Note: Descriptions are shown in the official language in which they were submitted.
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LIGHT DIFFUSIN~; DEVI~E
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light
diffusing device. Particularly, the present invention
relates to an improved light diffusing device useful for
- every illuminating a relatively large area at a signifi-
cantly reduced optical loss.
2. Description of the Related Art
Various known light diffusing devices are
useful as a plane light source for transmitting light
received from a light source to a desired object to
evenly illuminate a relatively large area. These light
diffusing devices are practically employed as an
illumination means for display devices, for example,
advertising display devices, and further, as rear face
illumination means for liquid crystal display devices.
Also, various known light diffusing plates,
for example, frosted glass plates and milk (opal) white
glass plates, are used for light diffusion. The light
diffusing plates are usually utilized in such a manner
that a light source is located ~y and spaced fxom a rear
surface of the light diffusing plate at a predetermined
distance.
In recent types of liquid crystal display
devices, however, it has been attempted to arrange the
light source in the vicinity of an edge face of a light
diffusing plate which has been utilized as a light
incident face, to minimize the size of the display
devices. In this attempt, it has been found that, where
the light source is merely arranged at the edge face of
the usual light diffusing plate, for example, a frosted
glass plate or milk white glass plate, it fails to
evenly illuminate the entire surface of the light
diffusing plate.
'~o eliminate the above-mentioned disadvantage,
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U.S. Patent No. 4,059,916 discloses a concept wherein a
rear surface of a light transmitting p:Late is matted
(roughed) in a hairline mode and a light reflecting
layer is formed on the mat rear surface so that light
irradiated from a light source can be transmitted
thro~gh the light diffusing plate in an enhanced
directivity, and the thickness of the light transmitting
plate is gradually decreased from the edge face facing
the light source toward the opposite edge face of the
plate, so that the brightness at the opposite edge face
of the plate is increased and, thus, the brightness
throughout the entire surface of the plate becomes
uniform.
~he above-mentioned type of light diffusing
plate is, however, disadvantageous in that the production
of the light diffusing plate can be attained only by
very fine, delicate and precise work on a surface of a
transparent light transmitting plate, and this work
causes an extream increase in the production cost. This
is disadvantageous since, rom a commercial viewpoint,
the cost for producing the light diffusing plate must be
reduced. Therefore, it is clear that the above-mentioned
type of light diffusing plate is still unsatisfactory in
view of the cost thereof.
To remove the above-mentioned disadvantage,
Japanese Unexamined Patent Publication (Kokai~
No. 61-55684 discloses an improved type of light
diffusing device comprising a ~ase plate composed
essentially of a transparent light transmitting layer
corresponding to a substantially major portion of the
plate, a light diffusing layer formed on at least a
front surface of the transparent light transmitting
layer, and an intermediate layer formed between the
transparent light transmitting layer and the light
diffusing layer and having intermediate light trans-
mitting and diffusing properties between those of the
light transmitting and diffusing layers, at least one
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edge face of the base plate being a light incident face;
and a light reElecting face layer formed on a rear
surface of the base plate.
The above-described light diffusing device is
significantly advantageous in cost for producing the
device.
~ owever, in view of the recent demand for a
display on a large screen having a size of 10 to 14
inches, there is an increased demand for the provision
of an even further increased uniformity (evenness) in
brightness over the entire surface of such a large
screen.
Japanese Unexamined Utility Model Publication
(Kokai) No. 61-104,490 discloses a new type of light
diffusing device wherein a light diffusing plate i5
arranged on the above-mentioned base plate to improve
the uniformity of the brightness thereof.
In the above-mentioned type of light diffusing
device wherein light is introduced from a light source
into the device through at least one edge face of a
transparent light transmitting layer, there is a problem
in that a brightness at a location close to the light
incident edge facé is different from that at another
location far from the light incident edge face.
Therefore, it is strongly desired to increase the
uniformity of the brightness throughout the entire front
surface o~ the device.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a
light diffusing device useful for illuminating a rela-
tively large display surface with a uniform brightnessO
Another object of the present invention is to
provide a light diffusing device having a significantly
decreased optical loss.
Still another object of the present invention is to
provide a light diffusing device capable of being
manufactured easily and at a low cost.
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The above~mentioned objects can be attained by thelight diffusing device of the present invention which
comprises~ (1) a light source member and ~2) a light
diffusing member which comprises (A) a base plate
comprising ~a) a transparent light transmitting layer
having at least one light incident edge face thereof
facing the light source member, (b) a light diffusing
layer formed on a front surface of the transparent light
transmitting layer, (c) an intermediate layer formed
between the transparent light transmitting layer and the
light diffusing layer, and (d) a light reflecting surface
layer ormed on a rear surface of the transparent light
transmitting layer; (B) a light diffusing plate super-
imposed over the base plate; and (C) a light reflecting
film located between the light diffusing layer in the
base plate and the light diffusing plate without coming
into contact with them and effective for reflecting
portions of light irradiated from the light diffusing
layer in the base plate and for evenly distributing the
irradiated light into the light diffusing plate.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a partially notched perspective view of
an embodiment of the light diffusing device of the
present invention while in use;
2S Fig. 2 is a partially notched cross-sectional view
of the device indicated in Fig. 1 along the line II - II
therein;
Fig. 3 is a cross-sectional view of a portion of a
base plate in the light diffusing device of the present
invention;
Fig. 4 is a plane view of an embodiment of the
light reflecting film usable for the light diffusing
device of the present invention;
Fig. 5 is a graph showing a distribution of light
reflection on a light reflecting film as shown in Fig. 4;
Fig. 6 shows a cross-sectional view of an embodiment
of the light source member usable for the light diffusing
~S~ 55
device of the present invention; and
Fig. 7 shows a distribution of brightness on the
light diffusing plate in the light diffusing device
described in Example 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The light diffusing device of the present invention
comprises a light source member and a light diffusing
member.
Referring to Figs. 1 and 2, a light diffusing
member A comprises a base plate 1, a light diffusing
plate 6, and a light reflecting film 7 effective for
evenly distributing light transmitted from the base
plate 1 to the light diffusing plate 6.
The base plate 1 comprises a transparent light
transmitting layer 2 which usually occupies a major por-
tion of the volume of the base plate 1, a light diffusing
layer 3 formed on a front surface (an upper surface in
Fig. 1) of the transparent light transmitting layer 2,
and an intermediate layer 4 formed between the transpa-
rent light transmitting layer 2 and the light diffusing
]ayer 3. Usually, the intermediate layer 4 has light
transmitting and diffusing properties in intermediate
intensities between those of the transparent light
transmitting layer 2 and the light diffusing layer 3.
The transparent light transmitting layer 2 has at
least one light incident edge face facing a light source
(lampJ in the light source member.
Preferably, a li~ht reflecting surface layer 5 is
formed on a rear surface (a lower surface in Fig. 1~ of
the transparent light transmitting layer.
An ordinary type light diffusing plate 6 is super-
imposed over the light diffusing layer 3 in the base
plate 1 through a small gap. A light reflecting film 7
is interposed between the light diffusing plate 6 and
the light diffusing layer 3. This light reflecting
film 7 consists of a transparent substrate film and a
number of light reflecting small spots or small places
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formed on the transparent substrate film in a pattern
effective for evenly distributing the quantity of light
transmitted from the base plate 1 to the light diffusing
plate 6. The light reflecting film 7 is not forced into
close contact or adhesion with the light diffusing
plate 6 and the light diffusing layer 3 in the base
plate 1. That is, the light reflecting film 7 is spaced
from the light diffusing plate 6 by a very thin gap and
from the light diffusing layer 3 also by a very thin
gap. These very thin gaps form very thin air layers.
In Fig. 2, the gaps formed between the light
diffusing plate 6 and the light reflecting film 7 and
between the light reflecting film 7 and th~ light
diffusing layer 3 are shown on an enlarged scale to give
a clear indication of the arrangement of the above-men
tioned plate 6, film 7, and layer 3.
In the embodiment of the light diffusing device
indicated in Fig. 1, the base plate 1 the light
reflecting film 7, and the light diffusing plate 6 have
rectangular plane configurations similar in shape and
dimensions to each other.
The base plate 1 has at least one light incident
edge face thereof. Referring to Fig. 1, the base
plate 1 has a pair of light incident edge faces facing
and exposed to light sources (for instance, fluorescent
lamps) s and C which are provided with reflectors D
and E, respectively. ~lso, the base plate 1 has edge
aces thereof other than the at least one light incident
edge face. Preferably, the other edge faces of the base
plate 1 are slanted or inclined at an acute angle ~ to a
front face of the base plate 1 r as shown in Fig. 3.
The edge faces other than the light incident face
of the base plate and the edge faces of the light
diffusing plate 6 and the light reflecting film 7 are
provided with light reflecting edge face layers 8 as
shown in Fig. 2.
In the embodiment of the light di~fusing device
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shown in Fig. 1, the base plate 1 has two light incident
edge faces thereof facing and exposed to two light
sources B and C in the light source membex. However,
the light diffusing member may have another type of base
plate having, or example, only one light incident edge
face thereof exposed to the single light source.
In the light diffusing device of the present
invention, the transparent light transmitting layer
usually consists of a highly transparent plastic
material, for example, an alkyl methacrylate polymer
sheet, especialiy a methyl methacrylate polymer sheet,
preferably having a thickness of from 0.3 mm to 20 mm,
more preferably from 3.0 to 15 mm.
The light diffusing layer usually consists of a
matrix consisting of an alkyl methacrylate polymer
produced by a multi-stage polymerization method and a
light diffusing agent, for example, titanium dioxide
fine powder, dispersed in the matrix. This type of
alkyl methacrylate polymer is disclosed in U.S. Patent
20 Nos. 3,804,925, 4,052,523, 4,173,600 and 4,508,875.
Usually, the light diffusing layer has a thickness
of from 0.05 to 1 mm.
The base plate usable for the present invention can
be produced by any known method.
For example, à front surface of a methyl methacry-
late polymer plate (film) is coated with a mixture of a
methacrylate monomeric liquid and a light diffusing
agent so as to cause the front surface of the methyl
me~hacrylate polymer plate to be dissolved or swollen by
the monomeric liquid and to allow a portion of the
liquid diffusing agent to diffuse into and to be mixed
with the dissolved or swollen front surface of the
methyl methacrylate polymer plate. Then, the methacrylic
monomeric liquid is polymerized to provide a light
diffusing layer and an intermediate layer between the
light diffusing layer and a transparent light trans-
mitting layer.
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Alternatively, a thin light diffusing film consist-
ing of an alkyl methacrylate polymer containing a light
diffusing agent dispersed therein is brought into
contact with a ~ayer consisting of an alkyl methacrylate
monomer or syrup to cause a surface portion of the light
diffusing film to be dissolved or swollen by the monomer
or syrup and to allow a portion of the monomer or syrup
to diffuse into the dissolved or swollen surface oE the
light diffusing film. Then, the monomer or syrup is
polymeri7ed, preferably under hea~ and pressure, to
provide a transparent light transmitting layer and an
intermediate layer which bonds the transparent light
transmitting layer to the light diffusing film layer to
form a body of a base plate. The abo~e-mentioned method
15 is disclosed in U.S. Patent No. 4,415,509.
In another method for producing the base plate,
surface of a light diffusing film consisting of an
acrylic polymer matrix and a light diffusing agent
dispersed in the matrix, and a transparent light trans-
mitting pla~e consisting of a transparent methacrylic
polymer, are partially dissolved or swollen and the
partially dissolved or swollen surfaces are brought into
contact so as to form an intermediate layer between the
light transmitting layer and the light diffusing layer.
Usually, the intermediate layer is formed in a
thickness of from 0.01 to O.Z mm.
The intermediate layer is highly effective for
firmly bonding the transparent light transmitting layer
to the light diffusing layer and for enhancing the
diffusion of light transmitted through the transparentlight transmitting layer into the light diffusing layer.
The base plate usually has a flat plate-like shape
and a rectangular plane configuration as shown in
Figs. 1 and 2. ~owever, the shape and configuration of
- 35 the base plate are not restricted to those mentioned
above, and may be other than those shown. Also, the
base plate shown in Figs. 1 and 2 has a uni~orm thickness
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throughout the entire body of the base plate. However,
the thickness of the base plate may be variable depending
on the distance from each light incident edge face of
the base plate. For example, the thicXness may be
gradually decreased from each light incident edge face
facing a light source toward the center of the base
plateO That is, the dimensions and shape of the base
plate can be varied depending upon the intended use of
the light diffusing device.
Referring to Fig. 2, the light reflecting layer 5
can be provided, for instance, by vapor depositing or
plating a metal, for example, aluminum, on the rear
surface of the base plate 1. Alternatively, the light
reflecting surface layer 5 is formed by adhering a light
reflecting tape having a light reflecting metal surface
layer provided by means of a vapor deposition of a
metal, for instance, aluminum, on a surface of a plastic
tape, to the rear surface of the base plate 1. The
thickness of the light reflecting surface layer 5 is not
restricted to a specific value as long as it can satis-
factorily serve as a light reflector.
The light diffusing plate 6 as indicated in Figs. 1
and 2 may consist of a conventional light diffusing
plate, for example, frosted glass plate, milk white
glass plate or a thermoplastic plate containing a light
diffusing agent dispersed therein. Usually, the thick~
ness of the light diffusing plate 6 is 1/4 that of the
base plate l or less.
The light reflecting film 7 is arranged between the
base plate l and the light diffusing plate 6 for the
purpose of evenly distributing the quantity of light to
be transferred from the base plate l to the light
diffusing plate 6. Usually, the quantity of light
irradiated from the base plate is variable depending on
the distance from the light incident edge face of the
base plate. That is, the smaller the distance from the
light incident edge face of the base plate to a portion
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thereof, the larger the quantity of light transmitted
through the base plate. This phenomenon causes the
distribution of brightness on the front surface of the
light diffusing plate to be uneven. To make the bright-
ness dis~ribution uniform, it is necessary to reflectlight irradiated from a portion of the base plate close
to the light incident edge face toward the base plate.
The amount of light to be reflected on the light
reflecting film is variable depending on the distance
from the light incident edge face~ That is, the smaller
the distance from the light incident edge face, the
larger the amount of light to be reflected.
Usually, the light reflecting film comprises a
transparent film substrate and a number of light
reflecting small spots or small places formed on the
film substrate. The size, configuration, and distribu-
tion density oE the light reflecting spots are designed
so that th~y cause the distribution of light transmitted
through the light reflecting film to be uniform.
Referring to Fig. 4, a light reElecting film 7
comprises a transparent film substrate 7a consisting of,
for example, a transparent polyethylene terephthalate
film having a thickness of 25 to 125 ~m, and the light
reflecting spots 7b formed on the transparent film
~5 substrate 7a.
Referring to Fig. 4, the size (area) and the
distribution density of the light reflecting spots 7b
decreases with an increase in the distance from the
light source B or C. A total area of the spots in the
light reflecting film 7 in the above-mentioned end
portions thereof increases with decrease in the distance
from the light source B or C. In the middle portion of
the light reflecting film, the light reflecting spots
are not arranged on the transparent film substrate.
Referring to Fig. 5, in the end portions of the
light reflecting film having a distance x from end
points 0, the average reflectance (r) of the light by
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the transparent film decreases with an increase in the
distance x. In the middle portion of the light
reflecting film, light reflection does not occur.
The distance x and the average reflectance r are
not restricted to specific values. However, in Fig. 5,
the distance x is in the range of from 30 mm to 40 mm
and the average reflectance r is in the range of from
30% to 50~.
In the device shown in Fig. 4, two light sources s
and C are arranged. However, the device of the present
invention may contain a single light source. In this
case, the density of the light reflecting spots aecreases
with an increase in the distance from the single light
source.
The light reflecting spots can be produced by vapor
depositing a light reflecting metal, Eor example,
aluminum, on an entire surface of a transparent film
substrate and then removing ~etchingJ portions of the
vapor-deposited metal layer in accordance with a prede-
termined pattern.
In anothex method, a transparent film substrate is
coated on the entire surface thereof with a paste
containing a light reflecting metal and a photosensitive
resin, the coatings are then masked in accordance with a
predetermined pattern and are exposed to light. There-
after, the exposed portions or unexposed portions of the
coating layer are removed.
The pattern of the light reflecting spots is not
limited to that shown in Fig. 4 and may be striped or
checkered.
The size of the light reflecting spots may vary
with the distance from the light source, as shown in
Fig. 5. Also, the light reflecting spots having the
same size may be distributed at a different distribution
density on the transparent film substrate.
The light reflecting film may have a continuous
light reflectance distribution as shown in Fig. 5.
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Referring to Figs. l and 2, the light reflecting
edge face layers 8 are provided with an irregular
reflection surface having a high reflectance. Usually,
the light reflecting edge face layers 7 are made of a
retroreflection tape.
As shown in Figs. 2 and 3, the light reflecting
edge face layers 8 are preferably slanted or inclined at
an acute angle ~ to the front surface of the base
plate 1. The anyle B is preferably in the range of
from 75 to 88 degrees. The slanted light reflecting
edge face layers 8 are effective for enhancing the
uniformity of the brightness of the light diffusing
layer surface of the base plate.
The light source member of the present invention
usually has one or two light sources, for example,
tube-shaped fluorescent la~ps, as shown in Fig. l. The
light source preferably has a cross-sectional profile as
shown in Fig. 6.
In E`ig. 6, a tube-shaped light source 9, Eor
example, a tube-shaped fluorescent lamp is covered by a
light reflector lO having a slit ll extending along the
longitudinal axis of the tube-shaped light source 9 and
ha~ing a width Y shown in Fig. 6. The slit ll of the
light reflector lO is located in such a manner that the
light incident edge face of the base plate faces the
tube-shaped light source lO through the slit ll. The
width Y of the slit is preferably similar to the height
of the light incident edge face of the base plate.
The light reflector lO is preferably made of a
light-reflecting film or sheet consisting of a trans-
parent film substrate consisting of, for example, atransparent polyethylene terephthalate film or a trans-
parent polypropylene filml a light reflecting metal
layer formed on a surface of the film substrate by means
of a metal vapor depositing, and a top coating layer
consisting of, for example, a polyurethane resin, and
formed on the opposite surface of the film substrate.
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In another embodiment, the light .reflector lO
consists of, for example, a composite sheet consisting
of a metal reflecting metal foil, for example, an
aluminum foil, and two transparent plastic layers
consisting of a polyester resin or polypropylene resin
and formed on both surfaces of the metal foil.
In still another embodiment, the light reflector lO
consists of a cGmposite sheet composed of a light
reflecting metal foil, a transparent plastic film
laminated on a surface of the metal foil and a top
coating layer consisting of, for example, a polyurethane
resin laminated on the other surface of the metal foil.
The light reflector lO preferably has a light
reflectance of about 80% or more and is capable of
resisting a temperature of 100C or more.
In the preparation of the light source as indicated
in Fig. 6, a light reflecting sheet i9 cut to provide a
preparatory sheet having a length similar to the length
of the light source to be covered and a width corre-
sponding to a length adequate to form a slit ll having awidth Y, which is the same as the height Al of the light
incident edge face A, when the preparatory sheet is
wound on the peripheral surface of the light source B,
and the preparatory sheet is wound on the light source B
so as to form the slit ll facing the light incident edge
face A. The light reflector lO is adhered to the
peripheral surface of the light source B with an adhesive
tape or an adhesive agent.
The light reflector lO indicated in Fig. 6 is made
of a material in the form of a film. However, the form
of the light reflector is not limited to the film, and
may be in another form, for example, a sheet, as long as
the material for the light reflector l0 has a satisfac-
tory light reflectance, and an adequate flexibility and
formability for winding it around the light source.
In the light diffusing device of the present
invention, the tube-shaped light source is not limited
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to a tube-shaped fluorescent lamp, and may be selected
from other luminesc~nt lamps and incandescent lamps in a
tuhe shape.
Referring to Figs. l, 2 and 4, when the light
sources (fluorescent lamp) s and C are lit, the
irradiated light is introduced into the transparent
light transmitting layer 2 through the light incident
edge face thereof facing the light sources. The
introduced light, portions of which are re~lected by the
light reflecting surface layer 5 and by the light
reflecting edge face layer 8 and returned into the
transparent light transmitting layer 2, are transmitted
to the light diffusing layer 3 through the intermediate
layer 4. The light is diffused by the light diffusing
layer 3 and is irradiated to the light diffusiny plate 6
through the light reflecting film 7.
When the diffused light is irradiated from the
light diffusing layer 3, a portion of the irradiated
light from an end portion of the light diffusiny layer 3
(close to the light incident edge face of the transparent
light transmitting layer 2~ is reflected by the light
reflecting spots 7b in the light reflecting film 7,
returned into the light diffusing layer 3 and then
irradiated from another portion of the light diffusing
layer 3 far from the li~ht incident edge face. Accord-
ingly, the diffused light is evenly introduced from the
light diffusing layer 3 into the light diffusing plate 6
through the light reflecting film 7.
The introduced light is evenly diffused in the
3~ light diffusing plate 6 and evenly irradiated to the
. outside of the device.
The light diffusing device of the present invention
provides a highly uniform illumination with evenly
scattered light at a reduced optical loss. That is, the
light diffusing aevice of the present invention i5
extremely useful for a large size display system.
The present invention will be more fully explained
3a 2~i8~5~;
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by means of examples, but it should be understood that
these are merely representative and do not restrict the
scope o the present invention in any way~
Example l
(l) Production of Base Plate
A rutile type titanium oxide powder in amount
of 1.5% by weight was dry blended with 38.5% by weight
of acrylic resin pellets consisting of a methylmethacry-
late-butylacrylate copolymer ("Hipet", registered trade
mark, made by Mitsubishi Rayon Co.J. The blend was
subjected to an ordinary process for producing an
acrylic resin film having a thickness of 50 ~m.
The film was spread on an inorganic g7ass
plate and tempoxarily adhered thereto with a methyl
methacrylate adhesive. Spacers were placed on edge
portions of the film and another glass plate was place
on the spacers to produce a cell formed by the two glass
plates facing each other through the spacers. The film
was located within the resultant cell. The cell had a
~0 gap having a thickness of about lO mm and formed between
the two glass plates.
A syrup consisting of partially polymerized
methyl methacrylate was poured into the gap and polymer-
ized to provide a transparent acrylic resin plate having
a thickness of about lO mm.
When the syrup was brought into contact with
the titanium dioxide-containing acrylic resin film, a
s~rface of the film was partially dissolved or swollen
to allow a portion of the syrup to diffuse into the
surface of the film and to form an intermediate layer
between the transparent acrylic resin plate and the
titanium dioxide-containing acrylic resin film.
A light reflecting layer was formed in a
thickness of about lOOO angstrom by means of a vacuum
vapor deposition of aluminum on a rear surface opposite
to the front surface of the acrylic resin plate.
The resultant composite plate was cut into a
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rectangular piece having a length of 200 mm and a width
of 100 mm. That is, the piece had a pair of longitudinal
edge faces having a length of 200 mm and a pair of
transverse edge faces having a length of 180 mmD The
two longitudinal edge faces were flame polished, and the
two transverse edge faces were cut to form slanted edge
faces inclined at an angle ~ of about 82 degrees to the
front suxface of the piece. Thus, a base plate provided
with the light reflecting surface layer formed on the
rear surface of the base plate was obtained.
(2) Production of Light Reflecting Film
A metal image-forming negative-positive type
photosensitive film laminate ("K.D.P.", registered trade
mark, made by Kimoto Co.) having dimensions of 200 mm
x 100 mm and consisting of a polyethylene terephthalate
film substrate having a thickness of about 100 ~m, an
aluminum foil layer formed on the film substrate, a
photosensikive resin layer placed on the foil layer, an
adhesive layer coated on the resin layer and a trans-
parent cover film layer placed on the adhesive layer,was used as a material for the light reflecting film.
The photosensitive resin layer was exposed
through the cover film to light in accordance with a
predetermined masking pattern and was developed by an
ordinary method for the K.D.P. film laminate.
The resultant light reflecting film had a
number of light reflecting metal spots in the pattern as
shown in Fig. 4. In the light reflecting film, the
light reflecting metal spots having a square form are
arranged in longitudinal and transverse densities of 30
sq~are layers/inch. Referring to Fig. 5, the light
reflecting film exhibited a maximum light reflectance r
of 40~ and a distance x of 40 mm.
(3~ Preparation of Light Diffusing Plate
A milk white light diffusing plate
("Acrylite #432", registered trade mark, made by
Mitsubishi Rayon Co.) was cut into a rectangular piece
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having dimensions of 200 mm x 180 mm.
~4) Assembling of Light Diffusing Device
The rectangular light reflecting film was
superimposed on the front surface of the rectangular
base plate and the rectangular light diffusing plate was
superimposed on the light reflecting film in such a
manner that the light reflecting spots in the light
reflecting film face the front surface of the base plate
and are not in direct contact with each other.
The base plate, the light reflecting film and
the light diffusing plate were integrated into one body
by applying a double surface adhesive tape to each of
the transverse edge faces of the base plate, light
reflecting film, and light diffusing plate.
A recurring reflection sheet ("Sparklite",
registered trade mark, made by Unichika Co.) having a
vapor deposited aluminum layer was applied to the double
surface adhesive tape layer on the integrated structure
in such a manner that a surface of the vapor deposited
aluminum layer came into contact with the adhesive tape.
Thus, a light diffusing member was obtained.
~5) Combining of Light Sources
Two tube-shaped fluorescent lamps ~"FL-6W",
trade mark, made by Toshiba Ltd.) having a diameter of
25 15 mm, a length o 210 mm and an output of 5 ~ were
arranged in vicinity of the longitudinal edge faces of
the base plate. The outer surfaces of the fluorescent
lamps were covered bv light reflectors consisting of
aluminum plate, except for portions of the outer surface
facing the longitudinal edge faces.
The resultant light diffusing device had the
construction as shown in Figs. 1, 2 and 4.
When the fluorescent lamps were lit, and light
diffusion on the light diffusing plate was observed by
the naked eye, it was found that the light was evenly
diffused and irradiated.
The brightness on the light diffusing plate
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was measured in the following manner. That is, the
front surface of the light diffusing member was parti-
tioned into 20 sections as shown in Fig. 7.
The brightnesses in cd/m2 at the center points
of the sections were measured by means 3f a brightness
meter (nt l degree, made by MINOLTA CO.J.
The results are shown in Fig. 7. The average
value of the measured`20 brightnesses was 73S dd/m2.
The brightnesses in the 20 sections are similar to each
other. In the obser~ation of the light diffusing
surface of the light diffusing plate by the naked eye,
no specific mark corresponding to the light reflecting
layers was found in the light irradiation on the light
diffusing surface.
xample 2
The same procedures as those described in Example l
were carried out except that tube-shaped fluorescent
lamps (FL-6W, 100 V, 6 W) were lit by a stabilized 100 V
AC current source, and the lamps were covered by a light
20 reflecting sheet having dimensions of 200 mm x 38.7 mm
and consisting of a polyester film substrate having a
thickness of about 70 ~m and a light reflecting aluminum
layer formed by means of a vapor depositing. The light
reflecting sheets were wound around the outer surfaces
of the lamps so as to form slits facing the light
incident edge faces of the base plate.
The ends of the wound light reflecting sheet were
placed on the ends of the lamps, and fixed thereto by
mea~s of transparent adhesive tapes.
3Q The resultant light sources had a construction as
shown in Fig. 6. The width Y of the slit was
about 10 mm.
The front surface of the resultant light diffusing
de~ice was partitioned into 10 sections. In each
section, a brightness was measured by means of a
brightness meter (nt l/3 degxees) made by MINOLTA CO..
The results are shown below.
` 3 :25;~C!~5
-- 19 --
~ :
N
N
N
~,N~
