JPH03254007A - Lighting device with cover having non-absorbency and variable transmittivity - Google Patents

Abstract

PURPOSE: To unify luminance of all the points on a cover by providing a reflector with a longitudinal light regular reflection characteristic and a cover in which a non-absorbing characteristic is provided and transmittance in an optical point on its surface represents a function of the point. CONSTITUTION: A reflector 34 is provided with a reflection part partially transmitting light and a plurality of dielectric interfaces, and a light source 32 includes the reflector 34 showing a longitudinal light regular reflection characteristic. At the same time, light is emitted to the outside through a cover 38 showing a light-non-absorbing characteristic. Transmittance in an optional point on the cover 38 is varied as a function of the position of the point, and light discharged from the cover 38 in this point shows a set light divergence degree. In this way, luminance in all the points on the cover 38 can be unified.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an illumination device having a cover that is substantially non-absorbent to light and has variable transmittance. According to the present invention, the emission of light transmitted through the cover and emitted to the outside can be controlled as a function of the position on the cover.

(Prior Art) Generally, it is often desired that the degree of divergence of light emitted to the outside from a lighting device be uniform. That is, the brightness of the light emitted externally from a lighting device is preferably essentially constant at all emission points on the device. For example, considering back-lit signboards, a type of sign commonly used for advertising, light emitted from one or more light sources placed behind a semi-transparent board with text on it illuminates the translucent board. pass through and go outside. At this time, the brightness of the light emitted at all points on the outside surface of the sign so that the person viewing the sign can perceive a comfortable and evenly illuminated image without feeling any difference in brightness or darkness depending on the position on the sign. Ideally, they are essentially the same.

In order to smoothly manufacture a lighting device, reduce maintenance costs, make the device smaller, and improve device reliability, it is desirable to minimize the number of light sources used in the above-mentioned lighting device. A single expensive light source is more reliable than multiple inexpensive light sources in the film, and is also cheaper overall).

When using a single light source or a small number of concentrated light sources, appropriate light distribution is required to equalize the degree of light emission from the device. A reflector is usually placed inside the device, so that the light emitted from the light source is reflected multiple times within the device before exiting through a light emitting port such as the translucent advertising signboard surface mentioned above. It is composed of

This ensures that the amount of light emitted from various points on the device is substantially the same, resulting in uniform illumination.

In certain devices belonging to the prior art, such as the well-known lampshade and backlight plate, a diffuse reflector is used, i.e. a reflector that reflects light in any direction (in other words (The intensity of the reflected light is proportional to the modulus of the angle the reflected light makes with respect to the normal direction of the surface from which the light is emitted.)

With this configuration, there are significant limitations on the distance over which light can be distributed. For example, in order to distribute light within a circle whose average diameter is "n", the device must be n! It has been found that it is necessary to reflect the light. It is inevitable that a portion of the incident light will be absorbed each time the light is reflected from the reflector, causing the efficiency of the device to decrease extremely rapidly as the distribution distance increases.

To solve this problem, another type of device uses specularly reflective material in the longitudinal direction. In this type of specularly reflective material, the traveling direction of the reflected light line is made to be the same as the directionality of the material. In this case, it reflects light according to its unique properties. This direction typically coincides with the longitudinal axis of the device. Since the traveling direction of each reflected light ray along the longitudinal axis of the device does not change arbitrarily and remains constant, the light distribution distance of a particular light ray increases in proportion to the number of times the light ray is reflected. Therefore, light can be distributed over a long distance while maintaining appropriate efficiency.

(Problems to be Solved by the Invention) However, materials that can reflect light over a wide range of angles of incidence and have specular reflection properties in the longitudinal direction, such as those used in the above configuration, are extremely expensive. There's a problem. On the other hand, there are inexpensive longitudinally specular reflective materials that reflect light only within a narrow range of incident angles; however, when using these types of inexpensive materials, it is difficult to There are significant restrictions on the shape of the device, and the types of light sources that can be used in the device are also limited.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an inexpensive illumination device that can reflect light over a wide range of changes in the angle of incidence and has specular reflection in the elongated direction.

(Means for Solving the Problems) According to the present invention, the above object is achieved by providing a light source, a light reflector having specular reflection in the longitudinal direction, and a cover substantially non-absorbing to light. The illumination device has a light emitting portion with a light emitting portion and is configured such that the transmittance of the cover at any point on its surface varies as a function of the position of that point.

(Operation) According to the above-described configuration, the light that passes through the cover at that specific point has a degree of light divergence that is set as a function of that point. Further, by changing the transmittance of the cover, the brightness of light transmitted through the cover can be more uniform than the brightness at all points on the cover when there is no change in the transmittance of the cover. and the transmittance of the cover varies such that the intensity of light transmitted through the cover and emitted is substantially equal at all points on the cover.

A reflector, on the other hand, will have many characteristics. For example, the reflector may be spatially coextensive with the cover, which allows the cover and reflector to be manufactured as one piece, simplifying manufacturing. In order to balance the two factors of cost and efficiency, the reflector may also be configured to be partially transparent to light. The shape and orientation of the reflector may be configured such that the majority of the light emitted from the light source travels away from the light source substantially parallel to the cover surface closest to the light source;
This effectively extends the light distribution distance. In addition, the reflector needs to undergo total internal reflection in order to minimize light absorption within the reflector and improve the efficiency of the device, and a prismatic dielectric material with good reflectance is used.

In addition, the reflector can also be stacked with one or more dielectric interfaces to improve its efficiency.

(Example) Prior to detailed description of the present invention, first, materials having diffusivity and specular reflection property of illumination light will be described.

A bulk material in which the material thickness of the light reflector is "t", and a part "a" of the light transmitted through it is absorbed per unit length, and a part "r" of the transmitted light is reflected. Consider a general light reflector with characteristics. The part of the light that enters the reflector and is reflected backwards is called "R", and the part of the light that enters the reflector and passes through it is called "T", and the part of the light that enters the reflector and is reflected back is called "T". Let the part of the absorbed light be "A". The sum of these amounts to 100% of the light incident on the reflector (i.e. R
+A0T=1). Generally R, A, and T are r,
It can be said that it is a relatively complex function of a and t. At this time, if a/r(], a t(b, r t)l, these functions can be simplified as shown in the following equation.

R=rr t/(1+ r l)) (2a t/3
) -II) A=a l
...(2) T = (1/(1+r
t )) −(a t /3) −(3) above,
While the two prior art illumination devices described above used either a diffuse or specular reflector, the present invention utilizes a mixed diffuse and specular reflector.

Here, referring to FIG. 1, light #22 is emitted from an inner layer of a material having a thickness of t that has specular reflection properties in the longitudinal direction and an outer surface layer of a material thickness of t6 that has diffusivity and specular reflection properties. and a mixed type reflector 2 in which both have the same a and r values.
A lighting bag ft20 containing 4 is shown.

Mixed here (i.e., has both diffusive and specular reflective properties)
To begin with the characteristics that characterize the configuration of a type reflector, both diffusive and specular, this type of mixed reflector has a configuration in which the degree of light divergence can be varied as a function of position on the device. A lighting device configuration may be taken.

The average light distribution distance "X" (i.e., the average distance the light travels through the device 20 before exiting the device 20) is - The average number of reflections off an inner layer of specularly reflective material is multiplied by the square root of the average number of reflections off an outer layer of diffusive material for a particular ray to exit the device 1120. It is proportional to the product.

This can be written algebraically as the following equation.

X=(1-ML,)(1+rL)"' - (4) Formula (
1), (2), and (3) are applicable to combinations of diffusive and longitudinally specularly reflective materials.

Total absorption “A” and total transmittance “T” of mixed reflector 24
” becomes like the Roji equation.

A = a (t, + t,)
−(5) T = 1/ (II r (t, tent,))
-(6) Now, since all the light emitted from the light source 22 is ultimately either absorbed or transmitted, these ratios are simply A/T, and therefore the total Efficiency "E" is expressed by the following formula.

E ” 1- a r (t-+ LJ”
(7) Next, in order to evaluate the relative merits of various lighting devices, consider the specific costs of materials with specular reflection in the longitudinal direction and materials with diffuse reflection. Optimizing the design involves many points to overcome, but it is a reasonable method to model these to reduce costs to a certain level and then design materials while maintaining this cost.

In this case, it is assumed that a material with specular reflection in the longitudinal direction is M times more expensive in use than a corresponding material with diffuse reflection. At this time, the cost "C" of the lighting device having a mixed type reflector is determined by the following equation.

C”=Mts+ta・
...(8) Now suppose a=0.1, r=100, and C
Consider the case where = 100. (here a/r
and M correspond substantially to the values of commonly available reflective materials such as paper or thin plastic chutes).

For a required value of the average light distribution distance of X, there exists a value of t that gives the required value of X when td=0.

In the opposite extreme case, there exists a value of 1.1 that gives the required X value when t,=D. Further, in an intermediate case where t and 16 are combined so as to satisfy the equation (4), the efficiency of the device can be calculated by the equation (7), and the cost can be calculated by the equation (8).

In FIG. 3, the efficiency and price values for various values of the average light distribution distance X are plotted. As is clear from the figure, a small value of the average light distribution distance X can be produced very cheaply using a pure diffusely reflecting material, and the lamp shade is also manufactured accordingly. On the other hand, the average light distribution distance X is 10
Beyond that, initial effects can be achieved effectively only by the use of specularly reflective materials, in this case producing prismatic light guides.

On the other hand, for intermediate values such as It is possible to achieve high efficiency at low cost.

Further considering the case of X=7 in detail, Fig. 4 shows the change from the case where the reflector is completely diffusive (i.e., L, = 0) to the case where the reflector is completely specular (i.e., t, = 0). The figure shows a plot of the efficiency versus cost ratio of the device as it changes to the point where it lasts. As is clear from the figure, the best efficiency-to-cost ratio is obtained when 20% of the diffusely reflective material is used to cause diffuse reflection in a pure specular reflector.

In view of the above-mentioned aspects, in the present invention, the large decrease in absorption rate is alleviated by adding a certain kind of material having specular reflection in the horizontal direction. The material having specular reflection in the longitudinal direction can be composed of a multilayer dielectric interface or a transparent material having a complex shape but a constant cross-sectional shape.

As the latter material, for example, a prismatic light guide material that has a significantly high reflectance at a certain angle of incidence can be used.

As shown in FIG. 2, the lighting device 3o according to the present invention includes a light source 3
2, and a light reflector 34 that is at least partially specularly reflective in the elongated direction. A light emitting portion, i.e., a substantially non-absorptive cover 38 (the portion shown cross-hatched on panel 36 in FIG.
The transparent plate 36 has a transparent plate 36 (partially cut away to clearly show the relationship between the reflector 34 and the reflector 34). Device 3
At 0, all surfaces other than the transparent plate 36 are connected to the device 3o.
It is preferably coated with a reflective material to trap the light therein until it is finally emitted from the cover 38. The transmissivity of the cover 38 (i.e., the portion of the incident light emitted through the cover 38) at any point on the surface of the cover 38 is varied as a function of the position of said point, thereby The light transmitted through and emitted by 38 has a light emittance set as a function of the position of said point. The change in the transmittance of the cover 38 means that the brightness of the light transmitted through the cover 38 and emitted is more uniform at all points on the cover 38 than if the transmittance of the cover 38 did not change. is preferred, but not necessarily required.

Furthermore, the reflector 34 may have several types of characteristics. For example, the reflector 34 may have virtually the same spatial area as the cover 38, which provides considerable simplification in manufacturing the reflector 34 and cover 38 together. . Further, in order to balance the two factors of efficiency and cost, the reflector 34 may also be partially transparent to light. In addition, the shape of the reflector 34,
The orientation is such that the majority of the light emitted from the light source 32 travels away from the light source 32 in a direction substantially parallel to the cover 38 surface closest to the light source 32 . This increases the distance over which light is distributed by the device 30, and requires total internal reflection within the device 30 to minimize light absorption within the reflector 34 and improve the efficiency of the device 30. , a prismatic dielectric having at least suitable reflectivity may be employed. Reflector 34 may also include one or more dielectric interfaces to improve its efficiency.

For a particular shape of illumination device, it is necessary to experimentally determine the change in transmittance necessary to obtain the required light emittance at various points on the device cover. Once this is determined, the device can be easily mass-produced. Also, the change in transmittance found here means that the brightness of the light transmitted through the cover and emitted is compared to when there is no change in transmittance.
The cover has a high degree of uniformity at all points.

Obtaining a transmittance variation such that the brightness of the light emitted through the cover of the lighting device is substantially the same at all points on the cover for a variety of practical uses (i.e. advertising signs) It is preferable to take the configuration.

A wide variety of configurations may be employed to vary the transmittance of the cover. For example, the thickness of the cover may vary depending on the position on its surface. Also, if the thickness of the cover is kept constant and no other configuration is adopted due to the transmittance change, a bright spot on the cover near the light source will be visible, and as the distance from the light source increases, that spot on the cover will become brighter. The brightness of is decreasing. On the other hand, the thickness of the cover is the thickest near the light source;
If the cover becomes thinner and thinner with increasing distance from the light source, the transmittance of the cover changes such that different types of light distributions exist on the cover. In particular, when determining the thickness change necessary to obtain uniform brightness at all points on the cover, the thickness of the cover could be experimentally varied in advance.

In addition, a material that is substantially non-absorbing and reflective of light may be coated or otherwise applied to the cover.

Adhesive materials include TYVEK, titanium-doped acrylic plastic, molded polymeric foam, metallic or non-metallic thin films, STYROFOAM, spongy polyethylene,
Examples include white paint. Preferably, these materials are applied such that the density of the applied material on the cover varies as a function of position on the cover to provide the desired transmission variation.

Still another method is to coat the cover with one to n layers of material that reflects light without substantially absorbing it.
It is also possible to change the transmittance of the cover by coating it in layers. Here the value of n is varied as a function of the position on the cover.

(Effects of the Invention) According to the present invention configured as described above, effective reflection is achieved over a wide range of changes in the angle of incidence, and effective reflection is achieved by functioning diffuse reflectivity and specular reflectivity. This method achieves remarkable effects such as providing good illumination and reducing costs.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of one embodiment of a lighting device according to the present invention, FIG. 2 is a perspective view of another embodiment of the present invention, and FIGS.
Each figure is a functional explanatory diagram of the lighting device according to the present invention. 20.30...Lighting device, 22.32...Light source, 2
4.36...Reflector, 38...Cover

Claims (19)

[Claims] (1) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. A lighting device characterized in that the reflector includes (i) a reflecting portion that partially transmits light, and (ii) one or more dielectric interfaces. (2) The change in transmittance is configured such that the brightness of light emitted through the cover is more uniform than the brightness when the transmittance does not change at all points on the cover. The lighting device according to item 1. (3) The lighting device according to claim 1, wherein the change in transmittance is configured such that the brightness of light emitted through the cover is substantially equal at all points on the cover. (4) The lighting device according to claim 1, wherein the reflector has substantially the same spatial extent as the cover. (5) The reflector is such that the majority of the light emitted by the light source is (a) substantially parallel to the surface of the cover closest to the light source, and (b) directed away from the light source. Claim 1 consisting of
The lighting device described in Section 1. (6) The reflector is arranged in such a way that the majority of the light emitted by the light source is (a) substantially parallel to the surface of the cover closest to the light source, and (b) directed away from the light source. 2. The illumination device according to claim 1, wherein the illumination device is configured to be oriented so as to direct the illumination device toward the direction of the illumination device. (7) The lighting device according to claim 1, comprising a hollow surrounding body. (8) The lighting device according to claim 7, wherein the light source is housed inside the surrounding body. (9) The lighting device according to claim 8, wherein the reflector is housed inside the surrounding body. (10) The lighting device according to claim 9, wherein the reflector is made of a prism-shaped dielectric material that does not substantially absorb light. (11) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device, the reflector includes a partially light-transmissive light-reflecting portion, and for most of the light emitted from the light source, (c) the surface of the cover closest to the light source is (d) an illumination device configured to be substantially parallel and oriented away from the light source; (12) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device, the reflector includes a partially light-transmissive light-reflecting portion, and for most of the light emitted from the light source, (c) the surface of the cover closest to the light source is (d) substantially parallel; and (d) configured to orient the reflector relative to the light source in a direction away from the light source. (13) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. A lighting device comprising: a reflector including a partially light-transmitting light reflecting portion and having a hollow surrounding body. (14) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device formed by (c) substantially parallel to the surface of the cover closest to the light source; and (d) configured to be oriented away from the light source. (15) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device formed by the reflector is configured to orient the reflector relative to the light source such that the portion thereof is (c) substantially parallel to the surface of the cover closest to the light source; and (d) directed away from the light source. A lighting device. (16) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device, the reflector is made of a prism-shaped dielectric material having a certain value of reflectance that causes total internal reflection at least inside the reflector, and the lighting device includes a hollow surrounding body. . (17) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device, the reflector is (c) a prismatic dielectric having a reflectance of a certain value that causes total internal reflection at least inside the reflector, and (d) spatially relative to the cover. (e) substantially parallel to the surface of the cover closest to the light source; and (f) substantially coextensive with the light source. A lighting device configured to point in a direction away from. (18) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device, the reflector is (c) a prismatic dielectric having a reflectance of a certain value that causes total internal reflection at least inside the reflector, and (d) spatially relative to the cover. (e) substantially parallel to the surface of the cover closest to the light source; and (f) substantially coextensive with the light source. An illumination device configured to orient a reflector with respect to a light source so as to point the reflector in a direction away from the light source. (19) (a) a light source having a reflector that specularly reflects light in the longitudinal direction; and (b) a light source having a substantially non-absorbing cover that is separate from the reflector. an emitting section, the transmittance at any point on the cover varies as a function of the position of said point, and the light emitted from the cover at said point has a light emittance set as a function of the position. In the lighting device, the reflector is (c) a prismatic dielectric having a reflectance of a certain value that causes total internal reflection at least inside the reflector, and (d) spatially relative to the cover. An illumination device comprising: a hollow enclosure substantially coextensive with the surrounding body.