WO2010066841A1

WO2010066841A1 - Led lamp system

Info

Publication number: WO2010066841A1
Application number: PCT/EP2009/066841
Authority: WO
Inventors: Jurjen Hilwert Visser; Guang Zhi Yu; Shuang He Zeng; Michael Friedrich Albert Staudt; Shu Kei Shea; Carl Rudolf Eduard Staudt
Original assignee: Ledned Holding B.V.
Priority date: 2008-12-11
Filing date: 2009-12-10
Publication date: 2010-06-17
Also published as: CN102292594A; EP2376834A1

Abstract

The invention relates to a LED lamp system comprising: a heat sink (30), a LED assembly (20) thermally coupled to the heat sink (30), an air inlet (Al) and an air outlet (AO), the air inlet (Al) and the air outlet (AO) being positioned for obtaining an air flow (115) along the heat sink (30), wherein the LED assembly (20) has a light-emitting side in operational use, wherein the air flow (115) is caused by heat generated by the LED assembly (20), the air inlet (Al) and the air outlet (AO) being located substantially in plane with the LED assembly (20) or on a back side of the LED assembly (20), wherein the back side is defined as being opposite to the light-emitting side. The LED lamp system in accordance with the invention is a lighting system which makes use of passive cooling only. The cooling mechanism relies on the airflow that runs along the heat sink which air flow is sustained by the heat generated by the heat sink itself. No additional power is required.

Description

LED lamp system

FIELD OF THE INVENTION

The invention relates to a LED lamp system comprising: a heat sink, a LED assembly thermally coupled to the heat sink, an air inlet and an air outlet, the air inlet and the air outlet being positioned for obtaining an air flow along the heat sink.

BACKGROUND OF THE INVENTION

Most lighting products in both the professional and private market consist of incandescent lamps and gas-discharge lamps. A major part of these lamps have an efficiency between 10 and 70 Lumen per Watt. Moreover, most lamps have a relatively short lifetime between 500 and 5000 operation hours and which implies regular replacement.

LED technology, a form of sold-state lighting (SSL), is developing fast, especially in the application areas of signal lighting (traffic lights, monitoring lights, etc) and for small scale compact light sources (for example reading lamps, flash lights, or decoration lights). The development of LED towards full-fledged light source has not yet been possible due to technological barriers, such as the incompatibility with existing lighting installations / lighting fixtures. Market leaders on the light market focus on the development of LED lighting in new systems, while focusing on traditional lighting technology (incandescent lamps, fluorescent lamps, low-energy bulbs) in the after market. They do not seem to realize that LED lighting can be a sustainable alternative for existing light sources in this market as well. When switching from traditional lighting to another technology (such as

LED technology) compatibility plays a major role. There is a major reluctance to step over to a new lighting technology due to large investments which have been done in lighting fixtures and installations, despite possible economic and ecologic advantages. Expressed differently, market acceptance for a new lighting technology is only quickly obtained on a short term where the lighting technology is fully replaceable with the existing lighting technology. Even the looks of the new lighting products must resemble the old ones. Thus there is a need for a environment-friendly lighting technology which can be replaced one- on-one with the current lighting systems.

The current compatibility problems with the retrofit-range are caused by the following aspects: - There is limited physical space for components, i.e. new lighting products need to be implemented in existing systems and therefore need to have the same dimensions as the current lighting products;

- The shape of the new products must resemble the shape of the old products. For the end-user the shape of the new product must be recognizable before he is willing to accept the new product. This aspect puts severe design constraints in LED lighting products.

Because of the above-mentioned additional requirements to retrofit- systems, one of the most important aspects of a LED lamp is at stake, namely the cooling of the LED. LED's, despite having a better efficiency as compared with traditional lighting, produce a considerable amount of heat. The cooling technology which is available at this moment is not suitable for absorbing the heat produced by the LED's. This may be caused either by the fact that the technology cannot be integrated into the lamp (due to the earlier-mentioned additional constraints) or by the fact that the cooling technology constitutes an active cooling, which is not desired in the current systems.

US2005/01 11234A1 discloses a LED lamp having such active cooling. The LED lamp includes an exterior shell that has the same form factor as a conventional incandescent light bulb, such as a PAR type bulb. The LED lamp includes an optical reflector that is disposed within the shell and that directs the light emitted from one or more LEDs. The optical reflector and shell define a space that is used to channel air to cool the device. The LED is mounted on a heat sink that is disposed within the shell. A fan moves air over the heat sink and through the spaced defined by the optical reflector and the shell. The shell includes one or more apertures that serve as air inlet or exhaust apertures. One or more apertures defined by the optical reflector and shell at the opening of the shell are used as air exhaust or inlet apertures.

A problem with the known LED lamp is that the cooling of the LED is not satisfactory, at least not in all circumstances. This non-optimal cooling shortens the operational lifetime of the LED lamp.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a LED lamp system with a better cooling of the LED, and thus a longer life time.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments. In a first aspect, the invention relates to a LED lamp system comprising: a heat sink, a LED assembly thermally coupled to the heat sink, an air inlet and an air outlet, the air inlet and the air outlet being positioned for obtaining an air flow along the heat sink, wherein the LED assembly has a light-emitting side in operational use, wherein the air flow is caused by heat generated by the LED assembly, the air inlet and the air outlet being located substantially in plane with the LED assembly or on a back side of the LED assembly, wherein the back side is defined as being opposite to the light-emitting side. The effect of the features of the LED lamp system in accordance with the invention will be explained hereinafter. Heat produced by the at least one LED is transferred to the heat sink because of the thermal coupling between these respective parts of the lamp system. The LED lamp system further comprises an air inlet and an air out let which are placed such that an air flow along the heat sink is obtained which is caused by the heat. However, the air inlet and the air outlet are placed such that they are located on a back side of the at least one LED, wherein the back side is defined as opposite to the light-emitting side in operational use. By placing both the air inlet and the air outlet substantially in plane with or on the back-side of the at least one LED it is ensured that the air flow that is caused by the heat is less thermally coupled to the at least one LED itself. Expressed differently, the at least one LED is less (re)heated by the air flow which is heated while cooling the heat sink. The junction temperature of the at least one LED is thus lower, which has a positive influence on the operational lifetime of the LED lamp system.

It must be noted that in the known LED lamp the above effect is not achieved. In the known LED lamp the air inlet and air outlet are placed such that the (warm) airflow flows fully along the optical reflector and thus heats up the reflector and also the LED. This will lead to a higher junction temperature of the LED and thus a lower operational lifetime of the known LED lamp.

In contrast with the LED lamp system in accordance with the invention, the known LED lamp requires an active element, i.e. a motor and a fan, for cooling the heat sink. In many lighting applications, however, such active element is not desired. In order to fit into a lamp the motor and the fan must be miniaturized. Such miniaturized components not only make the lamp more complex (and thus more costly), also lifetime of the lamp is negatively affected, because more components of the lamp can get broken. Another disadvantage is the noise which the motor and the fan produce during operation of the known LED lamp. It must also be noted that in known LED lamp the cooling effect is completely gone when the active components do not function properly.

In an embodiment of the LED lamp system in accordance with the invention the air inlet and the air outlet are displaced in a direction that is perpendicular to the light- emitting side. Such displacement of the air inlet and the air outlet in a longitudinal direction (direction perpendicular to the light-emitting side) provides for an effect cooling when the LED lamp system is oriented in an upward or downward direction with respect to the earth surface. In operational use the LED assembly heats up air that is close to the heat sink.

Warm/hot air is lighter than cold air. In order to facilitate a rising airflow along the heat sink

(when the lamp is oriented in an upward- or downward direction) the air inlet and the air outlet must be oriented one-above each other as is the case this embodiment. It must be noted that the air inlet and the air outlet exchange functions when the LED lamp system is oriented in an opposite direction (from upward to downward or vise versa). Still, in this embodiment the cooling effect is present in both orientations.

An embodiment of the LED lamp system in accordance with the invention comprises a support member for connecting to the heat sink such that an air path is formed between the back side of the heat sink and the support member, wherein the air path is in connection with the air outlet and the air inlet. The provision of the air path that is in connection with the air out let and the air inlet further improves the cooling effect of the LED lamp system.

An embodiment of the LED lamp system in accordance with the invention comprises an envelope arranged around the support member for forming an air channel between the air inlet and the air outlet, wherein the air inlet and the air outlet are formed at respective ends of the envelope. The combination of the support member and the envelope around the support member provides for a convenient implementation of an air channel between the air inlet and the air outlet. Also, the air inlet and the air outlet are conveniently formed at respective ends of the envelope. Various variations are possible for the formation of the air outlet and air inlet. More details on these variations are described later in this description.

In an embodiment of the LED lamp system in accordance with the invention the heat sink has a circular disc shape, wherein the LED assembly has been centered with respect to the heat sink. A circularly-shaped heat sink conveniently fits into a conventional light bulb shape.

In an embodiment of the LED lamp system in accordance with the invention the heat sink comprises a material selected from a group comprising: aluminum, brass, bronze, duraluminum, copper, goldplated metals, and silverplated metals. These materials are particularly advantageous because of their properties, such as: light weight, good heat conduction (which is good for the heat sink function), and low cost.

In an embodiment of the LED lamp system in accordance with the invention the support member has a cylindrical shape. A circularly-shaped support member conveniently fits into a conventional light bulb shape. In an embodiment of the LED lamp system in accordance with the invention the support member comprises a material selected from a group comprising: aluminum, brass, bronze, duraluminum, copper, goldplated metals, and silverplated metals. These materials are particularly advantageous because of their properties, such as: light weight, good heat conduction (which is good for the heat sink function), and low cost.

In an embodiment of the LED lamp system in accordance with the invention the support member is provided with fins distributed around a periphery of the cylindrical shape and extending in a direction parallel to a longitudinal axis of the cylindrical shape for increasing a radiation area of the support member and for defining sub-air channels for guiding the air flow. The provision of the fins around the periphery of the support member increases its radiation area, which is advantageous for the cooling of the LED lamp system. The support member is heated by the heat sink and from that point of view acts as a further heat sink.

In an embodiment of the LED lamp system in accordance with the invention the envelope has a cylindrical shape. A circularly-shaped envelope conveniently fits into a conventional light bulb shape.

In an embodiment of the LED lamp system in accordance with the invention the radius of the cylindrical shape of the envelope gradually increases towards one end. This measure makes the envelope fit the shape of a conventional light bulb even better.

In an embodiment of the LED lamp system in accordance with the invention the envelope comprises a material selected from a group comprising: aluminum, brass, bronze, duraluminum, copper, goldplated metals, and silverplated metals. These materials are particularly advantageous because of their properties, such as: light weight, good heat conduction (which is good for the heat sink function), and low cost.

In an embodiment of the LED lamp system in accordance with the invention the heat sink and the support member comprise the same material. Using the same material for these parts has the advantage that the thermal resistance between these two parts is lower, and thus the heat is better transferred from the heat sink to the support member. When the envelope also the same material this has the advantage that it also acts as an effective heat sink (so effectively a three-part heat-sink is obtained).

In an embodiment of the LED lamp system in accordance with the invention the support member and the envelope are mechanically connected through a thermally insulating member provided at a side of the support member opposite to a side where the heat sink is provided. In this embodiment the envelope is spaced apart from the support member and is only mechanically connected to the support member through the thermally insulating member. The thermally insulating member limits the heat conduction from the support member to the envelope. As a matter of fact there is almost only heat transfer from the support member to the envelope through radiation. There is a little bit of heat transfer through convection (by the air between the support member and the envelope), but this mechanism hardly plays a role. In summary, the heat transfer from the support member to the envelope is severely limited in this embodiment, which keeps the envelope cool so that it can be touched without causing burn.

In an embodiment of the LED lamp system in accordance with the invention the air inlet and/or the air outlet comprise a plurality of openings distributed over a periphery of the LED lamp system. The advantage of this embodiment is that the air flow will be more homogenously distributed over the LED lamp system which leads to a more uniform cooling effect. Besides, another advantage of this embodiment is that the cooling mechanism (airflow caused by rising hot air) now also works for a LED lamp system which is orientation in lateral directions with respect to the earth surface. This will be explained in more detail later in this description.

An embodiment of the LED lamp system in accordance with the invention comprises a glass bulb connecting to the heat sink and fully covering the LED assembly. The advantage of this embodiment is that the LED assembly is better thermally insulated from the heated air flow which leaves the air outlet. As a consequence of that the temperature of LED assembly remains lower (and the lifetime of the LED lamp system is longer).

An embodiment of the LED lamp system in accordance with the invention comprises a further glass bulb provided within the glass bulb connected to the heat sink and fully covering the LED assembly. A better thermal insulation of the LED assembly is obtained.

In an embodiment of the LED lamp system in accordance with the invention the glass bulb and/or the further glass bulb comprises diffuser material for diffusing light emitted from the LED assembly in operational use. In one embodiment of the LED lamp system the glass bulb is light-diffusing in operational use. In another embodiment of the LED lamp system the further glass bulb is light-diffusing in operational use. The two embodiments may be advantageously combined, which produces an even better light diffusion effect, and, additionally, an even better thermal insulation of the LED assembly from the heated air.

In an embodiment of the LED lamp system in accordance with the invention the LED assembly comprises one centered LED. The advantage of this embodiment is that the power consumption is low.

In an embodiment of the LED lamp system in accordance with the invention the LED assembly comprises three LED's arranged with respect to each other in a triangular orientation and having a triangular center that is aligned with a center of the LED assembly. The advantage of this embodiment is the higher light output.

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

Fig. 1 a shows a 3D-illustration of a LED lamp system in accordance with a first embodiment of the invention;

Fig. 1 b illustrates a dimension of the LED lamp system of Fig. 1a;

Fig. 2a shows a 3D-illustration of a first variant of the LED lamp system of Fig. 1a;

Fig. 2b shows a 3D-illustration of a second variant of the LED lamp system of Fig. 1a;

Fig. 3 shows an exploded 3D-illustration of the LED lamp system of Fig. 1a in accordance with the first variant of Fig. 2a;

Fig. 4a shows a 3D-illustration of a heat sink of the LED lamp system of Fig. 1 a in accordance with the first variant of Fig. 2a, which illustrates a front side of the heat sink;

Fig. 4b shows a 3D-illustration of the heat sink of the LED lamp system of Fig. 1 a in accordance with the second variant of Fig. 2b, which illustrates a front side of the heat sink;

Fig. 4c shows a 3D-view of a back side of the heat sink of Figs. 4a and 4b; Fig. 5a shows a 3D-illustration of a support member of the LED lamp system of Fig. 1a in accordance with the first embodiment of the invention, which illustrates a front side of the support member;

Fig. 5b shows a 3D-illustration of the support member of the LED lamp system of Fig. 1a in accordance with a second embodiment of the invention, which illustrates a front side of the support member;

Fig. 5c shows a 3D-view of a back side of the support member of Fig. 5a;

Fig. 6a shows a 3D-view of a front-side of an envelope of the LED lamp system of Fig. 1a in accordance with the first embodiment of the invention;

Fig. 6b shows a 3D-view of a back-side of the envelope of the LED lamp system of Fig. 1a in accordance with the first embodiment of the invention;

Fig. 7 shows a 3D-view of a back-side of the glass bulb of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention;

Fig. 8 shows a 3D-view of a PCB of the LED lamp system of Fig. la in accordance with the first embodiment of the invention; Fig. 9a shows a 3D-view of a front-side of a PCB-support member of the

LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention; Fig. 9b shows a 3D-view of a back-side of the PCB-support member of the LED lamp system of Fig. 1a in accordance with the first embodiment of the invention;

Fig. 10a shows a 3D-view of a front-side of an insulating member of the LED lamp system of Fig. 1a in accordance with the first embodiment of the invention; Fig. 10b shows a 3D-view of a back-side of the insulating member of the

LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention;

Fig. 1 1 a shows a 3D-view of a front-side of a fitting of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention;

Fig. 1 1 b shows a 3D-view of a back-side of the fitting of the LED lamp system of Fig. l a in accordance with the first embodiment of the invention;

Fig. 12 illustrates further aspects of the LED lamp system in accordance with the invention;

Fig. 13a illustrates a cut-view of the LED lamp system of Fig. 1a in which an aspect of the cooling effect is illustrated; Fig. 13b illustrates another cut-view of the LED lamp system of Fig. la in which another aspect of the cooling effect is illustrated;

Fig. 13c illustrates part of another cut-view of the LED lamp system of Fig. 1 a in which yet another aspect of the cooling effect is illustrated;

Fig. 14a illustrates the LED lamp system of Fig. 1 a having an upward- pointing orientation;

Fig. 14b illustrates the LED lamp system of Fig. 1 a having an downward- pointing orientation;

Fig. 14c illustrates the LED lamp system of Fig. 1a having a sideward- pointing orientation; Fig. 15a shows a photograph of an assembly comprising a heat sink with a

LED assembly mounted thereon;

Fig. 15b shows a photograph of the assembly of Fig. 15a after the provision of a first glass bulb thereon in accordance with another embodiment of the LED lamp system, and Fig. 15c shows a photograph of the assembly of Fig. 15b after the provision of a second glass bulb thereon, which results in a very advantageous embodiment of the LED lamp system.

List of reference numerals: 10 glass bulb

12 glass bulb rim

18 glass bulb opening 19 further glass bulb

20 LED assembly

20' another LED assembly

30 first variant of heat sink

30' second variant of heat sink

32 connection holes

32' further connection holes

34 ridge

36 further through-hole

37 intermediate spaces/air path

38 circular extensions

40 support member

42 cylindrical member

44 first variant of fins

44' second variant of fins

46 screw holes

47 further hole

48 inner space

50 PCB support member

52 PCB support member cylinder

54 protrusion

56 slits

58 PCB support member back-side opening

60 PCB

62 LED driver

70 envelope

72 further cylindrical member

74 openings

76 front opening

77 rim

78 back opening

80 insulating member

84 connecting structure

85 front-side rim

87 back-side rim

90 fitting

100 LED 110 cold air flow

115 air flow

1 15' additional air flow component

120 warm air flow 130 turbulent air flow

140 low radiation level of lower part of envelope

145 medium radiation level of higher part of envelope

150 high radiation level of higher part of support member

D glass bulb diameter

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention aims at providing a LED lamp system having a longer operational lifetime than the conventional LED lamp systems. This object is achieved in that a LED lamp system is provided with an improved cooling system. The improved cooling system comprises: a heat sink, a LED assembly thermally coupled to the heat sink, an air inlet and an air outlet, the air inlet and the air outlet being positioned for obtaining an air flow along the heat sink, wherein the LED assembly has a light-emitting side in operational use, wherein the air flow is caused by heat generated by the LED assembly, the air inlet and the air outlet being located substantially in plane with the LED assembly or on a back side of the LED assembly, wherein the back side is defined as being opposite to the light-emitting side. The improvement of the cooling system resides in keeping the cooling airflow away from the LED assembly or from components surrounding the LED assembly. The LED lamp system in accordance with the invention solves problems such as compatibility, performance, safety, quality and reliability by providing a passive thermal design which aims at keeping a junction temperature Tj of the LED's in a LED assembly low (wherein the junction temperature is directly or indirectly coupled to earlier mentioned properties). The LED lamp system is based upon exploiting heat convection. Embodiments of the LED lamp system are also based upon radiation and conduction. Such passive thermal design provides for a larger design freedom for retrofit LED lamp systems.

In order to facilitate the discussion of the detailed embodiments a few expressions are defined hereinafter.

Throughout this description the term "LED assembly" should be interpreted as an assembly comprising al least one LED which is arranged for emitting light into a light-emitting direction. Such LED may be provided on a carrier substrate, such as a PCB, which may have a heat-sink function as well. The LED may be provided with optics to further improve the light beam coming out of the assembly. The LED assembly may further comprise electrical terminals for connecting to at least one LED to a power supply. These days there are many different LED assembly suppliers. For the invention it is not very relevant which LED assembly is taken as long as other parts of the LED lamp system are adapted such that the LED assembly can be mounted thereon. Fig. 1 a shows a 3D-illustration of a LED lamp system in accordance with a first embodiment of the invention. The LED lamp system comprises a glass bulb 10, an envelope 70, and a fitting 90. Fig. 1 b illustrates a dimension of the LED lamp system of Fig. 1 a. The diameter D of the glass bulb equals 60mm, which is equal to the width of the well-known conventional incandescent light bulbs. Fig. 2a shows a 3D-illustration of a first variant of the LED lamp system of

Fig. 1 a. Fig. 2b shows a 3D-illustration of a second variant of the LED lamp system of Fig. 1 a. In these figures the glass bulb 10 has been drawn as a non-diffusive transparent element which is for illustration purposes only. In practice, the glass bulb 10 may also comprise a diffuser for diffusing light emitted from the LED assembly. In the variant of Fig. 2a, a LED assembly 20 is visible which comprises a single centered LED 100. In the variant of Fig. 2b, another LED assembly 20' is provided which comprises three LED's 100 that are arranged in a triangular orientation with respect to each other. However, the invention is not limited to such number of LED's or to such orientation in case of a plurality of LED's. The variant of Fig. 2a provides for a low-power dissipation LED lamp solution using only one LED 100. The variant of Fig. 2b provides for a higher light output using three LED's 100. In alternative embodiments a single LED assembly with two LED's is provided, or an alternative LED assembly with four LED's (multiple package).

Fig. 3 shows an exploded 3D-illustration of the LED lamp system of Fig. 1a in accordance with the first variant of Fig. 2a. The LED lamp system comprises the following main parts: the glass bulb 10, the LED assembly 20, a heat sink 30, a support member 40, a PCB support member 50, a PCB 60, the envelope 70, an insulating member 80, and the fitting 90. When the LED lamp system is assembled the glass bulb 10 is attached to the heat sink 30 onto which the LED assembly 20 is mounted. The heat sink 30 is mounted on the support member 40. The PCB 60 is mounted within the PCB support member 50, wherein the PCB support member 50 is contained within the support member 40. The structure comprising the glass bulb 10, the LED assembly 20, the heat sink 30, the support member 40, the PCB support member 50, and the PCB 60, is inserted in the envelope 70. The insulating member 80 provides for the mechanical connection between the envelope 70 and the other parts (in particular the support member 40, PCB support member 50, and the PCB 60 thereof). Also, the insulating member 80 is connected to the fitting 90. More details about the individual parts of the LED lamp system are described hereinafter. Fig. 4a shows a 3D-illustration of a heat sink 30 of the LED lamp system of Fig. 1 a in accordance with the first variant of Fig. 2a, which illustrates a front side of the heat sink. This variant of the heat sink 30 is meant for a LED lamp system having a LED assembly with only one LED that is centered with respect to the lamp system. Fig. 4b shows a 3D-illustration of the heat sink 30' of the LED lamp system of Fig. 1a in accordance with the second variant of Fig. 2b, which illustrates a front side of the heat sink. This variant of the heat sink 30' is meant for a LED lamp system having a LED assembly with three LED's arranged in a triangular fashion. Fig. 4c shows a 3D-view of a back side of the heat sink of Figs. 4a and 4b. Both heat sinks 30, 30' have been designed for multiple purposes. First of all, they serve as a connection means for the LED assembly (not shown). Second, they serve as a connection means for the glass bulb (not shown) and optionally an additional diffuser glass bulb (not shown). The heat sink 30 in Fig. 4a comprises in this example two connection holes 32 for connecting the LED assembly to the heat sink 30. The heat sink 30 in Fig. 4a further comprises a ridge 34 for mounting the glass bulb thereon. The heat sink 30' in Fig. 4b also comprises connection holes 32' but these are arranged at different locations. In order to make it possible to bring a LED driver cable (not shown) to the LED assembly a further through-hole 36 is provided in the heat sinks 30,30'. The heat sink 30' in Fig. 4b further comprises a similar ridge 34 for mounting the glass bulb thereon. The respective LED assembly's which need to be mounted on the respective heat sinks 30, 30' preferably comprise a printed circuit board (PCB) which is provided on an aluminum substrate. The aluminum substrate functions as heat sink, but also as a carrier for some conduction tracks that printed on the aluminum substrate but electrically insulated there from. These conduction tracks serve to connect the LED's on the LED assembly.

The heat sinks 30, 30' are mounted on an upper surface of the support member. In an advantageous embodiment the heat sink 30, 30' and the support member are both made from a same heat-conductive material, such as aluminum. In that embodiment the thermal resistance is low which is good for heat conduction from the heat sink 30, 30' to the support member. Preferably, a contact surface of the heat sink 30, 30' and the upper surface of the support member are flattened (polished) such that the thermal resistance is further reduced. In the example of Fig. 4c, a back side of the heat sink 30, 30' is provided with circular extensions 38. This has been illustrated for the heat sink 30'of Fig. 4b, but is, mutatis mutandis, applicable to the heat sink 30 of Fig. 4a. These extensions 38 serve different goals. First of all, an air path is created between the heat sink 30, 30' and the support member. This air path plays an important role in the cooling mechanism of the invention as will be elaborated on later in the description. Second, the extensions 38 ensure that not all heat of the heat sink 30, 30' is transferred to the support member by convection, i.e. part of the heat will be transferred by radiation as well.

In an advantageous variation of the heat sink 30' in Fig. 4b the upper surface may comprise tilted parts such that the LED assemblies provided thereon produce a more diverging light distribution. Another variation of the above-described embodiment comprises the situation where the extensions 38 are provided on the support member instead of the heat sink 30. The support member is discussed in the next paragraph.

Fig. 5a shows a 3D-illustration of a support member 40 of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention, which illustrates a front side of the support member. Fig. 5b shows a 3D-illustration of the support member 40' of the LED lamp system of Fig. 1 a in accordance with a second embodiment of the invention, which illustrates a front side of the support member. Fig. 5c shows a 3D-view of a back side of the support member of Fig. 5a. Both variants of the support member 40, 40' comprises a cylindrical member 42 which comprises an inner space in which the PCB and PCB support member are to be inserted. Both variants of the support member 40, 40' comprises a plurality of fins 44, 44' distributed around a periphery of the cylindrical member 42. The difference between the fins of Fig. 5a and 5b is the length of the cylindrical member 42 over which they extend.

As already mentioned, the support member 40, 40' serves as a basis for the heat sink 30. In some embodiments, and in particular in those embodiments where the support member 40 comprises a heat-conductive layer, such as aluminum, the support member 40 serves as a further heat sink for the LED lamp system. Further, it serves as a protection of the PCB (which comprises the LED driver). In operational use, the PCB also generates heat which is advantageously transferred to the environment by means of radiation of the support member 40, 40', in particular when the support member is made of a heat-conductive material.

The fins 44, 44' provide that the radiation surface is increased. Also, the fins 44, 44' define air channels in the space between the support member 40, 40' and the envelope. These air channels facilitate the convection mechanism (from air inlet to air outlet) of the LED lamp system.

The support members 40, 40' are also provided with two screw holes 46 in the upper surface for featuring the mechanical connection (by means of screws in this example) of the support members to an insulating member which is discussed later in this description. To achieve this mechanical connection the support members 40, 40' are provided with internal flanges (not shown) on the inner surface of the respective cylindrical members 42 through which the screws are put after which they are screwed into the insulating member. The support members 40, 40' are further provided with a further hole 47 for feeding a LED driver cable to the LED assembly.

In an advantageous embodiment the heat sink 30, 30' and the support member 40, 40' are both made from a same heat-conductive material, such as aluminum. Fig. 6a shows a 3D-view of a front-side of an envelope 70 of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention. Fig. 6b shows a 3D-view of a back-side of the envelope 70 of the LED lamp system of Fig. 1a in accordance with the first embodiment of the invention. In an embodiment the envelope 70 also comprises aluminum. In this embodiment it also serves as a heat sink. The envelope 70 comprises a further cylindrical member 72 having a front opening 76 for receiving the structure comprising the glass bulb 10, the LED assembly 20, the heat sink 30, the support member 40, the PCB support member 50, and the PCB 60. The cylindrical member 72 further comprises a back opening 78 for receiving the insulating member 80. Further, the cylindrical member 72 has a diameter that increases towards the side having the front opening. In this way the shape of the envelope is matched to the support member 40 having the fins 44. In all embodiments the envelope 70 plays an important role in the cooling mechanism of the LED lamp system. To this end the envelope 70 comprises openings 74 at one side thereof, which serve either as air inlet or as air outlet. This cooling effect will be explained in more detail later in this description. The envelope 70 in the example of Fig. 6b is only in physical contact with a lower part of the support member 40 through a rim 77 at the bottom side of the cylindrical member 72. This small physical contact area results in the fact that the envelope 70 is almost only heated by radiation of the support member. It therefore remains relatively cool in operational use, which prevents skin burn of the fingers when the lamp is held at the envelope 70. Another function of the envelope is to further define the air channel for a continuous air flow (in operational use) between the air inlet and the outlet as will be elaborated on later in the description.

Fig. 7 shows a 3D-view of a back-side of the glass bulb 10 of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention. Light that is produced by the light-emitting diode (LED) in the LED assembly is directed through a lens and produces a divergent light beam with an angle that generally lies between 90 and 1 10 degrees. Further, it is desired that the light beam is made even more divergent. To this end a glass bulb 10 is provided that is made of glass with a coated diffuser material thereon. The diffuser material serves to scatter the light diffusely. In other words, the diffuser material achieves that the uniformity of the light intensity distribution of the light emitted by the light emission window during operation is further enhanced, i.e. the light is emitted over a wider angle. Another advantage of using glass is that it is a good thermal insulator and is therefore very suitable for keeping heat (the warm airflow) outside that 5 was generated by the heat sink 30, the support member 40, and the envelope 70. Another advantage of using glass is that color changes and deformations are less likely to occur than when using polymers or plastics, for example. Particularly suitable materials for the diffuser material are calcium halophosphate and/or calcium pyrophosphate. Such a diffuser is preferably provided as a paint to which a binder, for example a fluorine copolymer, is added. It must be noted that it falls within the scope of the invention to provide other materials for the glass bulb 10, such as a synthetic resin, or Perspex, which scatters the light, preferably diffusely (for example so-called milk-glass). The glass bulb 10 comprises a glass bulb rim 12 for being mounted to the heat sink 30. During the mounting the LED assembly 20 (on the heat sink 30) is put into a glass bulb opening 18 of the glass bulb 10.

Fig. 8 shows a 3D-view of a PCB of the LED lamp system of Fig. la in accordance with the first embodiment of the invention. The printed-circuit-board (PCB) 60 comprises the earlier mentioned LED driver for driving the LED's. The driver is an important part of the LED lamp system and must be designed with special care. The LED lamp system as illustrated in the figures is designed for replacing conventional incandescent light bulbs. One of the desired properties of the LED lamp system is that the light can be dimmed using conventional dimming systems. This requires that the LED driver provides a variable output current which is controlled by a supply voltage applied to the fitting. The LED driver further comprises a galvanically separated transformer (not shown). The input side (high-voltage side) of the transformer is electrically connected with the fitting 90 and the output side (low-voltage side) of the transformer is connected to an integrated circuit for rectifying the voltage and regulating the output current for driving the LED's. Benefits of using the transformer in the PCB are: lower voltages such that wires need thinner insulation (which means that conductive core of the wires can be thicker, resulting in less resistance and thus less heat, and eventually less load for the transformer). A second benefit is safety. In case the glass bulb gets broken the LED assembly with its electrical terminals is exposed. However, only low voltages are present on these terminals. Typical specifications for the LED lamp system as illustrated in the figures are:

- Input voltage: 110-250V ac/dc; - Power factor (PF) > 0,85;

- LED driver output: 3,2-12,4V / 350-70OmA. Fig. 9a shows a 3D-view of a front-side of a PCB-support member 50 of the

LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention. Fig. 9b shows a 3D-view of a back-side of the PCB-support member 50 of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention. The PCB- support member 50 comprises a PCB support member cylinder 52 for containing the PCB 60. On a back-side of the cylinder 52 there are two opposing slits 56 for featuring the earlier mentioned screw connection between the support member 40 and the insulating member. On the back-side of the cylinder 52 there is also a PCB support member backside opening 58 for receiving the insulating member 80. On a front-side of the PCB support member cylinder 52 there is the earlier-mentioned protrusion 54. This protrusion 54 may be inserted into one of the power supply holes 46 of the support member 40. The protrusion 54 facilitates the feeding of a LED driver cable (not shown) from the PCB 60 to the LED assembly 20.

The PCB support member in Fig. 9b is made of an electrical insulator in order to comply with all safety requirements for lighting products. It may comprise materials such as polycarbonate. Another function of the PCB support member is to contain and fix the PCB. With the design of Fig. 9b it is prevented that an open connection is created between the print and the open air. Moreover, the design also prevents damaging of the wiring (not shown).

Fig. 10a shows a 3D-view of a front-side of an insulating member 80 of the LED lamp system of Fig. l a in accordance with the first embodiment of the invention. Fig. 10b shows a 3D-view of a back-side of the insulating member 80 of the LED lamp system of Fig. l a in accordance with the first embodiment of the invention. The insulating member 80 serves to mount the fitting 90, the support member 40, the envelope 70 and the PCB support member 50. Also, the insulating member 80 serves to electrically insulate the fitting 90 from the envelope 70. Such electrical insulation can be achieved by using polycarbonate as material for the insulating member 80. However, other materials are also possible. Polycarbonate is advantageous because it is a mechanically strong material. On a front-side of the insulating member 80 there is provided a connecting structure 84 for connecting to the PCB support member 50 and a front-side rim 85. On a back-side of the insulating member 80 there is provided a back-side rim 87 for connecting to the fitting 90. Fig. 1 1 a shows a 3D-view of a front-side of a fitting 90 of the LED lamp system of Fig. 1 a in accordance with the first embodiment of the invention. Fig. 1 1 b shows a 3D-view of a back-side of the fitting 90 of the LED lamp system of Fig. la in accordance with the first embodiment of the invention. In the example illustrated in these figures the fitting is of the E27 type. However, this can be any type of fitting, as long as the insulating member 80 is adapted to the dimensions of this fitting. The fitting 90 is provided over the back-side rim 87 of the insulating member 80.

Fig. 12 illustrates further aspects of the LED lamp system in accordance with the invention. The various parts, which have already been discussed in previous paragraph and drawings, are illustrated in the drawing. What is important in the invention is that the air flow which cools the heat sink 30 does not re-heat the LED assembly 20 again. In order to achieve that effect the invention prescribes that the air inlet Al, and the air outlet AO are both located in, or behind, a reference plane RF through the LED assembly. The air inlet Al and the air outlet AO are the openings between which the air flow is sustained by the heat generated by the LED assembly 20. It must be stressed that the earlier mentioned openings 74 in the envelope 70 may serve both as an air inlet Al as well as an air outlet AO. This all depends on the orientation of the LED lamp system as will be explained later in the description. Same is true for the other openings which are defined by the spaces between the rims 44 of the support member 40. These openings may also serve as air inlet Al or air outlet AO depending on the orientation of the LED lamp system.

Fig. 13a illustrates a cut-view of the LED lamp system of Fig. 1a in which an aspect of the cooling effect is illustrated. The cut-view is done through the heat sink 30 and the support member 40 (just above the envelope 70) such that the circular extensions 38 are visible. The circular extensions are arranged such that there are intermediate spaces 37 between them which are in connection with each other and with the air inlet and air outlet. These connected intermediate spaces 37 form an air path. In the LED lamp system of Fig. 13a the lamp is oriented in an upward direction. In this orientation the openings 74 in the envelope 70 operate as air inlets Al. In operation, relatively cold air flow 1 10 is flowing into these openings. After entering the openings 74, the air flow rises between in the space between the envelope 70 and the support member 40 and gets heated by the support member (through radiation) and leaves the LED lamp through the air outlets (not shown) as a warm air flow 120. As long as the LED lamp system is operated the air flow is sustained by the heat generation. The sustained air flow effectively provides heat convection along the heat sink 30 (only circular extensions 38 of heat sink are visible in the figure). Fig. 13a further serves to illustrate that this heat convection is further enhanced by so-called turbulent convection in the spaces 37 between the heat sink 30 and the support member 40. This turbulent convection is caused by temperature gradients in the heat sink 30 in combination with the above-described sustained airflow. The turbulent convection is illustrated in the figure with the large arrows which represent the turbulent airflow 130. Although all arrows point in an outward direction, in reality the turbulent airflow 130 goes back-and-forth through the spaces 37. It must be noted that this turbulent convection is rendered possible by the fact that the heat sink 30 and the support member 40 are arranged such that there is a free space between them, while at the same time the circular extension ensure also that there is direct heat conduction from the heat sink 30 to the support member 40. Fig. 13b illustrates another cut-view of the LED lamp system of Fig. 1 a in which another aspect of the cooling effect is illustrated. This cut-view is done through a lower part of the support member 40 and the envelope 70. The figure illustrates the radiation levels of the LED lamp system, which are directly relates to respective temperatures of the radiating parts. In the example of Fig. 13b the LED lamp system is also oriented in an upward-pointing direction, similar to Fig. 13a. From the figure it can be clearly deducted that the envelope 70 is spaced apart from the support member 40. As already mentioned earlier in this description the envelope 70 is only in physical contact with the support member 40 at a bottom side thereof, near the insulating member (not shown). The envelope 70 is thus for a significant part heated through radiation from the support member 40. The support member 40 has the highest temperature at the side which touches the heat sink and the lowest temperature at the side that is connecting with the insulating member. As a consequence of that, a lower part of the envelope 70 has a low radiation level indicated by light-colored arrows 140. A higher part of the envelope 70 has a medium radiation level indicated by darker-colored arrows 145, which is a consequence of the high radiation level of the support member 40 indicated by the darkest-colored arrows 150. Nevertheless, experiments have proven that the temperature of the envelope stays within safe limits such that is can be held (during or right after operational use) without getting skin burn. Fig. 13c illustrates part of another cut-view of the LED lamp system of Fig.

1 a in which yet another aspect of the cooling effect is illustrated. This figure illustrates in more detail the convection mechanism as already briefly discussed in Fig. 13a with the LED lamp system in the same orientation. The cold airflow 1 10 enters the envelope 70 at a bottom side thereof, and then the air flow 115 (indicated by the upward pointing arrows) flows in upward direction and gets heated by the support member 40 and the heat sink 30 and finally leaves the LED lamp system at the upper side of the envelope. It must be stressed that the examples given here elaborate on a support member 40 having a heat- sink function (to achieve this effect it may be made of aluminum just like the heat sink 30). Expressed differently, the heat sink 30 onto which the LED assembly (not shown) is mounted is expanded by the support member 40, i.e. it has a larger surface area and is in better contact with the air flow 1 15 and the turbulent air flow 130. However, it must be noted that it is not essential that the support member is made of a material that is suitable for acting as heat sink. Even in such embodiment the convection mechanism in accordance with the invention is present. Fig. 14a illustrates the LED lamp system of Fig. 1a having an upward- pointing orientation. Fig. 14b illustrates the LED lamp system of Fig. 1 a having an downward-pointing orientation. Fig. 14c illustrates the LED lamp system of Fig. 1 a having a sideward-pointing orientation. The situation in Fig. 14a complies with the situation in Figs 13a-13c (upward point direction). Arrows 1 15 indicate the path of the air flow. The air flow 1 10 enters the LED lamp system through the opening in the envelope, moves upwards between the envelope and the support member, and subsequently leaves 120 the LED lamp system between the glass bulb and the envelope. Along the way the air flow 115 passes along the heat sink (wherein the support member may also behaves as a heat sink extension, as earlier described. It must be noted that the arrows nicely illustrated that warm/hot air 120 which leaves the LED lamp system at the upper side is kept away from the LED assembly. The glass bulb 10 further enhances this thermal separation (insulation) effect. The situation in Fig. 14b illustrates the same LED lamp system, but then in a downward-pointing direction. Again, the air flow 1 15 is sustained by the heat generation of the heat sink. However, with respect to the LED lamp itself, the air flow 115 reverses direction. Air inlets Al become air outlets AO and vise versa. Again, warm/hot air 120 is kept away from the LED assembly. The situation in Fig. 14c illustrates the same LED lamp system, but then in a side-ward pointing direction. Again, the air flow 115 is sustained by the heat generation of the heat sink. However, the air flow 1 15 becomes more complicated. Whereas, in the up-ward and down-ward pointing directions the air flow in the spaces between the heat sink and the support member was a turbulent convection, in Fig. 14c this becomes predominantly a normal convection, which provides a better cooling effect. It must be noted that this effect is rendered possible by the particular design of the heat sink and the support member (using the circular extensions for creating a space between those parts). In any case, on a lower side of the LED lamp the openings are now air inlets Al and on the upper side these openings are air outlets AO. Similarly, on a lower side of LED lamp the openings (also defined by the fins of the support member) between the envelope and the glass bulb serve as air inlets Al and on the upper side these openings are air outlets AO. In the orientation of Fig. 14c there is also an additional air flow component 115' which runs from the bottom left side to the upper right side of the envelope. This component also contributes to the cooling effect.

Fig. 15a shows a photograph of an assembly comprising a heat sink with a LED assembly mounted thereon. Fig. 15b shows a photograph of the assembly of Fig. 15a after the provision of a first glass bulb thereon in accordance with another embodiment of the LED lamp system. Fig. 15c shows a photograph of the assembly of Fig. 15b after the provision of a second glass bulb thereon, which results in a very advantageous embodiment of the LED lamp system. This embodiment will be discussed in as far as it differs from the earlier mentioned embodiments. In this embodiment the heat sink 30 is prepared for receiving a further glass bulb 19 within the glass bulb 10. This embodiment is multiple advantages. First of all, this embodiment provides a better thermal insulation between the warm/hot air coming out of the air outlets and the LED assembly. Second, the further glass bulb may comprise diffuser material for further enhancing the diffusive effect of the LED lamp system. This will be at the cost of some light output, but experiments have shown that the light output loss is minimal (in the order of a few percent). In an advantageous variant the further glass bulb 19 and the glass bulb 10 are made of the same material, for example a glass with a diffuser coating thereon.

The invention thus provides a LED lamp system comprising: a heat sink (30), a LED assembly (20) thermally coupled to the heat sink (30), an air inlet (Al) and an air outlet (AO), the air inlet (Al) and the air outlet (AO) being positioned for obtaining an air flow (115) along the heat sink (30), wherein the LED assembly (20) has a light-emitting side in operational use, wherein the air flow (1 15) is caused by heat generated by the LED assembly (20), the air inlet (Al) and the air outlet (AO) being located substantially in plane with the LED assembly (20) or on a back side of the LED assembly (20), wherein the back side is defined as being opposite to the light-emitting side. The LED lamp system in accordance with the invention is a lighting system which makes use of passive cooling only. The cooling mechanism relies on the airflow that runs along the heat sink which air flow is sustained by the heat generated by the heat sink itself. No additional power is required. The invention may be applied in various application areas. For example, the invention may be applied in retrofit lighting products such as a replacement for incandescent light bulbs. However, it must be stressed that the passive cooling system in accordance with the invention is not restricted to those kind of lamps only.

Various variations of the LED lamp system in accordance with the invention are possible and do not depart from the scope of the invention as claimed. These variations for example relate to respective material choices for the components, to respective shapes of the respective components, to the number of LED's in the LED assembly, etc. The embodiment illustrated in the figures resembles the conventional incandescent light bulb, i.e. it has the same shape. This is done in order to obtain a quick market acceptance of this product. However, it must be noted that the invention is not limited to these kind of lamp shapes. The passive cooling system in accordance with the invention is applicable to any kind of LED lamp system having any kind of shape.

In various embodiments the following materials have been mentioned as advantageous: aluminum, brass, bronze, duraluminum, copper, goldplated metals, and silverplated metals. These materials are mentioned because of their good thermal conductivity. Nevertheless, it is very likely that in near future also plastics and ceramics may be used as heat sink material. This may be rendered possible as soon as the efficiency of the LED's is further increased and smaller thermal conductivities are required.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. 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. Throughout the Figures, similar or corresponding features are indicated by same reference numerals or labels.

Claims

1. A LED lamp system comprising: a heat sink (30), a LED assembly (20) thermally coupled to the heat sink (30), an air inlet (Al) and an air outlet (AO), the air inlet (Al) and the air outlet (AO) being positioned for obtaining an air flow (1 15) along the heat sink (30), wherein the LED assembly (20) has a light-emitting side in operational use, wherein the air flow (1 15) is caused by heat generated by the LED assembly (20), the air inlet (Al) and the air outlet (AO) being located substantially in plane with the LED assembly (20) or on a back side of the LED assembly (20), wherein the back side is defined as being opposite to the light-emitting side.

2. The LED lamp system as claimed in claim 1 , wherein the air inlet (Al) and the air outlet (AO) are displaced in a direction that is perpendicular to the light-emitting side.

3. The LED lamp system as claimed in claim 1 or 2, wherein the LED lamp system comprises a support member (40) for connecting to the heat sink (30) such that an air path (37) is formed between the back side of the heat sink (30) and the support member (40), wherein the air path (37) is in connection with the air outlet (AO) and the air inlet (Al).

4. The LED lamp system as claimed in claim 3, wherein the LED lamp system comprises an envelope (70) arranged around the support member (40) for forming an air channel between the air inlet (Al) and the air outlet (AO), wherein the air inlet (Al) and the air outlet (AO) are formed at respective ends of the envelope (70).

5. The LED lamp system as claimed in claim 4, wherein the heat sink (30) has a circular disc shape, wherein the LED assembly (20) has been centered with respect to the heat sink (30).

6. The LED lamp system as claimed in claim 5, wherein the support member (40) has a cylindrical shape.

7. The LED lamp system as claimed in any one of claims 3 to 6, wherein the support member (40) is provided with fins (44, 44') distributed around a periphery of the cylindrical shape and extending in a direction parallel to a longitudinal axis of the cylindrical shape for increasing a radiation area of the support member (40) and for defining sub-air channels for guiding the air flow (1 15).

8. The LED lamp system as claimed in any one of claims 5 to 7 in as far as directly or indirectly dependent on claim 5, wherein the envelope (70) has a cylindrical shape.

9. The LED lamp system as claimed in claim 8, wherein the radius of the cylindrical shape of the envelope (70) gradually increases towards one end.

10. The LED lamp system as claimed in any one of claims 4 to 9 in as far as directly or indirectly dependent on claim 4, wherein the heat sink (30) and the support member (40) comprise the same material.

1 1. The LED lamp system as claimed in any one of claims 4 to 10 in as far as directly or indirectly dependent on claim 4, wherein the support member (40) and the envelope

(70) are mechanically connected through a thermally insulating member (80) provided at a side of the support member (40) opposite to a side where the heat sink (30) is provided.

12. The LED lamp system as claimed in any one of the preceding claims, wherein the air inlet (Al) and/or the air outlet (AO) comprise a plurality of openings (74) distributed over a periphery of the LED lamp system.

13. The LED lamp system as claimed in any one of the preceding claims, further comprising a glass bulb (10) connecting to the heat sink (30) and fully covering the

LED assembly (20).

14. The LED lamp system as claimed in claim 13, further comprising a further glass bulb (19) provided within the glass bulb (10) connected to the heat sink (30) and fully covering the LED assembly (20).

15. The LED lamp system as claimed in claim 14, wherein the glass bulb (10) and/or the further glass bulb (19) comprises diffuser material for diffusing light emitted from the LED assembly (20) in operational use.