Patent Description:
Lenses are commonly used to alter the shape of the illumination/radiation pattern produced by a light source. Elongated illumination patterns are often required for camera flash lamps, vehicle head lamps, street lighting, and so on.

discloses a lens that provides an elongated illumination pattern for a vehicular lamp by increasing the divergence of light from a light emitting device along one axis. To compensate for the greater intensity of light when viewed from the center of the light emitting source, compared to the off-center intensity, the lens includes a concave portion about an optical center of the light emitting device, and a convex portion on either side of the optical center, the convex portions having a larger emission surface than the concave portion. The resultant lens is "peanut shaped", the concave portion corresponding to the narrowed center portion of a peanut shell.

<CIT>discloses a lens with an outer area and a concave central area wherein both the central area and the outer area are in the form of a rectangle with rounded corners.

<FIG> illustrate an example peanut shaped lens <NUM> that provides an elongated illumination pattern from a single light source that emits a Lambertian radiation pattern. <FIG> is a perspective view that illustrates the peanut shape having a narrowed center region <NUM> separating two larger lobes <NUM>. The illustrations are not to scale, and may include exaggerated features for ease of illustration and explanation. In some embodiments, the difference in size/volume between the larger lobes <NUM> and the smaller center region <NUM> may be substantially less than illustrated in these figures.

<FIG> illustrates a top view of the peanut shaped lens of <FIG>, while <FIG> illustrate cross-section views taken along views C-C and D-D, respectively, of <FIG>. The view C-C is taken along the long axis <NUM>, and the view D-D is taken along the short axis <NUM>. As illustrated in <FIG>, the larger lobes <NUM> form a convex surface, and the center region <NUM> forms a concave structure, as viewed along cross-section C-C. As illustrated in <FIG>, the cross-section of the center region <NUM> forms a convex surface. This convex cross-section extends for the entire length of the lens through the long axis <NUM> of the lens, include the larger lobes <NUM>, the radius of the convex surface changing accordingly. Light source <NUM> may be a semiconductor light emitting device (LED), or a plurality of light emitting devices, and may be arranged within a recess of the lens or situated on or near the lower surface of the lens.

<FIG> illustrate the light propagation through the lens <NUM> with respect to each axis <NUM>, <NUM>, respectively. As disclosed, the lens <NUM> includes a concave lens portion <NUM> and two convex lens portions <NUM> on either side of the concave lens <NUM>. Each of these lens portions provide an optical axis with respect to the light source <NUM>. The concave lens portion <NUM> provides optical axis <NUM>, and each of the convex lens portions <NUM> provides an optical axis <NUM>. Each optical axis <NUM> extends from the light source <NUM> through the center of curvature <NUM> of the convex len potions <NUM>. The concave lens <NUM> serves to disperse the light emitted from the light source <NUM> away from the optical axis <NUM>, forming an elongated light emission pattern along the long axis <NUM>. Each of the convex lenses <NUM> serve to converge the light toward its respective optical axis <NUM>, which results in an elongated light emission pattern along the long axis <NUM>. By proper selection of the size and curvatures of the lenses <NUM>, <NUM>, a uniformly illuminated elongated light emission pattern may be formed.

The cross section of the lens <NUM> relative to the short axis <NUM> forms a convex lens <NUM>. The cross section taken along any point on the long axis <NUM> forms a similarly shaped convex lens, as indicated by the dashed line <NUM>', the size being relative to the height and width of the lens <NUM> along the long axis <NUM>. As illustrated, the convex lens <NUM> serves to concentrate/ collimate the light from the light source <NUM>, forming a relatively narrow light emission pattern along the short axis <NUM>. The convex lens <NUM>' will similarly concentrate/ collimate the light from the light source <NUM>, maintaining a narrower light emission pattern along the short axis <NUM>.

The overall emission pattern formed by the lens <NUM> is long in one axis, and narrow in the other axis, forming a substantially rectangular, or oval illumination pattern. However, the complex shape of the lens <NUM> introduces interdependencies between the parameters in each dimension. For example, if a wider illumination pattern is desired relative to the short axis (<FIG>), the radius of curvature of the convex lens <NUM> may need to be decreased. This change of shape of the lens <NUM> may limit the feasible shapes of the lenses <NUM>. Constraints on the physical size of the lens as well as methods of forming a suitable mold may also limit the shape of the lens.

It would be advantageous to provide a lens that provides an elongated illumination pattern that allows for greater independence with regard to the shape of the illumination pattern in each axis. It would be advantageous, for example, to provide a lens that provides a substantially rectangular or oval illumination pattern with greater independence of control of each dimension of the rectangle/oval.

To better address one or more of these concerns, the present invention is provided according to claim <NUM>.

In a non-claimed embodiment an elongated lens is formed with an elongated trough along the long axis on the light emitting surface of the lens. The elongated lens may include a curved wall about its perimeter, and a smooth transition between the curved wall and the trough. The trough may include a concave shape along both the long axis and the short axis, although the radius of curvature of the concave shape may differ between the long and short axes. The eccentricity of the illumination pattern may be controlled by the size of the trough and these radii of curvature.

A light emitting device may be formed by providing a light emitting element and an elongated lens having a short axis, a long axis, and an upper surface through which desired light from the light emitting element is emitted; wherein the upper surface of the lens includes a trough that extends along the long axis, and a perimeter of the lens includes a curved wall.

The trough may be symmetric about the short axis and/or the long axis with respect to an optical axis of the light emitting element. There may be a smooth transition joining the trough to the curved wall, and at least a portion of the curved wall may be reflective.

The lower surface of the trough may have a curvature along the short axis that differs from a curvature along the long axis, and may have a perimeter that is substantially oval. In like manner, the perimeter of the lens may be substantially oval. The oval perimeter may also be truncated in the long or short dimension.

The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:.

Throughout the drawings, the same reference numerals indicate similar or corresponding features or functions. The drawings are included for illustrative purposes and are not intended to limit the scope of the invention.

In the following description, for purposes of explanation rather than limitation, specific details are set forth such as the particular architecture, interfaces, techniques, etc., in order to provide a thorough understanding of the concepts of the invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments, which depart from these specific details. In like manner, the text of this description is directed to the example embodiments as illustrated in the figures, and is not intended to limit the claimed invention beyond the limits expressly included in the claims. For purposes of simplicity and clarity, detailed descriptions of well-known devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

For ease of explanation and understanding, directions and/or orientations are specified with reference to a "top-emitting" light emitting device, wherein, for example, light is assumed to propagate 'up' from a light source then exit from an "upper surface" of the lens, opposite the location of the light source. Typically the light source will be a parallelepiped where two of the surfaces will be larger than the other four. One of the larger surfaces is designated as the "top" of the light emitting device. The four smaller surfaces are the "side surfaces" of the light emitting device which typically emit little or no light. Most of the light is emitted from the "top" of the light emitting device. The "upper surface" of the lens is opposite the "top" of the light emitting device.

Some light may exit the 'side surfaces' of the lens i.e. the portions of the lens opposite the "side surfaces" of the light emitting device. The lens of this invention is designed such that a substantial majority of the light from the light source exits the upper surface, in contrast to lenses that are designed to create side-emitting devices that emit a substantial majority of the light through surfaces that are not directly opposite the light source.

<FIG> illustrate an example light emitting device that includes a light source <NUM>, and an elongated lens in accordance with aspects of this invention. The light source <NUM> may include a single light emitting element, such as a light emitting diode, or multiple light emitting elements.

In any of the described embodiment the lens may be made of epoxy, silicone, sol-gel, glass or compounds, mixtures, or hybrids thereof. The index of refraction at the wavelength of the light source may range from <NUM> to <NUM>. High index nano-particles with particle sizes less than <NUM> and preferably less than <NUM> dispersed in silicone or a silicate binder may be used to enhance or tune the index of refraction of the lens. Details of the materials can be found in <CIT>.

In one embodiment the light source may be a light emitting diode (LED) with a dimension ranging from <NUM> to <NUM>. The lens may have an outside dimension ranging from <NUM> to <NUM> times the dimension of the LED. The aspect ratio of the long to short dimension of the lens can range from <NUM> to <NUM>.

<FIG> illustrates a perspective view of the elongated lens <NUM>. <FIG> illustrates a top view of the elongated lens <NUM>, through which light is emitted. <FIG> illustrates a cross section view C-C taken along the long axis <NUM>. <FIG> illustrates a cross section view D-D taken along the short axis <NUM>. The perimeter <NUM> of the lens <NUM> is an oval shape with long and short dimensions. The perimeter <NUM> has curved ends along the short dimension and straight lines along the long dimension. In the alternative, not covered by the claims, the straight lines may have a convex curvature so as to form, for example, an elliptical perimeter.

As illustrated, the lens <NUM> includes a trough <NUM> formed in the upper surface <NUM>. For the purposes of this disclosure, a trough is defined as a depression in the upper surface <NUM>, along an axis of the lens <NUM> that is shorter than the length of the lens along that axis. The trough <NUM> may have an oval shape with a long dimension and a short dimension. The ratio of the dimension of the trough may be the same or different than the ratio of the long and short dimensions of the lens <NUM>, and the perimeter <NUM> of the trough <NUM> may be similar in shape to the perimeter <NUM> of the lens <NUM>. As detailed further below, to provide a continuous dispersion of the light emitted from the light source <NUM>, the perimeter <NUM> of the lens <NUM> may include a curved wall <NUM>, and there may be a smooth transition <NUM> between the curved wall <NUM> and the trough <NUM>. Similarly, the trough <NUM> may include curved surfaces <NUM>. For ease of explanation and understanding the term "upper surface <NUM>" is used herein to refer to the surface of trough <NUM>, the surface of curved portions <NUM> and <NUM>, and the surface of the curved portion of the curved wall <NUM>, collectively the surface of the lens <NUM> emitting the desired light.

The lens <NUM> includes a base <NUM>, which may include a recess for receiving the light source <NUM>; alternatively, the light source <NUM> may be flush with the base or slightly below the base <NUM>. Light source <NUM> may include a reflector, a reflector cup, or a reflector ring.

One of skill in the art will recognize that discontinuous surfaces may be used, but in general, a smooth continuous surface is preferred to provide an illumination pattern that does not include abrupt transitions in illumination intensity. However, if abrupt transitions are desirable, discontinuous surfaces may provide the desired illumination pattern. The lens <NUM> may be formed via a mold that provides the shapes of the lens <NUM>, including the trough <NUM>. Other techniques for forming the lens <NUM> are feasible, including milling the trough <NUM> out of a preformed elongated lens.

As illustrated in <FIG>, the trough <NUM> introduces a lower elevation of the lens <NUM> at or near the optical axis <NUM>, and a higher elevation on the upper surface <NUM> of the lens <NUM>.

In the example cross-section C-C of <FIG>, a lower surface <NUM> of the trough <NUM> may be nearly flat near the optical axis <NUM>, then curves upward <NUM> toward the higher elevation of the upper surface <NUM>. This substantially flat region 315C may introduce more loss of the light emitted by the light source <NUM> than a more sharply shaped convex region. Light striking the flatter region 315C of the depression <NUM> at greater than a critical angle will be totally internally reflected (TIR) away from the region 315C, thereby increasing the likelihood of the light being absorbed in the device.

In the example cross-section D-D of <FIG>, the lower surface <NUM> of the trough <NUM> along the short axis <NUM> provides a concave shape 315D, which also disperses light from the light source <NUM>, but not as far spatially because the convex lobes <NUM> are more closely spaced along the short axis <NUM> than for the long axis <NUM>.

The degree of dispersion of the light in the center region of the lens <NUM> is determined by the shape (length, width, depth, shape) of the trough <NUM>, including the radius of curvature of the lower surface <NUM> along each axis <NUM>, <NUM>. The surface <NUM> along the cross-section C-C includes three radii of curvature, a radius of curvature for each of the curved portions <NUM>, and a radius of curvature for the center portion 315C, which may be very large. The surface <NUM> along the cross section D-D includes the radius of curvature of concave portion 315D. In this example, the degree of dispersion will be greater along the long axis <NUM>, and the total internal reflection at the surfaces <NUM> may augment the illumination intensity at angles farther from the optical axis <NUM>.

<FIG> illustrate the propagation of light through the lens <NUM> relative to the long axis <NUM> and short axis <NUM>, respectively.

As illustrated in <FIG>, the cross section shape along the long axis <NUM> comprises a concave lens 410A and two convex lens portions <NUM>. The concave lens portion 410A will disperse the light away from the optical axis <NUM>, albeit to a lesser extent than it would if the convex lens portions <NUM> were more widely spaced apart. The two convex lens portions <NUM> converge the light toward their corresponding optical axes <NUM>.

The overall effect of the lens portions 410A, <NUM> is an elongation of the illumination pattern along the long axis <NUM>. The extent of the elongation may be controlled by the orientation of the optical axes <NUM>, the centers of curvature <NUM>, as well as the radii of curvature for each of the lens portions 410A, <NUM>, and other parameters related to the shape of the profile along the long axis <NUM>.

As illustrated in <FIG>, the cross section shape along the short axis <NUM> comprises a concave lens portion 410B and two convex lens portions <NUM>. Of particular note, although both the concave lens portion 410A (<FIG>) and the concave lens portion 410B are formed by the trough <NUM> (<FIG>), the shape of each lens portion 410A, 410B are substantially independent of each other. In this example, lens portion 410A is flatter than lens portion 410B, which is continually curved.

In like manner, the two convex lens portions <NUM> of <FIG> may differ substantially from the convex lens portions <NUM> of <FIG>. Although in this example, the lens portions <NUM> and <NUM> are somewhat similar, one of skill in the art will recognize that the surface <NUM> (<FIG>) that forms these lens portions <NUM>, <NUM> need not be uniformly thick around the lens <NUM>, nor uniformly tall. One of skill in the art will recognize that illumination analysis programs may be used to determine the appropriate shape for transitioning between such differing shapes.

As in <FIG>, the extent and uniformity of the illumination pattern relative to the short axis <NUM> may be controlled by the orientation of the optical axes <NUM> of the convex lens portions <NUM>, the centers of curvature <NUM> of these lenses <NUM>, as well as the radii of curvature for each of the lenses 410B, <NUM>, and other parameters related to the shape of the profile along the short axis <NUM>.

One of skill in the art will recognize that the particular shape of the trough, as well as the overall shape of the lens, will be based on the desired light illumination pattern, as well as the intensity distribution. In some embodiments, for example, it may be desirable to provide uniform intensity near the center of the illumination pattern, tapering off, gradually or more sharply, at a given off-axis angle in each dimension. Conventional light propagation and illumination analysis tools may be used to determine a combination of shapes in each dimension that produces the desired illumination pattern and intensity distribution.

<FIG> illustrate another example light emitting device that includes an elongated lens in accordance with aspects of this disclosure. As contrast to the lens <NUM>, which includes a substantially oval perimeter and substantially oval trough <NUM>, the lens <NUM> of <FIG> includes a substantially elliptical profile and substantially elliptical trough <NUM>.

For the purposes of this disclosure, the term oval is used to describe an elongated shape having a curved perimeter, including elliptical or other shapes. For ease of explanation and understanding the term "upper surface <NUM>" is used herein to refer to the surface of trough <NUM>, the surface of curved portion <NUM>, and the surface of the curved portion of the curved wall <NUM>, collectively the surface of the lens radiating the desired light.

As illustrated, the curved wall <NUM>, having no linear portions, forms a substantially elliptical perimeter of the lens <NUM>, and the trough <NUM> also has substantially elliptical perimeter. In this example, the lower surface <NUM> provides a substantially continuous concave profile 515C in the long axis <NUM>, and a substantially continuous concave profile 515D in the short axis <NUM>. The profile 515C along the long axis <NUM> may correspondingly provide a more disperse emission pattern from the center of the lens <NUM> with less loss than the flatter profile 315C of lens <NUM>. One of skill in the art will recognize, however, that portions of the lower surface <NUM>, in either axis, may be less curved, to increase the intensity of light at the center of the lens <NUM>.

As noted above, conventional light propagation analysis tools may be used to determine the shape of the lens, the shape of the trough, the radii of curvature within the trough, as well as the radius of curvature of the curved wall <NUM>, and the radii of curvature forming the smooth transition between the curved wall <NUM> and the trough <NUM>.

<FIG> illustrate other example elongated lenses with troughs in accordance with aspects of this disclosure. Each of these example lenses include features that augment the light emission pattern produced by the lenses conforming to those (<NUM>, <NUM>) of <FIG> and <FIG>, as well as other shapes conforming to the principles of this disclosure. These features may serve to provide a more uniform light distribution, for example, by further dispersing light emitted from areas that might otherwise form "bright regions", or "dark regions" on a lens without these features. One of skill in the art will recognize that fewer or more features, in different sizes and shapes than illustrated may be used to achieve a desired illumination pattern.

The dimensions of each feature, including its radius of curvature, its position and orientation on the main body of the lens, and the characteristics of the main body of the lens itself will determine how these features may affect the illumination pattern provided by the lens with these features. In each embodiment, conventional computer-aided-design tools, and/or light propagation analysis tools may be used to determine the effect that the shape and dimensions of each augmentation/feature will have on the resultant light emission pattern produced by the lenses.

In <FIG>, the features <NUM> are added to a lens <NUM> that includes a trough <NUM> that has a perimeter <NUM> that is similar in shape to the perimeter <NUM> of the lens <NUM>. ; and in <FIG>, the features <NUM> are added to a lens <NUM> that has a trough <NUM> that has a perimeter <NUM> that is different in shape from the perimeter <NUM> of the lens <NUM>.

In these examples, the lens <NUM> includes a trough <NUM> that is shorter and deeper that the trough <NUM> of lens <NUM>, such that it affects the profile of the lens, as illustrated in <FIG>, serving to illustrate that the particular arrangement of the trough with respect to the main body of the lens may vary, depending upon the desired illumination pattern. Features <NUM> and <NUM> may be convex dimples, each having a surface that is a portion of the surface of sphere or the surface of an ellipse.

In <FIG>, a convex feature <NUM> is added at the center of the trough <NUM> of lens <NUM>, and in <FIG>, a concave feature (dimple) <NUM> is added at the center of the trough <NUM> of lens <NUM>. One of skill in the art will recognize that the features <NUM> or <NUM> may be a flat surface as well. Features <NUM> and <NUM> may each have a surface that is a portion of the surface of sphere or the surface of an ellipse.

In each of the <FIG>, the features are illustrated as having sharp edges where they intersect the main body of the lens; one of skill in the art will recognize, however, that a smooth transition from the main body to each feature may provide for a more uniform illumination pattern.

For example, it is possible to operate the invention in an embodiment wherein the lower surface of the lens as well as the upright portions of the curved wall are reflective, thereby reducing absorption losses and/or light propagation in unwanted directions. The transition between the convex and concave regions of the lens (e.g. <NUM> of lens <NUM> in <FIG>) may also be reflective, to augment the total internal reflection (TIR) in these regions. The concave region may also be entirely or partially coated with reflective material to increase total internal reflection.

Claim 1:
A light emitting device comprising:
a light emitting element (<NUM>); and
an elongated lens (<NUM>) having a short axis (<NUM>), a long axis (<NUM>), and an upper surface (<NUM>) through which a substantial majority of the light from the light emitting device is emitted; the upper surface (<NUM>) of the lens being smooth and continuous and including a curved wall (<NUM>, <NUM>) and a trough (<NUM>) that extends along the long axis of the lens, the trough having a concave shape (315C) along the long axis of the lens and a concave shape (315D) along the short axis of the lens; and wherein
the perimeter (<NUM>) of the lens is an oval shape with long and short dimensions, having curved ends along the short dimension and straight lines along the long dimension, and wherein
at least a portion of the curved wall (<NUM>, <NUM>) is reflective.