EP2553333B1

EP2553333B1 - Cooling and anti-glare arrangement for street light

Info

Publication number: EP2553333B1
Application number: EP11762076.5A
Authority: EP
Inventors: Hannu MÄÄTTÄ
Original assignee: Selmic Oy
Current assignee: Selmic Oy
Priority date: 2010-03-30
Filing date: 2011-03-30
Publication date: 2016-05-04
Anticipated expiration: 2031-03-30
Also published as: FI20105326A; FI20105326A0; WO2011121183A1; FI123058B; EP2553333A1; RU2012146918A; EP2553333A4; RU2543421C2

Description

The invention relates to an arrangement for cooling leds comprised in a lamp in a street or in public spaces and for decreasing the glare from the leds. The invention also relates to a lamp in a street or in public spaces, where the arrangement has been utilized.

Prior art

Lamps may be implemented with several different techniques of generating light. One possible lamp technique is the utilizing of leds (Light Emitting Diode) as the element generating light in the lamp. Such a lamp is comprised of several leds or led groups, which are connected either on a planar or a curved surface. In the lamp the leds form an essentially limited radiation surface, the luminous flux produced by which is steered to the use target. An optical part in front of the leds may be used for directing the light. The optical part may also function as a mechanical protection of the leds comprised in the lamp.
The led is characterised in that its luminance is great, so the direct radiation emerging from it may glare. The glare from leds may be decreased with various optical elements in front of the leds, which for example filter, steer or treat the light generated by the leds.
Another disadvantage with a led is its rather small efficiency, with which the electric energy fed into the led is transformed into light. It is common that only 20-40 % of the electric energy fed into the led is transformed in the led into visible light. The rest of the fed electric energy is transformed into lost heat. It is preferable to conduct the lost heat away from the lamp, since if the temperature of the led rises, the luminosity of the led decreases, which is not a desired property with regards to the lamp. It is also known that a high use temperature over time affects the wavelengths of the light radiating from the led, so that the hue of the light radiating from the led changes from the initial situation. Additionally a rise in the use temperature of the led shortens its life expectancy compared to a situation, where the led would function at a lower use temperature. Especially in use targets, where there are several lamps or servicing and changing them is laborious, the long working life of the lamp and the stability of the amount and quality of the light during the working life are desirable properties. Some examples of such use targets are the illumination arrangements in public spaces and street and road illumination.
One way of lowering the temperature of leds is to install it on a circuit board or a base, the thermal resistance of which is low. Via such a base having a low thermal resistance the lost heat generated by the led may be conducted into a separate cooling element. For the sake of the performance and life expectancy of the led it is desirable that there is an element or elements, the thermal resistance of which is as low as possible, between the heat-generating led and the cooling element. It is common to use a cooling rib or ribs as the cooling element, the air flow passing between which ribs cools down the cooling element. The cooling ribs used as cooling elements are often situated on the rear side of the led lamp, whereby there is only the circuit board or other installation base needed for the installation of the led and a possible frame element of the lamp between the led and the cooling ribs.
One problem with the structure described above is how the upper surface of the lamp is kept free from for example snow, pigeon droppings, tree leaves and other trash.
Additionally the flush or surface mounting of lamps, which is commonly used in public spaces, does not allow for cooling elements behind the lamps, which utilize air flow.
Led lamp structures are also known, where the heat produced by the leds is conducted via a separate cooling channel to a separate cooling element outside of the attaching base of the leds. An example of such a cooling solution is presented in patent publication CN 101266038 .
Led lamp structures are also known, where there are cooling ribs used for the cooling of the leds also on the light-producing lower surface of the lamp. In the known solutions the additional cooling ribs are situated essentially in the edge areas if the lamp. Examples of such a led lamp solution are presented in publications CN 201262363 and CN 101414588 .
Figure 1 shows the cooling solution for a led lamp found in reference CN 101414588 . The led lamp 10 comprises a uniform lamp frame 11. The light-producing led group 12 is attached on the lower surface of the lamp frame 11. The led group 12 comprises several separate leds. The main part of the cooling ribs 14 comprised in the lamp are situated on the rear/upper surface of the lamp 10. There are, however, cooling ribs 13a and 13b also on the lower surface of the lamp, on the illuminating side, in its two edges. The lost heat produced by the leds is conducted to the upper cooling ribs 14 on the rear surface of the lamp directly via the lamp frame 11. The air, which has been heated up in the led group 12, is steered to the cooling ribs 13a and 13b on the lower surface of the lamp by means of the air flow provided by the heated air. Colder air flows from outside the lamp to replace the heated air. The convection of the air heated in the led group 12 to the cooling ribs 13a and 13b improves the cooling of the led group 12.
If the cooling ribs are placed apart from the leds at the outer edge of the lamp, such as in reference CN 101414588 , this unavoidably leads to a situation, where the heat-transferring structure would need to be very thick, and thus the structure also becomes heavy.
Publication CN 201262363 depicts a led lamp 1 according to the preamble of claim 1 that comprises also a uniform lamp frame 1. The light-producing led group is attached on the lower surface of the lamp frame 1. One part of the needed cooling ribs of the lamp is situated on the upper surface of the lamp. There are also cooling ribs 2 on the lower surface of the lamp in its two sides. The lost heat produced by the leds is conducted to the upper and lower cooling ribs directly via the lamp frame 1.
Solutions are also known, where air circulation in the led group is boosted in a forced manner. In such lamps the air circulation is boosted with a fan comprised in the lamp.
It is an object of the invention to bring forth a new led lamp structure applicable as a road or street light, where the removal of lost heat provided by means of convection of the led group is boosted and simultaneously the glare of the leds in the lateral direction can be decreased and directed at a desired use target.
The objects of the invention are obtained with a led lamp structure, where the leds comprised in the lamp are divided into advantageously rectangular groups, of which each group is surrounded by its own cooling rib structure. When the lamp is in its use position, the cooling achieved by means of the convection of each led group is boosted by the cooling rib structures closest to (surrounding) it. The outermost cooling ribs are arranged to function advantageously also as glare shields for the lamp, by means of which the direct radiation of the leds may be limited at least in one lateral direction of the lamp. Thereby the glare of the leds may be decreased and the generated light may be directed to a desired area.
It is an advantage of the lamp according to the invention that the use temperature of the leds comprised in the lamp may be decreased in comparison to lamp structures, which have a corresponding luminosity.
It is further an advantage of the invention that the use temperature of the lamp may be decreased without a separate forced cooling arrangement.
It is further an advantage of the invention that when the lamp according to the invention is in its use position, its surfaces stay clean by means of gravity and convection flow.
It is further an advantage of the invention that the glare provided by the leds may be limited at least in one lateral direction of the lamp.
It is further an advantage of the invention that the outer surface of the lamp may be formed to repel snow, trash and dirt, because the cooling elements of the leds are situated on the lower surface of the lamp.
It is further an advantage of the invention that the structure of the lamp does not require a massive and heavy frame structure for evaporating the lost heat produced by the leds.
The lamp according to the invention is characterised in that the leds comprised in the lamp are arranged as at least two separate led groups, so that each led group in the plane parallel to the plane defined by the lonqitudinal and transverse axis of the lamp is completely surrounded by cooling elements which comprise cooling ribs in the direction of the longitudinal axis of the lamp, and that between the led group and the outer edge in the direction of the longitudinal axis of the lamp the height of the cooling rib is arranged to grow when moving from the led group toward said outer edge.
Some advantageous embodiments of the invention are presented in the dependent claims.
The basic idea of the invention is the following: In the lamp according to the invention the leds of the lamp are advantageously divided into separate groups. The group formed by the leds advantageously has a rectangular shape. Each led group of the lamp is surrounded by cooling elements. Therefore the distance, which the air heated by the leds must travel from the leds to the cooling element, is short in the lamp according to the invention.
In a use situation the lost heat produced by the leds generates a convection flow in the air surrounding the leds, which flow travels through the lamp in the direction of the cooling elements. In the lamp according to the invention the air flow generated by the lost heat of one led group encounters the closest cooling element quickly, because the leds and the surrounding cooling elements are advantageously divided into several led groups. Thus in the lamp structure according to the invention the heat transfer from the air heated by the leds to the cooling element is boosted, because the air heated in the led group encounters the adjacent cooling element immediately. In the solution according to the invention the air also does not have time to heat up in the led group as much as in known solutions, where the cooling elements are only at the edges in the direction of the longitudinal axis of the lamp. Due to the boosted heat transfer, the use temperature of the leds of the lamp decreases, which results in that the luminosity of the lamp remains constant and its working life is prolonged:
The direction of the illumination of the led lamp according to the invention and the lateral glare generated with the leds may advantageously be controlled at the height of the outermost cooling ribs in the direction of the longitudinal axis.
In the following, the invention will be described in detail. In the description, reference is made to the appended drawings, in which

Figure 1: shows the structure of a led lamp according to prior art,
Figure 2a: shows as an example a led lamp according to the invention as a perspective view,
Figure 2b: shows the led lamp of Figure 2a seen from below,
Figure 2c: shows the lamp of Figure 2a seen from its free end,
Figure 2d: shows a second advantageous embodiment of the invention seen from the free end of the lamp and
Figure 3: shows a third embodiment of the invention as a perspective view.

The embodiments shown in the following description are given as examples only and someone skilled in the art may carry out the basic idea of the invention also in some other way than what is described in the description. Though the description may refer to a certain embodiment or embodiments in several places, this does not mean that the reference would be directed towards only one described embodiment or that the described characteristic would be usable only in one described embodiment. The individual characteristics of two or more embodiments may be combined and new embodiments of the invention may thus be provided.
Figure 1 is described in connection with the description of prior art.
Figure 2a shows as a perspective view one led lamp 20 according to the invention, where the light is produced with four separate, advantageously rectangular led groups 23a, 23b, 23c and 23d. The led groups are advantageously in the same plane, which is essentially parallel with the plane defined by the longitudinal and transverse axes of the lamp. The lamp according to the invention may be a road/street light or a lamp in public spaces. The lamp 20 is attached to a lamp post (not shown in Figure 2a) with connecting means 21. The use position of the lamp may advantageously differ essentially from the horizontal plane. The connecting means 21 advantageously comprise both mechanical connecting means needed for connecting the lamp and electric connecting means. Below in the text the direction, which is parallel to the direction of the attachment enabling the attaching means 21 of the lamp 20, is called the longitudinal axis of the lamp according to the invention.
In the exemplary lamp 20 according to Figure 2a the leds 28 are divided into separate groups 23a, 23b, 23c and 23d, which will below be called also led matrixes. Each of the led matrixes advantageously comprises several leds (reference 28 in Figure 2b). The leds may for example be a part of a LTCC component (Low Temperature Co-fired Ceramic), which is attached mechanically and electrically to the lamp frame 22. The LTCC component in question may also contain components associated with the controlling and power supply of the lamp 20.
Each of the advantageously rectangular led matrixes 23a, 23b, 23c and 23d of the lamp 20 is completely surrounded by cooling elements, which in the example in Figure 2a are cooling rib structures. The direction of the cooling ribs in the example in Figure 2a is the direction of the longitudinal axis of the lamp 20. For example the led matrix 23a comprised in the lamp 20 is enclosed by the cooling elements 24a, 27, 26 and 25a. Correspondingly also the other led matrixes 23b, 23c and 23d comprised in the lamp 20 are surrounded by some combination of the cooling elements 24a, 24b, 25a, 25b, 26 or 27. In the embodiment according to Figure 2a the lost heat produced by the leds generates an air flow in the lamp 20, the direction of which air flow is the same as the direction of the cooling ribs.
Figure 2b shows the lamp 20 in Figure 2a seen from below. The lamp 20 according to the example in Figure 2b advantageously has a square shape. In one advantageous embodiment of the invention the outer dimensions of the lamp 20 are in the magnitude of 400 x 400 mm. In the lamp according to the invention the led matrixes 23a, 23b, 23c and 23d are advantageously situated symmetrically with regards to the longitudinal and transverse axes of the lamp 20.
In the example in Figure 2b each led matrix 23a, 23b, 23c and 23d comprises an exemplary amount of twenty-four leds 28. The led matrixes 23a, 23b, 23c and 23d are situated in the lamp 20 so that the width of the cooling element remaining between two led matrixes is advantageously about twice as wide as the cooling element remaining between a led matrix and the outer edge of the lamp 20. The cooling elements thus advantageously cover all of the lower surface of the lamp 20, which remains outside the led matrixes 23a, 23b, 23c and 23d.
Figure 2c shows the lamp 20 seen from its free end. The frame/casing of the lamp 20 is shown with reference 22. The dimensions of the cooling ribs 24a, 24b, 25a and 26 according to the invention have been altered from what is real in order to clarify the matter included in Figure 2c.
The cooling elements 24a and 24b on both edges in the direction of the longitudinal axis of the lamp and the cooling element 26 in the direction of the longitudinal axis of the lamp 20 consist of several, gradually lengthening/- shortening cooling ribs. With the shown structure the cooling effect of the cooling element grows at the same rate as the surface area of the cooling ribs ending up in the convection flow in the direction of the longitudinal axis of the lamp grows. On the other hand the short cooling ribs 27 between the led matrixes and the short cooling ribs 25a and 25b at the edges of the lamp enable a large free air flow through the lamp 20 in the direction of its longitudinal axis.
Figure 2d shows an advantageous embodiment of a lamp 20 according to the invention, where the lamp frame 22a and the cooling elements 24a, 24b, 25a and 26 are extruded as one entity. In this embodiment the upper side 22a of the lamp 20 is formed to be curved, whereby it does not collect dirt or snow in the use situation.
Figure 3 shows as a perspective view a third embodiment 30 of a led lamp according to the invention, where the light is produced with two separate led groups 33a and 33b, which are parallel with the plane of the longitudinal and transverse axis of the lamp. The lamp 30 according to the invention may be a road/street light or a lamp in public spaces. The lamp 30 is attached to a lamp post (not shown in Figure 3) with connecting means 31. The connecting means 31 advantageously comprise both mechanical connecting means needed for connecting the lamp and electric connecting means.
In the lamp 30 according to this embodiment the leds are divided into two led groups 33a and 33b.
Both of the led groups 33a and 33b of the lamp 30 are completely surrounded by cooling elements, which in the example in Figure 3 are cooling rib structures. The direction of the cooling ribs in the example in Figure 3 is the direction of the longitudinal axis of the lamp 30. For example the led group 33a comprised in the lamp 30 is enclosed by the cooling elements 34a, 37, 34b and 35a or their parts. Correspondingly also the second led group 33b comprised in the lamp 30 is surrounded by cooling elements 34a, 35b, 34b and 37 or their parts. In this embodiment the outer dimensions of the lamp 30 are advantageously in the magnitude of 400 x 200 mm. In the lamp 30 according to this embodiment the led matrixes 33a and 33b are advantageously situated symmetrically with regards to the transverse axis of the lamp 30.
In the example in Figure 3 each led matrix 33a and 33b comprises an exemplary amount of twenty-four leds 28. The led matrixes 33a and 33b are situated in the lamp 30 so that the width of the cooling element remaining between the led matrixes 33a and 33b is advantageously about twice as wide as the cooling element 34a, 34b, 35a or 35b remaining between either of the led matrixes 33a or 33b and the outer edge of the lamp 30. The cooling elements thus advantageously cover all of the lower surface of the lamp 30, which remains outside the led matrixes 33a and 33b.
The lamp 30 advantageously also comprises a lamp frame 32, where the led groups and cooling elements have been mechanically connected. The lamp frame 32 may advantageously comprise also a convex cover, which forms the upper/rear surface of the lamp 30.
A fourth advantageous embodiment of the invention comprises a led lamp, which advantageously has only one led group. Also in this embodiment the only led group of the lamp is surrounded completely with four cooling elements. To its structure the lamp according to this embodiment may for example be half of the lamp 30 in Figure 3, where for example one of the led groups 33a has been removed. The remaining led group 33b is in this embodiment surrounded with cooling elements 34a, 35b, 34b and with a cooling element, the width of which is half of the width of the cooling element 37 shown in Figure 3.
In the advantageous embodiments described above the highest cooling ribs of the cooling elements 24a, 24b, 34a and 34b in the direction of the longitudinal axis of the lamps 20 or 30 and of the middle cooling element 26 of the lamp 20 function in the lateral direction also as anti-glare elements and/or elements for forming the light beam of the led lamp. An angle may be defined at the height of the outermost cooling ribs, outside which angle the leds do not generate a glare, even if one looks in the direction of the lamp.
Based on performed tests the cooling power of a lamp 20 may with the dimensions according to the invention be improved. By dividing the leds 28 of the lamp 20 into four groups 23a, 23b, 23c and 23d four hotter spots are generated in the lamp in the centres of the led groups. The maximum temperature in the middle of each led group is about 40°C. Correspondingly the temperature in the edge area in each led group has decreased to about 35 °C.
In the led lamp according to prior art, which is shown in Figure 1 and which produces the same luminosity, which lamp has one uniform led group, the temperature in the centre of the led group rises to 65 °C. The lamp structure according to the invention thus decreases the maximum temperature of the led lamp by 25 °C.
Some advantageous embodiments according to the invention have been described above, by means of which leds comprised in street lights or lamps in public spaces may be cooled and simultaneously the glare generated by the leds may be decreased. The invention is not limited to the solutions described above, but the inventive idea can be applied in numerous ways within the scope of the claims.

Claims

A lamp (20, 30), which comprises:
- connecting means (21, 31) for connecting the lamp mechanically and electrically to an illumination arrangement

- a lamp frame (22, 22a, 32), on the lower surface of which the following have been arranged
- leds (28) and

- cooling elements (24a, 24b, 25a, 25b, 26, 27, 34a, 34b, 35a, 35b, 37), characterised in that

- in order to lower the use temperature of the lamp (20, 30) the leds (28) of the lamp have been arranged in at least two rectangular led groups (23a, 23b, 23c, 23d, 33a, 33b) so that each led group in a plane parallel to the plane defined by the longitudinal and transverse axis of the lamp is surrounded by cooling elements (24a, 24b, 25a, 25b, 26, 27, 34a, 34b, 35a, 35b, 37), which comprise cooling ribs in the direction of the longitudinal axis of the lamp (20, 30), and that

- between the led groups and the outer edge in the direction of the longitudinal axis of the lamp the height of the cooling rib is arranged to grow when moving from the led group toward said outer edge.
The lamp according to claim 1, characterised in that the cooling elements (24a, 24b, 25a, 25b, 26, 27, 34a, 34b, 35a, 35b, 37) cover the entire lower surface of the lamp (20, 30) except for the surface area required for the led groups (23a, 23b, 23c, 23d, 33a, 33b).
The lamp according to claim 2, characterised in that each led group (23a, 23b, 23c, 23d, 33a, 33b) is surrounded by four cooling elements (24a, 24b, 25a, 25b, 26, 27, 34a, 34b, 35a, 35b, 37).
The lamp according to claim 3, characterised in that the width of the cooling element (26, 27, 37) between two adjacent led groups (23a, 23b, 23c, 23d, 33a, 33b) is twice as wide as the width of the cooling element (24a, 24b, 25a, 25b, 35a, 35b) remaining between any led group (23a, 23b, 23c, 23d, 33a, 33b) and the outer edge of the lamp.
The lamp according to claim 1, characterised in that an illuminated area has been arranged to be defined also at the height of the outermost cooling ribs in the direction of the longitudinal axis of the lamp (20, 30), outside of which area the leds (28) of the lamp (20, 30) do not cause a glare.
The lamp according to claim 1, characterised in that of the cooling ribs in the direction of the longitudinal axis of the lamp, which cooling ribs are between two led groups (23a, 23b, 23c, 23d) of the lamp, the middle one is additionally the highest and that the height of the cooling ribs is arranged to decrease toward each led group.
The lamp according to claim 6, characterised in that the height of the cooling ribs between two led groups (23a and 23b, 23c and 23d, 33a and 33b) in the direction of the longitudinal axis of the lamp (20, 30) or between a led group and the outer edge in the direction of the transverse axis of the lamp is additionally constant.
The lamp according to claim 7, characterised in that said constant height of the cooling rib is smaller than the height of the lowest cooling rib between a led group (23a, 23b, 23c, 23d, 33a, 33b) and the outer edge in the direction of the longitudinal axis of the lamp.
The lamp according to claim 8, characterised in that the lamp (20, 30) is a street or road light.
The lamp according to claim 8, characterised in that the lamp (20, 30) is a lamp in a public space.