Patent Description:
The disclosure herein relates generally to a light emitting device and an optical lens for improving luminance uniformity.

Light-emitting diode (LED) light sources are commonly and widely used for direct-lit backlight illumination. Computers, personal digital assistants (PDAs), mobile phones, and thin liquid crystal display (LCD) televisions (TVs) are a few examples of backlight screen devices that use direct-lit LED backlights. However, the light intensity distribution range of LEDs is narrow, so a lens may be used on an LED to help distribute the light, for example as disclosed in <CIT>.

In direct-lit backlight, an array of lenses is placed in front of the light sources to provide a more uniform light output on the surface of the backlight device. A large number of LEDs may be needed depending on the size of the light spot right above the lens, thus increasing the cost. The number of LEDs needed for a backlight can be decreased by increasing the spot size of each individual LED device.

The disclosure herein describes optical lens and light emitting device designs to achieve uniform light distribution without producing a light "hot spot" with a benefit of reducing the number of light sources needed and overall cost for direct-lit backlight devices. The disclosure herein relates to an optical lens with a coated annular region, and, optionally, structures on the bottom surface thereof, and a backlight device, or other light emitting device, incorporating said lens, to produce a uniform distribution of light at a target surface. The disclosed lens and light emitting device is particularly useful when a wide or extremely wide transfer function of backlight is needed.

The present invention relates to a light emitting device according to independent apparatus claim <NUM>. Further advantageous realization modes are covered by the dependent claims.

Herein, LED device may be used interchangeably with light-emitting device, or backlight device, such that an LED light source or any other type of light source may be similarly used in a light-emitting device. <FIG> is a cross-sectional view of an example LED device <NUM> (or light emitting device <NUM>) designed to elaborate the effect of a refractive optical lens <NUM> commonly used in a backlight (cross-section shown in the X-Z plane). The LED device <NUM> may include, but is not limited to include, the following components: a lens <NUM>, including an inner curved surface <NUM> and an outer curved surface <NUM>; a light source <NUM> (e.g., an LED or other light source) disposed on a socket <NUM>; terminals <NUM>; and/or a fixing portion <NUM> to attach the lens <NUM> to the socket. LX represents the major axis of the outer curved surface <NUM> and SX represents the minor axis of the inner curved surface <NUM>. The light source <NUM> may be disposed at a central and lower portion of the optical lens <NUM> (e.g., below the LX and SX axes and centered around the optical axis Z of the lens <NUM>). For example, a red LED, a blue LED, or a green LED may be employed as the light source <NUM>. The light source <NUM> may be electrically connected to a circuit board (not shown) through the terminals <NUM> to apply electrical power to the light source <NUM>.

The refractive optical lens <NUM> may be a convexo-concave lens. For example, both the inner curved surface <NUM> and the outer curved surface <NUM> of the optical lens <NUM> may have roughly elliptical shapes. For such a convexo-concave lens as lens <NUM>, the light spot emitted from the lens <NUM> is confined by the bright center of intensity above the lens <NUM> (directly above the light source <NUM> centered on the Z axis). Thus, LED device <NUM> is limited to applications where the light spot requirement (i.e., the distribution or spread of the light emitted from LED device <NUM>) is not too large.

As explained above, a much wider light distribution provided by an LED lens can significantly reduce the cost of a backlight by reducing the overall number of LED devices needed in the backlight. <FIG> is a cross-sectional view of an example LED device <NUM> (or light emitting device <NUM>) with a concave optical lens <NUM>. The LED device <NUM> may include, but is not limited to include, the following components: a lens <NUM>, including an inner curved surface <NUM> (also referred to as a light incident surface <NUM>) and an outer curved surface <NUM> (also referred to as a light exit surface <NUM>); a light source <NUM> (e.g., LED); a base surface <NUM>; and/or a diffuser plate <NUM> (or more generally a light receiver <NUM>). Sockets and/or terminals as in <FIG> may be included, but are not shown in the example LED backlight device <NUM> of <FIG>. The diffuser plate <NUM> may be used, in screen backlights, to evenly distribute light from the light source <NUM> to reduce or eliminate bright spots, and may be composed of many sheets of plastic in varying thickness, opacity or reflectivity, for example.

The shape of the concave optical lens <NUM> increases the light scattering angles, shown by arrows, of the light emitted from the light source <NUM> (e.g., in comparison to the lens <NUM> used in LED device <NUM> in <FIG>) thereby enlarging the light spot above. However, a part of the light generated from the light source <NUM> is likely to be reflected due to total internal reflection occurring at the lens-air interface, mostly around the center (Z axis) of the light exit surface <NUM>. This also contributes to the "hot spot" of fairly intense light in the center of the illumination field (at and around the Z axis). Thus, the backlight device <NUM> using concave lens <NUM>, while providing a better light distribution than the backlight (LED) device <NUM> in <FIG>, still creates an unsatisfactorily non-uniform light distribution pattern.

Therefore, an object of the present disclosure is to provide an optical lens for a light source that can alleviate the aforementioned drawbacks of existing optical lenses and achieve uniform light distribution on the luminance field. Rapid developments in the direct-lit backlight industry have caused a need for innovative, wider and more uniform lens designs. The lens designs disclosed herein enable uniform light distribution without producing a light "hot spot", and thus have a wider transfer function of light compared with other lenses and decrease the overall cost of the direct-lit backlight device.

The present disclosure relates to a lens with coating portions and, optionally, structures on the bottom surface thereof, and a backlight device, or other light emitting device, incorporating said lens to produce a uniform distribution of light at a target surface. The disclosed lens is particularly useful when extremely wide transfer function of backlight is needed. The present disclosure is described in more detail below. While the disclosure is described with respect to backlight devices and LED light sources, it is understood by one skilled in the art that the disclosed lens designs may be similarly used with other light sources and light source devices.

<FIG> is a diagram of the transfer function (TF) of the normalized luminance (i.e., intensity of light emitted from a surface per unit area in a given direction, shown normalized in arbitrary units (a. )) generated by three backlight devices (centered at the -<NUM> millimeter (mm), <NUM>, and <NUM> positions along the X axis) each similar to the backlight device shown in <FIG>. In this case, the optical distance (OD), which is the distance traveled by light multiplied by the refractive index of the medium, is as thin as <NUM> while the target full width at half maximum (FWHM) (describing the width of the curve in the TF as the distance between points on the curve at which the function reaches half its maximum value) is <NUM>. There are three hot spots of fairly intense light shown in the TF above the center positions of each of the three light sources/backlight devices (at -<NUM>, <NUM>, and <NUM>). Thus, a backlight device using the lens described in <FIG> creates an unsatisfactorily non-uniform light distribution pattern on the illumination field, as shown in <FIG>.

<FIG> is a diagram of the luminance (in units of candela per square meter, cd/m<NUM>) versus position for the three backlight devices used in <FIG>. As in <FIG>, the three backlight devices (LED light source and lens) used in <FIG> have center positions respectively at <NUM>, <NUM> and -<NUM>. The OD is <NUM>, and the LED pitch, which is the relative distance between adjacent LEDs/backlight devices, is <NUM>. The hot spot above each LED is still intense even with the cross absorption and refraction of light by the lens of the backlight devices.

Referring to <FIG>, a cross-sectional view of an example light emitting device <NUM> (e.g., a backlight device) is shown, in accordance with the disclosure herein. The backlight device <NUM> may include, but is not limited to include, the following components: a lens <NUM>, including a light incident surface <NUM> (also referred to as an inner curved surface <NUM>) and a light exit surface <NUM> (or outer curved surface <NUM>), a first cylindrical portion <NUM>, a second convex portion <NUM>, and a recessed portion <NUM>; an LED light source <NUM> coupled to the lens <NUM>; an annular mounting surface <NUM> coupled to the lens <NUM> and the LED light source <NUM>; a coating portion <NUM> covering at least a portion of the mounting surface <NUM>; and/or a diffuser plate <NUM> at the OD from the LED light source <NUM>. The LED light source <NUM> is at the center of circular (X, Y, Z) coordinates.

The lens <NUM> may include a light incident surface <NUM> and a light exiting surface <NUM> opposite to the light incident surface <NUM>. Light generated by the LED light source <NUM> is refracted into the lens <NUM> through the light incident surface <NUM> and then refracted out of the lens <NUM> from the light exit surface <NUM>. The lens <NUM> has an optical axis Z extending through the light incident surface <NUM> and the light exit surface <NUM>. The light incident surface <NUM> and the light exit surface <NUM> each are radially symmetrical with respect to the optical axis Z of the lens <NUM>. The optical axis of the LED light source <NUM> is coincident with the optical axis Z of the lens <NUM>.

The lens <NUM> further includes an annular mounting surface <NUM> that interconnects the light incident surface <NUM> and the light exit surface <NUM>. The light incident surface <NUM> is located at a center of the mounting surface <NUM> and recessed inwardly towards the light exit surface <NUM> from an inner periphery of the annular mounting surface <NUM>. The light incident surface <NUM> may be a part of an ellipsoid, a sphere, a paraboloid or a continuous spline curve that is machinable (i.e., producible with machinery). The light exit surface <NUM> includes a first cylindrical portion <NUM> extending upwardly from an outer periphery of the mounting surface <NUM> and a second convex portion <NUM> bending inwardly and upwardly from a top periphery of the first cylindrical portion <NUM>. The second convex portion <NUM> includes a recessed portion <NUM> at the central region that recesses inwardly toward the light incident surface <NUM> of the lens <NUM>.

Light generated from the LED light source <NUM> is refracted into the lens <NUM> through the light incident surface <NUM>, and mostly refracted out of the lens <NUM> from the light exit surface <NUM> to the light field at the diffuser plate <NUM>. However, a part of the refracted light impinging on the light exit surface <NUM> with an incident angle larger than a critical angle for total internal reflection at the lens-air interface (at the light exit surface <NUM>) is reflected back into the lens <NUM> due to total internal reflection. For example, if the lens <NUM> is made of polymethyl methacrylate (PMMA) material, the refractive index of the lens <NUM> is <NUM>, and the critical angle for the total internal reflection at the lens-air interface (at the light exit surface <NUM>) is <NUM> degrees.

As described above, the portion of the refracted light with an incident angle smaller than <NUM> degrees is refracted out the lens <NUM> from the light exit surface <NUM> of the lens <NUM>, and directs to the center of the light field along path <NUM>. In an example scenario, outside the scope of the present invention, where the backlight device <NUM> does not have a coating portion <NUM> on annular mounting surface <NUM>, then the portion of the refracted light with an incident angle larger than <NUM> degrees is reflected by the light exit surface <NUM> due to the total internal reflection, along paths <NUM> and <NUM>, which is mostly reflected to the outer part of the annular mounting surface <NUM> and then reflected to the center of the light field at the diffuser plate <NUM>, thereby creating a sharp peak of light distribution, which may not meet wider TF requirements. Thus, the backlight device <NUM> without a coating portion <NUM> creates a non-uniform light distribution.

In another example scenario, within the scope of the present invention, the lens <NUM> of the backlight device <NUM> includes a coating portion <NUM> on the annular mounting surface <NUM>. The coating portion <NUM> is provided on a portion of the annular mounting surface <NUM>, and the length of the coating portion <NUM> may vary according to the application. In an example, the coating portion <NUM> may be a black coating that absorbs all colors of light refracted onto the annular mounting surface <NUM>, or may be any other colored coating that only reflects light with the same color as the coat and absorbs all other colors of light. For example, for a blue coating for coating portion <NUM> on the annular mounting surface <NUM>, only blue light will be reflected or transmitted and all the other colored light from the light source <NUM> is absorbed by the coating portion <NUM>. In another example, for a yellow coating portion <NUM>, only yellow light is refracted and all the other colored light from the light source <NUM> is absorbed by the coating portion <NUM>.

In another example, the coating portion <NUM> may be a partially absorbing coat, meaning only a certain ratio of light is absorbed by the coating portion <NUM> and all the other light is reflected or transmitted. The partially absorbed light may be of a single color, a plurality colors or all the colors emitted from the LED light source <NUM>. The light that is not absorbed by the coating portion <NUM> may be reflected or transmitted, and will partially add to the center light intensity of the light field at the diffuser plate <NUM>. For example, a partially absorbing coating portion <NUM> may absorb light at a ratio of <NUM>%~<NUM>%, or below <NUM>%, depending on the real TF of the lens <NUM> and the needs of the targeted application.

In another example, outside the scope of the present invention, the coating portion <NUM> may cover the entire annular mounting surface <NUM>. In this case, a part of the refracted light with an incident angle larger than <NUM> degrees is absorbed or refracted by the coating portion <NUM>, thus attenuating the light along paths <NUM> and <NUM>. In an example, a backlight device <NUM> using a coating portion <NUM> can create a uniform light intensity distribution pattern on the light field at the diffuser plate <NUM> and eliminate the "hot spot" effect (e.g., removing the light hot spot shown in <FIG>).

Moreover, with reference to path <NUM> in <FIG>, the refracted light with an angle smaller than <NUM> degrees is refracted out the lens from the light exit surface <NUM>, and is directed toward the center of the light field at the diffuser plate <NUM>. As is the case for an LED light source <NUM>, the color of light in narrow angle may be a little bluish compared to the color of wider angle light from the LED light source <NUM>. Thus, if the coating portion <NUM> on the annular mounting surface <NUM> is yellow, the reflected and transmitted light from the yellow coating portion <NUM> may also be directed to the center of the light field at the diffuser plate <NUM> and can compensate the bluish light coming from path <NUM> to produce a white light distribution on the diffuser plate <NUM>.

<FIG> is a three-dimensional (3D) perspective (underside) view of the example backlight device <NUM> with optical lens <NUM> shown in <FIG>. With reference to <FIG>, the backlight device <NUM> includes a lens <NUM> coupled to an annular mounting surface <NUM> and coupled to the LED light source <NUM>. The ring on the bottom of the annular mounting surface <NUM> is the coating portion <NUM>, and may vary in color, size, length, and absorption ratio, among other things, depending on the intended application of the backlight device <NUM>, as described herein.

<FIG> is a diagram the TFs of the normalized luminance generated by the backlight device <NUM> in <FIG>, shown by a solid line, and the normalized luminance generated by the backlight device <NUM> of <FIG> (with coating portion <NUM>), shown by a dashed line. The optical axis Z of the LED light source (<NUM> and <NUM>) of the backlight devices (<NUM> and <NUM>) extends through the projected plane at the <NUM> position of the x axis (and y axis). For the TFs shown in <FIG>, the OD <NUM> and the target FWHM is <NUM>. <FIG> illustrates that the center of light intensity (i.e., the peak of the TF) is greatly decreased using the lens <NUM> and backlight device <NUM> according to <FIG>, in comparison to the lens <NUM> and backlight device <NUM> of <FIG>. Thus, the backlight device <NUM> of <FIG> provides a more uniform distribution of light at the diffuser plate <NUM>.

Referring to <FIG>, a cross-section view of another example backlight device <NUM> is shown, in accordance with the disclosure herein. The backlight device <NUM> may include, but is not limited to include, the following components: a lens <NUM>, including a light incident surface <NUM> and a light exit surface <NUM>, a first cylindrical portion <NUM>, a second convex portion <NUM>, and a recessed portion <NUM>; an LED light source <NUM> coupled to the lens <NUM>; an annular mounting surface <NUM> coupled to the lens <NUM> and the LED light source <NUM>; a structure <NUM> mounted on at least a portion of the annular mounting surface <NUM>; and/or a diffuser plate <NUM> at the OD from the LED light source <NUM>. The LED light source <NUM> is at the center of circular (X, Y, Z) coordinates.

The structure <NUM> may be mounted on part of the annular mounting surface <NUM> and may scatter and redirect light that would otherwise travel along paths <NUM> and <NUM> without structure <NUM> in other directions. In an example, a coating portion (e.g., using any of the coating techniques described with respect to <FIG>), not shown, may be included on structure <NUM> to further enhance the refractivity of light. In an example, the structure <NUM> may be made out of any material, including, but not limited to, the following example materials: PMMA, silicon, aluminum, and/or silicon carbide. The structure <NUM>, with or without a coating, may redirect the light away from its default path. In an example, a portion of the light is reflected and refracted from the structural portion <NUM> of the optical lens <NUM> so that luminance uniformity of the backlight device <NUM> is increased.

<FIG> is a 3D perspective view of the example backlight device <NUM> with optical lens <NUM> shown in <FIG>. With reference to <FIG>, the backlight device <NUM> includes the lens <NUM> coupled to the annular mounting surface <NUM> and coupled to the LED light source <NUM>. The ring on the bottom of the annular mounting surface <NUM> is the structure portion <NUM>, and may vary in color, size, length, and coating, among other things, depending on the intended application of the backlight device <NUM>.

Claim 1:
A light emitting device (<NUM>, <NUM>, <NUM>, <NUM>) comprising:
- a light source (<NUM>, <NUM>, <NUM>, <NUM>) coupled to an annular mounting surface (<NUM>), and configured to emit light in an angular distribution about an optical axis (Z); and
- a lens (<NUM>, <NUM>, <NUM>, <NUM>) coupled to and located above the light source, and configured to redistribute the light emitted from the light source into a uniform light intensity distribution pattern on a light field above the light emitting device;
the lens including a concave inner curved surface (<NUM>, <NUM>, <NUM>, <NUM>) that faces the light source,
the lens including the annular mounting surface (<NUM>, <NUM>, <NUM>) that is substantially orthogonal to the optical axis and extends radially outward from a periphery of the concave inner surface,
the lens including an outer curved surface (<NUM>, <NUM>, <NUM>, <NUM>) that faces away from
the light source and adjoins the annular mounting surface at the outer periphery of the annular mounting surface,
the outer surface including a cylindrical portion (<NUM>, <NUM>, <NUM>) positioned adjacent to the annular mounting surface, such that all locations on the cylindrical portion are substantially equidistant from the optical axis, the inner curved surface and the outer curved surface being radially symmetrical with respect to the optical axis;
characterized in that
the annular mounting surface (<NUM>) of the lens includes a coated annular region (<NUM>) on which a coating is disposed, wherein the coating is configured to absorb at least a portion of the light inside the lens that strikes the coated annular region;
an uncoated inner annular region between the coated annular region and the concave inner surface; and
an uncoated outer annular region between the coated annular region and an outer periphery of the planar surface.