LED unit

An LED unit includes an LED and an envelope receiving the LED therein. The envelope includes a bottom substrate fixing the LED thereon, a sidewall angling upwardly from the substrate and surrounding the LED, and a lens formed in the sidewall and located above the LED. The lens has two aspheric surfaces with different curvatures to collect light deflected at a small angle relative to an axis of the LED into a parallel pattern. The sidewall has upper and lower conical inner circumferences and a parabolic outer circumference to direct light deflected at a large angle relative to the axis of the LED into parallel pattern. The lower inner circumference of the sidewall has an angle of 2π/5 to 13π/30, and the upper inner circumference of the sidewall has an angle of 5π/36 to 7π/36.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to light emitting diode (LED) units and, more particularly, to an LED unit comprising a lens having two aspheric surfaces.

2. Description of Related Art

LEDs, available since the early 1960's, have been increasingly used in a variety of applications, such as residential, traffic, commercial, and industrial settings, because of high light-emitting efficiency. A typical LED includes an LED die emitting light and a transparent encapsulant enveloping the LED die. The encapsulant protects the LED die from contamination and damage, and acts as a lens. However, due to size limitations of the encapsulant, the light cannot be significantly converged. The divergent light results in limited brightness of the LED. Therefore, light-adjusting devices, such as a catadioptric light distribution system, are utilized for further collimation of the light from the LED.

A typical catadioptric light distribution system includes a reflector mounted below and surrounding the LED, and a convex lens mounted above the LED. The reflector reflects light toward the lens from a perimeter of the encapsulant. The lens consolidates light emitted from the LED and reflected by the reflector into a single beam. Using the catadioptric light distribution system, most of the light emitted from the LED can be converged, and the brightness of the LED is increased.

However, since the lens of the catadioptric light distribution system is often spherical, the lens cannot effectively culminate the light into a narrow beam. The light incident on an opposite surface of the lens, after passing through the spherical surface of the lens, is still divergent, resulting in a scattered light beam, oriented away from the lens, and thus unsuitable for long-distance illumination.

What is needed, therefore, is an LED unit which can overcome the limitations described.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring toFIGS. 1 and 3, an embodiment of an LED unit includes an LED10(seeFIG. 3) and a catadioptric light distribution system20seating the LED10. The catadioptric light distribution system20has an optical axis parallel with that of the LED10. The LED10may be any LED, but an LED capable of emitting white light with high brightness is preferred The LED10includes a rectangular base12with an LED die14fixed on a top thereof and an encapsulant16enveloping the LED die14and fixed on the top of the base12. The encapsulant16may be dome-shaped, thereby acting as a primary convex lens to collimate the light emitted from the LED die14into a drop-like pattern.

Also referring toFIG. 2, the catadioptric light distribution system20may be integrally made of a light-permeable material, such as PC or PMMA. The catadioptric light distribution system20includes a substrate22, a sidewall24angling upwardly from a periphery of the substrate22and a lens26formed within the sidewall24. An outer circumferential surface of the sidewall24is coated with a light reflective material. The substrate22is circular with a central hole220defined through the substrate22and surrounded by an annulus222. Four triangular cutouts224may be defined in the annulus222, around and communicating with the central hole220, cooperatively defining a rectangular space (not labeled). The four cutouts224each have a depth less than a thickness of the substrate22for receiving the base12of the LED10in the rectangular space. An inner circumferential surface of a lower portion of the sidewall24is conical having an opening facing downwardly and gradually expanding downwardly. The lower portion of the sidewall24cooperates with a bottom surface of the lens26to enclose a cavity240within the catadioptric light distribution system20. A bottom of the cavity240communicates with the central hole220of the substrate22, thereby receiving the encapsulant16of the LED10therein. The cavity240separates the encapsulant16of the LED10from the sidewall24and the lens26with an air gap so that the light emitted from the LED die14is refracted twice when incident onto the sidewall24and the lens26, wherein the light biased at a large angle with respect to an axis of the LED10(such as light I referenced inFIG. 3) is incident on the inner circumferential surface of the sidewall24, and the light deflected at a small angle with respect to the axis of the LED (such as light II referenced inFIG. 3) is incident on the bottom surface of the lens26. An inner diameter of the cavity240at a bottom thereof may be less than that of the central hole220of the substrate22, thereby forming a step242between the cavity240and the central hole220. The outer circumferential surface of the sidewall24is parabolic, totally reflecting the light from the inner circumferential surface of the sidewall24toward a top of the catadioptric light distribution system20. The top of the catadioptric light distribution system20defines a recess244surrounded by an inner circumferential surface of an upper portion of the sidewall24and above a top surface of the lens26. The inner circumferential surface of the upper portion of the sidewall24is a conical surface having an opening gradually expanding upwardly, whereby the light totally reflected by the outer circumferential surface of the sidewall24is refracted by the inner circumferential surface of the upper portion of the sidewall24into parallel light pattern. An angle of the inner circumferential surface of the upper portion of the sidewall24is less than that of the inner circumferential surface of the lower portion of the sidewall24. An angle of the inner circumferential surface of the upper portion of the sidewall24may range between 5π/36 to 7π/36. An angle of the inner circumferential surface of the lower portion of the sidewall24may range between 2π/5 to 13π/30. An annular flange246may be protruded horizontally and outwardly from a top of the sidewall24, facilitating a handle of the catadioptric light distribution system20.

The lens26may be located just above the LED10to culminate the light from the LED10into a straight beam. The bottom surface and the top surface of the lens26may be particularly configured to a first aspheric surface262and a second aspheric surface264, respectively. The second aspheric surface264has a curvature larger than that of the first aspheric surface262, both of which consolidate light having a small emergent angle from the encapsulant16of the LED10into a parallel light pattern. Due to favorable light-converging characteristics of the aspheric surfaces262,264, the light near the optical axis is collected by the lens26more concentrically to a narrow beam of relatively high intensity, able to travel a long distance without significant dissipation. In addition, due to the divisional cooperation of the lens26and the sidewall24, with the sidewall24converting the light from the LED10with a large emergent angle into parallel light by two refractions and one total reflection, and the lens26converting the light from the LED10with the small emergent angle into parallel light by two refractions, the light travelling within the catadioptric light distribution system20does not interfere with each other; thus, consistency of the light output from the catadioptric light distribution system20is ensured. Using the catadioptric light distribution system20, the light output from the LED unit is 50% concentrated within a conical angle deflected at 5° with respect to the axis of the LED unit, whereby a light-extracting efficiency of the LED unit is raised to nearly 90%.

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.