Liquid-cooled LED lighting device

A liquid-cooled LED lighting device can be provided in which a temporal increase in the temperature of the tubing and the circulation pump when the LED light sources are turned off is prevented to ensure high reliability. The liquid-cooled LED lighting device can include an LED light source, a liquid cooling system including a heat receiving jacket and a radiator, an LED light source-driving power supply for supplying power to the LED light source, and a liquid cooling system-driving power supply for supplying power to the liquid cooling system. The LED lighting device can include a control unit, such as a timer circuit. The control unit can maintain supply of the power to the liquid cooling system for a predetermined period of time after supply of the power to the LED light source is stopped.

This application claims the priority benefit under 35 U.S.C. §119 of Japanese Patent Applications No. 2008-299042 filed on Nov. 25, 2008, No. 2009-124948 filed on May 25, 2009, and No. 2009-125409 filed on May 25, 2009, which are hereby incorporated in their entirety by reference.

TECHNICAL FIELD

The presently disclosed subject matter relates to an LED lighting device. In particular, the presently disclosed subject matter relates to a liquid-cooled LED lighting device that employs a liquid-cooling system for cooling LED light sources.

BACKGROUND ART

In recent years, high intensity lamps, such as xenon lamps and sodium lamps, used as the light sources of lighting devices such as vehicle headlamps and exterior lighting devices are being replaced with semiconductor light emitting apparatuses (for example, such as LEDs) that have long life and low power consumption. Therefore, there is a demand for higher power LED lighting devices including LEDs as light sources.

Most xenon lamps currently in widespread use have an output power of about 200 W to about 2000 W. Therefore, the power inputted to LED lighting devices that are replacing the xenon lamps is also increasing. Recent development shows that the power inputted to one LED lighting device can be greater than 200 W.

As the power of LED lighting devices increases, the amount of heat generated from the LED light sources increases. Since the light conversion efficiency of the LED light sources is lowered and life thereof is shortened with temperature increases, an important task is to develop a cooling structure for reducing the temperature of the LED light sources to drive them stably. For example, in a cooling structure proposed in Japanese Patent Application Laid-Open No. 2002-299700, an LED-mounted substrate is pressed against and secured to a metal heat dissipating-securing plate by a metal heat dissipating cover, and the heat dissipating-securing plate, which has the LED-mounted substrate secured thereto, is disposed in a sealed space formed by a light-transmitting cover and a resin case. A plurality of heat dissipating fins are formed on the heat dissipating-securing plate. In this structure, the heat generated from the LED light sources is transferred to the heat dissipating-securing plate through the LED-mounted substrate and through the heat dissipating cover. The heat transferred to the heat dissipating-securing plate is dissipated into the atmosphere through the heat dissipating fins and the resin case, and the LED light sources are thereby cooled.

However, with the above natural cooling-heat dissipating structure, a high cooling effect is not expected, and, thus, there is a limit to the increase in the output power.

In view of the above, a liquid cooling system that cools LED light sources by circulating cooling liquid through a closed circulation path is proposed (for example, see Japanese Patent Application Laid-Open No. 2006-047914). This liquid cooling system includes a heat receiving jacket, a radiator, a circulation pump, a reserve tank, and a fan. The cooling liquid is circulated through the circulation path by the circulation pump and receives the heat generated from the LED light sources when passing through the heat receiving jacket. The cooling liquid, increased in temperature due to reception of heat generated from the LED light sources, is then cooled in the radiator by heat exchange with outside air. In this system, the above cycle is repeated to liquid-cool the LED light sources.

Referring toFIGS. 1 to 3, a description will be given of the basic configuration of a liquid-cooled LED lighting device having the above liquid cooling system and its control flow when the device is turned on and off.

FIG. 1is a block diagram illustrating the basic configuration of the power supply system of the conventional liquid-cooled LED lighting device. An LED on-off switch127is connected to a power supply (main power supply)126such as a commercial power supply. An LED light source-driving power supply128for supplying power to LED light sources110and a liquid cooling system-driving power supply130for supplying power to a fan and a circulation pump103of the cooling system are connected in parallel to the LED on-off switch127.

FIG. 2is a flowchart showing the control flow when the liquid-cooled LED lighting device is turned on. As shown inFIG. 2, the main power supply126is turned on (step S41) and the LED on-off switch127is switched on (step S42). Thereby, the LED light source-driving power supply128and the liquid cooling system-driving power supply130are simultaneously turned on (steps S43and S44). Therefore, the LED light sources110are turned on (step S45), and the liquid cooling system103(including a fan, a pump, and the like) is actuated to cool the LED light sources110.

FIG. 3is a flowchart showing the control flow when the liquid-cooled LED lighting device is turned off. As shown inFIG. 3, when the LED on-off switch127is switched off (step S51), the LED light source-driving power supply128is turned off, and the LED light sources are turned off (step S52). At the same time, the liquid cooling system-driving power supply130is turned off, and the fan and the circulation pump of the liquid cooling system103are stopped (step S53). Then the entire operation of the liquid cooling LED lighting system is stopped (step S54).

In the conventional liquid-cooled LED lighting device, at the same time as the LED on-off switch127is switched off, the liquid cooling system-driving power supply130is turned off, and the fan and the circulation pump of the liquid cooling system103are stopped, as shown in the flowchart inFIG. 3. Therefore, the efficiency of dissipation of the heat received by the cooling liquid to the outside air is significantly reduced. In addition, since the circulation of the cooling liquid is stopped, the flow of heat to the components connected to the heat receiving jacket and those in the downstream side are interrupted, and this results in thermal insulation.

A general liquid-cooled LED lighting device is required to have heat dissipation performance that ensures that the temperature of the LED light sources is maintained at 150° C. or less. Under normal operation, the temperatures of the heat receiving jacket and the cooling liquid contained therein are midway between the temperature of the LED light sources and the temperature of ambient air. Therefore, assuming that the temperature of outside air is about 20° C., the temperature of the liquid cooling system is about 85° C. at maximum.

Therefore, when, as described above, the heat receiving jacket is thermally insulated because the liquid cooling system is stopped at the same time as the LED light sources are turned off, the heat accumulated in the LED light sources and the heat receiving jacket is not dissipated from the radiator. Although the temperature of the LED light sources does not increase, the temperature of the heat receiving jacket and the cooling liquid therein temporarily increases. This heat is transferred through the liquid in tubing, resulting in an increase in the temperature of other components such as the circulation pump and rubber hoses.

Table 1 shows the results of the measurement of the temperatures of the components (LED light sources, heat receiving jacket, circulation pump, and radiator) of the conventional liquid-cooled LED lighting device when the device is ON and just after the device is turned off (outside air temperature: 25° C.).

For example, the temperature of the rubber hoses temporarily increases to about 110° C., which is higher than their heat resistant temperature. This causes a reduction in the reliability of the device. As the temperature of the cooling liquid increases, its volume increases. Therefore, the volume of the cooling liquid passing through the rubber hoses increases. This causes a problem in that the size of the reserve tank should be increased.

The life of the circulation pump is known to be largely affected by temperature. As described above, when the LED light sources are turned off and at the same time the liquid cooling system is stopped, the temperature of the circulation pump temporarily increases to about 100° C. This also causes a reduction in the reliability of the device.

Furthermore, in the LED lighting device with the above configuration, the temperature of the cooling liquid depends on the temperature of ambient air, assuming that the heat dissipation performance of the lighting device is not varied. In this case, as the temperature of the ambient air increases, the temperature of the cooling liquid is also increased, resulting in the increase of the LED temperature when the LEDs are turned on. As a result, the light conversion efficiency may deteriorate, and accordingly, the illumination intensity may also deteriorate. At the same time, the life of the LED device is also shortened.

In addition to the temperature change of ambient air, several causes that can lower the heat dissipation performance over time may be involved. Examples of the causes include variations in the flow rate of the pump, the rate at which the fans blows air, and the LLC concentration of the cooling liquid, etc. Accordingly, the liquid-cooling system is likely to be affected by temperature changes during operation of the LED as compared with heat dissipation caused by a heat dissipation structure utilizing an air cooling mechanism (such as a heat sink) with natural heat dissipation. This system poses a problem in that a stable illumination intensity and life cannot be ensured.

Furthermore, if the circular pump and/or the fan do not properly operate due to unexpected external causes, breaking of the power supplying wire, and/or the expiration of its useful life, heat generated by the LEDs cannot be transferred from the heat receiving jacket to the downstream components. This means that the entire temperature of the components of the heat dissipation structure, including LEDs increases. In some worst cases, the temperature of cooling liquid may exceed its boiling point, which may cause the tubing to be broken, leading to liquid leakage.

Lighting devices for use in dangerous areas such as chemical plants, mine cavities, areas where dangerous objects should be handled, gas stations, oil storages, manholes, tunnels, factories for fireworks production, ammunition dumps, and the like generally use, as their light source, metal halide lamps, high-pressure mercury lamps, halogen lamps, and other discharge type light source lamps. Such lighting devices have been provided with various countermeasures for preventing surrounding flammable gases from catching fire. For example, in Japanese Patent Publication No. 4099603 (B), an explosion protection lighting device has been proposed, in which socket holders are disposed at respective ends of a main body, and a straight-tube lamp is disposed between the socket holders while the lamp is enclosed within a lamp protection cylinder.

However, it is difficult for a conventional lighting device that utilizes a discharge type light source lamp to completely prevent the occurrence of explosions caused by a lamp burst. Accordingly, in order to lower the risk of explosion as much as possible, several explosion-protection structures have been developed, but these have not provided sufficient protection.

Furthermore, such a structure may require a thick glass member that has an increased strength for the discharge type light source lamp, and may employ complex connecting structures for components to enhance the hermeticity. These structures may have a disadvantageously increased weight or volume caused by the used lamp.

Furthermore, since the discharge type light source lamp should be periodically replaced with a new one, there is a problem because maintenance, such as replacement of the lamp, may take a large amount of time and labor due to the complex structures, as described above.

The presently disclosed subject matter was devised in view of these and other problems and in association with the conventional art. According to an aspect of the presently disclosed subject matter, a liquid-cooled LED lighting device can be provided in which a temporal increase in the temperature of the tubing and the circulation pump when the LED light sources are turned off is prevented to ensure high reliability.

According to another aspect of the presently disclosed subject matter, the liquid-cooled LED lighting device can suppress excess temperature increases when the LED light sources are turned off to maintain a stable state, thereby achieving stable output illumination intensity and life. Furthermore, the liquid-cooled LED lighting device can ensure the safety of the device, including the LED light sources by interrupting the drive current if the temperature of the cooling liquid abnormally increases.

According to still another aspect of the presently disclosed subject matter, the liquid-cooled LED lighting device can be used in a dangerous area while the device can prevent possible explosion risks and also facilitate the maintenance thereof.

According to still another aspect of the presently disclosed subject matter, a liquid-cooled LED lighting device can include: an LED light source, a liquid cooling system including a heat receiving jacket and a radiator, an LED light source-driving power supply configured to supply power to the LED light source, a liquid cooling system-driving power supply configured to supply power to the liquid cooling system, and a control unit configured to control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply.

In the liquid-cooled LED lighting device as configured above, the control unit can control and maintain the supply of power from the liquid cooling system-driving power supply to the liquid cooling system for a predetermined period of time after supply of the power from the LED light source-driving power supply to the LED light source is stopped.

The liquid-cooled LED lighting device as configured above can further include an LED on-off switch configured to transmit an ON signal and an OFF signal to the control unit, and the control unit can include a timer circuit configured to be activated in response to the OFF signal transmitted from the LED on-off switch. In this configuration, the control unit can maintain the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system for the predetermined time in response to an output signal from the timer circuit.

In the liquid-cooled LED lighting device as configured above, the control unit can include a temperature control circuit including a temperature detection element that is secured to one of the LED light source, the heat receiving jacket, and a metal base in contact with the heat receiving jacket. In this configuration, the control unit can maintain the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system for a period of time in response to an output signal from the temperature control circuit.

In the liquid-cooled LED lighting device as configured above, when a temperature detected by the temperature detection element after the supply of the power from the LED light source-driving power supply to the LED light source is stopped is higher than a first predetermined threshold value, the control unit can maintain the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system until the temperature detected by the temperature detection element is equal to or lower than the first predetermined threshold value.

In the liquid-cooled LED lighting device as configured above, if a temperature detected by the temperature detection element at a time when the supply of the power from the LED light source-driving power supply to the LED light source is started is lower than a second predetermined threshold value, the control unit can prevent the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system until the temperature detected by the temperature detection element is equal to or higher than the second predetermined threshold value.

Alternatively, in the liquid-cooled LED lighting device configured to include the basic components as above, the control unit can include a temperature control circuit including a temperature detection element that is secured to one of the LED light source, the heat receiving jacket, and a metal base in contact with the heat receiving jacket. In this configuration, the control unit can control a drive current for the LED light source based on a temperature detected by the temperature detection element. Furthermore, the control unit can control the drive current for the LED light source to be within a range of from zero (0) to a normal LED drive current.

Still alternatively, the liquid-cooled LED lighting device configured to include the basic components as above can be used to illuminate an area where a flammable gas having a flash point is present. In this liquid-cooled LED lighting device, the temperature detection element can be secured to the LED light source to detect a temperature of the LED light source, and the control unit can control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply to maintain the temperature of the LED light source to be lower than the flash point of the flammable gas. In this case, the control unit can control the temperature of the LED light source so that the highest temperature of the LED light source at its emission portion is equal to or lower than 95° C.

In the liquid-cooled LED lighting device as configured above, the temperature detection element can be any of a thermistor and a temperature detection IC.

The liquid-cooled LED lighting device as configured above can further include a pilot lamp configured to be turned on when the liquid cooling system is stopped by interruption of the supply of the power from liquid cooling system-driving power supply to the liquid cooling system.

The liquid-cooled LED lighting device as configured above can further include an air cooling heat dissipation system. In this case, the heat receiving jacket can be disposed between the LED light source and the air cooling heat dissipation system.

The liquid-cooled LED lighting device as configured above can further include a metal circuit casing configured to cover the control unit for controlling the drive of the LED light source, the LED light source-driving power supply, and the like. In this case, the circuit casing can include an atmospheric heat dissipation portion. Furthermore, the circuit casing can be disposed so as to be in close contact with the heat receiving jacket. Then, the atmospheric heat dissipation portion formed in the circuit casing can serve as the air cooling heat dissipation system.

Alternatively, the heat receiving jacket can be provided with an atmospheric heat dissipation portion. In this case, the atmospheric heat dissipation portion formed in the heat receiving jacket can serve as the air cooling heat dissipation system.

In the liquid-cooled LED lighting device as configured above, the atmospheric heat dissipation portion can be composed of a heat dissipation pin and/or a heat dissipation fin.

In the liquid-cooled LED lighting device including the air cooling heat dissipation system as configured above, if the liquid cooling system does not work properly, the control unit can control the LED light source-driving power supply so that the detected temperature of the LED light source can be maintained lower than the flash point of the flammable gas through only the air cooling heat dissipation system. In this case, the control unit can control the current to be supplied to the LED light source to a value such that heat generated by the LED can be absorbed by the air cooling heat dissipation system.

Furthermore, in the liquid-cooled LED lighting device as configured above, the liquid cooling system can further include a circulation pump, a reserve tank, and a fan.

According to one aspect of the presently disclosed subject matter, the liquid-cooled LED lighting device as configured above can include a control unit configured to control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply. This configuration can provide an appropriate cooling effect by controlling the system in various ways. For example, even after the supply of the power from the LED light source-driving power supply to the LED light source is stopped and the LED light source is turned off, the supply of the power from the liquid cooling system-driving power supply to the liquid cooling system is controlled to be maintained for a predetermined period of time so that the fan and the circulation pump can remain energized. Therefore, a temporal increase in the temperature of the tubing such as rubber hoses and the circulation pump can be prevented, and the reliability of the liquid-cooled LED lighting device can be improved.

Furthermore, in the liquid-cooled LED lighting device as configured above, even after the LED light source is turned off, the fan and the circulation pump of the liquid cooling system can remain activated for a period of time set by the timer circuit. Therefore, a temporal increase in the temperature of the tubing such as the rubber hoses and the circulation pump is prevented, and this ensures high reliability of the liquid-cooled LED lighting device.

In the liquid-cooled LED lighting device as configured above, when the temperature detected by the temperature detection element after the LED light source is turned off is or higher than a predetermined threshold value, the supply of the power to the liquid cooling system is maintained until the temperature detected by the temperature detection element is equal to or lower than the predetermined threshold value. Since the fan and the circulation pump remain energized during this period, the tubing such as the rubber hoses and the circulation pump can be cooled to a preset temperature in a reliable manner.

In the liquid-cooled LED lighting device as configured above, under cool conditions in which the temperature detected by the temperature detection element when the LED light source is turned on is lower than a predetermined threshold value, the power is not supplied to the liquid cooling system until the temperature detected by the temperature detection element is equal to or higher than the predetermined threshold value. Since cooling is not effected during this period, the entire liquid-cooled LED lighting device can be rapidly warmed to the required operating temperature.

In the liquid-cooled LED lighting device as configured above, the control unit can be provided with a temperature detection element, and can control the drive current for the LED light source based on a temperature detected by the temperature detection element. In this case, the LED drive current can be controlled within a range of from zero to a normal LED drive current. This control can suppress the excessive temperature increase when the LED light source is driven. As a result, the lighting device can utilize a higher power LED light source and ensure the stable illumination intensity and life as well as the high reliability of the device.

When the liquid-cooled LED lighting device is used in the area where a flammable gas with a certain flash point is present, the liquid-cooled LED lighting device can have a liquid cooling system disposed adjacent to the light source portion, including LEDs, and can control at least one of the LED light source-driving power supply and the liquid cooling system-driving power supply to maintain the temperature of the LED light source (the highest temperature of the LED light source at its emission portion) to be lower than the flash point of the flammable gas (for example, equal to or lower than 95° C.). Accordingly, even when the liquid-cooled LED lighting device of the presently disclosed subject matter is used in a dangerous area, it is possible to prevent possible explosion risks due to catching fire of the surrounding flammable gas.

The liquid-cooled LED lighting device of the presently disclosed subject matter utilizes as its light source an LED(s) that is substantially maintenance free. Accordingly, the replacement of light sources can be eliminated, thereby facilitating the maintenance thereof.

In the liquid-cooled LED lighting device as configured above, the temperature of any of the LED light source, the heat receiving jacket, and the metal base in contact with the heat receiving jacket is correctly detected by the thermistor or the temperature detection IC, and the liquid cooling system can thereby be appropriately controlled.

In the liquid-cooled LED lighting device as configured above, the liquid cooling system can remain energized for a predetermined time after the LED light source is turned off. Subsequently, when the supply of the power to the liquid cooling system is stopped and the liquid cooling system is stopped, the pilot lamp is turned on to indicate this condition. Therefore, a main power source switch can be switched off after the state of the pilot lamp is checked.

In the liquid-cooled LED lighting device as configured above, when the liquid cooling system, having operating portions such as a circulation pump and a fan, cannot work properly due to some accidents (namely, the cooling function is damaged), the control unit can control the current to be supplied to the LED light source to a value such that heat generated by the LED can be absorbed by the air cooling heat dissipation system. Accordingly, overheating of the LED can be prevented. In this case, although the illumination intensity may be lowered due to the suppressed current, the maximum temperature of the light source can be controlled to be lower than the flash point of the surrounding flammable gas. Thus, even when the liquid-cooled LED lighting device of the presently disclosed subject matter is used in a dangerous area, it is possible to prevent possible explosion risks.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

A description will now be made below to liquid-cooled LED lighting devices according to the presently disclosed subject matter with reference to the accompanying drawings in accordance with exemplary embodiments. In the description of the subject application with reference toFIGS. 4 to 22, irrespective of the posture of the illustrated lighting device, the light emission direction may be referred to as “front (front surface side),” and the opposite direction may be referred to as “rear (rear surface side).”

First, the basic configuration of a liquid-cooled LED lighting device made in accordance with principles of the presently disclosed subject matter will be described with reference toFIGS. 4 to 7.

FIG. 4is a perspective view illustrating the internal structure of the liquid-cooled LED lighting device according to the presently disclosed subject matter.FIG. 5is an exploded perspective view of a device body of the liquid-cooled LED lighting device.FIG. 6is a cross-sectional view of the device body.FIG. 7is a diagram illustrating the basic configuration of a liquid cooling system of the liquid-cooled LED lighting device.

As shown inFIG. 4, the liquid-cooled LED lighting device1of the presently disclosed subject matter can include a liquid cooling system3installed in a device body2, and all the components can be covered with a resin cover (not shown).

A description of the configuration of the device body2will be given with reference toFIGS. 5 and 6. The device body2can include a cover lens4, LED light source modules5, a metal base6, a heat receiving jacket7, a driving circuit box8, and a housing9, and these components may be disposed in that order in a direction (the upward direction in the figures) opposite to the direction of light emission. A space can be defined by the cover lens4and the housing9. The LED light source modules5, the metal base6, the heat receiving jacket7, and the driving circuit box8can be contained in this space.

The number of the LED light source modules5is, for example, nine (9) in this exemplary embodiment. In each LED light source module5, an LED light source10and a connector11can be mounted on a substrate12. As shown inFIG. 6, each LED light source module5can be attached to the metal base6formed of a high-thermal conductivity metal such as copper or aluminum through an insulating heat conduction sheet13.

The LED light source may be a white LED that is fabricated by mounting an LED chip on a substrate made of ceramic or copper that has a high heat conductivity and resin-sealing the chip and the like with a sealing resin containing a phosphor material. This configuration can lower the heat resistance. Appropriate combinations of the wavelength of light emitted from the LED chip and the type of the phosphor material can generate various colors of light other than white light.

The substrate on which the LED light sources are mounted can be formed of a rigid substrate or a flexible substrate. Examples of rigid substrate material include materials having a favorable heat conductivity such as metal materials, including copper, aluminum, and the like and ceramic materials. Examples of flexible substrates include polyimides and the like.

As shown inFIG. 5, the nine LED light source modules5can be arranged in a 3×3 matrix form. The cover lens4can have lens-cut portions4aformed at positions corresponding to the positions of the LED light source modules5, respectively.

The heat receiving jacket7can be attached to the metal base6on the rear surface (the side opposite to the surface on which the LED light source modules5are mounted). Here, the metal base6and the heat receiving jacket7can be in surface contact with each other. The heat receiving jacket7can be formed to have a hollow rectangular plate shape. As shown in the cross sectional view ofFIG. 6, a hollow portion S serving as a passage for a cooling liquid (non-freezing fluid) can be formed inside the heat receiving jacket7. The heat receiving jacket7can also include an inlet port7athrough which the cooling liquid cooled by heat exchange with outside air flows, and a discharge port7bfrom which the cooling liquid that has received heat from the heat receiving jacket7is discharged (seeFIG. 5). It should be noted that the cooling liquid (cooling medium) may be a mixture of LLC and water in a predetermined ratio.

The driving circuit box8can be attached to the heat receiving jacket7on the rear surface (on the side opposite to the surface to which the metal base plate6is attached). Although not shown in the drawings, the driving circuit box8can contain therein electronic and circuit components including a constant current power supply circuit for driving the LED light sources10.

As shown inFIG. 5, tube connection joints14and15are attached to the housing9. A tube (rubber hose)16connected to the inlet port7aof the heat receiving jacket7is connected to the joint14, and another tube (rubber hose)17connected to the discharge port7bof the heat receiving jacket7is connected to the joint15.

Next, a description will be given of the configuration of the liquid cooling system3with reference toFIGS. 4 and 7.

The liquid cooling system3can include the heat receiving jacket7serving as a heat exchanger, a radiator18in which the cooling liquid that increased in temperature due to reception of heat from the heat receiving jacket7is cooled by heat exchange with outside air, a fan19that supplies cooling wind to the radiator18, a circulation pump20that circulates the cooling liquid through a closed loop, and a reserve tank21that stores the cooling liquid. The fan19can be disposed so as to face the radiator18.

As shown inFIG. 5, a tube (rubber hose)22extending from the joint15connected to the discharge port7bof the heat receiving jacket7through the tube17can be connected to an inlet port18aof the radiator18. A tube (rubber hose)23extending from a discharge port18bof the radiator18can be connected to an inlet port21aof the reserve tank21. A tube (rubber hose)24extending from a discharge port21bof the reserve tank21can be connected to an inlet port20aof the circulation pump20. A tube (rubber hose)25extending from a discharge port20bof the circulation pump20can be connected to the joint14that is connected to the inlet port7aof the heat receiving jacket7through the tube16. As described above, the heat receiving jacket7, the radiator18, the reserve tank21, and the circulation pump20can be connected through the tubes22to25(16and17), so that a closed circulation path is formed. The required cooling effect can be achieved by circulation of the cooling liquid through the circulation path.

With reference toFIG. 7again, the cooling liquid circulating through the circulation path by means of the circulation pump20can receive the heat generated by the LED light sources10when passing through the heat receiving jacket7, and the LED light sources10are thereby cooled. The cooling liquid, increased in temperature due to reception of the heat, can be introduced into the radiator18through the tube22. In the radiator18, the heat of the cooling liquid can be dissipated to the outside through the cooling wind supplied from the fan19, and the cooling liquid can be thereby cooled. The cooling liquid, now decreased in temperature, can be stored in the reserve tank21through the tube23and can be then sent from the reserve tank21to the circulation pump20through the tube24. The cooling liquid can be pressurized in the circulation pump20and then introduced into the heat receiving jacket7through the tube25to cool the LED light sources10. The above action (cooling cycle) can be continuously repeated to cool the LED light sources10, so that their temperature rise is suppressed.

FIG. 8is a block diagram illustrating the basic configuration of a power supply system of a liquid-cooled LED lighting device according to one exemplary embodiment of the presently disclosed subject matter. As shown inFIG. 8, an LED on-off switch27can be connected to a power supply (main power supply)26such as a commercial power supply. An LED light source-driving power supply28for supplying power to the LED light sources10and a timer circuit29that can be activated in response to a signal from the LED on-off switch27can be connected to the LED on-off switch27.

A liquid cooling system-driving power supply30for supplying power to the fan19and the circulation pump20of the cooling system3can be also connected to the power supply (main power supply)26. The timer circuit29can be connected to the liquid cooling system-driving power supply30. As shown by broken lines inFIG. 8, a liquid cooling system switch31may be provided between the power supply26and the liquid cooling system-driving power supply30, and the timer circuit29may be connected to the liquid cooling system switch31. In the configuration shown inFIG. 8, a main power supply switch32may be additionally provided after the power supply26, as shown inFIG. 9. Moreover, the LED on-off switch27may be provided separately as shown inFIG. 10, and the timer circuit29may be activated in response to an OFF signal from the LED on-off switch27.

The present exemplary embodiment can be configured as follows. After the LED on-off switch27is switched off to stop the supply of power from the LED light source-driving power supply28to the LED light sources10so that the LED light sources10are turned off, the timer circuit29can be activated in response to the OFF signal from the LED on-off switch27. The supply of power from the liquid cooling system-driving power supply30to the liquid cooling system3can be maintained for a preset time so that the fan19and the circulation pump20can remain energized.

First, the exemplary control flow when the device is turned on will be described using a flowchart shown inFIG. 11.

When the main power supply26is turned on (step S1), the liquid cooling system-driving power supply30is turned on so that the fan19and the circulation pump20are actuated (step S2). Thereby the cooling liquid is circulated through the circulation path shown inFIG. 7to cool the LED light sources10, as described above. Subsequently, when the LED on-off switch27is switched on (step S3), the LED light source-driving power supply28is turned on. The power is thereby supplied to the LED light sources10(step S4), and the LED light sources10are turned on (step S5).

Next, the control flow when the device is turned off will be described using a flowchart shown inFIG. 12. When the LED on-off switch27is switched off (step S11), the LED light source-driving power supply28is turned off (step S12). The supply of power to the LED light sources10is thereby stopped, and the LED light sources10are turned off. Then the OFF signal from the LED on-off switch27is sent to the timer circuit29, and the timer circuit29is thereby activated to determine whether or not the predetermined preset time has elapsed after the LED on-off switch27is switched off (step S13).

The supply of power from the liquid cooling system-driving power supply30to the liquid cooling system3is maintained until the predetermined preset time has elapsed after the LED on-off switch27is switched off (if the determination result in step13is NO). Since the liquid cooling system3remains energized, the LED light sources10are still cooled. After the predetermined preset time elapses after the LED on-off switch27is switched off (if the determination result in step13is YES), the liquid cooling system-driving power supply30is turned off. The operations of the fan19and the circulation pump20are thereby stopped (step S14), and the circulation of the cooling liquid in the liquid cooling system3is stopped. In this case, a separate pilot lamp may be provided. Then, the pilot lamp is turned on (step S15). Since the pilot lamp in the ON state indicates that the liquid cooling system3has been stopped, the entire operation of the liquid-cooled LED lighting device1can be stopped by, for example, switching off the main power supply switch32after the state of the pilot lamp is checked (step S16). Alternatively, a separate detection circuit may be provided to the control circuit to output a control signal. Then, the control signal can turn the main power supply switch32off to completely stop the entire operation of the liquid-cooled LED lighting device1(step S16).

As described above, in the present exemplary embodiment, even after the supply of power from the LED light source-driving power supply28to the LED light sources10is stopped to turn the LED light sources10off, the timer circuit29can maintain the supply of power from the liquid cooling system-driving power supply30to the liquid cooling system3for a preset time, so that the fan19and the circulation pump20can remain energized. Therefore, a temporal increase in the temperature of the tubes (being rubber hoses)16,17, and22to25and the circulation pump20can be prevented, and the reliability of the liquid-cooled LED lighting device1can be thereby improved.

Table 2 shows the results of the measurement of the temperatures of the components (the LED light sources10, heat receiving jacket7, circulation pump20, and radiator18) of the liquid-cooled LED lighting device1of the present exemplary embodiment when the device is turned on and just after the device is turned off (at the outside air temperature of 25° C.). In addition, the previous table 1 is shown again for comparison.

As is clear by comparing the results shown in Table 2 with the temperature measurement results for the conventional case shown in Table 1, the increase in the temperatures of the components just after the device is turned off can be suppressed in the liquid-cooled LED lighting device1of the present exemplary embodiment.

Next, a description will be given of another exemplary embodiments of the present invention.

FIGS. 13 to 15are block diagrams illustrating the basic configurations of the power supply systems for a liquid-cooled LED lighting device according to other exemplary embodiments of the presently disclosed subject matter. In the power supply systems shown in these drawings, the timer circuit29shown inFIGS. 8 to 11is replaced with a temperature control circuit33.

The temperature control circuit33can include a temperature sensor34secured to any of the LED light sources10, the heat receiving jacket7, and the metal plate6in contact with the heat receiving jacket7. The temperature control circuit33can control to maintain the supply of power to the liquid cooling system3for a period of time in response to a detection signal from the temperature sensor34. A thermistor or a temperature detection IC can be used as the temperature sensor34.

The exemplary control flow of the liquid-cooled LED lighting device1in the present exemplary embodiment, when the device is turned on under normal conditions, is the same as that in the previous exemplary embodiment (seeFIG. 11), and the description thereof is omitted. Hereinafter, a description will be given of other exemplary control flows of the liquid-cooled LED lighting device1when the device is turned off and when it is turned on under the cool conditions based onFIGS. 16 and 17, respectively.

As shown inFIG. 16, in the present exemplary control flow when the device is turned off, if the LED on-off switch27is switched off (step S21), the LED light source-driving power supply28is turned off (step S22). The supply of power to the LED light sources10is thereby stopped, and the LED light sources10are turned off. At the same time, the OFF signal from the LED on-off switch27is sent to the temperature control circuit33. The temperature control circuit33is thereby activated to determine whether or not the temperature detected by the temperature detection element is equal to or lower than a predetermined threshold value (step S23).

The supply of power from the liquid cooling system-driving power supply30to the liquid cooling system3is maintained if the temperature detected by the temperature detection element is higher than the threshold value (if the determination result in step S23is NO). Since the liquid cooling system3remains energized, the LED light sources10are still cooled. When the temperature detected by the temperature detection element is equal to or lower than the threshold value (if the determination result in step S23is YES), the liquid cooling system-driving power supply30is turned off. The operations of the fan19and the circulation pump20are thereby stopped (step S24), and the circulation of the cooling liquid in the liquid cooling system3is stopped. Then a pilot lamp (not shown) is turned on (step S25), and the entire operation of the liquid-cooled LED lighting device1can be stopped by, for example, switching off the main power supply switch32(step S26).

As described above, in the present exemplary embodiment, even after the supply of power from the LED light source-driving power supply28to the LED light sources10is stopped to turn the LED light sources10off, the supply of power from the liquid cooling system-driving power supply30to the liquid cooling system3can be maintained until the temperature detected by the temperature detection element is decreased to the threshold value or lower, so that the fan19and the circulation pump20remain energized. Therefore, a temporal increase in the temperature of the tubes (rubber hoses)16,17, and22to25and the circulation pump can be prevented, and the reliability of the liquid-cooled LED lighting device1is thereby improved.

Next, the exemplary control flow when the device is turned on under the cool conditions will be described with reference toFIG. 17.

In the case where the LED light sources10are turned on under the cool conditions in which the temperature of outside air is low, if the main power supply is turned on (step S31) and the LED on-off switch27is switched on (step S32), the LED light source-driving power supply28is turned on. The LED light sources10are thereby supplied with power (step S33), to be turned on (step S34).

At the same time, a determination is made whether or not the temperature detected by the temperature sensor34is equal to or higher than a predetermined threshold value (step S35). The OFF state of the liquid cooling system-driving power supply30is maintained when the detected temperature is lower than the threshold value (if the determination result in step S35is NO), and power is not supplied to the liquid cooling system3(step S36), so that the liquid cooling system3is not energized. When the temperature detected by the temperature sensor34is increased to the threshold value or higher (if the determination result in step S35is YES), the liquid cooling system-driving power supply30is turned on, and the fan19and the circulation pump20are actuated (step S37). The cooling liquid starts circulating in the liquid cooling system3, and the required cooling effect is achieved. Also in this case, control when the LED light sources10are turned off is performed according to the flow shown inFIG. 16.

As described above, in the present exemplary embodiment, under the cool conditions in which the temperature detected by the temperature detection element when the LED light sources10are turned on is less than the predetermined threshold value, power is not supplied to the liquid cooling system3until the temperature detected by the temperature detection element is equal to or higher than the predetermined threshold value. Since cooling is not effected during this period, the entire liquid-cooled LED lighting device1can be rapidly warmed to the required operating temperature.

Next, a description will be given of still another exemplary embodiment of the presently disclosed subject matter with reference toFIG. 18in which a configuration is illustrated as a modified example of the configuration ofFIG. 11. It should be noted that in the present exemplary embodiment a temperature detection element (being the temperature sensor34) is assumed to be mounted on the same substrate as the LED light sources10. Hereinafter, the exemplary operation flow chart will be described with reference toFIGS. 18 and 19.

As shown inFIG. 18, the system configuration of the LED lighting device1can be configured such that a power switch32connecting to an external power supply26can be connected to an LED light source-driving control circuit51and a liquid cooling system-driving control circuit52.

The LED light source-driving control circuit51can be connected to LED light sources10that can be driven with the control signal therefrom. The liquid cooling system-driving control circuit52can be connected to a liquid cooling system3that can be composed of a radiator, a fan that supplies cooling wind to the radiator and a circulation pump that circulates a cooling liquid.

A terminal of the temperature sensor34can be connected to an input terminal of a temperature control circuit33, an output terminal of which can be then connected to an input terminal of the LED light source-driving control circuit51. The output from the temperature sensor34can be delivered to the temperature control circuit33, and then, the temperature control circuit33can deliver an output that has been previously set based on the output from the temperature sensor34to the LED light source-driving control circuit51. The LED light source-driving control circuit51can output a control current to the LED light sources10for driving them.

When the components are classified by their functions, the LED light sources10, the temperature sensor34, the temperature control circuit33and the LED light source-driving control circuit51can constitute the LED light source drive unit55, while the liquid cooling system3and the liquid cooling system-driving control circuit52can constitute the liquid cooling system driving unit56.

FIG. 19is a flowchart showing an exemplary operational flow of the LED lighting device having the above configuration. First, in step S1the power switch32is turned on, and thereby the LED light source-driving control circuit51and the liquid cooling system-driving control circuit52are simultaneously supplied with power in steps S2and S3, respectively.

Then, in step S4the liquid cooling system3(including a fan and a circular pump) is actuated by the liquid cooling system-driving control circuit52. At the same time, an initial current Ip (A) is supplied to the LED light sources10by the LED light source-driving control circuit51to drive the LED light sources10(being turned on) in step S5.

When the LED light sources10are turned on, in step S6the temperature sensor34starts detecting the temperature of the substrate on which the LED light sources10are mounted. Next, in step S7the temperature control circuit33compares the detected substrate temperature x (° C.) with a preset temperature nD(° C.). If the substrate temperature x is equal to or lower than the preset temperature nD(nD≧x), the control process returns to step S2to maintain the initial current Ip (A) for the LED light sources10being turned on.

If the substrate temperature x is higher than the preset temperature nD(nD<x), the temperature control circuit33further compares in the next step S8the detected substrate temperature x (° C.) with another preset temperature nC(° C.). If the substrate temperature x is equal to or lower than the preset temperature nC(nCx), the temperature control circuit33delivers an output preset based on the substrate temperature x to the LED light source-driving control circuit51. In the next step S9, a drive-control current Ic (A) corresponding to the substrate temperature x is supplied to the LED light sources10for driving (being turned on).

If the substrate temperature x is higher than the preset temperature nC(nC<x) in step S8, the temperature control circuit33delivers an output for turning off the LED light sources10to the LED light source-driving control circuit51. In step S10, the drive current to the LED light sources10is interrupted by the LED light source-driving control circuit51to turn the LED light sources10off in step S11.

Hereinafter, a description will be given of the relationship between the substrate temperature detected by the temperature sensor34and the current supplied to the LED light source10with reference toFIG. 20.

FIG. 20is a graph illustrating a so-called degrading curve showing the relationship between the substrate temperature and the drive current for the LED light source10, which is the basis for suppressing the junction temperature (Tj) of an LED light source10to ensure the reliability of the device.

When the preset temperatures nD(° C.) and nC(° C.), the initial current Ip (A) and the control current Ic (A) in the above operation flow chart are considered with reference to the derating curve, the preset temperatures nD(° C.) and nc(° C.) can be determined as approximately 50° C. and 80° C., respectively. Accordingly, if the substrate temperature x is equal to or lower than the preset temperature nD(approximately 50° C.) (nDx), the initial current Ip can be set to approximately 1.4 (A). If the substrate temperature x is between these present temperatures nD(approximately 50° C.) and nc(approximately 80° C.) (ncx>nD), the control current Ip can be set to the current range read from the derating curve with respect to the substrate temperature x at that time (namely, between approximately 1.4 (A) and 0.7 (A)).

If the substrate temperature x is higher than the preset temperature nC(approximately 80° C.) (nC<x), the drive current for the LED light sources10is interrupted to turn the LED light sources10off.

In the present exemplary embodiment, the substrate temperature on which the LED light sources10are mounted can be detected to indirectly grasp the junction temperature (Tj) of the LED light sources10. Then, a drive control current can be set based on the derating curve to be supplied to the LED light sources10, thereby preventing the LED light sources10from being excessively increased in temperature and thereby increasing the reliability of the LED light sources10.

When the temperature of the substrate exceeds a predetermined temperature, the LED light sources10can be turned off. This configuration can protect the LED light sources10from the abnormal temperature increase, thereby ensuring safety, including that of the entire device.

In the present exemplary embodiment, the device body can include a plurality of LED light source modules5. However, the presently disclosed subject matter is not limited to this embodiment, and the device body can include a single LED light source module in which LED light sources10, connectors, and a temperature sensor34are mounted on a single substrate.

FIG. 21is a diagram illustrating the physical relationship between the LED light source modules5and the heat receiving jacket7according to another exemplary embodiment. The present exemplary embodiment can be configured in addition to the configuration of the previous exemplary embodiment by directly adhering the LED light source modules5to the heat receiving jacket7by utilizing a heat conductive adhesive (not shown) without the intervention of a heat conductive base plate. The other configuration can be the same as that of the previous exemplary embodiment. In this case, the substrate12on which the LED light sources10and the temperature sensor34are mounted can be the same as that in the previous exemplary embodiment, such as a metal substrate, a ceramic substrate, and/or a flexible substrate. Of these substrate materials, a thin substrate with flexibility can be used because the structure is bonded by using an adhesive.

In the disclosed embodiments, the substrate can be covered with a resist layer40at areas other than the area where the LED light sources10, the temperature sensor34and connectors (not shown) are mounted thereon. Namely, the temperature sensor34, the LED light sources10and the connectors for receiving drive power for the LED light sources10are mounted on an area where the resist layer40is not provided.

As described above, the LED lighting device1can be configured such that the device body does not need a heat conductive base plate. In this configuration, the heat generated from the LED light sources10can be effectively transferred to the heat receiving jacket7, thereby enhancing the suppression effect of the temperature increase of the LED light sources. Furthermore, it is possible to make the LED lighting device thinner, thereby lowering the manufacturing costs.

FIG. 22is a diagram illustrating the relationship between the LED light sources10and the heat receiving jacket7according to another exemplary embodiment. The present exemplary embodiment can be configured in addition to the configuration of the previous exemplary embodiment by mounting the LED light sources10and the temperature sensor34not on the substrate, but directly on the heat receiving jacket7. The other configurations can be the same as that of the previous exemplary embodiment. In this case, the heat receiving jacket7can have a wiring pattern formed on one surface thereof with an insulation layer interposed therebetween, and the heat receiving jacket7can be covered with a resist layer40at areas other than the area where the LED light sources10, the temperature sensor34and connectors (not shown) are mounted thereon.

Namely, the temperature sensor34, the LED light sources10and the connectors for receiving drive power for the LED light sources10are mounted on the area where the resist layer40is not provided.

As described above, the LED lighting device1can be configured such that the LED light sources10and the like are mounted directly on the heat receiving jacket7. In this configuration, the heat generated from the LED light sources10can be effectively transferred to the heat receiving jacket7, thereby enhancing the suppression effect of the temperature increase of the LED light sources. Furthermore, it is possible to make LED lighting device thinner, thereby lowering manufacturing costs.

In the above exemplary embodiments, the power switch is provided to the LED lighting device. Alternatively, the power switch can be provided outside the LED lighting device.

As described above, the liquid-cooled LED lighting device can have a liquid cooling system for heat dissipation of the LED light source. This system can improve heat dissipation efficiency as compared to an air cooling system, thereby allowing LED light sources having increased power. As a result, LED lighting device having higher illumination intensity can be manufactured.

Furthermore, the LED lighting device can have a temperature sensor that can output a detected temperature value, and accordingly, the LED light sources can be driven by a control current based on the detected temperature. The liquid-cooled LED lighting device can suppress excess temperature increases when the LED light sources are turned off to maintain a stable state, thereby achieving stable outputted illumination intensity and life. Furthermore, the liquid-cooled LED lighting device can ensure the safety of the device, including the LED light sources, by interrupting the drive current if the temperature of the cooling liquid abnormally increases.

FIG. 23is a perspective view illustrating a liquid-cooled LED lighting device according to another exemplary embodiment of the presently disclosed subject matter.FIG. 24is a diagram illustrating the liquid-cooled LED lighting device viewed from arrow A inFIG. 23.FIG. 25is a diagram illustrating the liquid-cooled LED lighting device viewed from arrow B inFIG. 23.FIG. 26is a cross-sectional view taken along line C-C ofFIG. 25.FIG. 27is a cross-sectional view taken along line D-D ofFIG. 25.FIG. 28is a cross-sectional view taken along line E-E ofFIG. 25.FIG. 29is an exploded perspective view of the liquid-cooled LED lighting device according to another exemplary embodiment of the presently disclosed subject matter.FIG. 30is a diagram illustrating the basic configuration of a liquid cooling system of the liquid-cooled LED lighting device of the presently disclosed subject matter.

The liquid-cooled LED lighting device of the presently disclosed subject matter can be used in dangerous areas such as chemical plants, gas stations, and the like. As shown inFIGS. 26 to 29, the liquid-cooled LED lighting device can be configured to include a light source unit503, an air-cooling heat dissipation system504and a liquid-cooling heat dissipation system505that are incorporated inside a cubic housing502. It should be noted that the air-cooling heat dissipation system504may not be provided if the liquid-cooling heat dissipation system505is sufficient for the intended purpose.

In the following description of the subject application with reference toFIGS. 23 to 35, the vertical direction (up and down, top and rear and the like) may be determined based on the orientation shown in the drawings. In other words, the liquid-cooled LED lighting device105is not installed with the orientation illustrated inFIG. 23.

The housing502can be formed of a resin material such as polycarbonate (PC) or a metal material such as aluminum. As shown inFIG. 23, inlet ports506including a plurality of longitudinal slits can be formed along the periphery of the housing502. Discharge ports507including a plurality of fan shaped slits can be formed on the top surface thereof. The housing502can have a lower opening, to which the light source unit503is fitted.

The light source unit503can be configured to include a metal substrate509on which a plurality of (nine (9) in the drawings) LED light sources508(seeFIG. 30) can be mounted, a rectangular plate-like metal base510to which the metal substrate509is attached, and a rectangular plate-like transparent lens511to be fitted to the lower opening of the housing502. Herein, the transparent lens511can be formed of a glass or an inflammable resin material. InFIG. 29, reference numeral512is a cable connector.

The nine metal substrate509on which the LEDs508have been mounted can be arranged in a 3×3 matrix form. Seats510a, the number of which is the same as that of the LED508, can be integrally formed with the metal base510prepared by aluminum die casting so that they protrude in a 3×3 matrix form (seeFIGS. 26 and 28). The metal substrates509can be secured by screwing them to the respective seats510aof the metal base510with the rectangular heat conductive sheets513interposed therebetween. The heat conductive sheets513each are formed of a silicone or similar material having a high insulation property and a high heat conductivity.

The air-cooling heat dissipation system504can include the cubic circuit casing514having a lower opening and a plurality of heat dissipation pins517serving as a heat sink. The heat dissipation pins517can be formed on the upper surface of the cubic circuit casing514as an atmospheric heat dissipation portion. Furthermore, a circuit substrate515on which various electronic components are mounted can be accommodated within the circuit casing514. The lower opening of the circuit casing514can be covered with a rectangular plate-like cover516. The circuit casing514is molded by aluminum die casting with a high heat conductivity, and the plurality of heat dissipation pins517constituting the atmospheric heat dissipation portion are protrudingly formed integrally on the top surface of the casing514. Then, the circuit substrate515is provided in close contact with the inside top surface of the circuit casing514with the heat conductive sheets518intervening therebetween, the sheet518being made of a silicone with high insulating and heat conductive properties. An O-ring519can be disposed in between the circuit casing514and the cover516at the point where they are joined together. The sealing effect of the O-ring519can provide a hermetically sealed space within the circuit casing514so that any dust and moisture can be prevented from entering the inside of the circuit casing514from outside. In the present exemplary embodiment, the heat dissipation pins517are protrudingly provided on the circuit casing514to serve as an atmospheric heat dissipation portion. In place of the heat dissipation pins517, heat dissipation fins may be formed in the circuit casing514.

As shown inFIGS. 26 to 30, the liquid-cooling heat dissipation system505can be configured to include a heat receiving jacket520, which acts as a heat exchanger, a radiator521configured to heat exchange between outside air flows (cooling air) and a cooling liquid that has been increased in temperature by receiving heat in the heat receiving jacket520, a fan522configured to supply cooling air to the radiator521, a circulation pump523configured to circulate the cooling liquid within a closed loop circulation path, and a reserve tank524configured to store the cooling liquid. The fan522can be disposed so as to face and be disposed above the radiator521.

The heat receiving jacket520can be formed to have a hollow rectangular plate shape. As shown inFIGS. 26 to 28, the inside thereof can serve as a passage of a cooling liquid. As shown inFIGS. 27 and 29, the heat receiving jacket520can also include, at its end, an inlet piping525through which the cooling liquid cooled by heat exchange with outside air flows at the radiator521, and a discharge piping526from which the cooling liquid that has received heat from the heat receiving jacket520is discharged (seeFIG. 5).

As shown inFIGS. 26 and 28, the heat receiving jacket520can be disposed horizontally on the bottom inside of the housing502. The air-cooling heat dissipation system504and the light source unit503can be disposed so that the heat receiving jacket520is interposed therebetween. The metal bases510of the light source unit503on the lower side of the heat receiving jacket520in the drawings can be in close contact with the lower surface of the heat receiving jacket520with the rectangular heat conductive sheets527interposed therebetween. Furthermore, the heat conductive sheets527can be formed of a silicone with high insulating and heat conductive properties.

The cover516of the air-cooling heat dissipation system504can be disposed on the upper side of the heat receiving jacket520so that the cover516can be in close contact with the surface of the heat receiving jacket520. In the present exemplary embodiment, the cooling liquid can be a non-freezing fluid composed of a mixture of water and propylene glycol.

As shown inFIGS. 26 and 28, the radiator521and the fan522can be disposed above and away from the heat receiving jacket520inside the housing502. A space S is formed between the heat receiving jacket520and the radiator521so that the air cooling unit504, the circulation pump523and the reserve tank524can be disposed inside the space S. Specifically, a gate-shaped chassis528can be provided on the heat receiving jacket520, and the air cooling unit504can be disposed inside the space surrounded by the chassis528. On the chassis528, there are the circulation pump523and the reserve tank524.

As shown inFIGS. 27 and 30, a tube (rubber hose)529can be provided upward from the discharge piping526of the heat receiving jacket520and connected to the inlet piping530of the radiator521. A tube (rubber hose)532can be extended from the discharge piping531of the radiator521and connected to the inlet side of the circulation pump523. A tube (rubber hose)533can be extended from the discharging side of the circulation pump523and connected to the inlet side of the reserve tank524as shown inFIG. 30. Furthermore, a tube (rubber hose)534can be provided downward from the outlet side of the reserve tank524and connected to the inlet piping525of the heat receiving jacket520. As described above, the heat receiving jacket520, the radiator521, the circulation pump523and the reserve tank524can be connected through the tubes529and532to534(or rubber hoses), so that a closed circulation path is formed. The required cooling effect can be achieved by circulation of the cooling liquid through the circulation path.

The liquid-cooled LED lighting device501as configured above can be activated to supply the light source unit503, the circuit substrate and the liquid-cooling heat dissipation system505within the circuit casing514with power. Accordingly, the plurality of (nine (9) in the present exemplary embodiment) LEDs508of the light source unit503can emit light, which can passes through the transparent lens511to be projected downward inFIG. 23. Thereby, the area in front of the lighting device501can be illuminated. The lighting control of the light source unit503can be performed by a circuit formed on the circuit substrate515inside the circuit casing514. Accordingly, the LEDs508of the light source unit503and the various electronic components (not shown) on the circuit substrate515can generate heat. If no countermeasure is taken, the light source unit503and the circuit substrate515become overheated and increase in temperature excessively.

In the present exemplary embodiment, at the same time when the LED s508are activated, the liquid-cooling heat dissipation system505can be activated. Accordingly, the light source unit503and the circuit casing514serving as the heat sink of the air-cooling heat dissipation system504can be forceably cooled by the cooling liquid circulating within the circulation path as shown inFIG. 30. This can decrease the temperature of the device. The heat generated from the light source unit503and the circuit substrate515can be transferred to the circuit casing514and is dissipated from the surface of the circuit casing514and the plurality of heat dissipation pins517that constitute the air-cooling heat dissipation system504. The heat dissipation can be facilitated by the cooling wind flowing from the inlet ports506toward the discharge ports507within the housing502by the fan522.

In the liquid-cooling heat dissipation system505, the cooling liquid circulating through the circulation path by the circulation pump523can receive the heat generated by the light source unit503and the circuit substrate515when passing through the heat receiving jacket520. The cooling liquid, increased in temperature due to reception of the heat, can be introduced into the radiator521through the tube529.

When the fan522is driven to rotate by a motor (not shown), outside air can be introduced into the housing502as cooling wind flowing from the inlet ports506formed on the peripheral surface of the housing502. The cooling wind can flow in the space S formed between the heat receiving jacket520and the radiator521upward. The air passing through the radiator521can be discharged from the discharge ports507formed on the surface of the housing502to the outside. In the radiator521, the heat of the cooling liquid can be dissipated to the outside through the cooling wind passing through the radiator521. The cooling liquid decreased in temperature can be sucked by the circulation pump523through the tube532.

The cooling liquid sucked by the circulation pump523can be pressurized and fed to the reserve tank524by the circulation pump523through the tube533. Part of the cooling liquid can be stored in the reserve tank524, and the remainder thereof can be fed from the reserve tank524to the heat receiving jacket520via the tube534, thereby cooling the light source unit503, the circuit casing514and the inside circuit substrate515again. The above action (cooling cycle) can be continuously repeated so that the cooling liquid flowing through the heat receiving jacket520can forcedly cool the light source unit503, the circuit casing514and the circuit substrate515. Accordingly, their temperature rise is suppressed to a predetermined temperature or lower.

In the present exemplary embodiment, the air-cooling heat dissipation system504(including the circuit casing514) and the light source unit503can be disposed so that the heat receiving jacket520is interposed therebetween. When the circulation pump523is activated to circulate the cooling liquid through the closed circulation path, the light source unit503, the circuit casing514and the circuit substrate515can be forcedly cooled simultaneously by the cooling liquid in the heat receiving jacket520, which is interposed therebetween. When the liquid-cooled LED lighting device501is used in a dangerous area, the liquid-cooling heat dissipation system505can suppress the maximum temperature of the light emission portion of the light source unit503to lower than the flash point of the surrounding flammable gas (for example, in the present exemplary embodiment, 95° C. or lower).

In addition to this, the present exemplary embodiment is configured such that the air-cooling heat dissipation system504can effectively absorb heat generated by the LEDs508of the light source unit503in addition to the liquid-cooling heat dissipation system505. Accordingly, the maximum temperature of the light emission portion of the light source unit503can be effectively suppressed to lower than the flash point of the surrounding flammable gas. Even when the liquid-cooled LED lighting device501is used in a dangerous area, it is possible to prevent possible explosion risks.

In the present exemplary embodiment, the lower surface of the circuit casing514is in close contact with the heat receiving jacket520, and the plurality of heat dissipation pins517are protrudingly formed on the upper surface of the circuit casing514. This means the LED lighting device501is provided with the air-cooling heat dissipation system504in addition to the liquid-cooling heat dissipation system505. Accordingly, the heat generated by the LEDs508of the light source unit503can be effectively dissipated. Therefore, the maximum temperature of the light emission portion of the light source unit503can be effectively suppressed to lower than the flash point of the surrounding flammable gas. Even when the liquid-cooled LED lighting device501is used in a dangerous area, it is possible to prevent possible explosion risks.

The liquid-cooled LED lighting device501of the presently disclosed subject matter utilizes as its light source the LEDs508that are substantially maintenance free. Accordingly, the replacement of light sources can be eliminated, thereby facilitating ease of maintenance.

In the present exemplary embodiment, the light source unit503can be entirely in closed contact with the lower surface of the heat receiving jacket520, with the heat conductive sheet527which has high heat conductivity. This means the entire surface of the light source unit503can serve as a heat transmission surface, thereby facilitating the effective cooling of the light source unit503by the cooling liquid through the heat receiving jacket520. It should be noted that the entire surface of the light source unit503can be maintained in close contact with the heat receiving jacket520through the use of the heat conductive sheet527. Without the heat conductive sheet527, the light source unit503can partly contact the heat receiving jacket520in practice, thereby making it impossible to enhance its cooling effects. If an attempt was made to place the entire surface of the light source unit503in close contact with the heat receiving jacket520without the use of the heat conductive sheet527, then, the contacting surface of the heat receiving jacket520should be subjected to a smoothening treatment, such as a polishing process to render it as smooth as the metal base510of the light source unit503. However, this disadvantageously increases the processing steps, man hours, and costs.

Furthermore, in the present exemplary embodiment, the air-cooling heat dissipation system504is disposed in the space S formed between the heat receiving jacket520and the radiator521of the liquid-cooling heat dissipation system505. When cooling wind is introduced into the housing502by the fan522, it can forceably cool the circuit casing514and the circuit substrate515. In addition to the forced cooling by the cooling liquid, the circuit casing514and the circuit substrate515can be cooled more effectively, thereby suppressing the increase in temperature effectively and sufficiently.

In the liquid-cooled LED lighting device501according to the presently disclosed subject matter, when the liquid-cooling heat dissipation system505having operating portions such as the fan522and the circulation pump523cannot work properly due to some accident (namely, the cooling function is damaged), the current to be supplied to the LEDs508of the light source unit503can be controlled to a value such that heat generated by the LEDs508can be absorbed by the air-cooling heat dissipation system504.

Accordingly, if the liquid-cooling heat dissipation system505is broken and the cooling function cannot work, the current to be supplied to the LEDs508of the light source unit503can be reduced. This control can suppress the heat generated by the LEDs508to the heat amount that can be absorbed by the air-cooling heat dissipation system504, i.e., the heat that can be sufficiently dissipated from the circuit casing514and the heat dissipation pins517, thereby preventing overheating of the LEDs508. In this case, although the illumination intensity from the LED lighting device501may be lowered due to the suppressed current, the maximum temperature of the light source unit503can be controlled to be lower than the flash point of the surrounding flammable gas. Thus, even if the liquid-cooled LED lighting device501of the presently disclosed subject matter is used in a dangerous area, it is possible to prevent explosion risks. Namely, if the LED lighting device501is used in a gas station or a chemical plant where dangerous works are carried out, accidental light-off can be prevented, thereby ensuring high safety in such dangerous areas.

In the liquid-cooled LED lighting device501of the present exemplary embodiment, when the air-cooling heat dissipation system504and the liquid-cooling heat dissipation system505are properly operated, the output with which the junction temperature of the LED does not exceed 100° C. is 200 W.FIG. 31shows the illumination intensity distribution when the LED lighting device is driven with an output of 200 W. As shown inFIG. 31, the LED lighting device501can illuminate an area of approximately 8 m square with an illumination intensity of 5 1× or more. It should be noted that the illumination intensity was observed when the LED lighting device was installed at a height of 6 m (the same condition is applied to the cases ofFIGS. 32 and 33). In the graph, the vertical axis is the distance in the right-to-left direction on the ground and the horizontal axis is the distance in the front-to-rear direction on the ground (unit: meter), and the numeral indicated in the graph is the illumination intensity (unit: 1×). (The same is applied to the cases ofFIGS. 32 and 33).

If the liquid-cooling heat dissipation system505is broken and the cooling function cannot work, the current to be supplied to the LEDs508of the light source unit503can be reduced. For example, the output can be suppressed to 50 W that is one-fourth of the normal output of 200 W. In this case, the illumination intensity is lowered, but the function as a lighting device is not damaged and it is possible to prevent possible explosion risks due to the surrounding flammable gases.FIG. 32shows the illumination intensity distribution when the LED lighting device is driven with an output of 50 W. As shown inFIG. 32, the LED lighting device501can illuminate an area of approximately 6 m square with an illumination intensity of 5 1× or more.

Suppose that when the LED lighting device does not have the air cooling unit504, but only includes a liquid-cooling heat dissipation system505, and the liquid-cooling heat dissipation system505is broken. In this case, cooling is achieved only by natural heat dissipation from the surface of the heat receiving jacket520. In addition, in such a case, the output when the junction temperature of the LED does not exceed 100° C. is 10 W, that is, one-twentieth of the normal output of 200 W.FIG. 33shows the illumination intensity distribution when the LED lighting device is driven with an output of 10 W. As shown inFIG. 33, the LED lighting device can illuminate an area of approximately 3 m square with an illumination intensity of 5 1× or more.

A description will be given of another exemplary embodiment of the presently disclosed subject matter with reference toFIGS. 34 and 35.

FIG. 34is a perspective view of a liquid-cooled LED lighting device of the presently disclosed subject matter when a housing is removed, andFIG. 35is a longitudinal cross-sectional view of the liquid-cooled LED lighting device.

The liquid-cooled LED lighting device501′ of the present exemplary embodiment can be used in dangerous areas. In the device501′, the heat sink for the air-cooling heat dissipation system504can include a plurality of heat dissipation pins517formed in the heat receiving jacket520. The other configuration is the same as the LED lighting device501of the previous exemplary embodiment. Accordingly, the same or similar components inFIGS. 34 and 35are denoted by the same reference numerals as those inFIGS. 23 to 30, and descriptions thereof will be omitted hereinafter.

Also in the present exemplary embodiment, the air-cooling heat dissipation system504and the liquid-cooling heat dissipation system505can suppress the maximum temperature of the light emission portion of the light source unit503to lower than the flash point of a surrounding flammable gas (for example, in the present exemplary embodiment, 95° C. or lower).

Furthermore, when the liquid-cooling heat dissipation system505having operating portions, such as a fan522and a circulation pump523, cannot work properly due to some accidents (namely, the cooling function of the system505is damaged), the current to be supplied to the LEDs508of the light source unit503can be controlled to a value such that heat generated by the LEDs can be absorbed by the air-cooling heat dissipation system504.

Accordingly, the present exemplary embodiment is configured such that the air-cooling heat dissipation system504can effectively absorb heat generated by the LEDs508of the light source unit503in addition to the liquid-cooling heat dissipation system505. By doing so, the maximum temperature of the light emission portion of the light source unit503can be effectively suppressed to lower than the flash point of the surrounding flammable gas. Even when the liquid-cooled LED lighting device501′ is used in a dangerous area, it is possible to prevent possible explosion risks.

When the liquid-cooling heat dissipation system505cannot work properly due to some accidents and the cooling function thereof is damaged, the current supplied to the LEDs508of the light source unit503can be controlled to a value such that heat generated by the LEDs508can be absorbed by the air-cooling heat dissipation system504. Namely, this control can suppress the heat generated by the LEDs508to the heat amount that can be absorbed by the heat receiving jacket520and the heat dissipation pins517, thereby preventing overheating of the LEDs508. Although the illumination intensity from the LED lighting device501′ may be lowered due to the suppressed current, the function as a lighting device is not damaged and it is possible to prevent the possible explosion risk due to the surrounding flammable gases as in the previous exemplary embodiment.

In the present exemplary embodiment, the heat dissipation pins517are formed in the heat receiving jacket520. However, the presently disclosed subject matter is not limited to this, and heat dissipation fins may be formed in the heat receiving jacket520instead of the heat dissipation pins517. The heat dissipation pins517and/or the heat dissipation fins can be integrally formed with the heat receiving jacket520. Alternatively, separate heat dissipation pins517and/or separate heat dissipation fins can be fixed to the heat receiving jacket520by soldering, calking, screwing or the like. When separate heat dissipation pins or fins are fixed to the heat receiving jacket520by soldering or the like, the pins and/or fins can be formed of thin metal springs or thin metal bellows. The shape of the atmospheric heat dissipation portion can be the same shape as those generally used for heat sink.

The liquid-cooled LED lighting device of the presently disclosed subject matter can be used as exterior lighting devices such as street lamps, garden lamps, and various sports arena lighting devices.

It will be apparent to those skilled in the art that various modifications and variations can be made in the presently disclosed subject matter without departing from the spirit or scope of the presently disclosed subject matter. Thus, it is intended that the presently disclosed subject matter cover the modifications and variations of the presently disclosed subject matter provided they come within the scope of the appended claims and their equivalents. All related art references described above are hereby incorporated in their entirety by reference.