EP3141794A1

EP3141794A1 - Led lighting device

Info

Publication number: EP3141794A1
Application number: EP16187443.3A
Authority: EP
Inventors: Hiromichi Hayashihara; Hiroshi Ohno; Tomoyuki Suzuki; Tomonao Takamatsu; Takeshi Morino
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2015-09-10
Filing date: 2016-09-06
Publication date: 2017-03-15
Also published as: JP2017054708A

Abstract

An LED lighting device (1) according to an embodiment includes: a light source including an LED (110); an optical element (104) including an incidence surface, a side surface perpendicular to the incidence surface, and an exit surface facing the incidence surface, the optical element being configured to receive light emitted from the light source with the incidence surface, transmit the light inside the optical element, and release the light from the exit surface; a covering portion (102) disposed on a side portion of the optical element, the side portion being located on a side of the incidence surface, the covering portion covering the side portion; and a light absorbing portion disposed on the covering portion, the light absorbing portion facing the side surface of the optical element.

Description

FIELD

Embodiments described herein relate generally to LED lighting devices.

BACKGROUND

An LED lighting device for general lighting is sometimes expected to have a shape like an incandescent bulb and emits light like an incandescent bulb. That is, retrofitting is sometimes desired. Particularly, there is often a demand for wide light distribution from a point light source inside a globe as in a case with a clear incandescent bulb, such as an incandescent bulb having a globe formed with clear glass. For example, there is a demand for lighting of approximately 270 degrees in 1/2 light distribution angle. However, if an LED continues to be used as a light source, the light distribution angle becomes narrower, and the 1/2 light distribution angle decreases to approximately 120 degrees. In view of this, the light distribution angle may be widened with an optical element, such as a wide distribution lens.
For example, there is a known optical element described below. This optical element has a scattering member at the edge of a light guiding rod. An LED is provided on the bottom surface facing the scattering member. Light emitted from the LED propagates in the light guiding rod through total reflection, and is guided to the scattering member. The light that has reached the scattering member is scattered by the scattering member, and is emitted to the outside. In this manner, an LED bulb that distributes light uniformly from the center of the bulb like a filament bulb can be achieved.
However, the LED bulb is made to look unattractive by light leaking from the root portion of the light guiding rod. Of the light scattered at the angle or the protruding portion existing on the light incidence side of the light guiding rod, this leakage light originates from light that does not satisfy the total reflection conditions in the light guiding rod or light that propagates without entering the light guiding rod.
Such leakage light makes the bulb look unattractive, and is preferably not to be seen.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an exploded perspective view of an LED lighting device according to a first embodiment.
Fig. 2 is a cross-sectional view of the LED lighting device according to the first embodiment.
Fig. 3A is a diagram for explaining that light is reflected or scattered by a corner portion.
Fig. 3B is a diagram for explaining the necessary height of a light absorbing portion.
Fig. 4A is a photograph of a light guiding rod without the light absorbing portion when the lighting device is off.
Fig. 4B is a photograph of the light guiding rod without the light absorbing portion when the lighting device is on.
Fig. 5A is a photograph of a light guiding rod with the light absorbing portion when the lighting device is off.
Fig. 5B is a photograph of the light guiding rod with the light absorbing portion when the lighting device is on.
Fig. 6 is a cross-sectional view of the relevant components of the LED lighting device of the first embodiment.
Fig. 7 is a photograph of the LED lighting device of the first embodiment when the LED lighting device is on.
Fig. 8 is a photograph of an LED bulb of a comparative example when the LED bulb is on.
Fig. 9 is a cross-sectional view of the relevant components of an LED lighting device of a second embodiment.
Fig. 10 is an exploded perspective view of an LED lighting device according to a third embodiment.
Fig. 11 is a cross-sectional view of the LED lighting device of the third embodiment.
Fig. 12 is a photograph showing leakage light from the protruding portion of a light guiding rod.
Fig. 13 is a cross-sectional view of the relevant components of the LED lighting device of the third embodiment.
Fig. 14 is a cross-sectional view of the relevant components of an LED lighting device according to a first modification of the third embodiment.
Fig. 15 is a cross-sectional view of the relevant components of an LED lighting device according to a second modification of the third embodiment.
Fig. 16 is a cross-sectional view of the relevant components of an LED lighting device according to a third modification of the third embodiment.
Fig. 17 is a cross-sectional view of the relevant components of an LED lighting device according to a fourth modification of the third embodiment.
Fig. 18A is a cross-sectional view of the relevant components of an LED lighting device according to a fifth modification of the third embodiment.
Fig. 18B is a perspective view of a light guiding rod of the fifth modification of the third embodiment.
Fig. 19 is a cross-sectional view of the relevant components of an LED lighting device according to a fourth embodiment.
Fig. 20 is an exploded perspective view of an LED lighting device according to a fifth embodiment.
Fig. 21 is a cross-sectional view of the LED lighting device according to the fifth embodiment.
Fig. 22 is a cross-sectional view of the relevant components of the LED lighting device according to the fifth embodiment.
Fig. 23 is a cross-sectional view of the relevant components of an LED lighting device according to a sixth embodiment.
Fig. 24 is an exploded perspective view of an LED lighting device according to a seventh embodiment.
Fig. 25 is a cross-sectional view of the LED lighting device according to the seventh embodiment.
Fig. 26 is a cross-sectional view of the relevant components of the LED lighting device according to the seventh embodiment.
Fig. 27 is a photograph for explaining the effects of the LED lighting device of the seventh embodiment.
Fig. 28 is a cross-sectional view of the relevant components of the LED lighting device according to a first modification of the seventh embodiment.
Fig. 29 is a cross-sectional view of the relevant components of the LED lighting device according to a second modification of the seventh embodiment.
Fig. 30 is a cross-sectional view of the relevant components of the LED lighting device according to a third modification of the seventh embodiment.
Fig. 31 is a cross-sectional view of the relevant components of the LED lighting device according to a fourth modification of the seventh embodiment.
Fig. 32A is a cross-sectional view of the relevant components of the LED lighting device according to a fifth modification of the seventh embodiment.
Fig. 32B is a perspective view of a light guiding rod of the fifth modification of the seventh embodiment.
Fig. 33 is a cross-sectional view of the relevant components of an LED lighting device according to an eighth embodiment.
Fig. 34 is a cross-sectional view of the relevant components of an LED lighting device according to a ninth embodiment.

DETAILED DESCRIPTION

An LED lighting device according to an embodiment includes: a light source including an LED; an optical element including an incidence surface, a side surface perpendicular to the incidence surface, and an exit surface facing the incidence surface, the optical element being configured to receive light emitted from the light source with the incidence surface, transmit the light inside the optical element, and release the light from the exit surface; a covering portion disposed on a side portion of the optical element, the side portion being located on a side of the incidence surface, the covering portion covering the side portion; and a light absorbing portion disposed on the covering portion, the light absorbing portion facing the side surface of the optical element.
The following is a detailed description of embodiments, with reference to the accompanying drawings.

(First Embodiment)

Referring to Figs. 1 and 2, a light emitting diode (LED) lighting device according to a first embodiment is described. Fig. 1 is an exploded perspective view of an LED lighting device 1 of the first embodiment. Fig. 2 is a cross-sectional view of the LED lighting device 1 of the first embodiment.
The LED lighting device 1 of the first embodiment includes a globe 100, a cover (a covering portion) 102, a light guiding rod (an optical element) 104, spacer fixing screws 106 and 107, a spacer 108, an LED 110, a housing 112, cover fixing screws 114 and 115, and a cap 116. That is, the LED lighting device 1 of the first embodiment is an LED bulb.
The LED 110 is located between a recess of the housing 112 serving as the base and the spacer 108. The spacer 108 is attached to the recess of the housing 112 with the spacer fixing screws 106 and 107, so that a portion of the LED 110 is pressed against and fixed to the surface of the recess of the housing 112 by the spacer 108. The opposite side of the housing 112 from the side having the LED 110 fixed thereto is a cylindrical portion, and this cylindrical portion is covered with the cap 116. A through hole into which the light guiding rod 104 is to be inserted is formed in the central portion of the spacer 108.
The light guiding rod 104 is formed with a transparent medium having a refractive index n (n > 1), or more specifically, with a material such as polymethylmethacrylate (PMMA), polycarbonate (PC), or silica glass. The light guiding rod 104 is a cylindrical structure that has an incidence surface 200 facing the LED 110, and a side surface 202 substantially perpendicular to the incidence surface 200. The incidence surface 200 and the side surface 202 of the light guiding rod 104 are mirror-finished. The light guiding rod 104 has a recess 204 at its edge, and a scattering member 206 formed with a white coating, for example, is provided in the recess 204. At the portion in contact with the spacer 108, the light guiding rod 104 is bonded to the spacer 108 with an adhesive. The LED 110 and the light guiding rod 104 are at a distance from each other, with the spacer 108 existing in between.
The cover 102 is provided at the side portion of the light guiding rod 104 on the side of the incidence surface 200, and this cover 102 is fixed to the housing 112 with the cover fixing screws 114 and 115. A light absorbing portion 302 is formed on the surface of the cover 102 facing the light guiding rod 104. This light absorbing portion 302 will be described later in detail. An air layer 130 exists between the light absorbing portion 302 and the side surface 202 of the light guiding rod 104.
The light guiding rod 104 and the cover 102 is covered with the globe 100, and are contained in the globe 100. The globe 100 is bonded and fixed to the housing 112 with an adhesive, for example.

(Principles of Lighting)

The principles of lighting in the LED lighting device 1 of the first embodiment are now described. The LED 110 is supplied with electric power from a power supply and an electric cable, and emits light. Light from the LED 110 is refracted by the incidence surface 200 of the light guiding rod 104, and enters the light guiding rod 104.
As described above, a gap or the air layer 130 exists between the light guiding rod 104 and the light absorbing portion 302 formed on the surface of the cover 102 facing the light guiding rod 104. Because of this, the light that has entered the light guiding rod 104 propagates while totally-reflected repeatedly by the side surface 202 substantially perpendicular to the incidence surface 200. The light that has propagated while totally-reflected repeatedly by the side surface 202 is scattered by the scattering member 206 formed in the recess 204 at the edge of the light guiding rod 104, and is omnidirectionally emitted. The light absorbing portion 302 absorbs the light emitted from the portions other than the scattering member 206 formed at the edge of the light guiding rod 104.
Next, the effects of the LED lighting device 1 of this embodiment are described. The light guiding rod 104 includes a flat surface formed with the incidence surface 200, the side surface 202 substantially perpendicular to the incidence surface 200, and a corner portion 300 forming the boundary between the incidence surface 200 and the side surface 202. Here, "being substantially perpendicular" implies that there are cases where the side surface 202 is tapered so as to facilitate the pullout in the injection molding process, or gather light at the edge of the light guiding rod 104, for example. That is, the side surface 202 might need to be not perpendicular to the light guiding rod 104 so that the light guiding rod 104 can be appropriately manufactured.
The incidence surface 200 and the side surface 202 of the light guiding rod 104 are mirror-finished, to minimize the unevenness on the surfaces. This mirror finish is performed through buff finish, for example. The recess 204 having the scattering member 206 formed with a white coating is formed at the edge of the light guiding rod 104. However, the recess 204 may be in any other form, as long as it can achieve the same effect. For example, the scattering member 206 may be formed by attaching fine hollow beads to the recess 204, performing blast processing on the recess 204, or filling the recess 204 with a resin formed with a scattering material. The recess 204 may have a spheroidal shape. Alternatively, the recess 204 may have some other shape, such as a conical shape or a cylindrical shape.
The air layer 130 exists between the light guiding rod 104 and the light absorbing portion 302. The light guiding rod 104 and the spacer 108 are fixed to each other with an adhesive, but may be fixed to each other by engaging with each other or by some other method. In a case where the light guiding rod 104 has a tapered edge, the inner diameter of the cover 102 is also tapered on the edge side, so that the light guiding rod 104 will not fall off the cover 102.
The corner portion 300 of the light guiding rod 104 does not have exactly a right angle, but is formed with a curved surface or flat faces. This corner portion 300 may not be mirror-finished but is a scattering surface. As shown in Fig. 3A, when light reflected or scattered by the corner portion 300 enters a side surface 203 on the opposite side of the central axis 210 of the light guiding rod 104, some of the light does not satisfy the total reflection conditions depending on the incident angle, and exits as it is. Also, some of the light is reflected or scattered by the surface of the cover 102 facing the light guiding rod 104, and exits through the light guiding rod 104. For the above reasons, leakage light is generated.
To counter this problem, the light absorbing portion 302 absorbs such leakage light in the LED lighting device 1 of the first embodiment. Referring now to Figs. 3A through 5B, this aspect will is described in detail.
Figs. 4A and 4B are photographs of light leaking from the light guiding rod 104. Fig. 4A is a photograph showing the light guiding rod 104 when the lighting device is off. Fig. 4B is a photograph showing the light guiding rod 104 when the lighting device is on. As can be seen from Fig. 4B, a blight line indicated by an arrow is observed when the lighting device is on. This indicates leakage light that has been reflected or scattered by the corner portion 300 of the light guiding rod 104.
To counter this problem, the light absorbing portion 302 shields this leakage light in this embodiment. This is shown in Figs. 5A and 5B. Fig. 5A is a photograph showing the light guiding rod 104 when the lighting device is off. Fig. 5B is a photograph showing the light guiding rod 104 when the lighting device is on. The light absorbing portion 302 is formed with a material that absorbs light, such as a matte-black coating, black alumite, a black plating, black paper, a black sheet, black alumina, black silicon, or black plastic.
As the air layer 130 is provided between the side surface 202 of the light guiding rod 104 and the light absorbing portion 302, the condition for total reflection of light on a surface of the light guiding rod 104 is expressed as $θ > \sin^{- 1} (1 / n) .$
Here, θ represents the incident angle of light that has been reflected or scattered by the corner portion 300 of the light guiding rod 104 and entered the side surface 203 facing the corner portion 300 as shown in Fig. 3B, and n represents the refractive index of the medium of the light guiding rod 104.
According to the above expression of the total reflection condition, the length L of the light absorbing portion 302 satisfies the condition expressed as $L = tanθ \times D,$
where D represents the diameter of the light guiding rod 104. Accordingly, the length L satisfies the condition expressed as $L > D / \sqrt (n^{2} - 1) .$
In Figs. 5A and 5B, the diameter D of the light guiding rod 104 is 13 mm, and the refractive index n of the light guiding rod 104 is 1.49. Therefore, the length L of the light absorbing portion 302 should be at least 11.77 mm. Where the length L of the light absorbing portion 302 was 12 mm, no leakage light was observed.
Fig. 6 shows the relevant components of the LED lighting device 1 of the first embodiment. In Fig. 6, the edge of the light guiding rod 104 and the like are not shown. The light absorbing portion 302 formed with a matte-black coating or the like is provided on the surface of the cover 102 facing the light guiding rod 104. As described above, the length L of the light absorbing portion 302 is expressed as $L > D / \sqrt (n^{2} - 1),$
where D represents the diameter of the light guiding rod 104, and n represents the refractive index of the light guiding rod 104. Fig. 7 shows a photograph of the LED lighting device equipped with the cover 102 having the light absorbing portion 302 when the LED lighting device is on. As can be seen from Fig. 7, no leakage light is observed in the LED lighting device 1 of the first embodiment.
Fig. 8 shows a photograph of an LED bulb of a comparative example when the LED bulb is on. The LED bulb of this comparative example has the same structure as the LED lighting device of the first embodiment, except for not including the light absorbing portion 302. As can be seen from Fig. 8, leakage light is observed in this comparative example, as opposed to the first embodiment.
As described above, the first embodiment can provide an LED lighting device capable of preventing leakage light.

(Second Embodiment)

Referring now to Fig. 9, an LED lighting device according to a second embodiment is described. Fig. 9 is a cross-sectional view of the relevant components of the LED lighting device of the second embodiment.
The LED lighting device 1 of the second embodiment has the same structure as the LED lighting device of the first embodiment, except that the light guiding rod 104 and the spacer 108 are replaced with a light guiding rod 104A and a spacer 108A.
The light guiding rod 104A and the spacer 108A each have a tapered engaging portion. The light guiding rod 104A is fixed to the spacer 108A with an adhesive (not shown) or the like.
In the second embodiment, the light guiding rod 104A and the spacer 108A each has a tapered engaging portion, so that light from the LED 110 can be reflected toward the edge of the light guiding rod 104A, and light use efficiency can be expected to increase.
Like the first embodiment, the second embodiment can also provide an LED lighting device capable of preventing leakage light.

(Third Embodiment)

Referring now to Figs. 10 and 11, an LED lighting device according to a third embodiment is described.
Fig. 10 is an exploded perspective view of an LED lighting device 1 of the third embodiment. Fig. 11 is a cross-sectional view of the LED lighting device 1 of the third embodiment.
The LED lighting device 1 of the third embodiment has the same structure as the LED lighting device of the first embodiment shown in Figs. 1 and 2, except that the light guiding rod 104 and the spacer 108 are replaced with a light guiding rod 105 and a spacer 108B, respectively.
The light guiding rod 105 of the third embodiment includes a cylindrical portion and a protruding portion 400 formed on the side of the spacer 108B. This protruding portion 400 has a flange-like shape so as to prevent the light guiding rod 105 from falling off. Unlike the light guiding rod and the spacer of the first embodiment, the light guiding rod 105 and the spacer 108B are not bonded to each other with an adhesive.
The spacer 108B has the same structure as the spacer 108, except for having a recess to accommodate the protruding portion 400 of the light guiding rod 105.
As described above, in the LED lighting device 1 of the third embodiment, the light guiding rod 105 has the protruding portion 400 that does not contribute to lighting. This is to facilitate the assembling by not bonding the light guiding rod 105 to the spacer 108B. This protruding portion 400 is formed with a curved surface or a combination of flat surfaces. The protruding portion 400 is not necessarily mirror-finished, and might have some scattering faces. When light reflected or scattered by the protruding portion 400 enters a side surface 203 on the opposite side of the central axis 210 of the light guiding rod 105, some of the light does not satisfy the total reflection conditions depending on the incident angle, and exits as it is. Also, some of the light that has entered the light guiding rod 105 from a surface of the protruding portion 400 does not satisfy the total reflection conditions in the light guiding rod 105, and exits as it is. These are the cause of leakage light.
Fig. 12 shows a photograph of leakage light from the protruding portion 400. Three bright lines can be seen in Fig. 12. This is because light that has been scattered by three corner portions 300, 300A, and 300B of the protruding portion 400 has exited without totally-reflected in the light guiding rod 105. The corner portion 300 is a corner portion on the surface of the protruding portion 400 on the side of the LED 110, and the corner portion 300A is a corner portion that is formed on the surface of the protruding portion 400 on the opposite side from the side of the LED 110 and faces the corner portion 300. The corner portion 300B is the joining portion between the cylindrical portion of the light guiding rod 105 and the protruding portion 400.
To prevent the leakage light in the third embodiment, a light absorbing portion 302 is provided on the surface of the cover 102 facing the light guiding rod 105, as shown in Fig. 13, as in the first and second embodiments. In the third embodiment, the length L of the light absorbing portion 302 satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$
Here, D represents the diameter of the light guiding rod 105, and n represents the refractive index of the medium of the light guiding rod 105. It should be noted that the diameter D of the light guiding rod 105 is the diameter of the cylindrical portion not including the protruding portion 400. Also, the length L of the light absorbing portion 302 is the length from the boundary between a side surface 202 of the light guiding rod 105 and the protruding portion 400. Further, α represents the correction factor of the protruding portion 400. This correction factor α is determined in accordance with the shape of the protruding portion 400.
The shape of the protruding portion 400 is not limited to the shape shown in Fig. 13, but may be any of the example shapes shown in Figs. 14 through 18.

(First Modification)

Fig. 14 shows the relevant components of an LED lighting device 1 according to a first modification of the third embodiment. The LED lighting device 1 of the first modification has the same structure as the LED lighting device of the third embodiment, except that the light guiding rod 105 and the cover 102 are replaced with a light guiding rod 105A and a cover 102A, respectively.
The light guiding rod 105A has the same structure as the light guiding rod 105, except that the joining portion between the cylindrical portion and the protruding portion 400 is in a tapered shape. As the joining portion of the light guiding rod 105A is in a tapered shape, the cover 102A has a structure in which the portion corresponding to the joining portion is also in a tapered shape.
As in the third embodiment, the length L of the light absorbing portion 302 of the first modification also satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$

(Second Modification)

Fig. 15 shows the relevant components of an LED lighting device 1 according to a second modification of the third embodiment. The LED lighting device 1 of the second modification has the same structure as the LED lighting device of the first modification, except that the light guiding rod 105A is replaced with a light guiding rod 105B. The light guiding rod 105B has the same structure as the light guiding rod 105A, except that the joining portion is a smooth, round portion, instead of a tapered portion.
As in the third embodiment, the length L of the light absorbing portion 302 of the second modification also satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$

(Third Modification)

Fig. 16 shows the relevant components of an LED lighting device 1 according to a third modification of the third embodiment. The LED lighting device 1 of the third modification has the same structure as the LED lighting device of the first modification shown in Fig. 14, except that the light guiding rod 105A is replaced with a light guiding rod 105C. This light guiding rod 105C has the same structure as the light guiding rod 105A, except that the tapered portion of the joining portion continues to the end portion of the protruding portion 400 or the side surface of the flange.
As in the third embodiment, the length L of the light absorbing portion 302 of the third modification also satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$

(Fourth Modification)

Fig. 17 shows the relevant components of an LED lighting device 1 according to a fourth modification of the third embodiment. The LED lighting device 1 of the fourth modification has the same structure as the LED lighting device of the first modification shown in Fig. 14, except that the light guiding rod 105A and the cover 102A are replaced with a light guiding rod 105D and the cover 102 of the first embodiment, respectively. The light guiding rod 105D has the same structure as the light guiding rod 105A, except that the cross-sectional shape of the end portion of the protruding portion 400 is a round shape, instead of a rectangular shape. That is, the side surface of the flange of the protruding portion 400 has a rounded shape.
As in the third embodiment, the length L of the light absorbing portion 302 of the fourth modification also satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$

(Fifth Modification)

Figs. 18A and 18B show the relevant components of an LED lighting device 1 according to a fifth modification of the third embodiment. The LED lighting device 1 of the fifth modification has the same structure as the LED lighting device of the third embodiment shown in Fig. 13, except that the light guiding rod 105 and the spacer 108B are replaced with a light guiding rod 105E and a spacer 108C, respectively.
The light guiding rod 105E has the same structure as the light guiding rod 105, except that the protruding portion 400 is not formed in a ring-like shape around the entire circumference of the cylindrical portion, but protruding portions 400 are discretely arranged around the circumference of the cylindrical portion. In accordance with the light guiding rod 105E, the spacer 108C is formed with first recesses to accommodate the protruding portions 400, and second recesses to accommodate the portions of the cylindrical portion at which the protruding portions 400 of the light guiding rod 105E are not formed.
The number of the protruding portions 400 may be any number not smaller than one, and may be two, three, or four, for example. Also, the protruding portions 400 may have any shape, as long as they can prevent the light guiding rod 105E from falling off. In any case, the length L of the light absorbing portion 302 is the length from the boundary between a side surface 202 of the light guiding rod 105E and the protruding portions 400.
As in the third embodiment, the length L of the light absorbing portion 302 of the fifth modification also satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$
As described above, in the third embodiment and the first through fifth modifications, the light absorbing portion 302 is provided on the surface of the cover facing the light guiding rod. Thus, an LED lighting device capable of preventing leakage light can be provided, as in the first embodiment.

(Fourth Embodiment)

Referring now to Fig. 19, an LED lighting device according to a fourth embodiment is described. Fig. 19 is a cross-sectional view of the relevant components of the LED lighting device of the fourth embodiment. The LED lighting device 1 of the fourth embodiment has the same structure as the LED lighting device of the third embodiment shown in Fig. 13, except that the light guiding rod 105 and the spacer 108B are replaced with a light guiding rod 105F and a spacer 108D, respectively.
The light guiding rod 105F has male screws formed at side end portions of the protruding portion 400. Meanwhile, the spacer 108D has female screws formed at side portions of the recess to accommodate the protruding portion 400. The female screws engage with the male screws of the light guiding rod 105F. That is, the light guiding rod 105F is screwed into the spacer 108D, and is fixed thereto. Consequently, the contact area between the light guiding rod 105F and the spacer 108D becomes larger. Thus, the light guiding rod 105F and the spacer 108D can be firmly fixed to each other.
As in the third embodiment, the length L of the light absorbing portion 302 of the fourth embodiment also satisfies the condition expressed as $L > (D / \sqrt (n^{2} - 1)) - α .$
Like the third embodiment, the fourth embodiment can also provide an LED lighting device capable of preventing leakage light.

(Fifth Embodiment)

Referring now to Figs. 20 through 22, an LED lighting device according to a fifth embodiment is described. Fig. 20 is an exploded perspective view of an LED lighting device 1 of the fifth embodiment. Fig. 21 is a cross-sectional view of the LED lighting device 1 of the fifth embodiment. Fig. 22 is a cross-sectional view of the relevant components of the LED lighting device 1 of the fifth embodiment.
The LED lighting device 1 of the fifth embodiment has the same structure as the LED lighting device of the first embodiment shown in Fig. 6, except that the cover 102 is eliminated, and the spacer 108 is replaced with a spacer 108E. Further, a light absorbing portion 302A is provided at the corner portion 300 of the light guiding rod 104. This light absorbing portion 302A is formed with a matte-black coating material, for example. The light guiding rod 104 is fixed to the recess of the spacer 108E with an adhesive (not shown) or the like.
In the LED lighting device 1 of the fifth embodiment, the light absorbing portion 302A coated with a matte-black coating material is provided at the corner portion 300 of the light guiding rod 104, so that no light will be reflected or scattered by the corner portion 300 of the light guiding rod 104. The light guiding rod 104 is fixed to the spacer 108E with an adhesive (not shown), but the light absorbing portion 302A may also serve as the adhesive.
Like the first embodiment, the fifth embodiment can also provide an LED lighting device capable of preventing leakage light.
It should be noted that the LED lighting device 1 of the fifth embodiment may be equipped with the above described cover 102 of LED lighting device of the first embodiment shown in Fig. 6. In this case, further unintended leakage light can be cut, and more leakage light can be prevented. In a case where the cover 102 is provided, the light absorbing portion 302 is preferably provided on the surface of the cover 102 facing the side surface of the light guiding rod 104, as in the first embodiment.

(Sixth Embodiment)

Referring now to Fig. 23, an LED lighting device according to a sixth embodiment is described. Fig. 23 is a cross-sectional view of the relevant components of the LED lighting device 1 of the sixth embodiment.
The LED lighting device 1 of the sixth embodiment has the same structure as the LED lighting device of the second embodiment shown in Fig. 9, except that the cover 102 is eliminated, the spacer 108A is replaced with a spacer 108F, and the light absorbing portion 302A is provided at the tapered portion of the light guiding rod 104A. The spacer 108F differs from the spacer 108A in that the entire engaging portion to be engaged with the light guiding rod 104A is in a tapered shape. The engaging portion of the spacer 108A partially has a flat portion to support part of the incidence surface 200 of the light guiding rod 104A. A matte-black coating material or the like is used as the light absorbing portion 302. The light guiding rod 104A is fixed to the tapered portion of the spacer 108F with an adhesive (not shown) or the like. The light absorbing portion 302A may also serve as the adhesive.
In the sixth embodiment designed as above, the light absorbing portion 302A is provided at the tapered portion of the light guiding rod 104A. Accordingly, light reflected or scattered by the tapered portion can be absorbed by the light absorbing portion 302A, and leakage light can be prevented.
It should be noted that the LED lighting device 1 of the this embodiment may be equipped with the above described cover 102 of LED lighting device of the second embodiment shown in Fig. 9. In this case, further unintended leakage light can be cut, and more leakage light can be prevented. In a case where the cover 102 is provided, the light absorbing portion 302A is preferably provided on the surface of the cover 102 facing the side surface of the light guiding rod 104A, as in the first embodiment.

(Seventh Embodiment)

Referring now to Figs. 24 through 26, an LED lighting device according to a seventh embodiment is described. Fig. 24 is an exploded perspective view of an LED lighting device 1 of the seventh embodiment. Fig. 25 is a cross-sectional view of the LED lighting device 1 of the seventh embodiment. Fig. 26 is a cross-sectional view of the relevant components of the LED lighting device 1 of the seventh embodiment.
The LED lighting device 1 of the seventh embodiment has the same structure as the LED lighting device of the third embodiment shown in Fig. 13, except that the light absorbing portion 302 is eliminated, the cover 102 is replaced with a cover 102B, and the light absorbing portion 302A is provided on the surface of the protruding portion 400 of the light guiding rod 105, or on the surface facing the side surface of the recess of the spacer 108B and the surface of the flange of the protruding portion 400 in contact with the cover 102B. A matte-black coating material, for example, is used as the light absorbing portion 302A, and this black coating material is applied onto the surface of the protruding portion 400, to form the light absorbing portion 302A. The cover 102B has the same shape as the cover 102, except that the portion in contact with the protruding portion 400 of the light guiding rod 105 is cut off by the amount equivalent to the thickness of the light absorbing portion 302A.
In the seventh embodiment designed as above, the light guiding rod 105 has the protruding portion 400 as in the third embodiment. This protruding portion 400 is designed to prevent the light guiding rod 105 from falling off when the LED lighting device 1 is put upside down. The light absorbing portion 302A is provided on the protruding portion 400. The region on which the light absorbing portion 302A is the region protruding as the protruding portion 400, excluding the incidence surface 200 of the light guiding rod 105 and the side surfaces 202 and 203 substantially perpendicular to the incidence surface 200. By virtue of the light absorbing portion 302A, no light is reflected or scattered by corner portions 300, 300A, and 300B of the light guiding rod 105. Also, no light enters the light guiding rod 105 from the surface of the protruding portion 400 of the light guiding rod 105 located between the corner portion 300 and the corner portion 300A, and the surface located between the corner portion 300A and the corner portion 300B.
Referring now to Fig. 27, the effects to be achieved in a case where the light absorbing portion 302A is provided on the protruding portion 400 are described. The photograph in the upper half of Fig. 27 shows the light guiding rod 105 at a time of the lighting device is off (left) and at a time of the lighting device is on (right) in a case where the light absorbing portion 302A has not been applied to the protruding portion 400 (before the measures are taken).
The photograph in the lower half of Fig. 27 shows the light guiding rod 105 at a time of the lighting device is off (left) and at a time of the lighting device is on (right) in a case where the light absorbing portion 302A has been applied to the protruding portion 400 (after the measures are taken).
Before the measures are taken, three bright light lines formed with line reflected or scattered by the protruding portion 400 of the light guiding rod 105 are seen. These bright lines are formed with light reflected or scattered by the three corner portions 300, 300A, and 300B of the protruding portion 400 of the light guiding rod 105.
After the measures are taken or in the case where a matte-black coating has been applied as the light absorbing portion 302A, on the other hand, no bright light lines can be seen.
The shape of the protruding portion 400 is not limited to the shape shown in Fig. 26, but may be any of example shapes according to first through fifth modifications shown in Figs. 28 through 32.

(First Modification)

Fig. 28 is a cross-sectional view of the relevant components of an LED lighting device 1 according to a first modification of the seventh embodiment. The LED lighting device 1 of the first modification has the same structure as the LED lighting device of the first modification of the third embodiment shown in Fig. 14, except that the light absorbing portion 302A is provided on the tapered portion and the side surface of the protruding portion 400 of the light guiding rod 105A. A matte-black coating material, for example, is used as the light absorbing portion 302A.

(Second Modification)

Fig. 29 is a cross-sectional view of the relevant components of an LED lighting device 1 according to a second modification of the seventh embodiment. The LED lighting device 1 of the second modification has the same structure as the LED lighting device of the second modification of the third embodiment shown in Fig. 15, except that the light absorbing portion 302A is provided on the round portion and the side surface of the protruding portion 400 of the light guiding rod 105B. A matte-black coating material, for example, is used as the light absorbing portion 302A.

(Third Modification)

Fig. 30 is a cross-sectional view of the relevant components of an LED lighting device 1 according to a third modification of the seventh embodiment. The LED lighting device 1 of the third modification has the same structure as the LED lighting device of the third modification of the third embodiment shown in Fig. 16, except that the light absorbing portion 302A is provided on the tapered portion and the side surface of the protruding portion 400 of the light guiding rod 105C. A matte-black coating material, for example, is used as the light absorbing portion 302A.

(Fourth Modification)

Fig. 31 is a cross-sectional view of the relevant components of an LED lighting device 1 according to a fourth modification of the seventh embodiment. The LED lighting device 1 of the fourth modification has the same structure as the LED lighting device of the fourth modification of the third embodiment shown in Fig. 17, except that the light absorbing portion 302A is provided on the round portion of the protruding portion 400 of the light guiding rod 105D. A matte-black coating material, for example, is used as the light absorbing portion 302A.

(Fifth Modification)

Fig. 32A is a cross-sectional view of the relevant components of an LED lighting device 1 according to a fifth modification of the seventh embodiment. Fig. 32B is a perspective view of the light guiding rod. The LED lighting device 1 of the fifth modification has the same structure as the LED lighting device of the fifth modification of the third embodiment shown in Figs. 18A and 18B, except that the light absorbing portion 302A is provided on the round portion of the protruding portion 400 of the light guiding rod 105E. A matte-black coating material, for example, is used as the light absorbing portion 302A.
In the fifth modification, the protruding portion 400 is not ring-shaped like a flange, but forms part of a ring. The number of the protruding portions 400 may be any number not smaller than one, and may be two, three, or four, for example. Further, the protruding portions 400 may have any shape, as long as they can prevent the light guiding rod 105E from falling off.
As described above, in the seventh embodiment and the first through fifth modifications, the light absorbing portion 302A is provided on the flange portion of the light guiding rod. Thus, an LED lighting device capable of preventing leakage light can be provided, as in the first embodiment.

(Eighth Embodiment)

Fig. 33 is a cross-sectional view of the relevant components of an LED lighting device 1 according to an eighth embodiment. The LED lighting device 1 of the eighth embodiment has the same structure as the LED lighting device of the fourth embodiment shown in Fig. 19, except that the cover 102 is eliminated, and the light absorbing portion 302A is provided on the surface of the joining portion between the spacer 108D and the light guiding rod 105F in a state where the male screws of the light guiding rod 105F are screwed into the female screws of the spacer 108D. A matte-black coating material, for example, is used as the light absorbing portion 302A.
According to the eighth embodiment designed as above, the light absorbing portion 302A is provided on the surface of the joining portion between the spacer 108D and the light guiding rod 105F. Thus, light reflected or scattered by the joining portions between the male screws and the female screws can be prevented from being emitted to the outside.
As described above, like the fourth embodiment, the eighth embodiment can also prevent leakage light.

(Ninth Embodiment)

Fig. 34 is a cross-sectional view of the relevant components of an LED lighting device 1 according to a ninth embodiment. The LED lighting device 1 of the ninth embodiment has the same structure as the LED lighting device of one of the first through eighth embodiments and their modifications, except that the light guiding rod 104 is not supported by a spacer or the like, but the light guiding rod 104 is fixed by the globe 100 via fixing rods 150. This structure is described below, with the LED lighting device of the first embodiment being taken as an example.
In the ninth embodiment, the light guiding rod 104 of the first embodiment shown in Fig. 2 or 6 is supported and fixed by the fixing rods 150 fixed by the globe 100. That is, the light guiding rod 104 is fixed to the globe 100 by the fixing rods 150. Thus, in the ninth embodiment, the spacer 108 is unnecessary, and the assembling is easier.
In the ninth embodiment, the light absorbing portion 302 is provided on the surface of the cover 102 facing the side surface of the light guiding rod 104, as in the first embodiment.
The fixing rods 150 should be able to fix the light guiding rod 104, and therefore, the fixing rods 150 may be designed to connect to the cover 102, for example. Further, the fixing rods 150 may have any shape, as long as the same effects can be achieved. The globe 100 may hold the light guiding rod 104, for example.
In the ninth embodiment, the light absorbing portion 302 is provided, and thus, leakage light can be prevented as in the first embodiment.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.

Claims

An LED lighting device comprising:
a light source including an LED;

an optical element including an incidence surface, a side surface perpendicular to the incidence surface, and an exit surface facing the incidence surface, the optical element being configured to receive light emitted from the light source with the incidence surface, transmit the light inside the optical element, and release the light from the exit surface;

a covering portion disposed on a side portion of the optical element, the side portion being located on a side of the incidence surface, the covering portion covering the side portion; and

a light absorbing portion disposed on the covering portion, the light absorbing portion facing the side surface of the optical element.
The device according to claim 1, wherein a gap is formed between the light absorbing portion and the side surface of the optical element.
The device according to claim 1, further comprising
a spacer disposed between the light source and the optical element, the spacer having an opening extending from a side of the optical element to a side of the light source, the spacer including an accommodating portion formed around the opening, a corner portion of the optical element on the side of the incidence surface being accommodated in the accommodating portion.
The device according to claim 3, wherein:
the corner portion of the optical element includes a tapered portion;

the opening includes: a first portion in a tapered shape, the first portion being tapered in a direction from the optical element toward the light source; and a second portion having the same size in a direction from the first portion toward the light source; and

the accommodating portion accommodates a portion of the incidence surface, the portion connecting to the second portion, the portion not being the tapered portion of the optical element.
The device according to claim 3, wherein:
the optical element has a protruding portion formed around the side surface on the side of the incidence surface of the optical element; and

the protruding portion is accommodated in the accommodating portion of the spacer.
An LED lighting device comprising:
a light source including an LED;

an optical element including an incidence surface, a side surface perpendicular to the incidence surface, an exit surface facing the incidence surface, and a protruding portion disposed around the side surface on a side of the incidence surface, the optical element being configured to receive light emitted from the light source with the incidence surface, transmit the light inside the optical element, and release the light from the exit surface;

a covering portion disposed on a side portion of the optical element, the side portion being located on the side of the incidence surface, the covering portion covering the side portion;

a spacer disposed between the light source and the optical element, the spacer including an accommodating portion configured to accommodate the protruding portion on the side of the incidence surface of the optical element; and

a light absorbing portion disposed at least on a surface of the protruding portion on the opposite side from the light source.
The device according to claim 6, wherein the light absorbing portion is also disposed on a side surface of the protruding portion.
The device according to claim 5, wherein the protruding portion is rectangular in cross-section perpendicular to the incidence surface.
The device according to claim 5, wherein the protruding portion is tapered in cross-section perpendicular to the incidence surface.
The device according to claim 5, wherein a joining portion between the protruding portion and the side surface of the optical element has a round shape.
The device according to claim 5, wherein the protruding portion has a side surface in a round shape.
The device according to claim 5, wherein the protruding portion is formed with a plurality of protruding portions, the protruding portions being discretely positioned.
The device according to claim 5, wherein a male screw is formed on a side portion of the protruding portion, and a female screw is formed on a side portion of the accommodating portion.
The device according to claim 1, further comprising:
a globe configured to house the light source, the optical element, and the covering portion; and

a fixing unit configured to fix the optical element to one of the globe and the covering portion.
An LED lighting device comprising:
a light source including an LED;

an optical element including an incidence surface, a side surface perpendicular to the incidence surface, and an exit surface facing the incidence surface, the optical element being configured to receive light emitted from the light source with the incidence surface, transmit the light inside the optical element, and release the light from the exit surface;

a spacer disposed between the light source and the optical element, the spacer including an accommodating portion configured to accommodate a corner portion of the optical element, the corner portion being located on a side of the incidence surface; and

a light absorbing portion disposed on the corner portion of the optical element.
The device according to claim 15, wherein:
the corner portion of the optical element has a tapered portion;

the accommodating portion of the spacer has a tapered portion; and

the light absorbing portion is disposed on the tapered portion of the optical element.
The device according to claim 1, wherein the exit surface of the optical element is a recessed surface, and a scattering member configured to scatter light is provided on the recessed surface.