[0001] The invention relates to a lighting fixture with a heat generating light source,
such as, for example, an LED. The lighting fixture further comprises a substantially
planar carrier which on a first side is provided with at least one light source and
on a second side opposite the first side is provided with a cooling body for dissipating
heat generated by the light source, wherein the cooling body comprises cooling elements
which extend from the planar carrier in a direction away from the carrier.
[0002] Such a lighting fixture module is generally known, for lighting, for example, offices,
corridors, receptions, hotels, residences. Such a lighting fixture can be, for example,
a circular downlight fixture.
[0003] Today, LEDs still produce more than half of their power in heat, which needs to be
dissipated to have an optimum light output and not to curtail the life span.
[0004] These lighting fixtures are often built into a false ceiling. A drawback of the known
embodiments is that an insufficient free height above the cooling body may strongly
curtail the operation of the cooling body, which will raise the temperature in the
LEDs and reduce their efficiency. In the art, reference is made to a thermal stop
when the free height above the cooling body is so small that no convection flow can
develop anymore through the cooling fins.
[0005] A known solution to this problem is providing perforations in the cooling body, so
that there is a connection between the local space and the space in the false ceiling.
A drawback of this embodiment is that there is a reduced acoustic separation between
the technical space in the ceiling and the local space. This can give rise to problems
of crosstalk. Another disadvantage is that these perforations need to have a considerable
diameter, which does not always fit within the design of the fixture.
[0006] Another known solution as an alternative to this passive cooling is active cooling.
This will always have the disadvantage that the power consumption of the lighting
fixture will increase and there will always be a slight sound increase.
[0007] The invention envisages providing a lighting fixture which counteracts at least one
of the above-mentioned disadvantages.
[0008] To this end, the invention provides a lighting fixture according to the opening paragraph
hereof, wherein the cooling body defines a flow path for a convection flow which extends
from the periphery of the carrier to a central part of the cooling body which is free
from cooling elements.
[0009] By arranging for the convection flow to flow into the central part of the cooling
body, more effective cooling can take place, especially of cooling elements that are
arranged close to the central part.
[0010] The lighting fixture has its use in a fixture that is mounted in a ceiling. And where
the free height between the fixture and the ceiling is smaller than half the width
of the cooling body.
[0011] By providing a good coupling between the LED and the cooling body, the heat of the
LED can be properly dissipated to the cooling body.
[0012] The design of the cooling element is such that an air flow can develop, through the
cooling element, in both horizontal and vertical direction. This can be done by making
the cooling element not solid but in the form of ribs, rods or a solid element with
holes.
[0013] By reducing the height of the cooling elements of the cooling body in the central
portion, centrally a relatively colder zone is created. Through the reduced boundary
layer buildup in horizontal direction, a radial convection air flow can get going,
from the radial outer side, to the radial inner side of the cooling body. This results,
in the horizontal plane, parallel to the carrier of the fixture, in a multidirectional
convection flow in the cooling body and a vertical flow-through possibility in the
central portion. As a result, in case of a limited free space above the cooling body,
there will be a reduced boundary layer buildup in the cooling body and hence a better
effective cooling.
[0014] In an optional embodiment in accordance with the invention the fixture is mounted
not in a false ceiling, but as a surface-mounted appliance against the ceiling. The
same advantageous form will provide that the space needed for a good cooling is reduced,
as a result of which the fixture in itself becomes less high.
[0015] The invention will be further elucidated on the basis of an exemplary embodiment
which is represented in a drawing.
[0016] In the drawing:
Fig. 1 shows a schematic perspective view of a downlight fixture in accordance with
the invention with lens optic, where the LEDs are positioned behind the lens, and
against the back of the LED the cooling body is attached.
Fig. 2 shows a schematic section of a downlight fixture in accordance with the invention.
[0017] It is noted that the figures are only schematic representations of advantageous embodiments
which are represented by way of non-limiting exemplary embodiments.
[0018] In the figures, the same or corresponding parts are indicated with the same reference
numerals.
[0019] Figure 1 shows a schematic perspective view of the lens optic 1 behind which are
the LEDs 1 which are connected with the cooling body 4.
[0020] Figure 2 shows a schematic cross section of a downlight fixture in accordance with
the invention. In this mode of implementation there are no LEDs 1 positioned under
the central portion 7 of the fixture. Cooling pins 2 of the cooling body are connected
with the carrier 5 on which the LEDs 1 are mounted. The shape of the cooling pins
2 is such that a central part 3 is not provided with cooling pins. As a result, a
central part 3 is provided where the air temperature is lower than at the cooling
pins 2. The cooling body comprises an annular segment which surrounds the central
part 3. As a result, not merely the usual vertical, upward air flow will arise, but
a virtually circular air flow is created via a first path P
1 from the radial outer side of the lighting fixture, horizontally over or alongside/through
the cooling pins 2 to the central portion 3 where the air rises via a second path
P
2 and against the ceiling 6, flowing back via a third path P
3 to the radial outer side of the fixture. Owing to the central space / created opening
3, even at small distances from the ceiling 6 to the cooling pins 2, still a circular
air flow will get going, which provides for a better cooling.
[0021] Thus the lighting fixture according to the invention comprises a substantially planar
carrier which on a first side is provided with at least one light source and on a
second side which is opposite the first side is provided with a cooling body for dissipating
heat generated by the light source, wherein the cooling body comprises cooling elements
which extend from the planar carrier in a direction away from the carrier, and wherein
the cooling body defines a flow path for a convection flow which extends from the
periphery of the carrier to a central part of the cooling body which is free from
cooling elements. Preferably, the flow path extends between the cooling elements,
more preferably substantially parallel to the substantially planar carrier.
[0022] Preferably, the substantially planar carrier is substantially rotation symmetrical.
[0023] A plurality of cooling elements may be set up along a substantially radial path.
The height of the cooling elements may be chosen variably, for example, such that
the height on the radial inner side and/or on the radial outer side is less than in
a more centrally located part of the ring segment-shaped cooling body.
[0024] The invention is not limited to the exemplary embodiments represented here.
[0025] Thus, the pin bed may be designed as free-standing cooling ribs or a solid cooling
body with holes.
[0026] Furthermore, the shape of the lighting fixture may vary.
[0027] Furthermore, in the central portion with limited cooling, ribs may yet be added,
as long as there remains sufficient free space for a good convection flow.
[0028] Furthermore, it is possible that the central portion does have LEDs provided in it.
[0029] Furthermore, the lighting fixture may be equipped only with a single LED.
[0030] Thus, the lighting fixture comprises a heat generating light source and a cooling
body therefor, for realizing a substantially radial convection flow by counteracting
a radial thermal boundary layer buildup. Also, provision is made for a central vertical
flow-through possibility.
[0031] In cross section the cooling body can have a U-profile.
[0032] By providing the lighting fixture in a central middle part thereof with a surface
that cools less, a concave shape may be created..
[0033] Most preferably, the lighting fixture has no cooling ribs in the central part. Optionally,
at the central portion no lighting sources are placed.
[0034] The cooling body can take the form of a pin bed. However, the cooling elements may
also, as cooling ribs, be made of ring-shaped design, around the central portion.
Optionally, the cooling elements are provided with flow-through openings for a radial
convection flow. Furthermore, cooling ribs may be placed radially, so that between
the radial cooling ribs radial channels are formed for passing a radial convection
flow to the central portion of the cooling body.
1. A lighting fixture, comprising a substantially planar carrier which on a first side
is provided with at least one light source and on a second side opposite the first
side is provided with a cooling body for dissipating heat generated by the light source,
wherein the cooling body comprises cooling elements which extend from the planar carrier
in a direction away from the carrier, wherein the cooling body defines a flow path
for a convection flow which extends from the periphery of the carrier to a central
part of the cooling body which is free from cooling elements.
2. A lighting fixture according to claim 1, wherein the substantially planar carrier
is substantially rotation symmetrical.
3. A lighting fixture according to claim 1 or 2, wherein a plurality of cooling elements
are arranged in a substantially circular pattern.
4. A lighting fixture according to any one of the preceding claims, wherein the flow
path extends at least partly between the cooling elements.
5. A lighting fixture according to any one of the preceding claims, wherein the flow
path extends at least partly parallel to the substantially planar carrier.
6. A lighting fixture according to any one of the preceding claims, wherein a plurality
of cooling elements are arranged along a substantially radial path.
7. A lighting fixture according to claim 6, wherein the distance over which the plurality
of cooling elements extend in the direction away from the carrier first increases
and then decreases, as a function of increasing radius.
8. A lighting fixture according to claim 6 or 7, wherein the cooling element that is
closest to the central part of the cooling body extends less far from the carrier
than a neighboring cooling element which is located further away from the central
part.
9. A lighting fixture according to any one of claims 6-8, wherein the cooling element
that is farthest removed from the central part of the cooling body extends less far
from the carrier than a neighboring cooling element which is closer to the central
part.
10. A lighting fixture according to any one of the preceding claims, wherein a cooling
element is pin-shaped.
11. A lighting fixture according to any one of the preceding claims, wherein the substantially
planar carrier comprises a central, lowered part.
12. A lighting fixture according to any one of the preceding claims, wherein the cooling
body comprises a ring segment-shaped part which, viewed in a direction transverse
to the plane in which the carrier extends, surrounds the central part of the carrier.
13. A lighting fixture according to any one of the preceding claims, wherein the carrier
is provided with an opening for physically contacting the light source with the cooling
body.
14. A lighting fixture according to any one of the preceding claims, wherein the light
source comprises a singular LED or a cluster of LEDs.
15. A lighting fixture according to any one of the preceding claims, in the embodiment
of a downlight.