Patent Application
20130003408
The present invention relates to a light guide film of a light emitting diode (LED) backlight unit, and, more particularly, to a light guide film of an LED backlight unit, which has a plurality of grooves carved into an incident plane of the light guide film to increase an incidence angle of which light can be transmitted through the light guide film.
Typically, a liquid crystal display (LCD) for handheld and notebook devices generally employs at least one lateral light emitting diode (LED) as a light source of a backlight unit. Such a lateral LED is generally provided to the backlight unit as shown in FIG. 1 of Yang U.S. Pat. No. 7,350,958.
Referring to
As shown in
Since the alternately formed light and dark spots are not desirable for the light guide film, they should be minimized and the length (l) should be shortened as much as possible. For this purpose, it is necessary to increase an angle of light entering the light guide film, that is, an incidence angle of light.
For this purpose, it is suggested to form protrusions on the input surface of the light guide film as shown in
Therefore an improved input edge design is needed to provide a more uniform surface illumination of the light guide film without sacrificing the efficiency of the backlight system.
The present invention is aimed at overcoming the problems (hot spots and secondary light collimation) associated with the above prior art and therefore yield a more uniform surface illumination of the light guide film without sacrificing the efficiency of the backlight system.
The present invention provides a planar light guide film for a backlight unit having at least one point light source, the light guide film comprising: a light input surface for receiving light from the point light source; a light redirecting surface for redirecting light received from the light input surface; a light output surface for outputting at least the light redirected from the light redirecting surface; wherein the light input surface further comprises a composite lens structure having a circular tip segment with a first contact angle, and a first and second circular base segments with a second contact angle, the second contact angle being less than the first contact angle and the second contact angle being equal to each other; and wherein the circular tip segment satisfies the following equation:
y
1
=a
1+√{square root over ((r12−x2))}
and the circular base segments satisfies the following equations:
y
2
=b
2−√{square root over ((r22−(x+a2)2))}
y
3
=b
3−√{square root over ((r32−(x−a3)2))}
In addition, the invention further provides a planar light guide film for a backlight unit having at least one point light source, the light guide film comprising: a light input surface for receiving light from the point light source; a light redirecting surface for redirecting light received from the light input surface; a light output surface for outputting at least the light redirected from the light redirecting surface; wherein the light input surface further comprises a composite lens structure having gaps there between, the lens structure having a circular tip segment with a first contact angle, and a first and second circular base segments with a second contact angle, the second contact angle being less than the first contact angle and the second contact angle being equal to each other; and
wherein the circular tip segment satisfies the following equation:
y
1
=a
1+√{square root over ((r12−x2))}
and the circular base segments satisfies the following equations:
y
2
=b
2−√{square root over ((r22−(x+a2)2))}
y
3
=b
3−√{square root over ((r32−(x−a3)2))}
Further, the invention provides a planar light guide film for a backlight unit having at least one point light source, the light guide film comprising: a light input surface for receiving light from the point light source; a light redirecting surface for redirecting light received from the light input surface; a light output surface for outputting at least the light redirected from the light redirecting surface; wherein the light input surface further comprises a serrated lens structure that is provided only where the point light source is incident on the light input surface, the lens structure having a circular tip segment with a first contact angle, and a first and second circular base segments with a second contact angle, the second contact angle being less than the first contact angle and the second contact angle being equal to each other; and
wherein the circular tip segment satisfies the following equation:
y
1
=a
1+√{square root over ((r12−x2))}
and the circular base segments satisfies the following equations:
y
2
=b
2−√{square root over ((r22−(x+a2)2))}
y
3
=b
3−√{square root over ((r32−(x−a3)2))}
a and 5b shows a schematic diagram illustrating a light guide film according to an embodiment of the invention;
a-6c show schematic diagrams illustrating the various segments of the composite lens feature according to an embodiment of the invention;
a and 7b show schematic diagrams illustrating the light diffusing capability of the composite lens feature with a gap between each adjacent feature;
a and 9b show the luminance intensity at various distances from the light input surface for a circular or arc shaped input feature;
a and 10b show the luminance intensity at various distances from the light input surface for a trapezoidal feature or feature with slanted sides; and
a and 11b show the luminance intensity at various distances from the light input surface according to an embodiment of the invention.
A light guide film in accordance with the present invention comprises a light output surface, a light redirecting surface and at least one light input surface that joins the light output surface and the light redirecting surface. The light input surface comprises a plurality of concave features consisting of a composite lens array. Each of the composite lenses is separated by a gap that is a flat surface perpendicular to the light output surface. The composite lenses and gaps are disposed along the light input surface, and extend from the output surface to the light redirecting surface. Each of the composite lenses has a symmetric cross-section consisting of a tip portion comprising a circular tip segment with a first contact angle and a base portion comprising two tilted circular base segments each with a second contact angle, the second contact angle being less than the first contact angle and where the radius for each of the two tilted circular base segments are equal.
According to the above embodiment, the geometrical profile of the composite lens allows for comparatively large light deflecting distances; that is, the composite lens structure has better light-diffusing capability. Thus, the distance between the point light source and the active area of the display can be shortened, and the dark spots between the point light sources can be minimized, with the brightness uniformity still being acceptable. The circular tip segment uniformly distributes the light in front of the discrete light source, typically a light emitting diode (LED). The two tilted circular base segments uniformly distribute the light between the LEDs. A smooth curvature of the circular tip segment and tilted circular base segments maximizes the uniformity of the light spatial distribution so that the light output is uniform. Further, it is also necessary that each two adjacent composite lens structures have a gap or flat therebetween so a greater degree of deflection on the propagation path of the incident light can be achieved to thereby increase the light-diffusing effect.
Referring to
Further, a plurality of concave composite lens structures 16 are serrated on the edge of the light input surface 12a, with their longitudinal directions being parallel to each other and having a gap (G) between each adjacent composite lens structure 16. Referring now to
The length T1 is the distance between the intersections of the extensions of a tangent at the top of the circular base segments 16b and 16c, and a tangent of the circular tip segment 16a, where the tangent of the circular tip segment 16a is parallel to the light input surface 12a. The length T2 is the total width of the circular tip segment 16a taken where the circular tip segment 16a intersects each the two circular base segments 16b and 16c. Note, T2 is parallel to T1. The contact angle A1 is the contact angle of the circular tip segment 16a at the point where the circular tip segment intersects the circular base segment 16b. Contact angle A1 is preferably greater than 0.1 degrees and less than or equal to 85 degrees. Referring now to
Advantageously, the shape of an XY section of the circular tip segment 16a satisfies the following expression (1):
y
1
=a
1+√{square root over ((r12−x2))} (1)
where the circular tip segment 16a has a first radius r1. The first radius r1 is defined as the quotient of half the distance T1 divided by the tangent of half the contact angle A1. The value a1 is defined as the total height H minus the radius r1 of the circular tip segment 16a. The value x is a value in the direction of the light input surface and is preferably set within the range of −r1×sin(A1)≦x≦r1×sin(A1). The value y1 is a value in the light propagation direction.
Referring now to
Advantageously, the shape of an XY section of the circular base segments 16b and 16c as shown in
y
2
=b
2−√{square root over ((r22−(x+a2)2))} (2)
y
3
=b
3−√{square root over ((r32−(x−a3)2))} (3)
r
2
=H
2/[cos(A21)−cos(A22)]
a
2=[(T2+B)/2−H2×√{square root over ((16r22−(B−T2)2−4H22)/(B−T2)2+4H22))}{square root over ((16r22−(B−T2)2−4H22)/(B−T2)2+4H22))}]/2
b
2=√{square root over (r22−(B/2−a2)2)}
B=T
2
+r
2×[sin(A22)−sin(A21)]+r3×[sin(A32)−sin(A31)]
r
3
=H
2/[cos(A31)−cos(A32)]
a
3=[(T2+B)/2−H2×√{square root over ((16r32−(B−T2)2−4H22)/(B−T2)2+4H22))}{square root over ((16r32−(B−T2)2−4H22)/(B−T2)2+4H22))}]/2
b
3=√{square root over (r32−(B/2−a3)2)}
H
2
=H−r
1×[1−cos(A1)]
Thus, the first circular base segment 16b has a radius r2 and the second circular base segment 16c has a radius r3. Referencing
The parameter a2 is equal to one half the quotient of the quantity of one half the quantity the total width T2 of the circular tip segment 16a plus the total width B of the composite lens feature 16 minus the quantity the height H2 of the first circular base segment 16b times the square root of the quotient of the quantity 16 times the square of the radius r2 of the first circular base segment 16b minus the square of the quantity of the total width B of the composite lens feature 16 minus the width T2 of the circular tip segment 16a, minus 4 times the square of the total height H2 of the first circular base segment 16b divided by the square of the quantity of the total width B of the composite lens feature 16 minus the width T2 of the circular tip segment 16a, plus 4 times the square of the total height H2 of the first circular base segment 16b.
The parameter b2 is equal to the square root of the quantity of the radius r2 of the first circular base segment 16b squared minus the quantity one half the total width B of the composite lens feature 16 minus the parameter a2 that quantity squared.
The coordinate x is a value in the direction of the light input surface or more specifically in the direction of the total width B of the composite lens feature 16 and is preferably set within the range of −B/2≦x≦−T2/2. The coordinate y2 is a value in the light propagation direction.
The total width B of the composite lens feature 16 is equal to the total width T2 of the circular tip segment 16a plus the quantity of the radius r2 of the first circular base segment 16b times the quantity sine of the contact angle A22 at the bottom of the first circular base segment 16b minus the sine of the contact angle A21 at the top of the first circular base segment 16b, plus the quantity of the radius r3 of the second circular base segment 16c times the quantity sine of the contact angle A32 at the bottom of the second circular base segment 16c minus the sine of the contact angle A31 at the top of the second circular base segment 16c. The contact angles for the composite lens feature can be described where A21=A31, A22=A32 and A1≧A22, A21. Preferably, A1≧A22, A21≦85 degrees.
Referencing
The parameter a3 is equal to one half the quotient of the quantity of one half the quantity the total width T2 of the circular tip segment 16a plus the total width B of the composite lens feature 16 minus the quantity the height H2 of the second circular base segment 16c times the square root of the quotient of the quantity 16 times the square of the radius r3 of the second circular base segment 16c minus the square of the quantity of the total width B of the composite lens feature 16 minus the width T2 of the circular tip segment 16a, minus 4 times the square of the total height H2 of the second circular base segment 16c divided by the square of the quantity of the total width B of the composite lens feature 16 minus the width T2 of the circular tip segment 16a, plus 4 times the square of the total height H2 of the second circular base segment 16c.
The parameter b3 is equal to the square root of the quantity of the radius r3 of the second circular base segment 16c squared minus the quantity one half the total width B of the composite lens feature 16 minus the parameter a3 that quantity squared.
The coordinate x is a value in the direction of the light input surface or more specifically in the direction of the total width B of the composite lens feature 16 and is preferably set within the range of T2/2≦x≦B/2. The coordinate y3 is a value in the light propagation direction.
a is a ray tracing for an array of a single composite lens feature 16 of this invention illustrating what happens to the light rays when the individual composite lens features are disposed on the light input surface 12a in a contiguous manner such that there is no gap G between adjacent composite lenses.
Referring now to
a shows a portion of the light input surface 32 of a light guide film 30 with an arc- or circular-type structure 36. The graph in
a shows a portion of the light input surface 42 of a light guide film 40 with a composite lens structure that has flat slanted sides 46. This result would also be applicable to a trapezoidal shaped light input structure. The graph in
a shows a portion of the light input surface 52 of a light guide film 50 with the composite lens feature 56 of this invention. The composite lens feature utilizes a circular tip segment and two tilted circular base segments. The radius of each of the two tilted circular base segments is equal. The bottom contact angle of each of the two tilted circular base segments is less than the contact angle of the circular tip segment. The circular tip segment uniformly distributes the light in the area immediately in front of the LED. The two tilted circular base segments uniformly distribute the light between the LEDs. The smooth curvatures of the circular tip segment and the two tilted base segments maximize the uniformity of the light spatial distribution so the output light is uniform. The graph in
Hence, an improved light guide film is provided with symmetric light redirecting features to improve light output uniformity without sacrificing light input efficiency. Namely, the improved light guide film 12 having composite lens structure 16 provides enhanced light diffusion in the plane parallel to the light extraction plane and light reflection plane (top and bottom surfaces), allowing greater light redistribution between discrete light sources (light traveling outside the critical angle of planar un-serrated input edge), so that the light output uniformity is improved. Moreover, the light distribution in the plane perpendicular to the light extraction plane and light reflection plane (top and bottom surfaces) is minimized, so that the condition of the total internal reflection is minimized for the inputted traveling light.
