A LIGHTING DEVICE COMPRISING A HOUSING AND A BAG

Abstract

It is an object of the invention to provide an improved lighting device, which may compensate a pressure drop occurring. Thereto, the invention provides a lighting device (10) comprising a housing (11) and a bag (15) made of a bag material; wherein the housing (11) comprises a light source (23) and a light exit window (22) for outputting light of the light source (23) to the exterior; wherein the housing (11) has a housing volume (12) filled with air (13) having a housing pressure (14); wherein the bag (15) is gastightly sealed (17) with a bag material, and is filled with a bag fluid (16), and is contained within the housing volume (12); wherein the bag (15) is configured to expand for reducing the housing volume (12) and for thereby compensating a pressure drop in the housing pressure (14) of the air (13).

Claims

1. A lighting device comprising a housing and a bag made of a bag material; wherein the housing comprises a light source and a light exit window for outputting light of the light source to the exterior; wherein the housing has a housing volume filled with air having a housing pressure; wherein the bag is gastightly sealed, and is filled with a bag fluid, and is contained within the housing volume; wherein the bag is configured to expand for reducing the housing volume and for thereby compensating a pressure drop in the housing pressure of the air; wherein the bag material comprises a Modulus of Elasticity of at least 0.1 GPa and at most 5 GPa; wherein the bag material comprises a plurality of material layers, wherein at least one of said plurality of layers comprises an insulation layer.

2. The lighting device according to claim 1, wherein the pressure drop in the housing pressure of the air is caused by a temperature drop of the air.

3. The lighting device according to claim 1, wherein the bag is configured to expand in respect to a temperature drop of the air of at least 10 Kelvin.

4. The lighting device according to claim 1, wherein the bag is configured to expand in respect to a temperature drop of the air occurring within a time period no longer than 160 seconds.

5. The lighting device according to claim 1, wherein the bag material comprises a thermal conductivity of at most 0.3 W/mK for reducing a rate of heat transfer from the air to the bag fluid.

6. The lighting device according to claim 1, wherein the housing volume is at least 0.001 cubic meters.

7. The lighting device according to claim 1, wherein the lighting device is one of the group of: street lighting, stadium lighting, faade lighting, and outdoor lighting.

8. The lighting device according to claim 1, wherein the housing further comprises an aperture and a panel for closing said aperture, wherein the bag is connected to said panel.

9. The lighting device according to claim 1, wherein the bag expands within a range between 10% and 40% of the housing volume.

10. The lighting device according to claim 1, wherein the bag is in connection with an optic of the lighting device.

11. The lighting device according to claim 1, wherein the bag is a paper bag and the bag material comprises paper.

12. A method of compensating a pressure drop in a lighting device, the lighting device comprising a housing and a bag made of a bag material, wherein the housing comprises a light source and a light exit window for outputting light of the light source to the exterior, wherein the housing has a housing volume filled with air having a housing pressure, wherein the bag is gastightly sealed, is filled with a bag fluid, and is contained within the housing volume, wherein the bag material comprises a Modulus of Elasticity of at least 0.1 GPa and at most 5 GPa, wherein the bag material comprises a plurality of material layers, wherein at least one of said plurality of layers comprises an insulation layer, wherein the method comprises: expanding the bag for reducing the housing volume and for thereby compensating a pressure drop in the housing pressure of the air.

13. The method according to claim 12, wherein the pressure drop in the housing pressure of the air is caused by a temperature drop of the air.

14. A method of equipping a lighting device with a bag made of a bag material, wherein the lighting device comprises a housing having a housing volume filled with air having a housing pressure, wherein the housing comprises a light source and a light exit window for outputting light of the light source to the exterior, wherein the housing further comprises an aperture and a panel for closing said aperture, wherein the bag is gastightly sealed and is filled with a bag fluid, wherein the method comprises: opening said panel for opening said aperture; equipping the lighting device with said bag for containing the bag within the housing volume; closing said panel for closing said aperture.

15. The method according to claim 14, wherein the bag is connected to said panel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The invention will now be further elucidated by means of the schematic non-limiting drawings:

[0059] FIG. 1 depicts schematically a side view of a first embodiment of a lighting device comprising a housing and a bag;

[0060] FIG. 2 depicts schematically a top view of a second embodiment of a lighting device comprising a housing and a bag;

[0061] FIG. 3 depicts schematically, by non-limiting example, an embodiment of a method compensating a pressure drop in a lighting device;

[0062] FIG. 4 depicts schematically, by non-liming example, within a chart, experimental results of a bag according to the invention present within a lighting device in comparison to the situation wherein no bag is present.

[0063] FIG. 5 depicts schematically, by non-limiting example, an embodiment of a method of equipping a lighting device with a bag.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0064] As mentioned, the present invention provides an improved lighting device 10. FIG. 1 depicts schematically a side view of a first embodiment of a lighting device 10 according to the invention. The lighting device comprises a housing 11 and a bag 15. The housing 11 is made of metal. Alternatively, the housing may be made of, or partly made of, steel, aluminum, ceramic, polymer, fiber reinforced polymer, copper, or a combination thereof. The lighting device 10 further comprises a light source 23 for providing light through a light exit window 22, which is driven by a driver 24 and controlled by control electronics (not shown). Alternatively, other configuration of components may be present. The light source 23 is a LED light source, but may alternatively be a conventional light source. The window 22 is a transparent plate such as glass or polymer, but may alternatively comprise further optical features. The window 22 is gastightly sealed to the housing 11 by means of the gasket 21. The lighting device 10 is an outdoor lighting device, which is part of street lighting and mounted on a light pole. Alternatively, the lighting device may be any other outdoor lighting device, such as a flood light, faade lighting, or sports lighting. Yet alternatively, said lighting device may be a troffer-based lighting device and/or an indoor luminaire. The housing may optionally comprise a heat sink.

[0065] The housing 11 further optionally comprises a breather 26 for allowing moisture to leave the housing 11. However, the flow rate through the breather 26 is limited, so that the breather 26 cannot timely equalize a pressure at the interior of the lighting device 10 with the exterior of the lighting device 10. When a pressure drop occurs within the housing 11, a negative pressure gradient exists with the exterior of the housing 11, and the breather becomes a weak point for ingress of contaminants. Similarly, the housing 11 further optionally comprises at least one cable gland (not shown) for feeding a cable (not shown) through light pole into the housing 11. Such a cable gland may also be a weak point for ingress of contaminants, as it may wear in time and be prone to leaks.

[0066] The housing 11 has a housing volume 12 filled with a housing fluid 13 having a housing pressure 14. The housing volume 12 contains the volume of fluid enclosed by the housing 11 of the lighting device 10. Here, and generally, the housing fluid 13 is the air in the atmosphere. The housing pressure 14 depends on the thermodynamic conditions present in the housing 11. For example: during operation of the lighting device 10 the light source 23 and/or driver 24 are a source of heat, which may increase the temperature inside the housing 11, and which hence may increase the housing pressure 14 of the housing fluid 13 of the housing volume 12 inside the housing 11.

[0067] Alternatively, the housing volume of the housing of the lighting device may be gastightly sealed and may contain a pre-defined housing fluid. Such a pre-defined housing fluid may comprise a composition having less oxygen or less contaminants relative to the standard composition of air. The mentioned composition may be selected such as to improve the lifetime of the lighting device, e.g. preventing browning of seals.

[0068] Referring to FIG. 1, as mentioned before, the housing volume 12 may be prone to pressure differences. Here, the housing fluid 13 experiences a pressure drop with respect to the ambient fluid or ambient conditions, i.e. e.g. the ambient fluid surrounding the housing 11 of the lighting device 10. Said pressure drop is caused by a temperature drop of the housing fluid 13 due to weather conditions 19, such as e.g. rain. The temperature drop causing the pressure drop is instantaneous. It may alternatively be because of a water spray hitting the housing 11 of the lighting device 10 due to cleaning activities, or an indoor HVAC system suddenly cooling the lighting device. Said temperature drop may be a temperature shock. The pressure drop is undesired, because it not only puts mechanical stress on gaskets, seals, joints, and/or walls, such as the gasket 21 holding the window 22; but it also allows contaminants such as water, moisture, dust, dirt, insects, etc. to be sucked into the housing via leaks or apertures due to the resulting negative pressure gradient, such as the breather 26. Here, the (rate of the) pressure drop as caused by the temperature drop is at least 10 mBar within 40 seconds.

[0069] Alternatively, the pressure drop, or better the rate of pressure drop, is at least 50 mBar within 150 seconds, at least 12 mBar within 60 seconds. Such pressure drop rates may last for at least 10 seconds, and/or last between 10-50 seconds, and/or last between 50-100 seconds, and/or last between 100-180 seconds. These are the instantaneous rates, wherein a pressure drop occurs within a relatively short period of time. Alternatively, the pressure drop may at least be 1 mBar within 1 seconds, wherein said rate may last for 10 seconds; or at least be 0.6 mBar within 1 seconds during between 10-70 seconds from the initial occurrence of the pressure drop; or at least be 0.1 mBar within 1 seconds during between 70-180 seconds from the initial occurrence of the pressure drop. Such values may be derived from experimental results.

[0070] Alternatively, instead of the rate of pressure drop, the rate of temperature drop may be quantified as at least 10 Kelvin within a time period no longer than 180 seconds.

[0071] Moreover, still referring to FIG. 1, the bag 15 is comprised by the housing 11. The bag is in connection with a part of the housing 11 and is contained within the housing volume 12. The bag 15 may for example be attached to or be freely lying on a surface of said housing 11. Alternatively, the bag may be arranged with respect to a heat source within the housing, such as the light source or driver electronics, or other electric components. The bag may in such alternative embodiments remain warmer than the housing volume in the housing, hence having an increased ability to expand with respect thereto. The bag may for example be connected to said light source.

[0072] The bag 15 is gastightly sealed with a bag material 17. The bag material 17 is polyethylene (PE), but may alternatively be one of: Polypropylene (PP), Polyethylene terephthalate (PET), Mylar (Al coated PET), polyethylene (PE), Polyimide (PI), or a combination of the above. Alternatively, the bag material may comprise a plurality of material layers, wherein at least one of said plurality of layers may comprise an insulation layer, such as e.g. PET, paper insulation or an air gap/bubbles. Furthermore, the bag material 17 comprises a thermal conductivity of at most 0.3 W/mK for reducing a rate of heat transfer from the housing fluid to the bag fluid. Alternatively, or additionally, said bag material may comprise a surface with a reflectivity of at least 0.6, such as a reflective coating.

[0073] The bag 15 reduces the mentioned undesired or disadvantageous consequences of said pressure drop. Namely: The bag is filled with a bag fluid 16. Here, the bag fluid 16 is also air, but may alternatively be one of: high molecular weight gas, or medium molecular weight gas, or a combination of the above. The higher the molecular weight of the gas, the more delay is present in cooling down or heating up, hence the pressure compensating effect will be improved. The bag 15 is configured to expand for reducing the housing volume 12 and for thereby compensating the pressure drop in the housing pressure 14 of the housing fluid 13. More specifically: When said pressure drop occurs in the housing 11, the bag 17 may initially not be affected by the occurring pressure drop, because the bag fluid 16 is isolated from the housing fluid, and in some embodiments also insulated from the housing fluid. Therefore, the bag 15 expands 18 whenever the housing volume 12 experiences this sudden pressure drop in the housing pressure 14 of its housing fluid 13. As the bag 15 is contained within the housing volume 12, the expansion 18 of the bag 15 will reduce the housing volume 12. A reduction of the housing volume 12 will subsequently result into an increase in of the housing pressure 14 of the housing fluid 13. Thus, the sudden pressure drop in the housing pressure 12 of the housing fluid 13 will be compensated.

[0074] Here, the housing volume is at least 0.001 cubic meters. The bag 15 may expand within a range between 10% and 80% of the housing volume. Here, the bag is at least 10% of the housing volume and expands to 25% of the housing volume. Alternatively, the ratio between the housing volume and the volume of the bag, i.e. housing volume:bag volume, may for example range between a ratio of 10:1 and 10:8, or be between a ratio of 10:1 and 10:7, or at least be 10:0.5.

[0075] The present invention therefore provides an improved lighting device, which is able to cope with a pressure drop occurring in the housing of the lighting device, because it reduces a negative pressure gradient caused by such a pressure drop; and consequently reduces the ingress of contaminants and/or undesired stress on parts of the lighting device. The lighting device according to the present invention does for example not require any structural modification, e.g. an introduction of apertures or conduits in the housing, to solve the above-mentioned problems and disadvantages, because the expanding effect of the bag solves these identified problems and disadvantages.

[0076] FIG. 2 depicts schematically a top view of a second embodiment of a lighting device 50 comprising a housing 51 and a bag 55; which is partly similar to the embodiment depicted in FIG. 1, but now wherein the lighting device 50 is a flood light for illuminating a large stadium area and wherein the housing 51 comprises a panel 60 for closing an aperture 59 of the housing 51.

[0077] Referring to FIG. 2, the lighting device 50 comprises a housing 51 made of fiber reinforced polymer material, such that the lighting device 50 is lightweight, but still able to cope with mechanical loads and/or heat transfer from its interior to its exterior. The lighting device 50 further comprises a light source 53 for providing light through an optical element being a lens plate 62. The lens plate 62 is gastightly sealed to the housing 51 by means of the gasket 61. The light source 53 is driven and controlled by the driver electronics 64. Optionally, the housing 51 may accommodate sensors and/or actuators, such as an electromotor which is able to aim the flood light. Said actuator may comprise parts protruding through the housing, but still having seals and/or gaskets to gastightly seal the housing at the location of said protruding parts, e.g. axes.

[0078] The housing 51 is gastightly sealed. However, during its lifetime, the housing 51 of the lighting device 50 may experience leaks, for example due to deteriorated seals/gaskets. Such leaks may become a point for ingress of contaminants whenever a pressure drop occurs in the housing 51 in respect to its surroundings.

[0079] As similarly mentioned before, the housing 51 has a housing volume 52 filled with a housing fluid 53 having a housing pressure 54. The housing volume 52 contains the volume of fluid enclosed by the housing 51 of the lighting device 50. Here, again, the housing fluid 53 is the air in the atmosphere. The housing pressure 54 depends on the thermodynamic conditions present in the housing 11.

[0080] Referring to FIG. 2, as mentioned before, the housing volume 52 may be prone to pressure differences. Here, the housing fluid 53 experiences a pressure drop with respect to the ambient fluid or ambient conditions, i.e. e.g. the ambient fluid surrounding the housing 51 of the lighting device 50. Said pressure drop is caused by a temperature drop of the housing fluid 53. The temperature drop causing the pressure drop is instantaneous, namely 10 Kelvin within a time period of 60 seconds. Alternatively, the rate of temperature drop may be at least 10 Kelvin within a time period of 30 seconds. The pressure drop associated with such an instantaneous temperature drop is undesired, because it not only puts mechanical stress on gaskets, seals, joints, and/or walls, such as the gasket 61 holding the lens plate 62; but it also allows contaminants such as water, moisture, dust, dirt, insects, etc. to be sucked into the housing via leaks or apertures due to the resulting negative pressure gradient.

[0081] Moreover, still referring to FIG. 2, the housing 51 comprises an aperture 59 and a panel 60 for gastightly closing said aperture 59. This panel 60 can be detached to access the housing 51 of the lighting device 50. Alternatively, the panel 60 may be a lid which is pivoting in the housing. Furthermore, the bag 55 is comprised by the housing 51. The bag 55 is attached to the panel 60 and is, in closed condition of the panel 60, contained within the housing volume 52. Thus the bag may be easily applied to the lighting device by opening the panel and attaching the bag thereto.

[0082] The bag 15 is gastightly sealed with a bag material 57. The bag material 57 is Polypropylene (PP) and comprises an insulation layer of a further paper layer. Here, the bag material 57 comprises a thermal conductivity of 0.15 W/mK for reducing a rate of heat transfer from the housing fluid to the bag fluid and/or the heat transfer from the panel to the bag fluid.

[0083] Still referring to FIG. 2, the bag 55 reduces the mentioned undesired or disadvantageous consequences of said pressure drop caused by said temperature drop. Namely: The bag is filled with a bag fluid 56. Here, the bag fluid 56 is also air, but may alternatively be carbon dioxide, nitrogen or argon. The bag 55 is configured to expand for reducing the housing volume 52 and for thereby compensating the pressure drop in the housing pressure 54 of the housing fluid 53. More specifically: When said pressure drop occurs in the housing 51, the bag 57 may initially not be affected by the occurring pressure drop, because the bag fluid 56 is isolated from the housing fluid, and also insulated from the housing fluid. Therefore, the bag 55 expands 58 whenever the housing volume 52 experiences this sudden pressure drop in the housing pressure 54 of its housing fluid 53. Here, the housing volume 52 is at least 0.002 cubic meters. The bag 15 is expandable within a range between 10% and 40% of the housing volume 52. As the bag 55 is contained within the housing volume 52, the expansion 58 of the bag 55 will reduce the housing volume 52. A reduction of the housing volume 52 will subsequently result into an increase in of the housing pressure 54 of the housing fluid 53. Thus, the sudden pressure drop in the housing pressure 52 of the housing fluid 53 will be compensated. Hence, reducing the occurring negative pressure gradient caused by the pressure drop and reducing ingress of contaminants and/or mechanical loads on parts of the housing 51 of the lighting device 50.

[0084] FIG. 3 depicts schematically, within a flowchart, an embodiment of a method 80 of compensating a pressure drop in a lighting device, such as e.g. a lighting device depicted in FIG. 1 and FIG. 2. The method comprises the step (81) of positioning a bag within a housing of a lighting device according to the invention. For example, in the embodiment depicted in FIG. 2, the panel may be opened, the bag may be positioned in connection with said panel, such that when closing the panel, the bag may be comprised within the housing volume of the housing thereof.

[0085] The method further comprises the step (82) of expanding the bag for reducing the housing volume and for thereby compensating a pressure drop in the housing pressure of the housing fluid. As mentioned before: As the bag is contained within the housing volume, the expansion of the bag will reduce the housing volume. A reduction of the housing volume will subsequently result into an increase in of the housing pressure of the housing fluid. Thus, the sudden pressure drop in the housing pressure of the housing fluid will be compensated. Hence, reducing the occurring negative pressure gradient caused by the pressure drop and reducing ingress of contaminants and/or mechanical loads on parts of the housing 51 of the lighting device 50.

[0086] FIG. 4 depicts schematically, by non-liming example, within a chart, experimental results 90 of a bag according to the invention present within a lighting device in comparison to the situation wherein no bag is present. The experiment is conducted with a lighting device according to the invention, being a pole top street lighting luminaire, with a gastightly sealed housing having a housing volume of approximately 0.003 cubic meters. A bag, being a gastightly sealed PE bag, is positioned in said housing, wherein the bag is contained within the housing volume. Both the bag as the housing volume comprise air as the housing fluid and the bag fluid. The lighting device is turn on and after three hours of operation the lighting device is continuously sprayed with pressurized water for inducing a temperature drop and consequently a pressure drop in the housing pressure of the housing fluid.

[0087] The experimental results 90 are presented in a chart. The chart shows a first graph 91 representing the lighting device without a bag according to the invention, and a second graph 92 representing the lighting device with a bag according to the invention and as mentioned above. The Y-axis 93 of the chart indicates the pressure drop in millibars. The X-axis 94 of the chart indicates the time in seconds. The experimental results 90 prove that the present invention, wherein the lighting device comprises a bag, compensates a pressure drop in the housing pressure of the housing fluid; because the bag expands and reduces the housing volume. This is clearly indicated in the second graph (representing the invention) having a lower pressure drop and having a lower initial slope in the rate of pressure drop.

[0088] FIG. 5 depicts schematically, within a flowchart, an embodiment of a method 800 of equipping a lighting device, e.g. a retrofit lighting device, with a bag. Such a lighting device comprises a housing having a housing volume filled with a housing fluid having a housing pressure, wherein the housing further comprises an aperture and a panel for closing said aperture. Said bag is gastightly sealed with a bag material and is filled with a bag fluid. It is the bag according to the invention. The method of equipping said lighting device with said bag comprises: (801) opening said panel for opening said aperture; (802) equipping the lighting device with said bag for containing the bag within the housing volume; (803) closing said panel for closing said aperture. Hereby, in an embodiment, the bag may be connected to said panel, or alternatively to the light source, or alternatively to a PCB of said light source, or alternatively to another part of an interior surface of said housing.