JPH04359858A - Surface light source device - Google Patents

Abstract

PURPOSE:To enhance the light utilization efficiency and increase the brightness by locating the opening in a fluorescent tube and the light incident surface of a light guide part so that they face each other, and forming an interferential film consisting of different types of optical films with differing refractive index on the inner surface or outer surface of the fluorescent tube opening. CONSTITUTION:An interferential film 103 is formed on the inner surface of a glass body 104 at the opening in a fluorescent tube 101. This film 103 shall consist of a laminate of a blue, green, and red interferential film element 10-12. The outgoing beam of light 102 emitted through the interferential film 103 is cast onto a light guide part 2, and the outgoing beam of light 3 therefrom is cast onto a transmission type display panel.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates primarily to transmissive display devices, and particularly to a surface light source device suitable for increasing brightness.

0002

2. Description of the Related Art FIG. 16 shows the structure of a conventional surface light source device disclosed in Japanese Unexamined Patent Publication No. 185781/1981. FIG. 16 shows the transmissive display panel 1, the light guide section 2, the light beam 3 irradiated to the back surface of the transmissive display panel 1, and the transmissive display panel 1.
viewing direction 4, aperture type fluorescent tube 20 as a light emitter
1. A light ray 202 entering the incident surface of the light guide section 2 from the fluorescent tube 201 is shown. In this conventional example, the opening of an aperture-type fluorescent tube 201 serving as a light emitter is arranged so that the light incident surface of the light guide section 2 faces each other, and the light emitted from the fluorescent tube 201 is condensed onto the light incident surface. This is a surface light source device in which the incident light is reflected and diffused inside the light guide section to obtain uniform surface light on the irradiation surface.

FIG. 17 shows a cross-sectional view of the aperture type fluorescent tube 201 and the intensity distribution of light emitted from the aperture. FIG. 17 shows the reflective film 203, the glass body 204 of the aperture type fluorescent tube 201, the fluorescent film 205, the excitation ultraviolet light 206 inside the fluorescent tube, the aperture angle θ0, and the light incident surface 2 of the light guide section 2.
09 shows a light ray 202 that enters the light entrance surface 209, light rays 207 and 208 that do not enter the light entrance surface 209, and a broken line 210 that shows the intensity distribution of light emitted from the opening. While normal fluorescent tubes emit light from all around, aperture type fluorescent tubes emit light only from the opening with an aperture angle of θ0, concentrating the light in a certain position direction and emitting it. It's a fluorescent tube. The aperture type fluorescent tube 201 has a reflective film 2 on the inner surface of the glass body 204 in a portion other than the opening inside the fluorescent tube 201.
03, a fluorescent film 205 is applied. Therefore,
The luminous flux emitted when the excitation ultraviolet light 206 inside the fluorescent tube 201 collides with the fluorescent film 205 is not emitted outside the fluorescent tube by the reflective film 203, but is reflected inside the fluorescent tube.
After being reflected several times, the light is concentrated at the opening where neither the reflective film nor the fluorescent film is coated, and is emitted to the outside of the fluorescent tube.

However, the light emitted from the aperture actually spreads out like an intensity distribution 210. Therefore, much light, such as light rays 207 and 208, does not enter the light incident surface 209, and the efficiency of using light emitted from the light emitter is low.

[0005]

[Problems to be Solved by the Invention] The above-mentioned prior art does not take into account the intensity distribution of light emitted from the opening of the aperture-type fluorescent tube as a light emitter, and the efficiency of light utilization is low.
It was difficult to achieve high brightness.

[0006] An object of the present invention is to improve the efficiency of using light from a light emitter and to achieve high brightness.

[0007]

[Means for Solving the Problems] The above object is to arrange the opening of an aperture type fluorescent tube to face the light incident surface of the light guiding section, and to set the refractive index of each other on the inner or outer surface of the opening of the fluorescent tube. This is achieved by forming an interference film with a multilayer structure in which two or more types of optical thin films with different values are alternately laminated.

[0008]

[Operation] The spectral transmittance of the interference film used in the present invention is the incident angle of the light ray (the angle of the light ray with respect to the normal direction of the surface of the interference film).
There are characteristics that depend on . For example, the transmittance of light rays incident at right angles to the interference film is high, and is transmitted through the interference film with almost no reflection. However, the transmittance of light incident at a large angle with respect to the normal direction of the interference film decreases, and conversely, the reflectance increases. Therefore, at the aperture of the aperture-type fluorescent tube of the present invention in which the interference film is formed, light rays that have a large incident angle among the light from inside the fluorescent tube are reflected by the interference film and returned to the inside of the fluorescent tube. The light beam that has returned to the inside of the fluorescent tube is reflected several times by the reflective film inside the fluorescent tube, and the light beam is again incident on the interference film at the opening. The reflection of the light beam on the interference film is repeated until the angle of incidence on the interference film becomes small and the light beam passes through the interference film. As a result, the light rays emitted from the aperture formed with the interference film have a strongly directional light intensity distribution in the normal direction of the aperture surface, and the light enters the light guide placed facing the aperture. The light is efficiently incident on the surface. Therefore, the efficiency of using light from the light emitter is improved, and a high-brightness surface light source device can be realized.

[0009]

[Embodiment] An embodiment of the present invention will be explained below with reference to FIG. FIG. 1 is a sectional view of a first embodiment of the invention. Figure 1
These are a transmissive display panel, a light guide section 2 having a function of obtaining uniform surface light, a light beam 3 irradiated to the back surface of the panel 1, a viewing direction 4 of the panel 1, and an aperture type fluorescent tube 10 of the present invention.
1. A light ray 102 entering the incident surface of the light guide section 2 from the fluorescent tube 101 and an interference film 103 formed on the inner surface of the opening of the fluorescent tube 101 are shown. FIG. 2 shows a cross-sectional view of the aperture type fluorescent tube in the first embodiment. FIG. 2 shows the glass body 10
4. The reflective film 105 and fluorescent film 106 coated on the inner surface of the glass body 104 other than the opening, the excitation ultraviolet ray 107, and the aperture angle θ1 are shown.

In the first embodiment, the opening of an aperture type fluorescent tube is arranged so as to face the light incident surface of the light guiding section, and a plurality of tubes having different refractive indexes are arranged on the inner or outer surface of the opening of the fluorescent tube. A multilayer interference film is formed by alternately laminating multiple optical thin films, and the intensity distribution of the light emitted from the aperture is strongly directional in the normal direction of the aperture surface. The emitted light is made to efficiently enter the light incident surface of the light guide section.

FIG. 3 shows the spectral transmittance characteristic 5 of the interference film and the emission spectrum distribution 6 of the fluorescent tube. Figure 1,
The aperture type fluorescent tube 101 in FIG.
), green (540 nm), and red (610 nm). The spectral transmittance characteristic 5 of the interference film is SPF (Short
This is a measurement example of a Pass Filter type filter, which exhibits the characteristic of transmitting light with short wavelengths and reflecting light with long wavelengths. A typical structure of an interference film is a multilayer film structure in which optical thin films of materials with a low refractive index and materials with a high refractive index are alternately laminated.

FIG. 4(a) is a structural diagram of the SPF type interference film 7, and FIG. 4(b) shows the characteristic values of each layer of the interference film 7. A substance L with a low refractive index (for example, silicon dioxide Sio2; refractive index nL≒1.46) is placed on the glass substrate 8.
and a substance H with a high refractive index (for example, titanium dioxide Ti
A total of 11 layers of O2; nH≈2.4) were alternately laminated. Here, the outermost layer (i.e. layer No. 1, layer N
o. Optical film thickness of each layer except 11) n. The average value in the plane direction of d (n is the refractive index of the relevant layer, d is the film thickness of the relevant layer) is 0.25・p・λR (λR is the red emission peak wavelength, p is 1.1 -1.4).

The interference film shown in FIG. 4 has a wavelength of λR=611 nm.
, p=1.2, and its structure is (L/2・H・L/2)5=(L/2・H・L/2)(
L/2・H・L/2) (L/2・H・L/2) (L/2
・H・L/2) (L/2・H・L/2)=(L/2・H
・L・H・L・H・L・H・L・H・L/2).

FIG. 5 shows the incident angle dependence of the interference film 7 in FIG. 4, that is, the change in spectral transmittance with respect to the change in the incident angle θ of the light beam incident on the interference film 7. or,
FIG. 6 shows the relationship between the incident angle θ of the light beam and the transmittance T at the red peak wavelength (λR=610 nm) of the fluorescent tube 101 in FIGS. 1 and 2. In the range of 0 to 30 degrees, the transmittance T is high and θ is 4
When the temperature exceeds 0 degrees, the transmittance decreases, and conversely the reflectance (1-T
) shows the characteristic of increasing.

FIG. 7 is a model diagram showing the incidence and reflection of light on the surface of the interference film. As shown in FIGS. 1 and 2, when the interference film 7 is formed on the inner surface of the opening glass body 104 of the fluorescent tube 101, the incident angle θ to the interference film 7 is small (θ<30 degrees) as shown in FIG. The light beam 150 passes through the interference film 7 and emerges forward. However, the incident angle θ is large
(θ>40 degrees) The light ray 151 is reflected by the interference film 7 and returned to the inside of the fluorescent tube. After the light ray 151 is reflected several times within the fluorescent tube by the reflective film 105 shown in FIG.
The light enters the interference film 7 again. Ray 15 on the surface of interference film 7
The reflection of light 151 is repeated until the angle of incidence of the light ray 151 on the interference film 7 becomes small and the light ray 151 passes through the interference film 7.

FIG. 8(a) shows the intensity distribution 8 of the emitted light at a point on the opening surface of a conventional aperture-type fluorescent tube without an interference film as shown in FIGS. 16 and 17, and FIG. 8(b) shows the 1,
2 shows an intensity distribution 9 of emitted light for the aperture-type fluorescent tube of the present invention in which the interference film shown in FIG. 2 is formed. The light intensity distribution 8 in FIG. 8(a) is a Lambertian distribution (cosine distribution), but the light intensity distribution 9 in FIG. 8(b) is a directional distribution in which the intensity increases in the portion where the angle α is small. , observation angle α
The light intensity increases in a region where is small.

FIG. 9 shows a sectional view of the light source portion of the surface light source device of the present invention and an intensity distribution diagram of the light emitted from the entire surface of the opening. FIG. 9 shows the intensity distribution 16 of the emitted light when the interference film 103 is formed on the inner surface of the opening of the aperture type fluorescent tube 101, and the intensity distribution 21 of the conventional fluorescent tube shown in FIGS. 16 and 17.
Indicates 0. By forming the interference film 103, the light intensity distribution 16 has strong directivity in the normal direction of the aperture surface, and the emitted light 102 is efficiently incident on the light incidence surface 108 of the light guide section 2, causing light emission. The utilization rate of body light is improved, and a high-brightness surface light source device can be realized.

However, the interference film 103 in FIGS. 1 and 2 formed on the inner surface of the opening of the fluorescent tube has a spectral transmittance that reflects infrared light as shown in FIG. 3 and transmits light in other wavelength ranges. If only a film with special characteristics were used, only the red component of the light emitted from the fluorescent tube would be affected by the interference film, and the red component would increase, making it reddish. Therefore, in order to accommodate light of three wavelengths (blue, green, and red), it is necessary to stack and form interference films each having different spectral transmittance characteristics for blue, green, and red.

FIG. 10 is an enlarged sectional view of the interference film formed on the inner surface of the opening of the fluorescent tube in the first embodiment. 1
Shows 0, 11, 12.

FIG. 11 shows the emission spectrum distribution of the fluorescent tube and the spectral transmittance characteristics of the interference films for blue, green, and red in the first embodiment. ，
The spectral transmittance characteristics 13, 14, and 15 of No. 12 and the emission spectrum distribution 6 of the fluorescent tube are shown. In FIG. 11, the interference film 10 for blue has a spectral transmittance characteristic 13 of reflecting light in a wavelength range between blue and green and transmitting light in other wavelength ranges, and the interference film 11 for green has , has a spectral transmittance characteristic 14 that reflects light in a wavelength range between green and red and transmits light in other wavelength ranges, and the interference film 12 for red color reflects infrared light and transmits light in other wavelength ranges. It has a spectral transmittance characteristic 15 that transmits light within a range. The interference films 103 in FIGS. 1 and 2 are replaced with interference films 10 and 10 having different spectral transmittance characteristics, respectively, as shown in FIG.
By laminating 11 and 12, the three wavelengths of light can be controlled independently, so the light emitted from the fluorescent tube is not colored, and the effects of the present invention can be obtained. .

FIG. 12 is a sectional view of a fluorescent tube showing another example of the structure of the aperture type fluorescent tube used in the first embodiment. As shown in FIG. 12, even if the interference film 103 is formed on the outer surface of the opening of the aperture type fluorescent tube 101, there is no problem in implementing the present invention.

FIG. 13 is an enlarged sectional view of the interference film formed on the inner surface of the opening of the fluorescent tube in the second embodiment. 251 is shown. In addition, FIG.
The emission spectrum distribution of the fluorescent tube used in the second embodiment and the spectral transmittance characteristic diagram of the interference film show the spectral transmittance of the interference film 12 for red color that reflects infrared light and transmits light in other wavelength ranges. Characteristic 18 shows an emission spectrum distribution 17 in which the blue and green emission spectra are larger than the red emission spectrum.

In the second embodiment, an interference film formed on the inner or outer surface of the opening of the fluorescent tube has spectral transmittance characteristics that control one color or two colors of light among blue, green, and red light. Assume that fluorescent tubes have emission spectrum peaks in blue, green, and red respectively, and the emission spectrum peaks of other colors are made larger than those controlled by the interference film, and the light emitted from the fluorescent tube is There is no coloration, and the same effects of the present invention as in the first embodiment can be obtained. The second embodiment shown in FIGS. 13 and 14 is a case in which an interference film for red light is formed at the opening of the fluorescent tube, and the overall cross-sectional view is the same as that in FIG. The interference film 12 has strong directivity in the direction normal to the film surface, and the emission spectrum distribution of the fluorescent tube is changed to distribution 1.
By making the emission spectra of blue and green light larger than that of red light as shown in 7, the three wavelengths of light emitted from the fluorescent tube will have the same peaks in the emission spectra of blue, green, and red. There is no coloration and the effects of the present invention can be obtained.

FIG. 15 is a cross-sectional view of a third embodiment, in which an aperture type fluorescent tube 101 having an interference film 103 formed on the opening surface of the present invention and a light guide using a transparent plate made of acrylic resin or the like as a light guide. The same light source section as in the first embodiment is shown, which includes a light source section 16, and a light incident surface 601 coated with a non-reflection coating onto which a light beam 102 from the light source section is incident. The third embodiment further improves the effects of the present invention, particularly when a light guide made of acrylic resin or the like is used in the light guide section. In FIG. 15, the light incidence surface 601 is SiO2,
By depositing MgF2 or the like in a non-reflective coating, surface reflection does not occur on the light incident surface 601, and the light beam 102 can be efficiently made to enter the light guide section 16 from the light source section.

[0025]

According to the present invention, the utilization efficiency of light emitted from a light emitter can be improved, and a high-luminance surface light source device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a first embodiment of the present invention;

[Figure 2
]A sectional view of an aperture type fluorescent tube of the first embodiment,

[Figure 3]
Emission spectrum distribution of fluorescent tube and spectral transmittance characteristic diagram of interference film,

[Fig. 4] An explanatory diagram of an interference film,

[Figure 5] Wavelength-transmittance characteristic diagram depending on the incident angle of the interference film,

[Fig. 6] Incident angle-transmittance characteristic diagram of interference film,

[Fig. 7] An explanatory diagram showing the incidence and reflection of light on the surface of the interference film,

[Figure 8] Light intensity distribution diagram of light emitted from a fluorescent tube,

FIG. 9 is an enlarged sectional view of the surface light source device of the first embodiment and an intensity distribution diagram of light emitted from the opening;

FIG. 10 is an enlarged cross-sectional view of the interference film on the surface of the opening in the first embodiment;

FIG. 11 is a diagram of the emission spectrum distribution of the fluorescent tube and the spectral transmittance characteristic of the interference film in the first embodiment;

FIG. 12 is a sectional view of a fluorescent tube showing another configuration example of the aperture type fluorescent tube used in the first embodiment;

FIG. 13 is an enlarged cross-sectional view of the interference film on the surface of the opening in the second embodiment;

FIG. 14 is a diagram of the emission spectrum distribution of the fluorescent tube and the spectral transmittance characteristic of the interference film in the second embodiment;

FIG. 15 is a sectional view of a third embodiment of the present invention;

FIG. 16 is a cross-sectional view of a conventional surface light source device.

FIG. 17 is a cross-sectional view of an aperture-type fluorescent tube and an intensity distribution diagram of light emitted from the aperture.

[Explanation of symbols]

2, 20... Light guide section, 101, 501... Aperture type fluorescent tube of the present invention, 103
...Interference film, 104...Glass body, 105...Reflection film, 106...Fluorescent film, θ1, θ2...Aperture angle.

Claims (4)

[Claims] 1. An aperture type fluorescent tube is used as a light emitting body, an opening of the aperture fluorescent tube is arranged to face a light incident surface of a light guiding section, and the light emitted from the aperture fluorescent tube is directed to the light incident surface. In the surface light source device, the incident light is reflected and diffused inside the light guiding section to obtain uniform surface light on the irradiation surface. A surface light source device characterized in that an interference film having a multilayer structure is formed by alternately laminating a plurality of types of optical thin films having different ratios. 2. In claim 1, the aperture fluorescent tube has emission spectrum peaks in blue, green, and red, respectively, and the interference film formed on the inner or outer surface of the opening of the aperture fluorescent tube comprises: It is formed by laminating interference films with different spectral transmittance characteristics for blue, green, and red, and the blue one reflects light in the wavelength range between blue and green, and reflects light in the other wavelength ranges. It has spectral transmittance characteristics that transmit light, and for green color,
It has spectral transmittance characteristics that reflects light in the wavelength range between green and red and transmits light in other wavelength ranges, and the red color reflects infrared light and transmits light in other wavelength ranges. It has spectral transmittance characteristics, and the aperture fluorescent tube emits blue, green,
A surface light source device that independently controls light in each red wavelength range. 3. According to claim 1 or 2, the interference film formed on the inner or outer surface of the opening of the aperture fluorescent tube comprises:
The aperture fluorescent tube has spectral transmittance characteristics that control one color or two colors of light among blue, green, and red light, and the aperture fluorescent tube has
A surface light source device having emission spectrum peaks for each of blue, green, and red, and in which the emission spectrum peaks for other colors are larger than the colors controlled by the interference film. 4. The surface light source device according to claim 1, wherein the light incident surface of the light guide section is coated with an anti-reflection coating.