GB2340301A - Side illuminating light emitting diode - Google Patents

Description

2340301 DESCRHMO SEDE IILLUMINATING LIGHT EMITTING DIODE The present

invention relates to light emitting diodes (LEDs).

Conventional LEDs are designed with plastics encapsulation which provides protection for the light emitting semiconductor and its electrical terminations. In addition, the refractive index of the plastic is matched to that of the semiconductor to increase the efficiency of the light emission at the semiconductor/plastic interface and usually the plastic is designed as a lens to collect and focus the light from the semiconductor chip as Wustrated by arrow A in the Fig. 1 of the accompanying drawings.

This is satisfactory for forward ffluminatingr LED's but there are some specific applications where the LED is advantageously mounted on a printed circuit board but where the light is required to be emitted from the side of the LED. An example is in the use of LED's to provide illumination for translucent panels (see arrow B in Fig. 1 of the accompanying drawings).

One object of the present invention is to improve the efficiency of light transmission in the sideways direction.

In accordance with the present invention, the plastics encapsulation of an LED is provided with a blind hole the inner end of which serves to reflect light from the LED sideways, or generally sideways, through an arc.

Preferably, the axis of the blind hole lies along the principal axis of the LED encapsulation.

2 Preferably the inner end of the blind hole forms a conical surface which serves to reflect light from the LED sideways through a 360' arc.

Advantageously, the plane of said 360 arc is at right angles to the axis of the LED lens.

Preferably, the blind hole is filled with a plastics material.

Advantageously, the plastics material within the blind bore is loaded with a pigment, preferably white, selected for optimal reflection of the light. 7 The particular dimensions and shape of the blind hole can be designed to reflect the light into a desired, not necessarily uniform, pattern.

The invention is described further hereinafter, by way of example only, with reference to the accompanying drawings, in which:- Fig. 1 illustrates diagrammatically a conventional LED mounted on a printed circuit board for side emission of light; Fig. 2 illustrates diagrammatically one embodiment of an LED in accordance with the present invention having enhanced sideways light emission; and Fig. 3 is a modified embodiment in accordance with the present invention fitted with an incandescent bulb type terminal fitting.

Fig. 1 shows a typical conventional LED 10 encapsulated in a generally cylindrical plastics housing 11 mounted on a printed circuit board 12. The two terminations for the LED extend through holes in the circuit board in this instance. The front end 14 of the plastics housing 11 for the LED is 3 approximately hemi-spherical so as to act as a lens directing light out of the LED in the axial direction A. On the other hand, light transmission in the sideways direction B from the plastics housing 11 is somewhat less efficient, for example where illumination of a translucent panel is required.

Fig. 2 shows one manner in which a conventional LED can be modified in accordance with the present invention in order to improve sideways illumination. This is achieved by the provision of a blind hole 15 drilled, or- otherwise f6fined, in the plastics lens region 14 with the angle on the drill tip being such that reflection occurs at the resulting conical bottom surface 17 whereby the light C from the LED is reflected sideways through a 3600 arc whose plane is at right angles to the axis of the lens.

Advantageously, the hole 15 is filled with a plastics material 18 which has been loaded with a pigment (eg white) designed to optimally reflect the light.

In other embodiments, the dimensions and shape of the hole 15 can be designed to reflect the LED light into a desired pattern.

In a still further embodiment shown in Fig. 3, the modified LED of Fig. 2 is combined with a holder 20 having the same type of terminations 22 as a conventional incandescent bulb, ie central first termination 24 and outer second termination 26.

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Claims (8)

1. A light emitting diode device having an LED encapsulated in plastics and wherein the plastics encapsulation of the LED is provided with a blind hole, the inner end of which serves to reflect light from the LED sideways, or generally sideways, through an arc.

2. A light emitting diode device as claimed in claim 1, wherein the axis of the blind hole lies along the principal axis of the LED encapsulation.

3. A light emitting diode device as claimed in claim 1 or 2, wherein the inner end of the blind hole forms a conical surface which serves to reflect light from the LED sideways through a 360' arc.

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4. A light emitting diode device as claimed in claim 3, wherein the plane of said 360 arc is at right angles to the axis of the LED lens.

5. A light emitting diode device as claimed in any of claims 1 to 4, wherein the blind hole is filled with a plastics material.

6. A light emitting diode device as claimed in claim 5, wherein the plastics material within the blind bore is loaded with a pigment selected for optimal reflection of the light.

7. A light emitting diode device as claimed in claim 6, wherein said pigment is white.

8. A light emitting diode device substantially as hereinbefore described, with reference to and as illustrated in Figure 2 or Figure 3 of the accompanymg drawings.

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8. A light emitting diode device as claimed in any of claims 1 to 7, wherein the dimensions and shape of the blind hole are designed to reflect the light into a desired, not necessarily uniform, pattern.