Lighting apparatus

A lighting apparatus according to an embodiment includes a globe, an optical element including a scattering portion inside and transparent to visible light, and a light source disposed to be opposed to a light incident surface of the optical element. The scattering portion is disposed inside the globe.

FIELD

Embodiments described herein relate generally to a lighting apparatus used in ordinary households, shops, and offices.

BACKGROUND

LED lighting apparatuses for ordinary lighting may be required to achieve (retrofit) a shape and a way of lighting close to those of incandescent light bulbs. In particular, there have been demands for lighting with wide light distribution (½ light distribution angle is substantially 270°) from a point light source inside the globe, like clear type incandescent light bulbs (light bulbs using a clear glass globe).

DETAILED DESCRIPTION

Embodiments will be explained hereinafter with reference to drawings.

A lighting apparatus according to an embodiment includes a globe, an optical element including a scattering portion inside and transparent to visible light, and a light source disposed to be opposed to a light incident surface of the optical element. The scattering portion is disposed inside the globe.

FIG. 1is a schematic diagram illustrating a lighting apparatus10according to a first embodiment.

The lighting apparatus10has a rotation-symmetrical shape with respect to a central axis C. The lighting apparatus10includes a transparent globe2of an ordinary bulb type, an optical element4formed of a material (acryl in the present embodiment) transparent to visible light, and a light source6disposed to be opposed to a light incident surface4aof the optical element4described later. The lighting apparatus10also includes a diffusion portion3supporting a substrate11including the light source6, and a base5connected with an opening end of the globe2. The optical element4, the light source6, the substrate11, and the diffusion portion3are disposed inside the globe2.

The globe2includes a surface including an R curved surface. The R curved surface means a curved surface that secures a fixed point having a fixed distance from each of successive points on the curved surface. In this example, the fixed point serves as the center of the globe2. The R curved surface may include a spherical surface, but the surface shape of the globe2is not limited to a spherical surface.

In any case, the globe2has a rotation-symmetrical shape with respect to the central axis thereof. The rotation-symmetrical shape means a shape in which the object agrees with the original shape when the object is rotated with respect to the central axis C, and the rotational angle around the central axis C is less than 360°. Examples of the object of a rotation-symmetrical shape include a column, a cone, a polygonal prism, and a polygonal pyramid.

The optical element4has a rotation-symmetrical shape with respect to the central axis C, and has a substantially cylindrical shape in the present embodiment. The material of the optical element4may be any material as long as the material is transparent to visible light. The optical element4may be formed of, for example, polycarbonate or glass, as well as acryl. The optical element4is disposed coaxially with the globe2. Specifically, the central axis (first rotation-symmetrical axis) of the optical element4agrees with the central axis (second rotation-symmetrical axis) of the globe2.

The optical element4includes a scattering portion8serving as a cavity in which the transparent material does not exist. The scattering portion8also has a rotation-symmetrical shape with respect to the central axis C. The scattering portion8is a recessed portion including an opening portion8aat a distal end (upper end in the drawing) of the optical element4and apart from the light source6. The scattering portion8has a length substantially half the whole longitudinal length of the optical element4. A bottom portion of the scattering portion8on the light source6side (lower end side in the drawing) gradually converges toward the central axis C and is closed. The scattering portion8is disposed inside the globe2.

The internal surface of the scattering portion8serves as a diffusion surface8bto diffuse light. The diffusion surface8bmay be formed by painting the internal surface of the scattering portion8white. Otherwise, the diffusion surface8bmay be a rough surface obtained by subjecting part of the internal surface of the scattering portion8to sandblasting. Instead of providing the diffusion surface8b, a scattering member (not illustrated) to scatter light may be filled into the scattering portion8.

The optical element4includes a light incident surface4aat a proximal end portion thereof distant from the opening portion8aof the scattering portion8. In the present embodiment, the light incident surface4ais a recessed portion recessed in a spherical shape from the proximal end portion of the optical element4. A light emitting surface6aof the light source6is opposed to the recessed portion4a. The optical element4also includes an external circumferential surface4bthat is gradually reduced in diameter toward the distal end. The external circumferential surface4bwith a reduced diameter is connected with the opening portion8aof the scattering portion8at the distal end of the optical element4. The external circumferential surface4bis a mirror surface.

The light source6includes an LED device (not illustrated) mounted on a surface11aof the substrate11, and a sealing resin12sealing the LED device on the surface11aof the substrate11. White paint is applied to the surface11aof the substrate11, to diffuse and reflect light. The sealing resin12has a substantially hemispherical shape, and a surface of the sealing resin12functions as the light emitting surface6a. The light source6is attached to the diffusion portion3, by supporting a back surface11bof the substrate11with the diffusion portion3. In this state, the light emitting surface6ais opposed to the light incident surface4aof the optical element4.

The diffusion portion3is formed of a metal material, and thermally contacts the back surface11bof the substrate11. Specifically, the diffusion portion3thermally contacts the light source6through the substrate11, to diffuse and radiate the heat of the light source6. The diffusion portion3also includes a surface3asubjected to surface treatment to diffuse and reflect light. For example, white paint is applied to the surface3aof the diffusion portion3.

In the present embodiment, the scattering portion8is disposed opposite to the light source6with respect to the center R of the globe2. Preferably, the scattering portion8is disposed such that the end portion thereof on the light source6side is positioned in the center R of the globe2, as illustrated inFIG. 2. The position of the scattering portion8along the central axis C can be changed by adjusting, for example, the length of the diffusion portion3in the axial direction.

The following is explanation of a way of spreading of light in when the lighting apparatus10described above is turned on.

Rays emitted from the light source6through the light emitting surface6aare made incident on the light incident surface4aof the optical element4. The light made incident on the optical element4through the light incident surface4ais guided through the optical element4, and diffused and reflected in the scattering portion8. The light diffused and reflected in the scattering portion8spreads in substantially all directions, and is emitted to the outside of the optical element4by refraction and transmission. As described above, most of light emitted from the optical element4is transmitted through the globe2, and used as illumination light.

By contrast, part of the light emitted from the optical element4is reflected by the internal surface of the globe2. In this state, reflection of light is Fresnel reflection, and more light is reflected as the incident angle of light with respect to the internal surface of the globe2increases. The incident angle of light herein means an angle between a normal H running through a point at which light is made incident on the internal surface of the globe2and a ray made incident on the point.

For example, a ray L1indicated with a broken line arrow inFIG. 1indicates a ray scattered by an end portion of the scattering portion8distant from the light source6. The ray L1is reflected by the internal surface of the globe2, and goes toward the substrate11and/or the diffusion portion3. Specifically, in this case, the direction in which the ray L1is reflected is a direction close to the base5beyond the center R of the globe2. In other words, in this case, the direction in which the ray L1is reflected is a direction opposite to a direction of going toward the top portion that is most distant from the base5of the globe2. The ray L1reflected in this direction is further reflected by the surface of the substrate11and/or the surface of the diffusion portion3, and serves as an optical component to cause the illumination light to have wide light distribution.

In addition, for example, a ray L2indicated with a solid line arrow inFIG. 1indicates a ray scattered by an end portion of the scattering portion8close to the light source6. The ray L2is reflected by the internal surface of the globe2, and goes toward the optical element4. Also in this case, the direction in which the ray L2is reflected is a direction close to the base5beyond the center R of the globe2. The ray L2reflected in this direction is reflected by the surface of the optical element4, or transmitted through the optical element4.

Specifically, as in the present embodiment, when the scattering portion8is disposed on a side opposite to the light source6with respect to the center R of the globe2, the ray L1and the ray L2are reflected in the direction close to the base5beyond the center R of the globe2, and hit against any of the optical element4, the substrate11, and the diffusion portion3. The ray that has reached the substrate11and/or the diffusion portion3is diffused and reflected in a direction going toward the base5.

By contrast, if no optical element4is provided, rays emitted from the light source6go toward the top portion of the globe2. Specifically, because the LED device of the light source6emits light with high directivity, when no optical element4is provided, light from the light source6goes toward the top portion of the globe2. For this reason, without the optical element4, many narrow light distribution components are emitted from the globe2.

Specifically, the optical element4provided as in the present embodiment enables scattering of rays emitted from the light source6with the scattering portion8, enables generation of wide light distribution components, and causes illumination light emitted from the globe2to have wide light distribution. The condition for emitting illumination light with wide light distribution as described above is to provide the scattering portion8inside the globe2.

In addition, in the present embodiment, the scattering portion8is disposed on a side opposite to the light source6with respect to the center R of the globe2. With this structure, the light component reflected by the internal surface of the globe2by Fresnel reflection without being transmitted through the globe2goes toward the direction of the base5. In addition, part of the light reflected by the internal surface of the globe2is further reflected by the surface of the substrate11and/or the surface of the diffusion portion3, to serve as wide light distribution components in the end, and is emitted from the globe2. For this reason, these optical components serve as optical components to cause the illumination light to have wide light distribution.

As described above, according to the present embodiment, Fresnel reflection components in the internal surface of the globe can be converted into wide light distribution components. This structure achieves an LED light bulb with wider light distribution, and enables emission of light with wide light distribution and retrofitting property. To convert all the Fresnel reflection components into wide light distribution components, the center R of the globe2is required to be positioned within a line segment connecting the scattering portion8of the optical element4with the light source6, at the optical element4outside the scattering portion8or close to the light source6.

By contrast, in diffusion reflection with the substrate11and/or the diffusion portion3, absorption loss of substantially several percent occurs. For this reason, Fresnel reflection should be suppressed as much as possible, in view of the luminaire efficiency. Fresnel reflection components increase as the incident angle of light with respect to the internal surface of the globe2increases. For this reason, the incident angle should be reduced as much as possible. The ray L1has the maximum incident angle, among the rays scattered in the scattering portion8. When the center R of the globe2is positioned at an end portion of the scattering portion8on a side close to the light source6, the incident angle of the ray L1becomes minimum. Specifically, in this state, the luminaire efficiency becomes maximum.

In addition, as in the present embodiment, when the rotation-symmetrical axis of the globe2agrees with the rotation-symmetrical axis of the optical element4, optical components transmitted and reflected by the globe2become uniform with respect to the orientation direction of rotation-symmetrical axis. This structure enables production of uniform lighting. By contrast, when their rotation-symmetrical axes are shifted from each other, unevenness occurs with respect to the orientation direction, and lighting becomes nonuniform.

The following is explanation of a lighting apparatus20according to a second embodiment with reference toFIG. 3.

The lighting apparatus20according to the present embodiment has a structure similar to that of the lighting apparatus10according to the first embodiment described above, except that the position of the scattering portion8along the central axis C is changed. Accordingly, constituent elements functioning similarly to those of the first embodiment are denoted by the same reference numerals, and detailed explanation thereof is omitted.

The scattering portion8of the lighting apparatus20according to the present embodiment is disposed in a position including the center R of the globe2. More preferably, the scattering portion8is disposed such that the center of the scattering portion8overlaps with the center R of the globe2.

When the lighting apparatus20is turned on, substantially several percent of Fresnel reflection components in the internal surface of the globe2are absorbed by the optical element4, the substrate11, or the diffusion portion3. For this reason, Fresnel reflection should be suppressed as much as possible in view of the luminaire efficiency. Fresnel reflection components increase as the incident angle of light with respect to the internal surface of the globe2increases. For this reason, the incident angle should be reduced as much as possible.

Among the rays scattered in the scattering portion8, the ray that has the maximum incident angle with respect to the internal surface of the globe2is the ray L1scattered at the end portion of the scattering portion8distant from the light source6, or the ray L2scattered at the end portion of the scattering portion8close to the light source6. When the center R of the globe2is located in a position of the scattering portion8obtained by dividing the length of the scattering portion8along the central axis C in half, the maximum values of the incident angles of the rays L1and L2become minimum. This structure minimizes Fresnel reflection components, and reduces reflection loss.

As described above, the present embodiment increases optical components in a direction of going toward the base5, with reflection loss in the internal surface of the globe2suppressed to the minimum, and enables emission of light with wide light distribution and retrofitting property.

The following is explanation of a lighting apparatus30according to a third embodiment with reference toFIG. 4.

The lighting apparatus30according to the present embodiment has a structure similar to that of the lighting apparatus10according to the first embodiment described above, except that the position of the scattering portion8along the central axis C is changed. Accordingly, constituent elements functioning similarly to those of the first embodiment are denoted by the same reference numerals, and detailed explanation thereof is omitted.

The scattering portion8of the lighting apparatus30according to the present embodiment is disposed in a position on the light source6side beyond the center R of the globe2. More preferably, the scattering portion8is disposed such that the end portion of the scattering portion8on a side opposite to the light source6is disposed in the center R of the globe2.

When the lighting apparatus30is turned on, the ray that has the maximum incident angle with respect to the internal surface of the globe2is the ray L2scattered at the end portion of the scattering portion8close to the light source6, among the rays scattered in the scattering portion8. By contrast, the ray that has the minimum incident angle with respect to the internal surface of the globe2is the ray L1scattered at the end portion of the scattering portion8distant from the light source6.

All the reflection components of the rays L1and L2in the internal surface of the globe2go in a direction (that is, a direction going away from the light source6) toward the top portion of the globe2. Specifically, rays reflected by the internal surface of the globe2do not go toward the optical element4, the substrate11, or the diffusion portion3. This structure increases narrow-angle components, and produces shine in the top portion of the globe2.

In addition, in view of the luminaire efficiency, Fresnel reflection should be suppressed as much as possible, and the center R of the globe2should be located in an end portion of the scattering portion8distant from the light source6. In the present embodiment, because rays reflected by the internal surface of the globe2do not go toward the optical element4, the substrate11, or the diffusion portion3, the rays are not absorbed, and loss is reduced.

As described above, the present embodiment reduces absorption loss of rays in the optical element4, the substrate11, or the diffusion portion3, increases narrow-angle components, while wide light distribution is maintained with the optical element4, and achieves a light bulb with a bright top portion of the globe2.

[Fourth Embodiment and Fifth Embodiment]

FIG. 5is a schematic diagram illustrating a lighting apparatus40according to a fourth embodiment, andFIG. 6is a schematic diagram illustrating a lighting apparatus50according to a fifth embodiment. The lighting apparatus40inFIG. 5is a light bulb of a chandelier bulb type, and the lighting apparatus50inFIG. 6is a light bulb of a ball bulb type.

The first to the third embodiments described above illustrate light bulbs of an ordinary bulb type, but the present invention is also applicable to light bulbs of the chandelier bulb type and the ball bulb type.

[Modification of Optical Element]

FIG. 7is a schematic diagram illustrating a modification of the optical element4incorporated in the lighting apparatuses according to the first to the fifth embodiments described above. An optical element60according to the modification has a structure similar to that of the optical element4described above, except that the optical element60includes a flat light incident surface61and a scattering portion62being a cavity of a rotation oval shape. Accordingly, constituent elements functioning similarly to those of the optical element4are denoted by the same reference numerals, and detailed explanation thereof is omitted.

The shape of the scattering portion62is not limited to a recessed portion opened to the distal end of the optical element or a rotation oval shape, but various shapes may be selected, such as a spherical shape, and a recessed portion opened to the proximal end of the optical element. In any case, any scattering portion may be used as long as the scattering portion has a rotation-symmetrical shape with respect to the central axis of the optical element.