WO2011157836A1

WO2011157836A1 - Luminaire, heat dissipation structure and street lighting device

Info

Publication number: WO2011157836A1
Application number: PCT/EP2011/060161
Authority: WO
Inventors: Alexander Paul Johannus De Visser
Original assignee: Lemnis Lighting Patent Holding B.V.
Priority date: 2010-06-18
Filing date: 2011-06-17
Publication date: 2011-12-22

Abstract

The invention relates to a luminaire including a housing and a light source. The light source includes one or more LEDs (6). The housing includes a heat conductive body (2) for accommodating the one or more LEDs, an upper surface having a plurality of first holes (12), a lower surface having a plurality of second holes (22), and a plurality of convection cooling ducts (14) connecting corresponding ones of the first and second holes. The convection cooling ducts are connected to the heat conductive body to form a heat conduction path from the one or more LEDs to the convection cooling ducts. Additionally, the convection cooling ducts are aligned substantially vertically when the luminaire is mounted for use, to form a cooling convection path through the ducts.

Description

LUMINAIRE, HEAT DISSIPATION STRUCTURE AND STREET LIGHTING

DEVICE

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a luminaire comprising one or more LEDs, and in particular to a heat conductive body for accommodating the one or more LEDs. The invention further relates to a street lighting device comprising such luminaire.

2. Description of the Related Art

[0002] Nowadays streetlight luminaires are ever more often provided with lighting units that make use of light emitting diodes (LED) instead of incandescent, fluorescent or gas discharge lamps. LEDs consume less power, have a long service life and can provide more useful light compared with other light sources used in streetlight luminaires. However, unlike other light sources, the optimal performance of LEDs is typically obtained when they operate at lower temperatures. A lower running temperature yields a higher efficacy for a given level of light output. Therefore, it is highly desirable to effectively remove heat from LEDs.

[0003] For this reason streetlight luminaires are typically provided with cooling fins to remove heat from the LEDs in such a streetlight. The LEDs are mounted on a heat-conductive structure with fins at the backside, such that heat can be transferred to the air by radiation using the increased surface area provided by the fins. Theoretically the use of cooling fins can be sufficient to cool the LEDs. However, in practice, the cooling capacity of fins reduces rapidly due to environmental contamination. Deposition of contaminants like dirt, grease, leaves and dust may disrupt airflow over the fins and create an insulating layer, causing the cooling fins to have a less than desirable performance.

SUMMARY OF THE INVENTION

[0004] It is desirable to provide a luminaire using LEDs for street lighting having a reliable and sufficient performance and being less susceptible to contamination, e.g. dust, dirt, fallen leaves. For this purpose, the invention relates to a luminaire comprising a housing and a light source, the light source comprising one or more LEDs, and the housing comprising a heat conductive body for accommodating the one or more LEDs, an upper surface having a plurality of first holes, a lower surface having a plurality of second holes, and a plurality of convection cooling ducts connecting corresponding ones of the first and second holes, wherein the convection cooling ducts are connected to the heat conductive body to form a heat conduction path from the one or more LEDs to the convection cooling ducts, and wherein the convection cooling ducts are aligned substantially vertically when the luminaire is mounted for use, to form a cooling convection path through the ducts.

[0005] Having cooling ducts extending from the first holes to the second holes enables effective cooling by convection. Air within the ducts warms up due to exposure to heat generated by the one or more LEDs and rises through the duct. As a result, cooler air is sucked into the duct through the second holes in the lower surface. The convection flow "exhaust" through the first holes in the upper surface into the environment. This cooling mechanism is very powerful as it operates under almost all environmental circumstances.

[0006] In some embodiments, the orientation of the ducts is within about 30 degrees, preferably within about 15 degrees, from a vertical orientation. Such orientation reduces contamination of the ducts caused by dust and/or dirt as these contaminants can fall through without adhering to the interior surface area of the ducts.

[0007] The one or more LEDs may be surrounded by the ducts. Such arrangement may reduce the average heat conduction path from the one or more LEDs to the convection cooling ducts, which allows for limited heat resistance.

[0008] In some embodiments of the invention, the cross-sectional area of the first holes is smaller than the cross-sectional area of the second holes. Such difference in cross-sectional area may cause a further reduction of adhesion of dust and/or dirt on interior side walls of the convection cooling ducts, and may prevent fallen leaves from entering and blocking the cooling ducts.

[0009] The lower surface may be absent at the location of the one or more LEDs. However, in some embodiments, the lower surface comprises a transparent portion which coincides with the location of the one or more LEDs. Such transparent portion is arranged to transmit radiation emitted by the one or more LEDs, while keeping contaminants away from the one or more LEDs.

[0010] The upper surface may be made of sheet metal or cast metal, for example using aluminum. The use of sheet metal or cast metal allows for easy manufacturing of the upper surface. Aluminum is a suitable material for both cast metal and sheet metal. Aluminum is a light weight material with sufficiently high thermal conductivity, typically about 230 W/mK, and is relatively easy to handle. The upper surface and ducts may be formed as a single one- piece structure. Using a single one-piece structure limits the number of components of the luminaire which makes it easier to assemble, and may further lead to a more robust luminaire. In embodiments of the invention, the single one-piece structure includes the upper surface, the ducts and the heat conductive body, which further reduces the number of components.

[0011] The ducts may connect to the second holes via a sealing member, such as an O-ring. The sealing member prevents dust from entering the luminaire, which may further improve the performance reliability of the luminaire.

[0012] In another aspect, the invention relates to a luminaire for street lighting comprising: a heat conductive body provided with a surface for accommodating at least one LED; a canopy for protecting the at least one LED, the canopy having an upper surface and a lower surface and being provided with a plurality of holes; a plurality of convection cooling ducts extending from the lower surface of the canopy such that the interior volume of the ducts is in communication with corresponding holes; and a plurality of heat conductive connection structures connecting the heat conductive body and the ducts, such that the ducts can dissipate heat by unforced thermal convection. Having cooling ducts extending from the canopy such that they can dissipate heat by unforced thermal LEDs can be cooled both efficiently and effectively. The convection operates under almost all environmental circumstances.

Furthermore, the cooling mechanism is reliable over a longer period of time. The ducts are relatively long, which provides the interior walls of the ducts with a relatively large surface area. Even though the heat transfer per unit surface area may decreases over time due to contamination, the ducts still provide sufficient convection cooling due to their length and resulting relatively large interior wall surface area.

[0013] In yet another aspect, the invention relates to a street lighting device comprising: any one of the embodiments of a streetlight luminaire described above; and a lamppost for supporting the luminaire at a height of at least 2.0 meters above the ground. Such street lighting device has low maintenance costs as the one or more LEDs operate efficiently over a long period of time due to effective cooling. Additionally, the luminaire does not have to be cleaned very often. [0014] The invention further relates to a heat dissipation structure for use in a streetlight luminaire, the heat dissipation structure comprising: a plurality of convection cooling ducts having an upper end, a lower end and an interior volume in between the upper end and the lower end; and a heat conductive body having a surface provided with at least one LED, the heat conductive body being connected to the plurality of ducts. The heat dissipation structure allows for effective cooling of the one or more LEDs by heat removal from the LEDs through conduction via the heat conductive body and heat convection through the ducts.

Accumulation of dust, leaves etc. can be prevented by orienting the heat dissipation structure such that these contaminants will not adhere to the structure but will fall through the ducts.

[0015] The heat conductive body and the heat conductive ducts may be connected via connection elements of a material with a thermal conductivity in a range of about 100 up to about 385 W/mK. The use of such material reduces heat resistance along the heat conduction path between the heat conductive body and the ducts, and facilitates effective cooling of the one or more LEDs.

[0016] The heat dissipation structure may further comprise a canopy comprising a plurality of through holes, the canopy being connected to the upper ends of the plurality of ducts such that the interior volume of each duct is in communication with at least one of the plurality of through holes. The canopy may shield elements of the heat dissipation structure, for example the heat conductive body, from external contamination elements, such as debris and/or dust.

[0017] The A projection of the surface of the heat conductive body onto the canopy may be substantially surrounded by the holes. Such arrangement may reduce the average heat conduction path from the one or more LEDs to the convection cooling ducts, which allows for limited heat resistance.

[0018] The canopy may be made of sheet metal or cast metal, for example using aluminum. The use of sheet metal or cast metal allows for easy manufacturing of the canopy. Aluminum is a suitable material for both cast metal and sheet metal. Aluminum is a light weight material with sufficiently high thermal conductivity, typically about 230 W/mK, and is relatively easy to handle. The canopy and ducts may be formed as a single one-piece structure. Using a single one-piece structure limits the number of components of a luminaire which makes it easier to assemble, and may further lead to a more robust luminaire. In embodiments of the invention, the single one-piece structure includes the canopy, the ducts and the heat conductive body, which further reduces the number of components.

[0019] The cross-sectional area of the ducts at their upper ends may be smaller than the cross-sectional area of the ducts at their lower ends. Such difference in cross-sectional area may cause a further reduction of adhesion of dust and/or dirt on interior side walls of the convection cooling ducts, as dirt may fall easier through the ducts without adhering to the interior walls, and may prevent fallen leaves from entering and blocking the cooling ducts.

[0020] In another aspect, the invention relates to a luminaire comprising an embodiment of a heat dissipation structure as described above, and a bottom cover with holes configured to receive the lower ends of the ducts. The bottom cover may cover all portions of the luminaire in the canopy with the exception of the ducts. By fitting the ducts walls into and through the holes it may be ensured that the inside wall of the ducts is smooth and continuous at the lower end, without a lip being formed due to the bottom cover overlapping the duct as a result of imperfect alignment of the holes and ducts. A smooth duct wall helps prevent buildup of dust and debris on the duct interior walls, resulting in better air flow through the ducts and better heat transfer from the duct walls to the air within the ducts.

[0021] The lower ends of the ducts may be arranged for receipt of a sealing member, such as an O-ring, for providing a sealed connection between the ducts and the bottom cover. Efficient sealing prevents dust from entering the luminaire, which may further improve the performance reliability of the luminaire.

[0022] The bottom cover may comprise a transparent portion which coincides with the location of the at least one LED. Such transparent portion is arranged to transmit radiation emitted by the one or more LEDs, while keeping contaminants away from the one or more LEDs.

[0023] In yet another aspect, the invention relates to a street lighting device comprising: a streetlight luminaire comprising a heat dissipation structure as described above or a luminaire as described above; and a lamppost for supporting the luminaire at a height of at least 2.0 meters above the ground.

[0024] Further aspects of the invention and embodiments as defined in the claims will be clarified with reference to the attached drawings and corresponding description. It will be understood that the invention is not in anyway restricted to the embodiments disclosed in these drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 schematically shows a cross-sectional view of a heat dissipation structure for use in a street lighting luminaire according to an embodiment of the invention;

[0026] FIG. 2 schematically shows a cross-sectional view of a duct as used in some embodiments of invention;

[0027] FIG. 3 schematically shows a cross-sectional view of a heat dissipation structure for use in a street lighting luminaire according to another embodiment of the invention;

[0028] FIGS. 4a, 4b show an elevated top view and an elevated bottom view of an embodiment of a luminaire respectively;

[0029] FIGS. 5a, 5b show an elevated top view and an elevated bottom view respectively of a bottom cover that can be mounted on the luminaire of FIGS. 4a, 4b;

[0030] FIG. 6 schematically shows a bottom view of another embodiment of a luminaire.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0031] The following is a description of certain embodiments of the invention, given by way of example only. FIG. 1 schematically shows a cross-sectional view of a heat dissipation structure 10 for use in a street lighting luminaire according to an embodiment of the invention. The heat dissipation structure 10 comprises a heat conductive body 2 with a surface 4 for accommodating a number of LEDs 6. The heat conductive body 2 is connected to convection cooling ducts 14. The ducts 14 have an orientation such that heat can be removed from the LEDs 6 through conduction via the heat conductive body 2 and heat convection through the ducts 14. The heat dissipation structure 10 remains clean as accumulation of dust, leaves etc. can be prevented by orienting the structure such that these contaminants will not adhere to the structure 10 but will fall through the ducts 14.

[0032] The heat conductive body 2 and the convection cooling ducts 14 may be connected via connection elements 16 of a material with a thermal conductivity in a range of about 100 up to about 385 W/mK. The use of such material reduces heat resistance along the heat conduction path between the heat conductive body 2 and the ducts 14, and facilitates effective cooling of the one or more LEDs 6. A suitable material for use in the connection elements 16 is aluminum, which typically has a thermal conductivity of about 230 W/mK.

[0033] The structure 10 may further comprise a canopy 8 for protecting the LEDs 6. The canopy 8 is provided with through holes 12 in its upper surface, and the canopy preferably has a smooth surface to avoid excessive accumulation of dirt and debris on its upper surface. The ducts 14 extend from the lower surface of the canopy 8 and their interior volume is in communication with the holes 12.

[0034] As described earlier, the connection between the ducts 14 and the heat conductive body 2 may be formed by heat conductive connection structures 16. The heat conductive connection structures 16 may be made of the same material as the ducts 14 and/or the heat conductive body 2, for example aluminum, or different materials may be used. Furthermore the heat conductive body 2, ducts 14, and connection structures 16 may be made as separate structures or as a single integral structure. Preferably the length of the heat conductive connection structures 16 is limited to allow a short heat conductive path towards the ducts 14 and keep heat resistance between the conductive body 2 and ducts 14 at a minimum.

[0035] The shown heat dissipation structure 10 is arranged to dissipate heat by thermal convection through the ducts 14 using the holes 12. Heat generated by the LEDs 6 is absorbed by the heat conductive body 2 and transferred to the ducts 14 via the heat conductive connection structures 16. Air in the volume within the ducts 14 will warm up due to the exposure to the heated inner walls of the ducts 14. The heating of the air results in a development of a convection flow through the ducts 14 from the lower open end towards the upper end at the canopy 8. Eventually the heated air leaves the structure 10 through the holes 12. The structure 10 enables effective cooling of LEDs 6, which improves their performance with respect to for example light output and efficiency and allows a longer lifetime of the LEDs 6. An elongated LED lifetime may reduce the product and maintenance costs of the streetlight luminaire.

[0036] To facilitate unforced convection flow of air (or other cooling fluid) through the ducts 14, the ducts are preferably oriented in a vertical or substantially vertical direction, with the upper end of the ducts positioned sufficiently above the lower end to enable the formation of a convection flow through the ducts. The heat conductive ducts 14 preferably have an orientation that does not exceed an angle of about 30 degrees, preferably less than 15 degrees, from a vertical orientation. Such orientation reduces contamination of the ducts 14 caused by dust and/or dirt as these contaminants can fall through without sticking to the inner walls of the ducts 14.

[0037] The canopy 8 is preferably made of a material with a high thermal conductivity that can be cast or formed into a sheet metal. A suitable material for both cast metal and sheet metal would be aluminum, which is a light weight material with sufficiently high thermal conductivity, typically about 230 W/mK. Additionally, a material like aluminum allows for easy manufacturing of the canopy 8. The canopy may alternatively be formed from another cast metal, sheet metal or plastic.

[0038] The luminaire may further comprise a bottom cover 18 provided with through holes 22 in its lower surface. The heat dissipation structure 10 may therefore be configured to receive such cover 18. Preferably, the bottom cover 18 is a removable cover, which provides the opportunity to remove the cover for cleaning and other maintenance operations. Fastening of the removable cover 18 to the structure 10 can be accomplished using, e.g. a male-female connection, a click-mechanism, screws, bolts and nuts, etc.

[0039] The bottom cover 18 may cover all portions of the luminaire in the canopy 8 with the exception of the ducts 14. Preferably, the through holes 22 have dimensions that exceed the dimensions of the lower ends of the ducts 14 so that the lower ends of the ducts 14 can be accommodated by the holes 22 in the cover 18. By fitting the ducts walls into and through the holes 22 (as shown in FIG. 2) it is ensured that the inside wall of the ducts is smooth and continuous at the lower end, without a lip being formed due to the bottom cover 18

overlapping the duct as a result of imperfect alignment of the holes 22 and ducts 14. A smooth duct wall helps prevent buildup of dust and debris on the duct interior walls, resulting in better air flow through the ducts and better heat transfer from the duct walls to the air within the ducts. Efficient sealing can be established by using a sealing member such as an O- ring positioned between the lower ends of the ducts 14 and the bottom cover 18.

[0040] The bottom cover 18 may extent over the location of the LEDs 6. In such case the cover 18 comprises a transparent portion 18a which coincides with the location of the LEDs 6 to allow illumination. The cover 18 provided with transparent portion 18a may protect the LEDs 6 from outside influences. [0041] Preferably, the canopy 8, heat conductive duct(s) 14 and heat conductive connection structure(s) 16 are formed together in one integrated piece as a single one-piece structure. This allows easy manufacturing of a heat dissipation structure that can accommodate a body provided with one or more LEDs. The single one-piece structure may be a high pressure cast metal sheet structure. Such structure is easy to manufacture, and due to the use of sheet metal, less material is needed which saves costs and reduced weight of the luminaire. The sheet metal may comprise aluminum, as this is a light weight material with good heat conductivity, typically about 230 W/mK.

[0042] In some embodiments the heat conductive body 2 also forms a part of the integrated single one-piece structure. This further simplifies assembly of the luminaire.

[0043] The cross-section of the ducts 14 may have an arbitrary shape, i.e. the cross- sectional shape may be circular, but can also have another shape, e.g. square, rectangular, ellipsoidal, etc. A non-circular cross-section increases the surface area of the interior walls of the ducts, increasing heat transfer between the duct walls and the air flowing within the ducts. However, a complex cross-sectional shape with walls forming acute interior angles may also increase the amount of dust and debris accumulating within the ducts, increasing resistance to airflow through the ducts and reducing heat transfer to the air. The cross-sectional area at any position within the duct 14 preferably lies within the range from about 10 mm² up to about

5000 mm 2. A cross-sectional area of about 10 mm 2 or more enables a natural convective air flow to develop, i.e. a convective flow without addition of force by e.g. a ventilator. A cross- sectional area below about 5000 mm results in a relatively efficient ratio between interior surface area of the duct walls and the volume or air within the duct to be heated to allow for efficient heat transfer from the duct walls to the air. Ducts with a relatively large cross- sectional area also form rigid structures which improve the structural integrity of the luminaire.

[0044] Preferably, the ducts 14 have sufficient length to enable development of a natural convection flow through the ducts without significant turbulence. Typical lengths of ducts 14 extending through the housing of a luminaire may be in the order of 5-25 cm, preferably 10- 15 cm. [0045] FIG. 2 schematically shows a cross-sectional view of a duct 14 as used in some embodiments of the invention, shown in the orientation when the luminaire is mounted in its operating position. The diameter Dj of the duct 14 at its upper end is smaller than the diameter D₂ of the duct 14 at its lower end. The difference leads to a difference in cross- sectional area at the ends, i.e. the upper end having a smaller cross-sectional area than the lower end. The different size of the duct at the ends reduces contamination and clogging of the ducts duct 14 because dirt, dust and other debris entering the duct 14 at the upper end will tend to fall through the duct without adhering to the walls of the duct. This helps to maintain the ducts open and the duct walls in a clean condition free of buildup of dust and debris, so that air flow through the ducts is not unduly impeded. Buildup of dust and dirt on the duct walls will also reduce the heat transfer from the duct walls to the air within the ducts, decreasing the cooling efficiency of the ducts. The luminaire for street lighting can therefore maintain its performance over a longer period of time than a luminaire that relies on cooling fins for cooling the LEDs.

[0046] FIG. 3 schematically shows a cross-sectional view of a heat dissipation structure 20 according to another embodiment of the invention. In contrast to the heat dissipation structure 10 shown in FIG. 1, the width of the ducts 14 is greater than the width of the holes 12. This arrangement of ducts 14 and holes 12 also reduces the chance that dust and dirt will settle on the inner walls of the ducts 14. Therefore, the reliability of the heat dissipation performance of the structure is improved.

[0047] Embodiments of the invention relate to a luminaire comprising a housing and a light source comprising one or more LEDs. The housing comprises an upper surface having a plurality of first holes, a lower surface having a plurality of second holes and a plurality of convection cooling ducts connecting corresponding ones of the first and second holes. The ducts are connected to a heat conductive body to form a heat conduction path from the one or more LEDs to the ducts.

[0048] Having cooling ducts extending through the entire width of the housing, i.e. from the upper surface to the lower surface enables effective cooling by convection via a so-called chimney-effect. Air within the ducts warms up due to exposure to heat generated by the one or more LEDs and rises through the duct. As a result, cooler air is sucked into the duct through the second holes in the lower surface. The convection flow "exhaust" through the first holes in the upper surface into the environment. This cooling mechanism is very powerful as it operates under almost all environmental circumstances. Furthermore, because the ducts are relatively long, the interior walls of the ducts have a relatively large surface area. Even if heat transfer per unit surface area would slightly decrease over time due to

contamination of the interior walls, the ducts still provide sufficient convection cooling due to their length and resulting large interior wall surface area.

[0049] Additionally, because the convection cooling ducts are aligned such that they have a substantially vertical orientation when the luminaire is mounted for use, the convection path will be very powerful, and contamination will be limited as dirt, dust, etc. may fall through the ducts without adhering to the interior surface thereof.

[0050] FIGS. 4a, 4b show an elevated top view and an elevated bottom view of an embodiment of a luminaire 30 respectively. The luminaire 30 comprises a housing

comprising an upper surface in the form of a canopy 8 which comprises a sheet or cast metal structure shaped in a form suitable for street lighting. The canopy 8 is provided with a plurality of holes 12. In the shown embodiment, the holes 12 are arranged in a ring

circumscribing the surface 4 of the heat conductive body for accommodating the LEDs (not shown). In the shown embodiment, the heat conductive body 2 takes the form of a box with walls from which heat conductive connection elements in the form of ribs 16 extend towards the heat conductive ducts 14. The ribs 16 are relatively short in length to maximize heat transfer to the ducts 14 and minimize heat accumulation within the heat conductive body 2. The upper ends of the ducts 14 extend downward from the holes 12, while the lower ends are arranged to receive a bottom cover that will be discussed with reference to FIGS. 5a, 5b. The luminaire further comprises additional elongated channels 24a connected to the heat conductive structure 2 for receipt of fastening elements such as screws or the like for connecting the bottom cover to the heat conductive body 2. Preferably, the additional channels provided with fastening elements facilitate additional heat removal.

[0051] Furthermore, both the ducts 14 near the bottom ends and the bottom end of the walls of the heat conductive structure may be arranged for accommodation of a sealing member, e.g. an O-ring. The sealing member ensures that the connection between a bottom cover and the luminaire can be made airtight. This prevents dust from entering the luminaire, which may further improve the performance reliability of the luminaire.

[0052] The upper external surface of the canopy 8 has a smooth contoured surface. This shape assists in preventing accumulation of dirt and debris such as fallen leaves on top of the luminaire. A buildup of dirt and debris forms an insulating layer on the canopy and reduces the release of heat from the upper surface of the canopy to the surrounding environment. The canopy slopes downwards around its periphery, and the holes 12 are located in the sloping portions, encouraging dead leaves and other debris to slide off the canopy rather than stick to the upper surface of the canopy where they may block the cooling ducts.

[0053] FIGS. 5a, 5b show an elevated top view and an elevated bottom view respectively of a bottom surface in the form of a bottom cover 18 that can be mounted to the luminaire 30 of FIGS. 4a, 4b. The luminaire 30 then thus comprises an upper surface, i.e. canopy 8, and a bottom surface, i.e. cover 18. The bottom cover 18 is provided with a transparent portion 18a. The location of the transparent portion is such that it coincides with the space surrounded by the walls of the heat conductive structure 2. Consequently, light emitted by the LEDs is not blocked by the cover 18, but may leave the luminaire via the transparent portion 18a of the cover 18.

[0054] The cover 18 is further provided with a plurality of holes 22. The dimensions of the holes 22 are such that they can accommodate the bottom ends of the ducts 14 of the luminaire 30. By placement of a sealing member between the cover 18 and the bottom end of the duct 14 an tight connection, preferably airtight, may be established. Air may then flow through the ducts 14 upwards through the entire luminaire without encountering any additional structure. Similarly, dust, grease and dirt would fall through the ducts 14 completely without being blocked by any structure extending into the interior of the ducts 14.

[0055] The bottom cover 18 is further provided with small additional channels 24b for accommodating fastening elements such as screws or the like for connecting the bottom cover 18 with the heat conductive body 2 shown in FIGS. 4a, 4b. The channels 24b coincide with the channels 24a to form a single channel through which a screw, pin or the like can be provided to fasten the cover 18. It will be understood that different methods of fastening the bottom cover 18 may be used as well in embodiments of the invention.

[0056] Embodiments of the invention relate to a luminaire for street lighting using one or more LEDs provided on a heat conductive body, in which the housing is provided with through holes forming heat conductive ducts through the housing such that, during use, heat generated by the one or more LEDs is removed via heat conduction through the heat conductive body and heat convection through the ducts. So far, embodiments of the invention have been described with reference to designs in which each duct corresponds to a single hole. However, this is not necessarily the case.

[0057] FIG. 6 schematically shows a bottom view of an embodiment of a luminaire 40 in which the interior volume of a duct 14 is in communication with a plurality of holes 12. The luminaire 40 is provided with a bottom cover 18 having openings 32a, 32b that coincide with the size of the ducts 14. Sealing of the bottom cover 18 to the other elements of the luminaire may be easier in this embodiment as the number of sealing members, e.g. O-rings, is limited.

[0058] The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.

Claims

1. A luminaire comprising a housing and a light source, the light source comprising one or more LEDs (6), and the housing comprising a heat conductive body (2) for accommodating the one or more LEDs, an upper surface having a plurality of first holes (12), a lower surface having a plurality of second holes (22), and a plurality of convection cooling ducts (14) connecting corresponding ones of the first and second holes, wherein the convection cooling ducts are connected to the heat conductive body to form a heat conduction path from the one or more LEDs to the convection cooling ducts, and wherein the convection cooling ducts are aligned substantially vertically when the luminaire is mounted for use, to form a cooling convection path through the ducts.

2. The luminaire of claim 1, wherein the luminaire does not include components for generating a forced air flow through the convection cooling ducts.

3. The luminaire of claim 1, wherein the cooling convection path through the ducts is an unforced cooling convection path.

4. The luminaire of any one of the preceding claims wherein the orientation of the ducts is within about 30 degrees, preferably within about 15 degrees, from a vertical orientation.

5. The luminaire of any one of the preceding claims, wherein the one or more LEDs are surrounded by the ducts.

6. The luminaire of any one of the preceding claims, wherein the cross-sectional area of the first holes is smaller than the cross-sectional area of the second holes.

7. The luminaire of any one of the preceding claims, wherein the lower surface comprises a transparent portion which coincides with the location of the one or more LEDs.

8. The luminaire of any one of the preceding claims, wherein the upper surface is made of sheet metal or cast metal.

9. The luminaire of claim 8, wherein the sheet metal or cast metal includes aluminum.

10. The luminaire of any one of the preceding claims, wherein the upper surface and the ducts are formed as a single one-piece structure.

11. The luminaire of claim 10, wherein the single one-piece structure is a high pressure cast metal structure.

12. The luminaire of claim 10 or claim 11, wherein the single one-piece structure further includes the heat conductive body.

13. The luminaire of any one of the preceding claims, wherein a cooling duct is connected with more than one of the first holes.

14. The luminaire of any one of the preceding claims, wherein a cooling duct is connected with more than one of the second holes.

15. The luminaire of any one of claims 1 - 12, wherein the shape of a duct corresponds to the shape of a first hole to which it is connected.

16. The luminaire of any one of the preceding claims, wherein the ducts connect to the second holes via a sealing member, such as an O-ring.

17. A luminaire for street lighting comprising:

a heat conductive body provided with a surface for accommodating at least one LED; a canopy for protecting the at least one LED, the canopy having an upper surface and a lower surface and being provided with a plurality of holes; a plurality of convection cooling ducts extending from the lower surface of the canopy such that the interior volume of the ducts is in communication with corresponding holes; and

a plurality of heat conductive connection structures connecting the heat conductive body and the ducts, such that the ducts can dissipate heat by unforced thermal convection.

18. Street lighting device comprising:

a streetlight luminaire according to any one of the preceding claims; and

a lamppost for supporting the luminaire at a height of at least 2.0 meters above the ground.

19. A heat dissipation structure for use in a streetlight luminaire, the heat dissipation structure comprising:

a plurality of convection cooling ducts having an upper end, a lower end and an interior volume in between the upper end and the lower end; and

a heat conductive body having a surface provided with at least one LED, the heat conductive body being connected to the plurality of ducts.

20. The structure of claim 19, wherein the heat conductive body and the heat conductive ducts are connected via connection elements of a material with a thermal conductivity in a range of about 100 up to about 385 W/mK.

21. The structure of claim 19 or claim 20, further comprising a canopy comprising a plurality of through holes, the canopy being connected to the upper ends of the plurality of ducts such that the interior volume of each duct is in communication with at least one of the plurality of through holes.

22. The structure of claim 21, wherein a projection of the surface of the heat conductive body onto the canopy is substantially surrounded by the holes.

23. The structure of claim 21 or claim 22, wherein the interior volume of a duct is in communication with more than one hole.

24. The structure of claim 21 or claim 22, wherein the shape of a duct corresponds to the shape of the hole its interior volume communicates with.

25. The structure of any one of claims 21 - 24, wherein the canopy is made of sheet metal or cast metal.

26. The structure of claim 25, wherein the sheet metal or cast metal includes aluminum.

27. The structure of any one of claims 21 - 26, wherein the canopy, the ducts and the heat conductive body are formed as a single one-piece structure.

28. The structure of claim 27, wherein the single one-piece structure is a high pressure cast metal structure.

29. The structure of any one of claims 19 - 28, wherein the cross-sectional area of the ducts at their upper ends is smaller than the cross-sectional area of the ducts at their lower ends.

30. A luminaire comprising:

a structure according to any one of claims 19 - 29; and

a bottom cover with holes configured to receive the lower ends of the ducts.

31. The luminaire of claim 30, wherein the lower ends of the ducts are arranged for receipt of a sealing member, such as an O-ring, for providing a sealed connection between the ducts and the bottom cover.

32. The luminaire of claim 30 or claim 31, wherein the bottom cover comprises a transparent portion which coincides with the location of the at least one LED. Street lighting device comprising:

a streetlight luminaire comprising a structure according to any one of claims 19 - 29 or a luminaire according to any one of claims 30 - 32; and