combined with at least one display element in such a way that, seen from one viewing direction against the light exit direction, the LC display device is located in front of the fluorescent plate. Included it is advisable to assign the light exit window of the fluorescent plate to the display elements.

The invention uses the fact that with the help of thin plastic plates in which fluorescent substances are dissolved. Can collect and guide ambient light with high efficiency and can be made to re-emerge at any point on the plate in a controllable and visible manner. For this reason, such a fluorescent plate, which is located behind an LC ^{display acting as a light vein 1} ', can produce a high luminance in the display elements that are electrically controlled for light transmission, which also adapts to the ambient light. By mixing fluorescent substances and using a pair of different selective polarizers, it is also possible to produce displays which can switch between two different colors.

A single or multi-color display device unier using a solution having fluorescence power is: se from US-S ⁿ 30 15 747.. In this display, which has been part of the state of the art for a long time, the solution does not serve to passively increase the brightness of a display; switched to a fluorescent state.

The invention will now be explained in more detail in connection with the figures of the drawing. In the figures Corresponding parts are provided with the same reference numerals. It shows

F i g. I a nematic FK rotary cell in a perspective view with parts exploded,

Fig.2 in a diagram the relative reflected Intensity of unpolarized light that strikes an air-glass interface as a function of the Angle of incidence,

3 shows in a diagram the relative reflected intensity of unpolarized light which is incident on a Glass-air interface meets, depending on the Angle of incidence,

F i g. 4 in the representation of FIG. 1 shows a first embodiment of the invention, namely a electro-optical display using a fluorescent plate,

Fig. 5 simple types of light extraction, shown on the basis of a cross section through a fluorescent plate according to the invention,

6 in a diagram on the basis of a typical For example, the viewing angle range depending on the ratio of the exit window width on the Fluorescent plate for the display segment width of the LC cell,

7 shows a perspective illustration of a further exemplary embodiment proposed by dr: r Fluorescent plate in which the brightness of an LC display can be increased with the help of an additional collector plate is further increased,

Fig. 8 Transmission curve: door three in your hands! different colored fluorescent plexiglass plates,

F i g. 9 for the materials from FIG. 8 the fluorescence emission curves.

The method for brightness enhancement described here is particularly suitable for all LC effects those between a light blocking and a light permeable state through an electric field can be switched. This light valve effect can be seen in all LC effects used in displays known with the help of additional polarizers and possibly other passive optical elements reach. In the following, the mode of operation of the device described here is only shown in context described with a »nematic rotating cell«. This is the case when using other LC effects Interaction with the device described here is easy for the person skilled in the art.

The embodiment of FIG. 4 contains the electro-optical element of the nematic liquid crystal rotary cell, which is shown in Fig. 1 and there is denoted by 10. This electro-optical element is in German patents 21 ^ 8 563 and 22 02 555 described; therefore should here. only a brief summary will be given. The function that element is it. the plane of polarization of a light beam passing through the element decreases by 90 ° Rotate when there is no voltage on the element (»field-off« state), and the incident polarized Leave the beam unchanged in the "field-on" state. Fig. I shows a perspective view of the Components that make up the nematic rotating element. This element consists of a nematic LC layer with positive dielectric anisotropy 5, which lies between two parallel glass plates 3 and 7 is included, on which an electrically conductive but optically transparent material, such as. B. SnO2. aef the inner surfaces (electrodes 4 and 6) is applied. These inner surfaces, the one typically have a distance between 5 μ and 50 μ, serve as electrodes and are connected to a voltage source 9 connected via a switch 8. Depending on the application, the electrodes can also be in different Way segmentier. be and precautions can be taken to reduce the voltage to different To switch segment combinations. In this case

the optical rotary cell shown in FIG. I is sketched . show only part of the LC display, namely a specific pair of electrode segments. The surface of the transparent electrode 4 is specially treated, e.g. B. by rubbing with a fine polishing agent in one and the same horizontal direction in order to uniformly orient the preferred direction of the nematic LC layer immediately adjacent to the electrode in this direction. The surface of the other transparent electrode 6 has been treated accordingly, but the F. electrode has been rotated by 90 ° so that the preferred direction is the one immediately adjacent! FK layer is vertical. When no voltage is applied to the electrodes, the local preferred orientation of the nematic liquid crystal to rotate smoothly through an angle of 90 ", when passing from one electrode to another. If the polarization plane of the light coming from a light source 1 and Hiirrh pinpn zwisrhpr. I irhtiiiipllp uni \ FK-Drrh / pllp IO located first polarizer 2 passing light is parallel (as shown in Fig. I) or perpendicular to the adjoining LC layer, then the plane of polarization of the light passing through the layer will be congruent with the twisted nematic structure turn, and exit again on the other side of the element rotated by 90 ° and are then absorbed in a second polarizer 11 arranged behind the element 10 and oriented parallel to the first polarizer the preferred orientation of the nematic liquid crystal will be reoriented and essentially in d he direction of the applied electric field. In this state, the light beam will pass through the element 10 without experiencing any change, and consequently the light horizontally polarized in the polarizer 2 can now pass through the second polarizer i 1.

The new type of component in connection with LC displays, which is referred to below as a fluorescent plate will now be described.

To do this, we consider a flat Plexiglas plate with a smooth surface, a few millimeters thick, in which a fluorescent substance is dissolved in such a concentration that, for example, from the incident daylight blue portion is fully absorbed. Furthermore, this plate should have end faces running perpendicular to the plane of the plate have, which should be ideally light-reflecting, so that no light emerges at the edges of the plate can. According to Fig. 2. in which the relative reflected intensity for unpolarized light as a function of Angle of incidence is indicated. with isotropic daylight distribution, approx. 82% of the intensity enters the Fluorescent plate. For the re-emergence of the fluorescent light emitted, for example, in green, from the plate, the reflection is now thinner Medium decisive, which in F i g. 3 is shown as a function of the angle of incidence. You can see that in with a good approximation can calculate as if all light falling at an angle <«,", ■ (angle of total reflection) hits the boundary surface, leaves the plate and the light of the remaining angular range as a result of total reflection remains in the plate The angle of total reflection results from the relationship

π - sin α, ο, - 1

(for the refractive index η = 1.49 for Plexiglas is οί, οτ = 420). The proportion of the fluorescent light that is not totally reflected, here referred to for abbreviation as the loss factor V, is

K = I-cos \ "" =

-! η ² - I η

(In the example, the loss factor is V = 25% at η = 1.49). All light emitted within the angular range of total reflection (in the example therefore 75% |

in is ir guided by the plane of the Piatten (i.e. the mean slump direction is parallel to the plane of the plate).

That in the Fhioreszcn / .plattc as a result of total reflexion captured fluorescent light can now pass through the

r> deflection of reflective or lichtstrciiender surfaces which are angcbrachi on the fluorescent plate, the exit from this disk ¹ are veranlaß. Such specially attached surfaces will be tm foltrpnHpn yur

: ik Ai; <; tritKfpn <; tpi

designated. Simple types of such Lichtauskopplun ^ from a fluorescent plate are shown in Fig. 5 in the cross section shown.

Neglecting the mentioned reflection and inevitable re-exit losses and under the assumption that otherwise there are no losses in the plate, the "brightness gain factor" d. H. the factor that increases the luminance (= brightness) of the exit window of the fluores zenzplatte indicates against the luminance of a non-fluorescent surface of the same color, irr essentially given by the ratio of the light-absorbing surface of the arrangement to the total area of the exit window of the fluorescent light.

The inventive combination of LC-Anzei ge and fluorescent plate is now based on de; Embodiment of Fig.4 explained. The order initially contains the electro-optical element of the nematic rotary cell 10. This element is mil provided individual electrically controllable electrode segments 12. The electrode segments in the example allow digits to be displayed using the 7-segment method. In the area of the digits are on the front and a polarizer 11 each on the back of the FK cell or 2 attached. The polarizers have mutually parallel planes of polarization. Behind the FK cell there is a fluorescent plate 13 with the mirrored end faces 14, 15, 16, 17 and the Exit windows 18. The exit windows simulate the electrode segments 12, their bar width isi but larger than the electrode segment width by the Parallax between LC segments and Aust '.ttsfenstern to compensate. Everything details, such as the viewing angle range of the display of the ratio depends on the width of the exit window and the width of the display segment, is illustrated by a typical example in FIG. 6 mil Explanations shown Behind the fluorescent plate 13 is a light-absorbing film 19, which is not in optical contact with the fluorescent plate. This film serves to protect the fluorescent plate, which naturally shows a characteristic inherent color in transmitted light, to make it appear as "black" as possible and thereby to influence the contrast of the display favorably. The excitation light comes from the front fluorescence in all directions through the FK cell plate, and only where there are no polarizers forwards in the direction of the FK cell through the exit window 18. Only such electrode elements 12

to which a voltage is applied become translucent; the others block the fluorescent light. Displayed In this case, digits appear light on a black background. Previously it was assumed that the polarizers 2 and Il are neutral polarizers, which means that they are light polarize all wavelengths in the visible range. You get an advantage if you have two instead Selective polarizers are used which pass through both directions of polarization in the area of the excitation light and only polarize the rest of the spectrum. In this case, the entire display area can be used as a Wcruen light collector surface, c!; ·. the stimulation light the polarizers passed unattenuated.

Another special embodiment for the advantageous design of the fluorescent plate is given in FIG. This embodiment is intended to demonstrate that part of the surface of a housing in which an LC display is installed is also easily used as an additional light collector surface and Siün Su uic ϊ icmg'KCii eiilei "Ail / .cigc WLii '"!

can increase. Here, an additional collector plate 20 made of fluorescent plastic is connected to the fluorescent plate 13 with access windows 18 via a mirrored 45 ⁿ face 21 for light coupling.

A further modification of the display device according to the invention also allows between two to switch different colors electrically. For this purpose, the fluorescent plate contains a two-colored mixture of fluorescent substances. For example, it emits red and green fluorescent light. Then you need only the polarizer 2 in FIG. 4 to replace '.jrch a combination of a horizontally polarizing selective polarizer, which only leaves green light unpolarized, with a vertically polarizing one another selective polarizer that only allows red light to be unpolarized. Then there is a fluorescent light after passing through this polarizer combination of horizontally polarized red light and vertically polarized green light. As a result, the overall arrangement leaves segments where none If there is voltage, only the green fluorescent light will pass, while only that will pass on the segments with voltage red light can happen.

In Figs. 8 and 9, respectively, are the light transmission curves or the fluorescence emission curves of three 4, different colored fluorescent plates, as shown in Are commercially available. The invention was tested on these plates.

In the following, the factors on which the brightness gain depends crucially are listed and briefly commented on. The functions of the fluorescent plate in cooperation with the LC display are divided into

A) Light collection

B) light transmission

C) light extraction

ZuA 1. Loss factor V.

i / i

K = I- cos ν ,,, =

η -

2. Fluorescence quantum yield F.

Number of light quanta absorbed
Number of light quanta emitted

F =

(should be as close as possible to 1)

3. Ratio of absorption bandwidth to emission bandwidth. This factor should be as large as possible; it becomes so when several fluorescent substances are mixed with one another whose absorption bands are different, but which have approximately the same emission band.

4. Fluorocarbon concentration.

Absorbed intensity / = / “· 10 ''<'.
Therein mean:

/ "= Output intensity;

f = F. extinction coefficient; typical value:

5 IO ⁴

liter
Mole cm

60

65

(A = proportion of the fluorescent light not totally reflected).

C = molar concentration of the fluorescent substance, the upper sensible limit for C is the concentration at which the fluorescence begins to self-extinguish; she lies z. B. at

ίο- ', ^Md

liter

<: / = Layer thickness.

Full absorption of the main absorption band can easily be achieved with a layer thickness of 1 mm.

5. Chemical (photochemical) stability of the fluorescent substance.

6. Reflectivity of the mirror layers.
To illustrate:

A vapor-deposited aluminum layer has an intensity reflectivity R = 0.913. After 20 reflections, the intensity has dropped to 15% of the initial value.
A vapor-deposited silver layer has an intensity reflectivity R = 0.985. After 20 reflections, the intensity has dropped to 73.5%. (R should be as close as possible to 1).

7. Absorption (and scattering) of the plastic matrix.

The absorption should be as small as possible. For a 4 mm thick clear Plexiglas plate which really absorbs 1% of the light when the light falls perpendicularly, the light would have dropped to 1 / e of the initial intensity after a distance of 40 cm.

8. Light scattering due to surface roughness or surface contamination.

Since the fluorescent light is much more frequent at the for Plate plane parallel boundary surfaces than is reflected on the mirrored end faces, comes it is particularly important that these reflections are lossless, i. H. in this case free of scatter get lost. The plates produced by injection molding generally meet this requirement Well

ZuC 9. Brightness gain factor H.

H =

Light collecting surface Light exit window area

10. Angular distribution of the emerging fluorescent light.

The angular distribution of the emerging fluorescent light depends very much on the type of coupling. which in turn affects the brightness of the display. This is briefly based on the examples given in FIG. 5 explained. In Examples I and 4, the front plane surface determines the size of the solid angle region into which fluorescent light is refracted at all, namely 2 π. In example 2, on the other hand, the solid angle range of the emerging light is already limited. These simple examples can be used to clarify the considerably different angular distributions.
Shaping of the reflective edges and the exit window.

The edges and windows should be designed so that the transit time of the light is short. It is easy understandable that in the event that there are no losses in the light propagation, the type of Light extraction and its effectiveness on the luminance of the exit window have no effect would have. As one approaches this ideal case, the demands on the Light extraction effectiveness lower.

The most favorable shape of the reflective edge surface of the fluorescent plate must be found empirically in each individual case. The rectangular shape is certainly not always the cheapest. Furthermore, it is easy to see that light extraction efficiency and uniform illumination of the exit window cannot be maximized at the same time. An adapted compromise must therefore be sought in each case.

Finally , once again, are the many advantages. which have the proposed fluorescent / .plate use compared to the known types of illumination and which above all expand the area of application of LC-An / .eigen, compiled in a concise form:

1. One can without an additional light source aiißcrg ^ · comfortably high, previously unattained brightness achieve high contrast.

2. The legibility of the display is independent of the ambient brightness within limits not previously achieved.

J. The displays are free of parallax and shadows.

4. The method also makes it possible to switch between 2 colors without further ado.

5. The device is simple, cheap, flexible because the fluorescent plastic plate is lightweight because of its light weight Moldability produced cheaply by injection molding in arbitrarily complex shapes can be, so that special display lighting requirements can easily be taken into account can.

For this purpose, S Bliill / ciclinuimen

Claims (1)

Patent claims: 1. Radiation collector and compressor in the form of at least partially at their end faces mirrored plastic plate in which fluorescent substances are dissolved and which have at least one Light exit window is provided (»fluorescent plate«), characterized by its use for passive brightness & amplification of single or multicolor display devices. 2. Radiation collector according to claim 1, characterized in that the light exit window (18) Contains notches in the fluorescent plate (13) with a metallic-reflective coating are provided (Fig. 4). 3. Radiation collector according to claim 1, characterized in that the light exit window (18) contain light-scattering color pigment layers on the fluorescent plate (13). 4. Stnalilungskollektor according to one of the claims ! to 3, characterized in that in the Fluorescent plate (13) a mixture of different fluorescent substances is dissolved, the different absorption bands, but approximately the same Have emission bands. 5. Radiation collector according to one of claims 1 to 4, with a housing, characterized in that that part of the housing surface is designed as an additional light collector surface 6. Radiation collector according to claim 5, characterized in that as the light collector surface serving part of the housing surface to a further collector plate (20) made of a fluorescent Plastic belongs to the fluorescent plate (13) via a mirrored 45 * end face (21) Light coupling is connected (Fig. 7). 7. Radiation collector according to one of claims 1 to 6, characterized in that the fluorescent plate is made by an injection molding process. 8. Display device with a fluorescent plate according to one of claims I to 7, characterized characterized in that, seen from a viewing direction opposite to the direction of light exit, in front of the fluorescent plate (13) a liquid crystal display device with at least one Display element is located, preferably the light exit window (18) of the fluorescent plate (13) are assigned to the display elements (FIG. 4). 9. Display device according to claim 8, characterized in that the liquid crystal display device between a light blocking and a translucent state is switchable. 10. Display device according to claim 8 or 9, characterized in that the display elements are additionally between two linear polarizers (2,11) (Fig. 1,4). 11. Display device according to claim 9 or 10, characterized in that the liquid crystal display device is based on the nematic principle Rotary cell works. 12. Display device according to claim 10 or 11, characterized in that the linear polarizers (2,11) form a regular shaped cohesive surface which just covers the display elements, but leaves the remaining surface of the liquid crystal display device free. 13. Display device according to one of claims 10 to 12, characterized in that the Polarization directions of the linear polarizers (2, U) are oriented parallel to one another. 14. Display device according to one of claims 10 to 12, characterized in that the Light exit window (18) on the fluorescent plate (13) the size and shape of the polarizer surface the liquid crystal display device and ίο that the polarization directions of the Liirearpolarisatoren (2, U) are perpendicular to each other. 15. Display device according to one of claims 10 to 13, characterized in that the Linear polarizers (2, 11) selective polarizers ! 5 which are only the fluorescence excitation light leave unpolarized. 16. Display device according to one of claims 10 to 12, characterized in that in the Fluorescence plate (13) a fluorescence substance mixture is solved, which fluoresces in two different colors, and that one of the two linear polarizers (2, 1!) by a combination of two Selective Poiarisatoren is replaced, the polarization directions are perpendicular to each other and polarize the two fluorescent colors perpendicular to each other. 17. Display device according to one of claims 8 to 16, characterized in that, seen from a direction opposite to Direction of light exit, behind the fluorescent plate (13) a light-absorbing film (19) is located, which is not in optical with the fluorescent plate (13) Contact is made and the fluorescent plate appears as black as possible (FIG. 4).