# Patent

## Title
LED unit

## Abstract

An LED unit includes an LED and a lens mounted on the LED. The lens includes a light-incident face adjacent to the LED, a light-emergent face remote from the LED, and a light-reflecting face between the light-incident face and the light-emergent face. The light-incident face includes a first light-incident face facing the LED, and the light-emergent face includes a first light-emergent face located opposite to the first light-incident face. The first light-incident face is a continuously curved face which has a curvature, along a bottom-to-top direction of the lens, firstly decreasing gradually to a first value; then increasing gradually to a second value; then decreasing gradually again to a third value; and then increasing gradually again. The light-emergent face has a first light-emergent face located above the first light-incident face and having a varied curvature.

## Background
BACKGROUND
1. Technical Field
The present disclosure relates to a light emitting diode (LED) unit and, more particularly, to an LED unit having a lens which can produce an effectively converged light beam.
2. Description of Related Art
LEDs, available since the early 1960's and because of their high light-emitting efficiency, have been increasingly used in a variety of occasions, such as residential, traffic, commercial, and industrial occasions. Conventionally, light directly output from the LED does not have a desirable pattern; therefore, a light-adjusting element, such as a lens, is used with the LED to modulate the light pattern thereof. However, a typical lens generally has a limited light-converging capability; that is, the light passing through the lens cannot be effectively converged to have a small light-emergent angle. Thus, the light pattern output from the lens may have a yellow annulus or shining annulus appearing at a periphery thereof, adversely affecting illumination effect of the lens.
What is needed, therefore, is an LED unit which can overcome the limitations described above.



BRIEF DESCRIPTION OF THE DRAWINGS
Many aspects of the present disclosure can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views.
FIG. 1 is an isometric view of an LED unit of the disclosure.
FIG. 2 is an inverted view of a lens of the LED unit of FIG. 1.
FIG. 3 shows a cross-section of the LED unit of FIG. 1, with a printed circuit board on which the LED unit is mounted.
FIG. 4 shows a curve of curvatures of a first light-incident face of the lens of FIG. 1 along different points of the first light-incident face along a bottom-to-top direction of the first light-incident face of the lens.
FIG. 5 shows a curve of curvatures of a first light-emergent face of the lens of FIG. 1 along different points of the first light-emergent face along a top-to-bottom direction of the first light-emergent face of the lens.



DETAILED DESCRIPTION OF THE EMBODIMENTS
Referring to FIGS. 1-3, an LED unit of the present disclosure is illustrated. The LED unit comprises an LED 10 and a lens 20 mounted on the LED 10. The LED 10 comprises a heat-conducting base 12, an LED die 14 mounted on a top of the base 12, and an encapsulant 16 covering the LED die 14 and fixed on the top of the base 12. The base 12 of the LED 10 is soldered on a printed circuit board 100 to conduct heat generated by the LED die 14 to the printed circuit board 100. In addition, the LED die 14 is electrically connected with the printed circuit board 100 via the base 12. The LED die 14 may be an InGaN chip, an InGaAs chip, a GaP chip or other suitable chips which could generate visible light with a desirable color. The encapsulant 16 is made of epoxy, silicon, glass or other transparent materials which have good light-permeable and water-proof capabilities. Phosphor may be doped within the encapsulant 16 to adjust the color of the light emitted from the LED die 14. The encapsulant 16 is shaped like a dome so as to collimate the light from the LED die 14 into a converged beam. The LED 10 has an optical axis I, around which the light emitted from the encapsulant 16 is symmetrical in a surrounding space.
The lens 20 is made of transparent materials such as PC (polycarbonate) or PMMA (polymethyl methacrylate). The lens 20 comprises an optical member 22, two opposite substrates 24 extending downwardly from a bottom face of the optical member 22 for supporting the optical member 22, and a flange 26 extending outwardly from a circumference of a top of the optical member 22, for being pressed by a clip (not shown) against the printed circuit board 100 to thereby secure the lens 20 on the printed circuit board 100. A cavity 220 is defined in an interior of the lens 20 by recessing upwardly from a bottom of the lens 20. The cavity 220 defines an opening (not labeled) at the bottom face of the optical member 22. When the lens 20 is assembled to the LED 10, the LED die 14 and the encapsulant 16 are received in the cavity 220, and the base 12 is sandwiched between the two substrates 24. The cavity 220 has a shape like a round column An inner face of the lens 20 facing the encapsulant 16 of the LED 10 functions as a first light-incident face 2201 of the lens 20 to receive the light emitted from the LED 10 with a small light-emergent angle (such as light A shown in FIG. 3). Another inner surface of the lens 20 surrounding the encapsulant 16 of the LED 10 functions as a second light-incident face 2202 of the lens 20 to receive the light emitted from the LED 10 with a large light-emergent angle (such as light B shown in FIG. 3).
The first light-incident face 2201 is curved and protrudes downwardly towards the LED 10, and the second light-incident face 2202 is a circumferential face of a round column The first light-incident face 2201 and the second light-incident face 2202 cooperatively form a light-incident face 200 to refract all of the light of the LED 10 into the lens 20. The first light-incident face 2201 is rotationally symmetrical relative to the optical axis I of the LED 10. Referring to FIG. 4 also, a length of the first light-incident face 2201 from a bottom to a top of the first light-incident face 2201 of the lens 20 is assumed to be 1 L. The first light-incident face 2201 has a curvature firstly decreasing gradually from a bottom (first position) towards a top end thereof; at a second position which is away from the bottom of the first light-incident face 2201 for about 20% of the length (0.2 L) of the first light-incident face 2201, the curvature starts to increase gradually; at a third position which is away from the bottom of the first light-incident face 2201 for about 50% of the length (0.5 L), the curvature starts to decrease gradually again; and then at a fourth position which is away from the bottom of the first light-incident face 2201 for about 80% of the length (0.8 L) of the first light-incident face 2201, the curvature starts to increase gradually again till reaching the top end of the first light-incident face 2201, which is designated as the fifth position. In the embodiment of this disclosure, the first light-incident face 2201 has a curvature of 0.0242 mm−1 at the first position (0 L), a first curvature of 0.0057 mm−1 at the second position (0.2 L), a second curvature of 0.025 mm−1 at the third position (0.5 L), a third curvature of 0.1964 mm−1 at the fourth position (0.8 L) and a curvature of 0.0382 mm−1 at the fifth position (1 L).
The optical member 22 has an upwardly-expanding bowl shape. An outer circumference of the optical member 22 functions as a light-reflecting face 300 of the lens 20 to totally reflect the light transferred from the second light-incident face 2202 towards the top of the lens 20. Alternatively, the light-reflecting face 300 can be further coated with a reflective layer (such as aluminum layer or silver layer) for promoting light reflection. The flange 26 is extended along the light-reflecting face 300. The light-reflecting face 300 is divided by the flange 26 into a first light-reflecting face 2203 and a second light-reflecting face 2204. The first light-reflecting face 2203 is conical and expands from the bottom towards the top of the lens 20. The second light-reflecting face 2204 is vertical.
The optical member 22 has a top face which is planar and circular. A center of the top face of the optical member 22 is concaved downwardly to form a columnar recessed portion 224. The recessed portion 224 is rotationally symmetrical relative to the optical axis I of the LED 10. The top face of the optical member 22 directly connects with the second light-reflecting face 2204. A protrusion 228 is protruded upwardly from a central area of a bottom face of the recessed portion 224. The protrusion 228 is shaped like a dome and has a continuously curved top face. The protrusion 228 is also rotationally symmetrical relative to the optical axis I of the LED 10. The curved top face of the protrusion 228 is located just opposite to the first light-incident face 2201. The curved top face acts as a first light-emergent face 2205 and takes charge mainly for the light transmitted from the first light-incident face 2201. The top face of the optical member 22 of the lens 20 acts as a second light-emergent face 2206 and takes charge mainly for the light totally reflected by the light-reflecting face 2203. The first and second light-emergent faces 2205, 2206 refract nearly all of the light from the LED 10 out of the lens 20 within a small light-emergent angle. In other words, the first light-emergent face 2205 and the second light-emergent face 2206 of the lens 20 cooperatively form a light-emergent face 400 to refract the light within the lens 20 towards a place above the lens 20.
Referring to FIG. 5 also, a length of the first light-emergent face 2205 from a top to a bottom thereof is assumed to be 1 S. The first light-emergent face 2205 has a curvature firstly increasing gradually from a top (first position) towards a bottom of the first light-emergent face 2205 of the protrusion 228; at a second position which is away from the top of the first light-emergent face 2205 for about 45% of the length (0.45 S) of the first light-emergent face 2205, the curvature starts to decrease gradually; at a third position which is located away from the top of the first light-emergent face 2205 for about 70% of the length (0.7 S) of the first light-emergent face 2205, the curvature starts to increase gradually again; and then at a fourth position which is located away from the top of the first light-emergent face 2205 for 95% of the length (0.95 S) of the first light-emergent face 2205, the curvature starts to decrease gradually again, within a small range, till a bottom (fifth position) of the light-emergent face 2205. In the embodiment of this disclosure, the first light-emergent face 2205 has a curvature of 0.0083 mm−1 at the first position (0 S), a first curvature of 0.182 mm−1 at the second position (0.45 S), a second curvature of 0.066 mm−1 at the third position (0.7 S), a third curvature of 0.1964 mm−1 at the fourth position (0.95 S) and a curvature of 0.1923 mm−1 at the fifth position (1 S) of the first light-emergent face 2205 of the protrusion 228.
Being adjusted by the first and second light-incident faces 2201, 2202, the first and second light-reflecting faces 2203, 2204, and the first and second light-emergent faces 2205, 2206, the light emitted from the LED 10 could be effectively converged within a small angle, thereby preventing a periphery of a light pattern output by the LED 10 via the lens 20 from being yellow or shining.
It is believed that the present disclosure and its advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the present disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments.

## Claims

1. An LED (light emitting diode) unit, comprising:
an LED; and
a lens mounted on the LED, the lens comprising a light-incident face adjacent to the LED, a light-emergent face remote from the LED, and a light-reflecting face between the light-incident face and the light-emergent face, wherein light emitted from the LED with a small angle is refracted by the light-incident face and the light-emergent face out of the LED unit, light emitted from the LED with a large angle is sequentially refracted by the light-incident face, reflected by the light-reflecting face and refracted by the light-emergent face out of the LED unit;
wherein the light-incident face comprises a first light-incident face facing the LED, and the light-emergent face comprises a first light-emergent face located opposite to the first light-incident face; and
wherein the first light-incident face is a continuously curved face which has a curvature, along a bottom-to-top direction of the lens, firstly decreasing gradually to a first value; then increasing gradually to a second value; then decreasing gradually again to a third value; and then increasing gradually again.

2. The LED unit as claimed in claim 1, wherein the curvature of the first light-incident face has a value of 0.0242 mm−1 at a bottom end of the first light-incident face.

3. The LED unit as claimed in claim 1, wherein the curvature of the first light-incident face has the first value of 0.0057 mm−1.

4. The LED unit as claimed in claim 1, wherein the curvature of the first light-incident face has the second value of 0.0648 mm−1.

5. The LED unit as claimed in claim 1, wherein the curvature of the first light-incident face has the third value of 0.025 mm−1.

6. The LED unit as claimed in claim 1, wherein the curvature of the first light-incident face has a value of 0.0382 mm−1 at a top end of the first light-incident face.

7. The LED unit as claimed in claim 1, wherein the light-emergent face further comprises a second light-emergent face surrounding the first light-emergent face.

8. The LED unit as claimed in claim 7, wherein the first light-emergent face is a curved top face of a protrusion which is shaped like a dome.

9. The LED unit as claimed in claim 8, wherein the second light-emergent face is an annular, planar face.

10. The LED unit as claimed in claim 9, wherein the first and second light-emergent faces are discontinuous from each other.

11. The LED unit as claimed in claim 7, wherein the light emitted from the LED with a large angle is refracted by the second light-emergent face out of the LED unit.

12. The LED unit as claimed in claim 11, wherein the light emitted from the LED with a small angle is refracted by the first light-emergent face out of the LED unit.

13. The LED unit as claimed in claim 1, wherein the light-reflecting face comprises a first light-reflecting face which is conical and expands upwardly along the bottom-to-top direction of the lens.

14. The LED unit as claimed in claim 1, wherein the light-incident face further comprises a second light-incident face surrounding the first light-incident face.

15. The LED unit as claimed in claim 1, wherein the first light-incident face and the first light-emergent face are both rotationally symmetrical relative to an axis.

16. The LED unit as claimed in claim 15, wherein the axis is an optical axis of the LED.

17. The LED unit as claimed in claim 1, wherein the first light-emergent face is a continuously curved face which has a curvature, along a top-to-bottom direction of the lens, firstly increasing gradually to a first value; then decreasing gradually to a second value; and then increasing gradually again.