WO2013057665A1

WO2013057665A1 - Illumination device

Info

Publication number: WO2013057665A1
Application number: PCT/IB2012/055641
Authority: WO
Inventors: Yan Xiong; Xiaolin Wang
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2011-10-19
Filing date: 2012-10-17
Publication date: 2013-04-25

Abstract

The present invention provides an illumination device (100) comprising: an envelope (105) mounted on a base (101), a light source (107) mounted to the top of the envelope (105), and a reflector (104) arranged inside the envelope (105) and being configured to reflect light emitted from the light source (107). An imaginary base plane (P) is defined substantially perpendicularly to a device symmetry axis (S) extending through a central end of the base (101) and a central extremity of the envelope (105). The reflector (104) is symmetrically arranged around the axis (S) at an angle (a) to the imaginary base plane (P), the angle (a) being configured based on a first diameter (D) of the envelope (105). The illumination device (100) of the present invention has an even luminous intensity distribution that meets the Energy Star requirements.

Description

ILLUMINATION DEVICE

FIELD OF THE INVENTION

The present invention relates to the field of lighting, more particularly to an illumination device with novel structures.

BACKGROUND OF THE INVENTION

A LED lamp is a lamp that uses the LED as the light source. Generally, a lamp or illumination device comprises a light source arranged to generate light and mounted on, or at least connected to, a circuit board. With the increase of the power of the LED lamp, more heat will be generated, which adversely affects the lifetime of the LED lamp. It is thus a challenge to design a good structure for heat dissipation in LED lamps so as to prolong the lifetime of the LED lamp. An example of a LED lamp may be found in the reference document CN 101858495 A. In the embodiment, there is provided an inverted LED lamp, of which the LED is positioned relatively far from the base and a reflector is simply attached to the base. However, such an LED lamp does not have a sufficiently even distribution of luminous intensity. For example, it cannot meet the requirements of the Energy Star specification on the luminous intensity distribution. The Energy Star specification on the luminous intensity distribution requires that the omnidirectional lamps shall have an even distribution of luminous intensity (candelas) within the 0° to 135° zone (vertically axially symmetrical). For example, as shown in Fig. 11, the luminous intensity at any angle within this zone (Zone 1) shall not differ from the mean luminous intensity for the entire 0° to 135° zone by more than 20%, at least 5% of total flux (lumens) must be emitted in the 135°- 180° zone (Zone 2). The distribution shall be vertically symmetrical as measured in three vertical planes at 0°, 45°, and 90°.

OBJECT AND SUMMARY OF THE INVENTION It is an object of the present invention to provide a lamp structure that has an even luminous intensity distribution, in accordance with the requirements of the Energy Star specification.

According to one aspect of the present invention, there is provided an illumination device, which may comprise: an envelope mounted on a base, a light source mounted to a top of the envelope, and a reflector arranged inside the envelope and being configured to reflect light emitted from the light source, an imaginary base plane (P) is defined substantially perpendicularly to a device symmetry axis (S) extending through a central end of the base (101) and a central extremity of the envelope (105), wherein the reflector may be symmetrically arranged around the axis at an angle a to the imaginary base plane, the angle a being configured based on a first diameter of the envelope.

According to one embodiment of the present invention, the reflector may comprise a conical reflector or a plurality of curved reflector parts.

According to a further embodiment of the present invention, the envelope may comprise a housing and a top portion, the light source may be mounted to the top portion having a second diameter, the second diameter of the top portion being configured based on the first diameter of the envelope.

According to another embodiment of the present invention, the angle a is further configured based on the second diameter of the top portion.

According to yet another embodiment of the present invention, the angle a decreases with the decrease of the second diameter of the top portion.

According to one embodiment of the present invention, the second diameter of the top portion is less than half of the first diameter of the envelope.

According to a further embodiment of the present invention, a distance between the light source and the imaginary base plane is adjusted based on the second diameter of the top portion. According to another embodiment of the present invention, the distance between the light source and the imaginary base plane increases with the decrease of the second diameter of the top portion.

According to yet another embodiment of the present invention, the distance between the light source and the imaginary base plane is 2/3 to 5/6 times of the first diameter of the envelope.

According to one embodiment of the present invention, a curvature radius of the curved reflector parts increases with the decrease of the second diameter of the top portion.

According to a further embodiment of the present invention, the curvature radius is 2.25 to 2.3 times of the first diameter of the envelope.

According to another embodiment of the present invention, the top portion may be a metal top cover mechanically connected with the housing, and the light source may be mounted to the metal top cover.

According to yet another embodiment of the present invention, the top portion may be a claw-shaped metal piece having a plurality of fingers, the housing contacts the inner surfaces of the plurality of fingers and sheathes over a cavity which is enclosed by the claw- shaped metal piece, and the light source is mounted in a palm of the claw- shaped metal piece.

According to one embodiment of the present invention, the housing may comprise a plurality of parts, each part being attached between two adjacent fingers from the inside of the cavity enclosed by the claw- shaped metal piece, wherein an upper end of each part is mechanically connected with the palm of the claw-shaped metal piece, and a lower end of each part is mechanically connected with the base.

According to a further embodiment of the present invention, each finger may have a groove opening outwards.

The illumination device designed in accordance with the present invention has a luminous intensity distribution that meets the Energy Star design criteria. That is to say, within the range of 0 to 135 , the luminous intensity of any angle of the illumination device is within the range of ±20% of the mean luminous intensity. In other words, the relative luminous intensity of any angle within the range of 0° to 135° is within the range of 80% to 120% of the mean luminous intensity (taking the mean luminous intensity as 100%). Thus, not only low-power lamps of e.g. 2-3w, but also high-power lamps of e.g. 75w, lOOw, meet the design criteria of the Energy Star on the luminous intensity distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows an exploded view of the illumination device according to one aspect of the present invention;

Fig. 2 schematically shows an appearance view of the illumination device according to one embodiment of the present invention;

Fig. 3 schematically shows a sectional view of the illumination device in Fig. 2 taken on the line A- A;

Fig. 4 schematically shows an exploded view of the illumination device in Fig.

2;

Fig. 5 schematically shows an exploded view of the illumination device according to a further embodiment of the present invention;

Fig. 6 schematically shows a vertical view of the illumination device as shown in Fig. 5;

Fig. 7 schematically shows a sectional view of the illumination device in Fig. 6 taken on the line B-B;

Figs. 8-9 schematically show appearance views of the illumination device as shown in Fig. 5; Fig. 10 schematically shows a simulated distribution profile of the luminous intensity of the illumination device according to the embodiments of the present invention.

Fig. 11 schematically shows the American Energy Star specification on the omnidirectional lamp zones with a lamp in base-up position.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

First, it will be explained that the term "mean luminous intensity" as mentioned in the description of the present invention complies with the general explanation in the field of optics, i.e., it refers to the mean value obtained from division of the sum of the luminous flux within the solid angle of 0° to 135° by the solid angle of 135°. The term "relative luminous intensity" as mentioned in the description of the present invention complies with the general explanation in the field of optics, which refers to the ratio of the luminous intensity and the maximum luminous intensity.

Fig. 1 schematically shows an exploded view of the illumination device according to one aspect of the present invention. An illumination device 100 according to this aspect of the present invention may comprise: an envelope 105 mounted on a base 101; a light source 107 mounted to the top of the envelope 105; a device symmetry axis S extending through a central end of the base 101 and a central extremity of the envelope 105; an imaginary base plane P being defined substantially perpendicularly to the device symmetry axis S at an interface between the envelope 105 and the base 101; and a reflector 104 arranged inside the envelope 105 and being configured to reflect light emitted from the light source 107, the reflector 104 being symmetrically arranged around the axis at an angle a (see the angle a shown in Fig. 7) to the imaginary base plane P, the angle a being configured based on a first diameter D of the envelope 105. In one embodiment of the present invention, the envelope 105 of the present invention may be an entire envelope (not shown), in which case, the light source 107 can be directly mounted to the top of the envelope 105, for example, at the inner surface of the top. Here, the area occupied by the light source 107 at the top can be called a top portion, and the second diameter d of this top portion can be configured with reference to the following description.

It will be pointed out that the terms "a first diameter D of the envelope 105" and "a second diameter d of the top portion" mentioned in respective embodiments of the present invention are only for the purpose of discrimination; it does not mean that the envelope 105 further has a second diameter, or the top portion further has a first diameter.

Alternatively, the envelope 105 of the present invention may comprise a housing 105 a and a top portion 105b. The housing 105 a may be an entire housing as shown in Figs. 2-4. The housing 105a may also be a housing consisting of a plurality of parts; as schematically shown in Figs. 1 and 5, the housing 105a consists of three parts. However, it does not mean that the housing 105 a can only consist of three parts, it may also consist of two parts or a plurality of other parts. The light source 107 may be mounted to the top portion 105b having a second diameter d (see second diameter d as shown in Fig. 4); for example, it may be mounted to the inner surface of the top portion 105b. The second diameter d of the top portion 105b can be configured based on the first diameter D of the envelope 105, which will be described in more detail hereinafter.

Alternatively, the light source 107 of the present invention may comprise white LED, blue LED, a RGB tricolor source and blue LED excited by fluorescence etc. For example, as for an illumination device (such as a lamp) of 40w, 60w, the white LED can be used as the light source; as for an illumination device of lOOw, the blue LED or the blue LED excited by fluorescence etc can be used. It is not difficult to understand for the skilled person in the art that for different power requirements an appropriate LED or RGB tricolor source should be selected as the light source.

It will be explained that the device symmetry axis S shown in Fig. 1 is an imaginary line extending through a central end of the base 101 and a central extremity of the envelope 105. The imaginary symmetry axis S in the illumination device, for example the lamp, is intended for the convenience of describing the structure and configuration of the reflector as well as other corresponding parameters in the lamp; it does not mean that a symmetry axis S in the sense of physics must exist in the actual structure of the lamp. Also the imaginary base plane P shown in Fig. 1 is intended for the convenience of describing the structure and configuration of the reflector as well as other corresponding parameters in the lamp; it does not mean that a base plane in the sense of physics substantially perpendicular to the device symmetry axis S must exist at an interface between the envelope 105 and the base 101 in the actual structure of the lamp. Similarly, the device symmetry axis S, the imaginary base plane P shown in Fig. 2, the imaginary base plane P shown in Fig. 3, the device symmetry axis S shown in Fig. 4, the device symmetry axis S, the imaginary base plane P shown in Fig. 5, and the imaginary base plane P shown in Fig. 7 are all for the convenience of describing the structure and configuration of the reflector as well as other corresponding parameters in the lamp; it does not mean that a symmetry axis S in the sense of physics must exist in the actual structure of the lamp nor that a base plane in the sense of physics substantially perpendicular to the device symmetry axis S must exist at an interface between the envelope 105 and the base 101 in the actual structure of the lamp.

The reflector 104 shown in Fig. 1 is arranged inside the envelope 105, and is configured to reflect light emitted from the light source 107, wherein the reflector 104 is symmetrically arranged around the axis at an angle a to the imaginary base plane P (see Fig. 7, which shows the angle a of the reflector 104 to the imaginary base plane P), the angle a being configured based on a first diameter D of the envelope 105 (see Fig. 2, which shows the first diameter D of the envelope 105). The first diameter D of the envelope 105 shown in Fig. 2 of the present invention and mentioned in respective embodiments of the present invention refers to the maximum transverse size of the envelope 105, but it does not mean that the envelope 105 is strictly spherical. The envelope 105 may also have a near-spherical shape, such that the size in the middle is largest and the sizes of the two ends are relatively small. The first diameter D refers to the maximum size in the middle of the envelope 105, i.e., the maximum transverse size.

It is pointed out that the reflector 104 is symmetrically arranged around the device symmetry axis S in the following situations. For example, in the event that the reflector 104 is a conical reflector (not shown), the device symmetry axis S can be taken as the central axis of the conical reflector, and the sides of the conical reflector reflect light emitted by the light source 107. Apparently, here the conical reflector is symmetrically arranged around the device symmetry axis S. In the event that the reflector 104 is constituted by a plurality of curved reflector parts, for example, two curved reflectors, the two curved reflectors can be symmetrically arranged relative to the device symmetry axis S; here the angle between the two curved reflectors is almost 180°. In the event that the reflector 104 is constituted by three curved reflector parts, as schematically shown in Figs. 1 and 5, here the three curved reflector parts are also symmetrically arranged around the device symmetry axis S, i.e., adjacent curved reflectors are separated with a uniform interval. In the event that the reflector 104 is constituted by four or even more curved reflector parts, the respective curved reflector parts are also symmetrically arranged around the device symmetry axis S, i.e., adjacent curved reflectors are separated with a uniform interval. This is not difficult to understand for the person skilled in the art. Separating the adjacent curved reflectors from each other with a uniform interval helps to uniformly reflect the light emitted by the light source 107.

In one embodiment of the present invention, the lamp of for example 60w, 40w, 25w, has a first diameter D of substantially 60mm, while the lamp of 75w has a first diameter D of substantially 67mm. That is to say, if the power of the lamp is determined, the first diameter D of the lamp is also substantially determined. For example, if the person skilled in the art intends to design a lamp of 40w according to the teachings of the present invention, the first diameter D of the lamp is 60mm. The angle a between the reflector 104 and the imaginary base plane P can be further configured based on the second diameter d of the top portion 105b (see Fig. 4, which shows the second diameter d of the top portion 105b). This can be ascribed to the fact that due to the decrease of the second diameter d of the top portion 105b, more light will be reflected to the top region of the lamp after the light emitted by the light source mounted to the top portion 105b is reflected by the reflector 104.

Therefore, the angle a between the reflector 104 and the imaginary base plane P can be further decreased with the decrease of the second diameter d of the top portion 105b. Since the angle a decreases with the decrease of the second diameter d of the top portion 105b, the reflector 104 tends to become more parallel to the imaginary base plane P. Because the light source mounted to the top portion 105b always occupies a certain area, it is impossible that the second diameter d of the top portion 105b decreases to zero. That is to say, it is impossible for the angle a that decreases with the decrease of the second diameter d to cause the reflector 104 to become completely parallel to the imaginary base plane P. Preferably, the second diameter d of the top portion 105b is less than half of the first diameter D of the envelope 105. In order to meet the requirement of the Energy Star better, the angle a between the reflector 104 and the imaginary base plane P can be selected between 105°-115°.

It will be further explained that a distance H between the light source 107 and the imaginary base plane P, i.e., the so called optical cavity height (as shown in Fig. 3), is adjusted based on the second diameter d of the top portion 105b. The distance H between the light source 107 and the imaginary base plane P increases with the decrease of the second diameter d of the top portion 105b. Preferably, the distance H between the light source 107 and the imaginary base plane P is 2/3 to 5/6 times of the first diameter D of the envelope 105. Since the reflector 104 is symmetrically arranged around the device symmetry axis S at an angle a to the imaginary base plane P, the following situations exist. In the event that the reflector 104 extends downwards from the plane in which the light source 107 is located to the imaginary base plane P of the base 101, the optical cavity height H is substantially equal to the projection length (also referred to as the height of the reflector 104) of the whole reflector 104 on the device symmetry axis S. In the event that the upper end of the reflector 104 is not in the same horizontal plane as the light source 107, i.e., in the event that the reflector 104 and the light source 107 are separated by a certain distance, the optical cavity height H is greater than the height of the reflector 104. Preferably, the height of the reflector

104 is equal to the optical cavity height H or less than 90% of the optical cavity height H. If the height of the reflector 104 is less than 90% of the optical cavity height H, then the upper end plane of the reflector and the plane in which the light source 107 is located are separated by at least 10% of the optical cavity height H. It is designed in this way because when the upper end plane of the reflector 104 is very close to the plane in which the light source 107 is located, for example, less than 10% of the optical cavity height H, there is too much reflection between the light source 107 and the upper end plane of the reflector 104, which results in a decrease of the optical efficiency.

As mentioned above, the reflector 104 shown in the respective embodiments of the present invention may comprise a conical reflector (not shown) or a plurality of curved reflector parts. What are shown in Figs. 1, 5 and 7 are structures of the reflector 104 being a plurality of curved reflector parts. More light emitted by the light source 107 can be reflected around the lamp by designing the reflector as a conical reflector (not shown) or a plurality of curved reflector parts, so as to meet the requirement of the Energy Star better. In the event that the reflector 104 is constituted by a plurality of curved reflector parts (for example, Figs. 1 and 5 show the situation in which the reflector 104 is constituted by three curved reflector parts), the curvature radius R of the curved reflector parts may increase with the decrease of the second diameter d of the top portion 105b. This means that the curved reflector becomes flatter with the decrease of the second diameter d of the top portion 105b, i.e. the reflector 104 has a shape closer to a conically curved surface. Preferably, the curvature radius R is 2.25 to 2.3 times the first diameter D of the envelope 105. The design order, for reference, is as follows: the second diameter d of the top portion is configured based on the first diameter D of the envelope, on the basis of which configuring is performed of the structure of the reflector, for example, the angle a between the reflector and the imaginary base plane P, the optical cavity height H and the curvature radius R in the event that the reflector is a curved reflector. The present invention is not limited to the value range given above, because the illumination device with a different power has a different first diameter D, thus, the second diameter d of the corresponding top portion is also different, and accordingly, there will be different values of angle a, optical cavity height H and curvature radius R etc.

In one embodiment of the present invention, as shown in Figs. 1-4, the top portion 105b is a metal top cover mechanically connected with the housing 105 a, the light source 107 is mounted to the metal top cover, for example, on the inner surface of the metal top cover. The metal top cover may be a top cover made from aluminum or an aluminum alloy; in this way, the heat generated by the light source 107 can be quickly dissipated, thereby improving the lifetime of the light source, and hence the lifetime of the illumination device 100.

In a further embodiment of the present invention, the top portion 105b may be a claw-shaped metal piece having a plurality of fingers 108, the housing 105a is sheathed in a cavity enclosed by the claw-shaped metal piece so as to contact the inner surfaces of the plurality of fingers 108, the light source 107 is mounted in the palm 112 of the claw-shaped metal piece. The claw-shaped metal piece is preferably made from aluminum or an aluminum alloy; in this way, the heat generated by the light source 107 can be quickly dissipated. Since the claw-shaped metal piece has a plurality of fingers 108, the heat dissipation area is further increased, so that the heat generated by the light source 107 in operation is dissipated faster and better, thereby further improving the lifetime of the light source 107 and the lifetime of the illumination device 100. Fig. 5 schematically shows the situation that the top portion 105b is a claw-shaped metal piece having a plurality of fingers 108. The housing 105a may be an entire housing. Or, alternatively, the housing 105a may comprise a plurality of parts, each part being attached between two adjacent fingers 108 from the inside of the cavity enclosed by the claw-shaped metal piece, wherein the upper end of each part is mechanically connected with the palm 112 of the claw- shaped metal piece, and the lower end of each part is mechanically connected with the base 101. Fig. 5 schematically shows the situation that the housing 105a comprises three parts. The upper end of each part can be mechanically connected with the palm 112 of the claw-shaped metal piece by means of buckling, welding, riveting, or bonding, etc., and the lower end of each part can be mechanically connected with the base 101 by means of buckling, welding, riveting, or bonding, etc. Preferably, each finger 108 may have a groove 109 opening outwards, as schematically shown in Figs. 5, 6, 8-9. Figs. 5 and 6 schematically show the situation that the top portion 105b is a claw-shaped metal piece having three fingers 108, each finger 108 having a groove 109 opening outwards. Preferably, the outer surface of the base 101 has a groove 110 forming a continuing surface with the groove 109 in each finger, thus, the heat dissipation area is further increased so as to facilitate heat dissipation; such a situation is shown in Figs. 8-9.

In order to describe more clearly how to design the illumination device of the present invention, an example is given below. For example, in order to design a lamp of 60w that meets the requirement of the Energy Star specification, the first diameter D of the envelope 105 can be selected to be 60mm, and then the second diameter d of the top portion

105b can be selected to be less than or equal to half of the first diameter D, e.g., 20mm. The angle a between the reflector 104 and the imaginary base plane P can be selected to be in the range of 105°-115°, and the optical cavity height, i.e., the distance H between the light source 107 and the imaginary base plane P can be selected to be 2/3 to 5/6 times of the first diameter D of the envelope 105, e.g., 40-50mm. In the event that the reflector 104 is a curved reflector, the curvature radius R of the curved reflector can be selected to be 2.25-2.3 times of the first diameter D of the envelope 105, e.g., 135-138mm.

In order to further explain the distribution effect of the luminous intensity obtained according to respective embodiments of the present invention, Fig. 10 schematically shows a simulated distribution map of the luminous intensity when the second diameter d of the top portion 105b is 10mm, 20mm, 30mm, respectively, in the event that the first diameter D of the envelope 105 is 60mm, the angle a between the reflector 104 and the imaginary base plane P is 109°, the distance H between the light source 107 and the imaginary base plane P is 45mm, and the curvature radius R of the curved reflector is 136.92. The simulated distribution map is obtained using the Floefd software commonly used in the art in the case of the above parameters. Since the Floefd software is known by the skilled person in the field of optics, it will not be elaborated on here. The skilled person in the art can also use other commonly used simulation software in the field of optics to perform simulation. It can be seen from the simulation result in Fig. 10 that the lamps configured according to the teachings of the present invention have an even luminous intensity distribution within the 0° to 135° zone, i.e. the luminous intensity at any angle within this zone does not differ from the mean luminous intensity for the entire 0° to 135° zone by more than 20%. In other words, the relative luminous intensity of any angle within the 0° to 135° zone is within the range of 80% to 120% of the mean luminous intensity (taking the mean luminous intensity as 100%); thus, the design criteria of the Energy Star on the luminous intensity dustribution are met.

The envelope 105, particularly the housing 105 a, used in the respective embodiments of the present invention is preferably made from diffusion plastic with good heat dissipation capability, silicon or silica gel material coated inside with remote phosphors so as to better dissipate the heat generated by the light source 107 in operation. Preferably, the envelope 105 is designed to be bulb-shaped; since the driver (not shown) is generally mounted in the base 101, such a bulb-shaped envelope 105 can increase the space volume near the driver so as to facilitate heat exchange and the heat cycle, reduce the temperature of the driver itself and improve the lifetime of the driver, thereby further prolonging the lifetime of the illumination device. It will be pointed out that although it has been described above with reference to the specific data range, the data ranges could be adjusted in accordance with the different sizes of the illumination device.

Although the present invention has been described with reference to the currently considered embodiments, it shall be understood that the present invention is not limited to the disclosed embodiments. On the contrary, the present invention intends to cover various modifications and equivalents comprised in the spirit and scope of the attached claims. The scope of the following claims complies with the broadest explanation so as to comprise all the modifications and equivalent structures and functions.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. An illumination device (100) comprising: an envelope (105) mounted on a base (101), a light source (107) mounted to a top of the envelope (105), and a reflector (104) arranged inside the envelope (105) and being configured to reflect light emitted from the light source (107), wherein an imaginary base plane (P) is defined substantially perpendicularly to a device symmetry axis (S) extending through a central end of the base (101) and a central extremity of the envelope (105), the reflector (104) is symmetrically arranged around the axis at an angle (a) to the imaginary base plane (P), the angle (a) being configured based on a first diameter (D) of the envelope (105).

2. An illumination device (100) according to claim 1, wherein the reflector (104) comprises a conical reflector or a plurality of curved reflector parts.

3. An illumination device (100) according to claim 1 or 2, wherein the envelope (105) comprises a housing (105a) and a top portion (105b), the light source (107) being mounted to the top portion (105b) having a second diameter (d), the second diameter of the top portion (105b) being configured based on the first diameter (D) of the envelope (105).

4. An illumination device (100) according to claim 3, wherein the angle (a) is further configured based on the second diameter (d) of the top portion (105b).

5. An illumination device (100) according to claim 4, wherein the angle (a) decreases with the decrease of the second diameter (d) of the top portion (105b).

6. An illumination device (100) according to claim 3, wherein the second diameter (d) of the top portion (105b) is less than half of the first diameter (D) of the envelope (105).

7. An illumination device (100) according to claim 3, wherein a distance (H) between the light source (107) and the imaginary base plane (P) is adjusted based on the second diameter (d) of the top portion (105b).

8. An illumination device (100) according to claim 7, wherein the distance (H) between the light source (107) and the imaginary base plane (P) increases with the decrease of the second diameter (d) of the top portion (105b).

9. An illumination device (100) according to claim 7, wherein the distance (H) between the light source (107) and the imaginary base plane (P) is 2/3 to 5/6 times of the first diameter (D) of the envelope (105).

10. An illumination device (100) according to claim 3, wherein a curvature radius (R) of the curved reflector parts increases with the decrease of the second diameter (d) of the top portion (105b).

11. An illumination device (100) according to claim 10, wherein the curvature radius (R) is 2.25 to 2.3 times of the first diameter (D) of the envelope (105).

12. An illumination device (100) according claim 3, wherein the top portion (105b) is a metal top cover mechanically connected with the housing, and the light source (107) is mounted to the metal top cover.

13. An illumination device (100) according to claim 3, wherein the top portion

(105b) is a claw-shaped metal piece having a plurality of fingers (108), the housing (105a) contacts the inner surfaces of the plurality of fingers (108) and sheathes over a cavity which is enclosed by the claw- shaped metal piece, and the light source (107) is mounted in a palm (112) of the claw-shaped metal piece.

14. An illumination device (100) according to claim 13, wherein the housing (105a) comprises a plurality of parts, each part being attached between two adjacent fingers (108) from the inside of the cavity enclosed by the claw-shaped metal piece, wherein an upper end of each part is mechanically connected with the palm (112) of the claw- shaped metal piece, and a lower end of each part is mechanically connected with the base (101).

15. An illumination device (100) according to claim 13 or 14, wherein each finger (108) has a groove (109) opening outwards.