Patent Application
20090052187
(a) Field of the Invention
The present invention relates to a lighting system that dissipates heat from a light source.
(b) Description of the Related Art
Conventional indoor and outdoor lighting systems utilize incandescent, fluorescent, or high-intensity discharge (HID) light sources. Recently, significant efforts have been made to develop white light-emitting diodes (LEDs) for lighting system applications. It is widely expected that LEDs will be the next generation of light source. However, unlike conventional light sources, which can operate at several hundred degrees Celsius, LEDs cannot operate at temperatures above around 85° C. It is therefore desirable to provide a lighting system that can dissipate the heat generated by LEDs, and maintain the LEDs at their optimum temperature.
A lighting system includes a light source attached to a coolant chamber, the chamber being defined by an outer and an inner wall. The coolant chamber defines a closed-loop coolant path with an upward, or warmed, coolant channel; and a downward, or cooled, coolant channel, separated by the inner wall.
Coolant is allowed to flow through the coolant chamber by natural convection. To this end, the light source may be disposed at a lower side surface of the chamber. Coolant near the light source absorbs heat from the light source, and moves upward along the warmed coolant channel by natural convection. Once the coolant at the upper portion of the chamber has cooled, it moves generally downwards along the cooled coolant path, also by natural convection.
A radiator may additionally be provided at a higher side surface of the coolant chamber, opposite the light source. A sun-shield may also be provided to shield the radiator and/or at least a portion of the chamber from the sun.
A volume change compensation device may also be provided. The device may be a vent, a deformable patch, or a bellows, on the surface of the coolant chamber.
Like reference numerals refer to corresponding parts throughout the several views of the drawings.
Recent breakthroughs have increased the brightness of light-emitting diodes (LEDs), making them candidates for light sources for high-intensity lighting systems, such as indoor and outdoor lighting, streetlamps, stadium lights, etc.
LEDs also provide several advantages over traditional light sources. First, they are longer lasting: currently, LEDs can last for 20,000-50,000 hours, and it is contemplated that their lifetime will exceed 50,000 hours in the future. Second, they are more efficient: the theoretical luminous efficacy of white LEDs is over 400 lumens/Watt (lm/W), and LEDs with luminous efficacies of 150 lm/W are already being manufactured. (For comparison, luminous efficacies of traditional light sources are about 5-35 lm/W for incandescent lights, about 45-100 lm/W for fluorescent lights, and about 150-200 lm/W for HID lights.) Third, LEDs are environmentally friendly or “green” light sources: they are lead-, halogen-, and mercury-free, and, unlike fluorescent lights, do not emit any ultra-violet light, which is harsh and potentially harmful.
While LEDs are currently more expensive than traditional light sources, their cost is ever decreasing, and it is contemplated that within a few years, they will be competitively priced. LEDs are therefore good candidates for light sources.
However, as mentioned above, LEDs typically cannot operate at temperatures over about 85° C. This means that they need to be cooled in many lighting systems, especially because, at their optimum temperatures, the temperature difference between the LED and the ambient air can sometimes be quite small, therefore making it difficult to transfer heat from the LEDs to the surrounding air. A simple, cheap, easily maintained thermal dissipation path is therefore necessary.
Some of the embodiments described herein provide a heat-dissipating lighting system that can effectively remove heat from a light source by natural convection, i.e. without the need for any machinery, such as fans or pumps, which use electricity and thereby decrease the efficiency of the light source.
Referring to
The light source 20 is thermally coupled to the chamber 30. In the illustrated embodiments, the light bulbs or LEDs 24 are housed in a thermally conductive light fixture 22, which is, in turn, attached to the chamber 30. However, in some embodiments, a separate light fixture 22 may not be necessary, as the chamber may include the fixture. These embodiments could be accomplished, for example, by attaching the bulbs or LEDS 24 directly to a fixture integral with the chamber wall 34.
In some embodiments, the chamber 30 houses coolant (designated by arrows in the figures). In some embodiments, the coolant is allowed to flow through the coolant chamber by natural convection alone, i.e. without fans, pumps, etc. In other words, thermal currents in the coolant are such that the coolant moves in a predetermined path around the chamber (anti-clockwise in the figures). To this end, in some embodiments, the light source 20 is disposed at a lower side surface of the chamber 30, e.g. at the 4 to 5 o'clock position shown in the figures. In operation, coolant near the light source 20 absorbs heat from the light source 20, and rises by natural convection in the direction of the arrow 36. Warmed coolant moves generally upwards within the warmed coolant path 36, and once the coolant has been cooled, such as by transferring the absorbed heat to the radiator 40, it moves generally downwards within the cooled coolant path 38.
Because, in some embodiments, the light source 20 is near the bottom and to one side (offset lower side) of the chamber 30, the coolant that is warmed by the light source 20 cannot flow backwards, i.e. in the direction opposite the arrows. For example, if the light source 20 were to be disposed at the exact bottom of the chamber 30, the coolant would be able to flow upwards along both coolant paths 36, 38, and the circular or oval flow path shown by the arrows could not be accomplished by natural convection. In some embodiments, the location of the light source 20 at the offset lower side of the chamber 30, as illustrated, allows natural convection alone to move the coolant in the generally circular or oval paths illustrated.
It should be understood that while the illustrated offset lower side placement of the light source 20 and associated lack of fans or pumps is currently considered advantageous from a cost and simplicity standpoint, the claimed invention is not limited thereto.
As mentioned above, the coolant chamber 30 may be defined by an outer wall 32 and an inner wall 34, 34a. Depending on the particular application of the lighting system 10, the walls 32, 34, 34a may be made of thermally conducting and/or thermally insulating materials.
For example, it will be appreciated that to maintain natural convection, the two coolant paths 36, 38 should advantageously be fluidly and thermally isolated from one another. Depending on size, material, and other constraints, this may, in some embodiments, be accomplished by a hollow inner wall 34, such as that illustrated in
Similarly, the outer wall 32 can be designed to have any appropriate thermal characteristics depending on the application. For example, in some embodiments, the entirety of the outer wall 32 is thermally conductive. In other embodiments, the portion of the outer wall 32 in thermal contact with the light source 20 and/or the radiator 40 is thermally conductive, while at least another portion of the outer wall 32 is thermally insulating. In further embodiments, such as those for use in particularly hot climates, the heated coolant channel 36 has a thermally conducting wall 32 or walls 32, 34, and the cooled coolant channel 38 has an insulating wall 32 or walls 32, 34 except for the portion in contact with the radiator 40. These embodiments may be particularly useful when a radiator 40 is included, as will be described below, and prevent the coolant cooled by the radiator 40 from being heated by the ambient air before returning to the portion of the chamber 30 near the light source 20.
The walls 32, 34, 34a may be made of any material with the appropriate structural and thermal characteristics, depending on the application. Some suitable materials are, without limitation: copper, aluminum, alloys thereof, and stainless steel.
In some embodiments, as mentioned above, a radiator 40 is further provided. In some embodiments, the radiator 40 is thermally coupled to the chamber 30 at an upper and to one side (offset upper side) surface of the chamber 30. In some embodiments, a major portion of the heat dissipation from the system 10 occurs at the radiator 40. Therefore, the coolant near the radiator 40 may experience a rapid temperature drop, causing it to sink by natural convection along path 38. For reasons discussed above regarding the placement of the light source 20, it may therefore be advantageous for the radiator to be disposed at the offset upper side of the coolant chamber 30. In some embodiments, the radiator 40 is disposed opposite the light source 20.
It should be appreciated that the radiator 40 is illustrated schematically for simplicity. The radiator 40 can be any radiator, heat sink, heat spreader, or any other element that dissipates heat from the system 10, and can be designed and implemented by a person of ordinary skill in the art based on the teachings herein.
In operation, in some embodiments, the coolant is heated at the bottom right of the figures, causing it to flow generally upwards along channel 36 as indicated by the arrows. Once the coolant reaches the radiator 40, it begins to cool, and flows generally downwards along channel 38 back toward the light source 20. As mentioned above, the light source 20 can thus be constantly cooled by the natural convection of the coolant and the radiator 40, without the need for fans or pumps.
In some applications, such as, for example, for outdoor lighting, it is advantageous to further provide a sun-shield 50. The sun-shield 50 may be made of insulating or reflective material, and may shield the radiator 40, and/or at least a portion of the chamber 30, from the sun. The sun-shield 50 may be attached to the chamber 30 with mounting brackets 52, which may be made of thermal insulators. Alternatively, the sun-shield 50 may be mounted to any structural element, such as a lamp-post (not shown).
In some embodiments, the portion of the chamber 30 and/or the radiator 40 that is shielded by the sun-shield 50 is in thermal and/or fluid communication with the atmosphere. For example, in the embodiment illustrated in
It should be appreciated that
The coolant disposed in the chamber 30 may be any suitable fluid, such as, without limitation: water, deionized water, ethylene glycol, diethylene glycol, propylene glycol, mineral oil, castor oil, silicone oil, or fluorocarbon oil.
Turning now to
Alternatively, the chamber wall may be made sufficiently strong to withstand any expansion of fluid.
While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
