Patent Grant
7182484
The present invention relates to an light appliance contained within a substantially sealed enclosure and an associated cooling arrangement for removing unwanted heat generated by the light appliance. This increases the operating lifetime of the light appliance.
By sealing a light source within an enclosed environment, the operating temperature of the source is seen to increase dramatically over its designed lifetime for an open-air operating temperature. This has the effect of reducing the lamp life to the point where the lamp is non-viable for consumer use. This is a particular concern for halogen and metal halide lamps, which use molybdenum foils to make electrical connections. These foils are at risk of premature oxidation if operated at high temperatures. The premature oxidation of the molybdenum lamp connections results in early lamp failure.
The rise of a sealed system's source temperature is due in part to the insulating qualities of the stagnant air within the sealed environment. The main cause of the source's temperature rise is the inability to remove heat from the source and from the sealed environment, and then to supply cooler air to the light source. Typically, the heat transfer from the source to an often cooler outer medium is primarily by conduction through essentially stagnant air within the enclosure.
In open-air operation, a cooling fan is often used to control the temperature of a light source. This works because of the large supply of relatively cool air available to draw over the source and ample room to exhaust hot air away from the source.
A second way to lower the temperature of a relatively hot component such as a light source is through the use of a heat sink. The heat sink increases the thermal mass and surface area of the component.
A purpose of the invention is to provide a system for more effectively cooling a light appliance within a substantially sealed environment.
A preferred form of the invention provides a light appliance and a cooling arrangement, comprising a light appliance and a substantially sealed enclosure for the light appliance that gives off unwanted heat into surrounding air within the enclosure during operation. The enclosure has an external wall at least part of which is thermally conductive. A medium, cooler than the external wall of the enclosure, contacts the external wall. An air circulating device is provided for circulating air, heated by the electrical appliance or by the air circulating device itself, to the thermally conductive portion of the external wall for removing heat from the air, by thermally dissipating the heat into the cooler medium through said thermally conductive portion.
The foregoing combination effectively cools a light appliance within a substantially sealed enclosure.
a and 5b show filamented and discharge lamps, respectively, with thermally sensitive molybdenum leads; and
d shows an LED in block form, which exhibits thermal sensitivity.
This description covers the three points of (1) general principles of the invention, (2) alternative cooling mediums that may be used, and (3) specific light appliance thermal issues.
The first part of these General Principles does not refer to the drawings.
Optionally incorporating a heat sink for a light source component increases thermal mass and reduces the overall temperature of the component. By having a larger surface area, it is easier for thermal energy, which is to be dissipated away from the component, to be cooled through conduction with stagnant air, or through convection if used with a fan. To maximize the cooling effect, a heat sink could be used in conjunction with a cooling fan. Occasionally, a high power lamp will have metal connectors on the end(s) of the lamp which can also act as heat sinks.
To effectively use a cooling fan within a sealed environment, some portion or all of the walls of the sealed environment are thermally conductive, and could be formed of any metal or even a plastic that transfers heat well. A fan or other air circulating device is placed within the sealed environment to create what may be called a convection cell by blowing air over the hot source and/or heat sink. Air blowing over the source is heated by the source and carries thermal energy away from the source. The heated air comes in contact with the thermally conductive wall(s) and heats the relatively cool wall(s). The walls are kept relatively cool due to contact with the lower temperature immersion medium. When thermal energy leaves the air and enters the wall, the air temperature is lowered. This cooler air circulates and becomes the cooler input air to the fan, which completes the convection cell.
Of course, the fan does not bring in cool ambient air and exhaust heated air, as in a normal open-air system. Instead it only circulates the air sealed within the sealed environment, which works due to the conductive nature of the sealed environment's walls which are in contact with a medium that is much cooler than the light source and/or heat sink which is to be cooled.
This sealed environment is currently used in submerged-in-water applications where the water cools the walls of the sealed environment very well and has a very good ability to remove heat from the system. However, this cooling system is not limited to an underwater environment. If the air temperature outside the sealed environment is substantially lower than the source temperature, and the containing walls are made of material with sufficient thermal conducting qualities, a convection cell can be made using a fan within the sealed environment that would increase the operating lifetime of the source by reducing its temperature. The sealed environment could even be placed within a solid medium, such as a concrete wall, and as long as the walls of the environment are sufficiently cool to allow an efficient convection cell to be made within the sealed environment. Cooling mechanisms for use within a solid may include, but are not limited to, thermoelectric cells, water cooled pipes wrapped around the conductive walls, or even an exterior fan cooling off the sealed environment itself.
Now, referring to the drawings,
Light appliance 10 may include, as shown, a light source 26, which may be supplied with an electrical driver 28 (shown in block). Driver 28 may comprise, for instance, an electrical or electromagnetic device for converting voltage and/or limiting current to light appliance 10. Light source 26 gives off unwanted heat during operation, and so may be supplied with a heat sink 30 for removing heat from the light source. Light source 26 may comprise, by way of example, a high pressure sodium lamp, a high pressure mercury vapor lamp, a halogen lamp, an incandescent lamp or an ultrahigh pressure mercury lamp.
To allow light to exit enclosure 16, the enclosure may includes optical material 32, typically comprising glass. The other wall material 14 of the enclosure may comprise stainless steel, thermally conductive plastic, or other material that is sufficiently thermally conductive to attain the cooling purpose set forth herein.
To prevent the ambient temperature in enclosure 16 from rising so high as to undesirably reduce the lifetime of light appliance 10, a cooling arrangement includes, as mentioned above, air circulating device 12, thermally conductive wall portion 14 of enclosure 16, and surrounding medium 20 that draws heat away from the enclosure as shown by arrows 24. Air circulating device 12 receives air 40 from the environment which has been cooled by contact with enclosure 16, and directs cooled air 42 onto appliance 10 for cooling the appliance.
By using the thermally conductive property of thermally conductive wall portion 14, heat from heated air 41 is drawn away—as indicated by arrows 24—into medium 20, which is substantially cooler than wall portion 14. When thermal energy is extracted from heated air 41, the resulting, cooled air is shown as 40 and 42. In this way, the ambient temperature within enclosure 16 can be kept below a destructive level that would undesirably shorten the lifetime of light appliance 10.
Air circulating device 12 may comprise an electrical fan, a heat pump or air pump, or other device for moving air, for instance.
Various mediums that are cooler than a thermally conducive wall of an enclosure are shown in
As with
As described in the Background of the Invention above, electrical leads made of molybdenum for lamps such as halogen lamps or metal halide lamps face premature oxidation if subjected to high temperatures.
Additionally, a light source comprising a light-emitting diode (LED) 96 such as shown in
The biggest thermal concern with LEDs is the effect of high temperature on device life. With repeated thermal cycling to high temperatures, the thermal expansion mismatches between different layers of the device will cause cracking and early failure of the device. This is a major problem for other solid state devices, such as the central processing chips in personal computers that are not related to the invention. In those cases a fan is used to force air from outside the enclosure over the device to keep it cool and prolong life of the device.
Finally, regarding LEDs, device efficiency changes with temperature. Modest increases in temperature of only 10–20 degrees C. have a small effect on device efficiency, i.e., with a drop of only 2–10%. But, if there is no limit to operating temperature, so-called runaway situations can result and temperatures in the device can rise upwards to 100 degrees C. This can cause a drop in efficiency of up to 50%, so an LED's output will drop by half as it warms up.
So, LEDs also greatly benefit from the cooling arrangement of the present invention.
While the invention has been described with respect to specific embodiments by way of illustration, many modifications and changes will occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true scope and spirit of the invention.
This application claims priority from U.S. Provisional Application No. 60/452,729 filed Mar. 7, 2003.
| Number | Name | Date | Kind |
|---|---|---|---|
| 3949213 | Paitchell | Apr 1976 | A |
| 4419716 | Koo | Dec 1983 | A |
| 4887189 | Garrett | Dec 1989 | A |
| 5432688 | Tobias et al. | Jul 1995 | A |
| 5556188 | Poppenheimer | Sep 1996 | A |
| 5727873 | Tyson | Mar 1998 | A |
| 5857768 | Ziegler et al. | Jan 1999 | A |
| 6241361 | Thrasher et al. | Jun 2001 | B1 |
| 6774571 | Choi et al. | Aug 2004 | B2 |
| 20040032740 | Kurashima et al. | Feb 2004 | A1 |
| 20040156191 | Biasoli et al. | Aug 2004 | A1 |
| Number | Date | Country | |
|---|---|---|---|
| 20040184284 A1 | Sep 2004 | US |
| Number | Date | Country | |
|---|---|---|---|
| 60452729 | Mar 2003 | US |
