Abstract:
A light emitting module ( 10 ) includes a metal circuit board ( 11 ), a number of light emitting units ( 12 ) arranged on a first surface of the metal circuit board, and a cooling system ( 13 ) mounted on an opposite second surface of the metal circuit board. A light source device ( 1 ) using the light emitting module further includes a housing ( 30 ) and a transparent light cover ( 20 ). The housing has a base with the light emitting module being mounted thereon. The transparent light cover covers the housing. The present light emitting module and light source device can improve the brightness of the light, and increase the utilization efficiency of light.

Description:
FIELD OF THE INVENTION 
   The present invention relates to light emitting modules, and more particularly, to a white light emitting module and a light source device using the same. 
   DESCRIPTION OF RELATED ART 
   In order to provide a proper contrast for items in an individual&#39;s viewing environment, it is desirable to have a white light output from a light source device. Incandescent bulbs and fluorescent lamps are capable of effectively providing such a white light or near white light output. However, there are significant drawbacks for the use of these types of light source devices for illumination, such as fragility of the lights themselves and their relatively short lifespan. 
   Because of the drawbacks in the use of incandescent bulbs and fluorescent lamps, the use of light emitting diodes (LEDs) for illumination has become increasingly popular. LEDs are diodes that have the “side effect” of producing light while electric current is flowing through them. In the simplest terms, an LED is made with two different kinds of semiconductor material: one type that has an excess of free electrons roaming around inside the material, and another that has a net positive charge and lacks electrons. When an electron from the first material, the donor, flows as a current across a thin barrier and into the second material, a photon or particle of light is produced. 
   Because LEDs produce light based on semiconductor principles of operation, the light output thereof is typically along a narrow wavelength band, i.e., a single color output. Recent advances, however, have resulted in LEDs that produce a near white light output. A known method being utilized to produce white light from LEDs employs a light emitting module that includes a plurality of regularly arranged red, green, and blue LEDs. 
   The light emitting module composed of LEDs typically lasts for 100,000 hours or more before the LEDs need to be replaced. The LEDs generate very little heat and require relatively little power. Therefore, LEDs are well suited for a wide variety of applications. The unique features of LEDs make them very attractive to many industries. However, one of the drawbacks of LED technology is that the brightness of an LED that is operated with a certain current is greatly affected by the ambient and its own temperature. For a circuit with a certain current, a typical LED will shine brighter in colder temperatures and more dimly in hotter temperatures. Further, the temperature of the light emitting module composed of LEDs will inevitably increase after an operation for a period of time, so its brightness will decrease. Thus, the brightness of the light emitting module is unstable during its use, and a utilization efficiency of light of the light emitting module is lowered after a long time of usage. 
   What are needed, therefore, are a light emitting module with high utilization efficiency of light, and a light source device using the light emitting module. 
   SUMMARY OF INVENTION 
   A light emitting module according to one preferred embodiment includes a metal circuit board, a number of light emitting units arranged on a first surface of the metal circuit board, and a cooling system mounted on an opposite second surface of the metal circuit board. 
   A light source device according to one preferred embodiment includes a light emitting module, a housing and a transparent light cover. The light emitting module includes a metal circuit board, a number of light emitting units arranged on a first surface of the metal circuit board, and a cooling system mounted on an opposite second surface of the metal circuit board. The housing has a base with the light emitting module being mounted thereon. The transparent light cover covers the housing. 
   Compared with conventional light emitting module, the present light emitting module has following advantages. Because the cooling system is used, with the circulation of the cooling liquid in the cooling passage, the heat generated by the light emitting units can be effectively dissipated. The temperature of the LEDs is lowered, and maintained in a safety range. Thus, the light emitting capability of the LEDs can be fully exploited. The brightness of the light emitting module is improved, and the utilization efficiency of light thereof is also increased, accordingly. 
   Other advantages and novel features will become more apparent from the following detailed description of present light emitting module, when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     Many aspects of the present light emitting module and light source device can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, the emphasis instead being placed upon clearly illustrating the principles of the present light emitting module and light source device. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       FIG. 1  is a schematic, side view of a light emitting module in accordance with a preferred embodiment; 
       FIG. 2  is a schematic, top view of the light emitting module of  FIG. 1 ; 
       FIG. 3  is a schematic, plan view of an exemplary light emitting unit of the light emitting module of  FIG. 1 ; 
       FIG. 4  is a schematic, cross-sectional view of a cooling system of the light emitting module of  FIG. 1 ; and 
       FIG. 5  is a schematic, cross-sectional view of a light source device in accordance with a preferred embodiment. 
   

   DETAILED DESCRIPTION 
   Reference will now be made to the drawings to describe preferred embodiments of the present light emitting module and light source device, in detail. 
   Referring to  FIG. 1 , a light emitting module  10 , in accordance with a preferred embodiment, is shown. The light emitting module  10  includes a metal circuit board  11 , a plurality of light emitting units  12  arranged on the metal circuit board  11 , and a cooling system  13  attached to an underside of the metal circuit board  11 . 
   The metal circuit board  11  may be a metal printed circuit board that has a plurality of driving circuits (not shown) thereon. The driving circuits can provide driving currents for controlling the plurality of light emitting units  12  to emit white light with desired brightness. The metal circuit board  11  can be made from a heat conducting material with a high heat conducting property, such as Cu, Al, or theirs alloy. Thus, heat generated by the light emitting units  12  can be effectively conducted to the metal circuit board  11 . 
   The cooling system  13  includes a hollow heat receiving portion  131 , a cooling pipe  132  communicating with the heat receiving portion  131 , and a cooling liquid with a high heat capacity, such as water or a supercritical liquid. The heat receiving portion  131  is attached to a bottom surface of the metal circuit board  11 . The heat receiving portion  131  and the cooling pipe  132  cooperatively define a circulatory liquid passage for the circulation of the cooling liquid therein. The cooling pipe  132  can be configured to be in a curved or spiral fashion for economizing space occupied by the light emitting module  10 . In addition, a pump  133  can be provided in the liquid passage for enhancing the flow of the cooling liquid in the liquid passage. Furthermore, a cooling tank  134  can be arranged in the liquid passage for supplying the cooling liquid and enhance the cooling efficiency of the cooling liquid. Preferably, a thermal interface material can be applied between the metal circuit board  11  and the heat receiving portion  131  for enhancing the heat conducting efficiency therebetween. Nanomaterials such as carbon nanotubes can also be admixed in the thermal interface material for further enhancing the heat conducting efficiency associated therewith. 
   Referring to  FIG. 2 , the plurality of light emitting units  12  are regularly arranged on the metal circuit board  11 . As illustrated, ten white light emitting units  12  are used in the preferred embodiment, of which six light emitting units  12  are evenly arranged on an intermediate portion of the metal circuit board  11  in two columns, and the other four light emitting units  12  are evenly, arranged adjacent two opposite lateral edges of the metal circuit board  11 . The four light emitting units  12  are preferably lengthways perpendicular to the six light emitting units  12 . This configuration ensures that an evenly brightness of the light emitting module  10  can be obtained. Understandably, of the configuration of the light emitting units  12  is not limited to the present embodiment. If the number of the light emitting units  12  arranged on the intermediate portion of the metal circuit board  11  is increased or decreased, the number of the light emitting units  12  arranged adjacent two edges of the center light emitting units  12  needs to be correspondingly increased or decreased. 
   Referring to  FIG. 3 , a configuration of an exemplary light emitting unit  12  is shown. The light emitting unit  12  includes at least a red (R) LED  123 , at least a green (G) LED  121 , and at least a blue (B) LED  122  as light emitting elements. In the preferred embodiment, the light emitting unit  12  includes two red LED  123 , two green LED  121 , and a blue LED  122 . The LEDs are arranged in an order of G-R-B-R-G thereby obtain a satisfactory white light. Alternatively, the LEDs of the light emitting unit  12  can also be arranged in the order of one of R-G-B-G-R, B-G-R-G-B, B-R-G-R-B, and G-B-R-B-G. The arrangement of the LEDs can be linear, as shown in  FIG. 3 , or curved, circular, etc. Alternatively, laser diodes (LDs) could also be used as the light emitting unit  12  in a similar way. 
   Referring to  FIG. 4 , a working process of the cooling system  13  is shown. The working process of the cooling system  13  includes the steps as follows: heat absorbed by the metal circuit board  11  is transferred to the heat receiving portion  131  (as indicated by the downward arrows). The heat is then transferred to the cooling liquid flowing in the heat receiving portion  131 . The cooling liquid is driven by the pump  133  and circularly flows in the cooling passage. The heat is finally dissipated into the ambient air. 
   Compared with conventional light emitting module, the present light emitting module  10  has following advantages. Because the cooling system  13  is used, with the circulation of the cooling liquid in the cooling passage, the heat generated by the light emitting units  12  can be effectively dissipated. The temperature of the LEDs is lowered, and maintained in a safety range. Thus, the light emitting capability of the LEDs can be fully exploited. The brightness of the light emitting module  10  is improved, and the utilization efficiency of light thereof is also increased, accordingly. 
   Referring to  FIG. 5 , a light source device  1  having the light emitting module  10  is shown. The light source device  1  includes a housing  30  with a base  31  for mounting the light emitting module  10  thereon, and a transparent light cover  20 . The housing  30  and the light cover  20  cooperatively form a sealing space for accommodating the light emitting module  10 . A shape of the housing  30  can be trumpet-shaped, cone-shaped, truncated cone-shaped, a combination of these shapes, or any other similar shapes. An inner surface of the housing  30  can be configured to be a reflective surface for reflecting the light emitted from the light emitting module  10  to the outside of the housing  30 . The transparent light cover  20  can be a lens, or a prism. In the preferred embodiment, the transparent light cover  20  is attached to edge portions of the housing  30 . Alternatively, the light cover  20  could be disposed at positions as indicated by broken line  20 ′, broken line  20 ″, or any positions therebetween. The light source device  1  can produce white light with high brightness, and is suitable for use as illumination light sources such as a desk lamp or a searchlight, or projection light sources. 
   It is to be understood that the above-described embodiment is intended to illustrate rather than limit the invention. Variations may be made to the embodiment without departing from the spirit of the invention as claimed. The above-described embodiments are intended to illustrate the scope of the invention and not restrict the scope of the invention.