Electric lamp

Abstract

 An electric lamp (1) comprising a socket (2), a lamp bulb (4) mounted on the socket in which bulb at least one semiconductor light source (5) is arranged. Cooling means (6) comprise at least two facing cooling fins (7,8) which are separated by at least one spacing (9). Said spacing being open to the environment and extending from the heart of the lamp bulb into the outer surface of the bulb. The lamp comprising a light redistributing, light transmittable wall (13) for redistributing light, optionally said light redistributing wall comprises separate, discernable wall parts (14,15). For example, each discernable bulb part is shaped as a surface of a halve prolate or halve oblate ellipse. Thus a desired double beam or homogeneous, omni-directional light distribution is obtainable.

Description

FIELD OF THE INVENTION

[0001] The invention relates to an electric lamp comprising:

• a socket for mounting the lamp along an insertion direction in a lamp holder,
• a lamp bulb mounted on the socket in which bulb at least one semiconductor light source is arranged,
• cooling means for cooling of the lamp during operation, the cooling means comprise at least two facing cooling fins which are separated by at least one spacing.

BACKGROUND OF THE INVENTION

[0002] Such an electric lamp is known from W02008154172. In the known lamp a semiconductor light source, i.e. a plurality of LEDs, are mounted on one of the cooling fins. Both the light source and the cooling fins are arranged in a lamp bulb, the lamp bulb having a lamp shell with a shape according to the lamp bulb of a common incandescent general light source (GLS). The known lamp has the disadvantage that cooling of the LEDs is not effective as the cooling fins are arranged in a fully closed lamp shell. Once the filling of the bulb has been warmed up by the heat generating LEDs inside the bulb, transport of heat from inside the bulb to the exterior has to occur through the lamp shell, said shell generally not being a good heat conductor. To enhance heat flow from the LEDs to the exterior in the known lamp the lamp is provided with a heat conductor inside the shell rendering the lamp to be of a relatively complex construction. In the known lamp the shell is filled with a liquid or a gel to counteract the detrimental effect of the shell on heat conduction, but renders the lamp to have the additional disadvantage of being relatively heavy. Furthermore, as the heat still has to be transported through the relatively bad heat conducting wall of the shell, the known lamp still has a relatively high temperature inside the bulb, rendering the lamp to have a relatively low efficiency as the operation of the LEDs at higher temperatures is relatively inefficient.

SUMMARY OF THE INVENTION

[0003] It is an object of the invention to counteract at least one of the disadvantages of the known electric lamp. Thereto the electric lamp as described in the opening paragraph has the additional features of:

said spacing being open,

a lamp axis extending along the insertion direction through a central end of the socket, through said spacing, and through a (virtual) central extreme of the bulb most remote from the socket,

the lamp comprising a light redistributing, light transmittable wall for redistributing light originating from the light source into a desired light distribution during operation of the lamp.

[0004] Open spacing in this respect means that the spacing is open to the environment to enable exchange of environmental air with air present in the spacing due to convection/free flowing as a result of heat generated by the light source(s) during operation. The feature of the lamp axis extending through the open spacing renders the open spacing to have a relatively large dimension and thus to extend over a relatively large fraction of the lamp bulb. Hence, the cooling capacity of the cooling fins is enhanced. Because of the spacing the effect occurs that the light distribution (beam characteristics) of the lamp is affected. The light redistributing, light transmittable wall for redistributing light having an original light distribution and originating from the light source into a desired light distribution during operation of the lamp can correct that effect. Moreover, the redistributing, light transmittable wall is capable of modifying the original light distribution into various, other light distributions, for example, a double narrow beam or a substantially homogeneous, almost omni-directional light distribution. The double narrow beam light distribution exemplifies the light distribution of a spot light with, for example, two relatively narrow, round beams emitted in two opposite directions, for example two beams mutually under 160-200 degrees each with a beam width having an apex angle of about 30 degrees. A homogeneous omni-directional light distribution means that in the far-field, i.e. at relatively large distances from the electric lamp, for example at least 50 cm, the measured light intensity is relatively homogeneous. For example, the maximum and minimum measured light intensity does differ at the most by 35 % within a space angle of about 300 degrees around the lamp bulb, thus being about the same as the light distribution as generated by a standard GLS. Other light distributions are envisaged, for example two oppositely directed elongated beams, or a light distribution according to a common flood light, i.e. a homogeneous light distribution within a space angle of about 160 or 180 degrees. The mutually facing cooling fins comprise mutual positions of cooling fins opposite to each other, possibly in a somewhat shifted and/or angled position.

[0005] Said desired light distributions are obtainable via various means provided to or present in or at the light distributing wall. Therefore in an embodiment, preferably said wall comprises at least one feature chosen from the group consisting of:

• a (remote) phosphor;
• a reflective means;
• a diffusing means;
• a shape deviating essentially from a part of sphere.

[0006] Said (remote) phosphor offers the advantage to the lamp of being both a diffuser and a means of changing the spectrum of the light as emitted by the light sources. The phosphor, for example, is a UV- and/or blue-absorbing and subsequently green, yellow, orange, or red emitting poly-crystalline powder or glass material. Said reflective means, for example, is a coating which, for example, could be provided in a pattern. Favorable patterns of said coating comprise a strip extending along the lamp axis over the bulb outer surface or a circle positioned opposite to the light source on the bulb outer surface. The light distributing wall provided with such a pattern renders the lamp to have an almost omni-directional light distribution, for example in the case of two LEDs mutually facing away in a direction perpendicular to the lamp axis. A similar effect applies to the diffusing means, but then light is not reflected but scattered by and transmitted through the diffusing means. The diffusing means for example being a diffusive powder coating on the wall or a diffusing foil or the wall being made of milky glass.

[0007] In the case of light distribution means being a shape deviating essentially from a part of a sphere, light is redistributed as a result of refraction. It is possible that said light transmittable wall is part of the lamp bulb, and/or part is of an inner bulb arranged inside the lamp bulb, and/or is comprised as a part in the light source. Light from the light source incident on said transmittable wall at different locations at different angles will be refracted differently depending on the angle of incidence of the light on said wall. Hence, the light distribution can be controlled by the design and/or shape of the wall.

[0008] It is not a prerequisite that said wall is formed in one, integral part, but it could alternatively be a wall comprising at least two, non-integral/essentially separate wall parts, thus rendering the lamp to have more freedom of design and hence to apply advantageous technical features to the lamp. For example, in an embodiment the electric lamp is characterized in that the spacing dividing the lamp bulb into at least two discernable bulb parts, each PCB together with a respective bulb part forming a respective discernable lamp bulb compartment. It is thus enabled to associate a bulb part with a respective light source rendering the lamp to be more flexible in realizing a desired light distribution. In embodiment in which the electric lamp according indeed is characterized in that in each bulb compartment at least one respective semiconductor light source is arranged each bulb part is enabled to generate its respective light distribution. For example, it is thus possible to have the electric lamp to generate at one side a seemingly lambertian light distribution, leading to a hemispherical, almost uniform light distribution, while on the opposite side, i.e. the opposite hemisphere, a light distribution resembling a spot light is generated by the lamp.

[0009] In an embodiment the electric lamp is characterized in that the light source is mounted on a respective PCB which is integral with a respective cooling fin. Thus efficient and effective cooling of the semiconductor light sources is obtained. Preferably each light source and respective PCB is arranged in a respective bulb part, rendering the lamp to have the advantage that the light sources are mutually independently controlled. More preferably the bulb parts mutually are arranged in mirror symmetry with respect to a plane P extending in between the PCB's. For example an embodiment of the electric lamp is characterized in that each discernable bulb part is shaped as a surface of a halve prolate ellipse having two equal radii and one deviating radius, the spacing extending through the two radii of the ellipse that are equal, thus the lamp parts are mirrorly positioned with respect to the spacing. The two halves of the prolate ellipse render the lamp to have a substantially homogeneous, almost omni-directional light distribution during operation. In an alternative embodiment the electric lamp is characterized in that each discernable bulb part is shaped as a surface of a halve oblate ellipse having two equal radii and one deviating radius, the spacing extending through the two radii of the ellipse that are equal. This renders the lamp to have a double beam light characteristics, the beams mutually pointing away from each other at an angle of about 180°.

[0010] An embodiment of the electric lamp is characterized in that the spacing has a width in the range of 3 mm to 20 mm. If the spacing has a width less than 3 mm the cooling efficiency of the cooling fins is decreased because at smaller widths of said spacing the natural air flow through the spacing due to heat convection is hampered. The decreased cooling efficiency of the cooling fins might result in the LEDs to become relatively hot thus decreasing the efficiency of the lamp. If the width of said spacing becomes more than 20mm a disturbing effect of the width on the light distribution becomes apparent, thus decreasing the quality of the lamp. Connecting the two discernable lamp bulb compartments via at least one bridge which bridges the spacing and which do(es) not effectively closes the spacing, i.e. the air flow due to convection is not significantly decreased, does not significantly influences the cooling efficiency of the cooling fins. Said bridges make the lamp more robust and thus better to withstand mechanical load, for example mechanical load that occurs in handling the lamp, for example during manufacturing or mounting.

[0011] An embodiment of the electric lamp according is characterized in that the lamp bulb essentially has a spherical shape. The lamp then has a shape which closely resembles the shape of an ordinary GLS and replacement of said GLS lamp by the electric lamp of the invention in existing luminaries/fixtures designed for GLS lamps is convenient.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention now will be elucidated further by means of the drawing in which

Fig.1A shows a first embodiment of the lamp according to the invention;

Fig.1B shows a graph of the relative luminous intensity in annular direction around the lamp axis of the lamp of Fig.1A;

FIG.1C shows a polar plot of the far field luminous intensity both in the direction along and transverse to the lamp axis of the lamp of Fig.1A;

Fig.2A-D show Figures analogous to Figs.1A-C for a second embodiment of the lamp according to the invention;

Fig.3A-C show Figures analogous to Figs.1A-C for a third embodiment of the lamp according to the invention;

Fig.4A-C show Figures analogous to Figs.1A-C for a fourth embodiment of the lamp according to the invention;

Fig.5A-C show Figures analogous to Figs.1A-C for a fifth embodiment of the lamp according to the invention; and

Fig.6A shows a sixth embodiment of the lamp according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

[0013] For reference orientation, a coordinate symbol with x,y,z-axes is added to the drawing.

[0014] Fig. 1A shows an electric lamp 1 comprising a socket 2 for mounting the lamp along an insertion direction 3 in a lamp holder. A lamp bulb 4 is mounted on the socket in which bulb 4 at least one semiconductor light source 5 is arranged, in the figure a pair of LEDs. In the figure, the lamp bulb is made of polycarbonate, but alternatively can be made of glass or any other light transmittable solid material, for example PMMA. Cooling means 6 for cooling of the lamp during operation are provided, the cooling means comprise at least two facing cooling fins 7,8 which are separated by a spacing 9, the spacing being 8 mm. Said spacing is in an open connection with the exterior of the lamp. The light source being mounted on a PCB which simultaneously acts as the cooling fin. A lamp axis 10 extends along the insertion direction through a central end 11 of the socket, through said spacing, and through a (virtual) central extreme 12 of the bulb most remote from the socket. The lamp comprises a light redistributing, light transmittable wall 13, comprising two halves 14, 15, for redistributing light originating from the light source, i.e. a LED in each of two halves bulbs 18,19 of the lamp bulb 4, into a desired light distribution during operation of the lamp.

[0015] Fig. 1B shows a graph of the relative luminous intensity in annular direction around the lamp axis 13, z-direction, of the lamp of Fig.1A. The relative luminous intensity has a large spread in intensity, with minima in intensity at 90° and 270°, i.e. in direction x perpendicular to the plane of the drawing, and with maxima at 0° and 180°, i.e. in direction y in plane of the drawing.

[0016] FIG.1C shows the same luminosity intensity distribution, but then represented as a polar plot of the far field luminous intensity in the x,y-plane.

[0017] Fig.2A-D show Figures analogous to Figs.1A-C for a second embodiment of the lamp according to the invention. In Fig.2A and 2B the light transmittable wall 13 of the lamp 1 has an elliptical shape, i.e. are two halves 14, 15 of a prolate ellipse having two equal radii x_r and z_r in the x-direction respectively in the z-direction and one deviating radius y_r in the y-direction, y_r being 1.5 times as big as the x_r and z_r. The spacing 9 of 18 mm width, extends through the two radii x_r and z_r of the ellipse that are equal. As shown in Figs. 2C and 2D the luminosity intensity distribution obtained by the lamp of Fig.2A is significantly influenced by the shape of the transmittable, light redistributing wall. Due to the shape of said wall, the annular and far field luminosity intensity distribution has only a very limited spread in intensity, with an intensity spread of less than 10%.

[0018] Fig.3A-C show Figures analogous to Figs.1A-C for a third embodiment of the lamp 1 according to the invention. In Fig.3A a diffuse reflective layer 16 is provided on each of the two halves 14, 15 of the transmittable, light redistributing wall of the lamp in a circular pattern around the y-axis direction. The overall lamp bulb is essentially a circular sphere, i.e. the same bulb shape as the lamp bulb of the lamp of Fig.1A. The effect of the reflective layer pattern 16 on the annular and far field luminosity intensity distribution is shown in Figs.3B and 3C, i.e. the luminous intensity showing a relatively small spread, i.e. about 20%, compared to the luminous intensity distribution obtained by the lamp of Fig. 1A.

[0019] Fig.4A-C show Figures analogous to Figs.1A-C for a fourth embodiment of the lamp 1 according to the invention. In Fig.4A a white, horn shaped reflector 17 is provided in each of the two halves 18, 19 of the lamp bulb 4. The horn-like shaped reflector has a virtual, annular circular opening around the y-axis direction, the light source 5 being arranged on the y-axis. The overall lamp bulb is essentially a circular sphere, i.e. the same bulb shape as the lamp bulb of the lamp of Fig.1A. The effect of the reflective horn-like shaped reflector 17 on the annular and far field luminosity intensity distribution is shown in Figs.4B and 4C, i.e. the luminous intensity showing a relatively small spread, i.e. about 20%, compared to the luminous intensity distribution obtained by the lamp of Fig. 1A.

[0020] Fig.5A-C show Figures analogous to Figs.1A-C for a fifth embodiment of the lamp according to the invention. In Fig.5A in each of the two bulb halves 18, 19 of the lamp bulb 4a prolate elliptical inner bulb halve 20, 21 is provided. These two inner bulb halves 20,21 of a prolate ellipse having two equal radii x_r and z_r in the x-direction respectively in the z-direction and one deviating radius y_r in the y-direction, y_r being 1.5 times as big as the x_r and z_r. The light source 5, a LED in each of the inner bulb halves, are arranged on the y-axis. The spacing 9 extends through the two radii x_r and z_r of the ellipse that are equal. The overall lamp bulb is essentially a circular sphere, i.e. the same bulb shape as the lamp bulb of the lamp of Fig.1A. In this lamp the lamp bulb 4 is strengthened in that bridges 22 are provided that connect the two bulb halves 18,19 by bridging the spacing 9. The effect of the two inner elliptical bulb halves 20,21 on the annular and far field luminosity intensity distribution is shown in Figs.5B and 5C, i.e. the luminous intensity showing a relatively small spread, i.e. about 15%, compared to the luminous intensity distribution obtained by the lamp of Fig. 1A.

[0021] Fig.6 shows a sixth embodiment of the lamp 1 according to the invention. In Fig.6 an optical open window 23 is provided on each of the two halves 14, 15 of the transmittable, light redistributing wall 4 of the lamp 1 in a circular pattern around the y-axis direction. The remainder of the wall is coated with a diffuse reflective layer. The overall lamp bulb is essentially a circular sphere corresponding to the shape of a general GLS bulb, and the same bulb shape as the lamp bulb of the lamp of Fig.1A. The optical open window 23 renders the lamp to have a double beam light distribution pattern on the annular direction around the z-axis and as the far field luminosity intensity distribution.

Claims

1. Electric lamp comprising:

- a socket for mounting the lamp along an insertion direction in a lamp holder,

- a lamp bulb mounted on the socket in which bulb at least one semiconductor light source is arranged,

- cooling means for cooling of the lamp during operation, the cooling means comprise at least two facing cooling fins which are separated by at least one spacing,

- said spacing being open,

- a lamp axis extending along the insertion direction through a central end of the socket, through said spacing, and through a (virtual) central extreme of the bulb most remote from the socket,

the lamp comprising a light redistributing, light transmittable wall for redistributing light originating from the light source into a desired light distribution during operation of the lamp.

2. Electric lamp according to claim 1, characterized in that said wall comprises at least one feature chosen from the group consisting of:

- a (remote) phosphor;

- a reflective means;

- a diffusing means;

- a shape deviating essentially from a part of sphere.

3. Electric lamp according to claim 1 or 2, characterized in that said wall comprises at least two, non-integral/essentially separate wall parts.

4. Electric lamp according to claim 1 or 2, characterized in that said light transmittable wall is part of the lamp bulb.

5. Electric lamp according to claim 1or 2, characterized in that said light transmittable wall is part of an inner bulb arranged inside the lamp bulb.

6. Electric lamp according to claim 1 or 2, characterized in that said light transmittable wall is part of the light source.

7. Electric lamp according to claim 1 or 2, characterized in that the light source is mounted on a respective PCB which is integral with a respective cooling fin.

8. Electric lamp according to claim 7, characterized in that the spacing dividing the lamp bulb into at least two discernable bulb parts, each PCB together with a respective bulb part forming a respective discernable lamp bulb compartment.

9. Electric lamp according to claim 8, characterized in that in each bulb compartment at least one respective semiconductor light source is arranged.

10. Electric lamp according to claim 8 or 9, characterized in that the two discernable lamp bulb compartments are connected via at least one bridge which bridges the spacing.

11. Electric lamp according to claim 1 or 2, characterized in that the spacing has a width in the range of 3 mm to 20 mm.

12. Electric lamp according to claim 1 or 2, characterized in that the lamp bulb essentially has a spherical shape.

13. Electric lamp according to claim 7 or 8, characterized in that the bulb parts mutually are arranged in mirror symmetry with respect to a plane P extending in between the PCB's.

14. Electric lamp according to claim 1 or 2, characterized in that each discernable bulb part is shaped as a surface of a halve prolate ellipse having two equal radii and one deviating radius, the spacing extending through the two radii of the ellipse that are equal.

15. Electric lamp according to claim 1 or 2, characterized in that each discernable bulb part is shaped as a surface of a halve oblate ellipse having two equal radii and one deviating radius, the spacing extending through the two radii of the ellipse that are equal.

Drawing