Abstract:
A blue light leakage-suppressing LED structure for emitting white light includes at least one LED chip, an encapsulation element, a light output lens, and an optical fuse coating formed of a thermosensitive material; or includes at least one LED chip and an encapsulation element formed of a mixture of an encapsulation material and a thermosensitive material; or includes at least one blue LED chip, a fluorescent powder layer, an isolation region, an optical fuse layer, and a light output lens. Thanks to the hue changing property of the thermosensitive material, the LED structure can reduce the intensity of its short-wavelength light component and its overall brightness significantly before reaching the L70 threshold, after passing which the LED structure will emit excessive blue light. Thus, the user is protected from overexposure to blue light and will be reminded to replace the LED structure when the LED structure is about to malfunction.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a white light-emitting diode (LED) structure and, more particularly, to a blue light leakage-suppressing LED structure in which a thermochromics material can change its hue as the temperature of the LED is changed. 
     2. Description of Related Art 
     Driven by the rising awareness of environmental protection and the expectation of sustainable development, energy-saving light sources are now in extensive use. In particular, the demand for LEDs, which feature very low power consumption and adequate brightness, has increased the most. 
     The estimated service lives of LEDs are generally specified with an L70 value, which indicates the time for which the luminous flux of an LED is expected to last before dropping to 70% of that which has been achieved under a thermally stable condition. Once an LED reaches the L70 threshold, its temperature (or more particularly the junction temperature inside the LED) will be approximately equal to or higher than 150° C., and the correlated color temperature (CCT) of the LED at this moment will be about 9000 K or above. 
     However, during the period in which a white LED is about to reach but has not reached the L70 threshold, the light emission efficiency of the white LED is already lowered by the heat generated, and the lowered light emission efficiency results in more. heat. Eventually, the absorption efficiency of the fluorescent material in the white LED will be reduced, leading to a significant leakage of blue light. 
     More and more researches spurred by the increasing popularity of LEDs have shown that blue light is highly detrimental to the structure of the human eye. The eyes may be injured beyond repair if exposed to blue light for an extended period of time. 
     In view of this, and in order to bring about substantial improvement in people&#39;s quality of life, the LED industry, if not the entire lighting industry, has made great efforts in developing a simple yet effective technology or LED structure that enables a portion of a white LED to effect a change in hue before the white LED generates a large amount of heat and emits excessive blue light. The change in hue is intended to prevent unnecessary injury otherwise attributable to a significant leakage of blue light and, by reducing the brightness of the white LED considerably, to remind the user that the light source needs to be replaced. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a blue light leakage-suppressing LED structure which emits white light and which includes at least one LED chip, an encapsulation element, a light output lens, and an optical fuse coating formed of a thermosensitive material. The present invention also relates to a blue light leakage-suppressing LED structure which emits white light and which includes at least one LED chip and an encapsulation element formed of a mixture of an encapsulation material and a thermochromics material. According to the present invention, the hue changing property of the thermochromics material enables the LED structure to be substantially reduced in brightness before the LED chip reaches the L70 threshold, after passing which the LED chip will emit a large amount of blue light. Thus, the user is kept from overexposure to blue light and will be reminded to replace the LED structure when the LED structure is about to malfunction. 
     The present invention provides a blue light leakage-suppressing LED structure which emits white light and which includes: at least one LED chip; an encapsulation element covering the LED chip in a sealing manner; a light output lens covering a light output surface of the encapsulation element; and an optical fuse coating formed of a thermosensitive material and applied to an outer surface of the light output lens. 
     The present invention also provides a blue light leakage-suppressing LED structure which emits white light and which includes at least one LED chip and an encapsulation element covering the LED chip in a sealing manner, wherein the encapsulation element is formed of an encapsulation material mixed with a thermochromics material. 
     The present invention further provides a blue light leakage-suppressing LED structure which emits white light and which includes: at least one blue LED chip electrically connected to and fixedly provided on a substrate; a fluorescent powder layer provided on a light output surface of the blue LED chip; an isolation region surrounding and covering the blue LED chip and the fluorescent powder layer on the substrate; an optical fuse layer formed of a mixture of a thermochromics material and silicone and covering the isolation region, the blue LED chip, and the fluorescent powder layer in a sealing manner; and a light output lens covering an outer portion of the optical fuse layer. 
     Implementation of the present invention at least involves the following inventive steps: 
     1. No complicated manufacturing process is required, and only a low implementation cost is incurred. 
     2. The utilization rate of white LEDs will hopefully be increased to promote the practice of energy saving and the use of green energy. 
     3. Excessive blue light irradiation is prevented to effectively protect human eyes. 
     4. A user will be explicitly reminded to replace the light source of illumination. 
     The features and advantages of the present invention are detailed hereinafter with reference to the preferred embodiments. The detailed description is intended to enable a person skilled in the art to gain insight into the technical contents disclosed herein and implement the present invention accordingly. In particular, a person skilled in the art can easily understand the objects and advantages of the present invention by referring to the disclosure of the specification, the claims, and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention as well as a preferred mode of use, further objectives and advantages thereof will be best understood by reference to the following detailed description of illustrative embodiments when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  schematically shows the blue light leakage-suppressing LED structure in an embodiment of the present invention; 
         FIG. 2A  schematically shows the blue light leakage-suppressing LED structure in another embodiment of the present invention; 
         FIG. 2B  schematically shows the blue light leakage-suppressing LED structure in  FIG. 2A  further including a light output lens; 
         FIG. 3  schematically shows the blue light leakage-suppressing LED structure in  FIG. 1  further including at least one heat dissipation element; 
         FIG. 4A  schematically shows the blue light leakage-suppressing LED structure in  FIG. 2A  further including at least one heat dissipation element; 
         FIG. 4B  schematically shows the blue light leakage-suppressing LED structure in  FIG. 2B  further including at least one heat dissipation element; 
         FIG. 5  plots the characteristic curves of an LED structure without a thermochromics material whose hue changes with the correlated color temperature of the LED chip; 
         FIG. 6  plots the characteristic curves of the blue light leakage-suppressing LED structure in an embodiment of the present invention, showing how the thermochromics material changes its hue in response to a change in the correlated color temperature of the LED chip; 
         FIG. 7  schematically shows how the thermochromics material in the blue light leakage-suppressing LED structure in an embodiment of the present invention changes its hue when the temperature of the LED corresponds to a correlated color temperature of 9000 K or above; 
         FIG. 8A  schematically shows how the thermosensitive material in the blue light leakage-suppressing LED structure in another embodiment of the present invention changes its hue when the temperature of the LED corresponds to a correlated color temperature of 9000 K or above; 
         FIG. 8B  schematically shows how the thermosensitive material in the blue light leakage-suppressing LED structure in yet another embodiment of the present invention changes its hue when the temperature of the LED corresponds to a correlated color temperature of 9000 K or above; and 
         FIG. 9  schematically shows the blue light leakage-suppressing LED structure in still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , the blue light leakage-suppressing LED structure  100  in an embodiment of the present invention is configured to emit white light and includes at least one LED chip  10 , an encapsulation element  20 , a light output lens  30 , and an optical fuse coating  40 . 
     As shown in  FIG. 1 , the LED chip  10  in the LED structure  100  is a light source for emitting light. The LED chip  10  may include at least one blue LED chip which emits light of wavelengths ranging from 400 to 480 nm. 
     The encapsulation element  20  in  FIG. 1  covers the LED chip  10  in a sealing manner. The constituent materials of the encapsulation element  20  may include a fluorescent material so that the blue light emitted by a blue LED chip can react with the fluorescent material, thereby enabling the LED structure  100  to emit white light. 
     The encapsulation element  20  can be formed of silicone, epoxy, or a like material featuring both light permeability and a sealing property. 
     Referring to  FIG. 3 , if the LED structure  100  requires more efficient heat dissipation, the encapsulation element  20  can be fixedly attached to a heat dissipation element  70  which enhances heat dissipation from the encapsulation element  20  and hence from the entire LED structure  100 . 
     The fluorescent material may be yttrium-aluminum garnet (YAG)-based fluorescent powder, silicate-based fluorescent powder, nitride-based fluorescent powder, quantum dot-based fluorescent powder, or a mixture of at least two of the foregoing. 
     If no fluorescent material is used, a plurality of LED chips  10  configured respectively for emitting light of different colors (e.g., blue and yellow; or blue, red, and green) can be used at the same time so that the differently colored light is mixed to produce white light. The production of white light can be achieved by various conventional techniques, which are not dealt with herein. 
     Referring back to  FIG. 1 , the light output lens  30  covers a light output surface  21  of the encapsulation element  20 . The light output lens  30  may be a common lens that allows passage of light or a lens with special optical effects such as a Fresnel lens or a Gauss lens. 
     With continued reference to  FIG. 1 , the optical fuse coating  40  is formed of a thermochromics material  60  and is applied to the outer surface of the light output lens  30 . In other words, the white light emitted by the LED structure  100  passes through the optical fuse coating  40  before leaving the LED structure  100 . 
     The thermochromics material  60  can be formed of cellulose, thermochromic paint, a thermochromic ink, a thermochromic pigment, polyvinylpyrrolidone (PVP), or a mixture of at least two of the foregoing. 
     Referring again to  FIG. 1 , the thermosensitive material  60  can be so chosen that it is colorless and transparent or is white when the LED structure  100  is in normal operation, or more particularly when the light emitted by the LED structure  100  has a correlated color temperature lower than 9000 K and the corresponding temperature of the LED chip  10  is lower than about 150° C., wherein the temperature of about 150° C. corresponds to the L70 threshold. 
     On the other hand, referring to  FIG. 7 , when the LED structure  100  begins to show signs of abnormality such that the correlated color temperature of the light it emits approaches or becomes higher than 9000 K, with the corresponding temperature of the LED chip  10  approaching or having reached about 150° C. (i.e., the L70 threshold) or above, the thermosensitive material  60  changes its hue to one which is neither colorless and transparent nor white (e.g., black, red, or yellow). 
     It is worth mentioning that, when the correlated color temperature of the light emitted by the LED structure  100  is 9000 K or above, the corresponding temperature of the LED chip  10  in the LED structure  100  varies from one LED chip to another but generally ranges between 150° C. and 200° C. 
     Thus, when the LED chip  10  in the LED structure  100  has reached or is about to reach the L70 threshold and hence generates a huge amount of heat such that the correlated color temperature of the light emitted by the LED structure  100  is close to or even above 9000 K, the thermochromics material  60  turns from colorless and transparent or white to a hue which is neither colorless and transparent nor white (e.g., black, red, or yellow); in other words, the hue of the entire optical fuse coating  40  is changed to one which is neither colorless and transparent nor white, and which therefore substantially reduces the passage of light, including blue light. The change in hue not only eliminates the risk of eye injuries attributable to overexposure to blue light, but also reminds the user to replace the light source, which is damaged already or has shown signs of damage. 
       FIG. 2A  shows the blue light leakage-suppressing LED structure  200  in another embodiment of the present invention, wherein the LED structure  200  is configured to emit white light and includes at least one LED chip  10  and an encapsulation element  20 ′. 
     The LED chip  10  in  FIG. 2A  is a light source for emitting light and may include at least one blue LED chip configured to emit light whose wavelength ranges from 400 to 480 nm. 
     The encapsulation element  20 ′ in  FIG. 2A  covers the LED chip  10  in a sealing manner and is formed of an encapsulation material mixed with a fluorescent material  50  and a thermochromics material  60 . The encapsulation material of the encapsulation element  20 ′ may be formed of silicone or epoxy. 
     The thermosensitive material  60  may be cellulose, a thermochromic paint, a thermochromic ink, a thermochromic pigment, PVP, or a mixture of at least two of the foregoing. 
     As shown in  FIG. 2B , the LED structure  200  may further include a light output lens  30  which covers a light output surface  21 ′ of the encapsulation element  20 ′. It is understood that, like its counterpart in the previous embodiment, the light output lens  30  may be a common lens that allows passage of light or a lens with special optical effects such as a Fresnel lens or a Gauss lens. 
     Moreover, referring to  FIG. 4A  and  FIG. 4B , the encapsulation element  20 ′ can be fixedly attached to a heat dissipation element  70  to enhance heat dissipation from the LED structure  200 , regardless of whether the light output lens  30  is present or not. The heat dissipation element  70  serves to increase the efficiency of heat dissipation from the encapsulation element  20 ′ and hence from the entire LED structure  200 . 
     Referring now to  FIG. 2A ,  FIG. 2B ,  FIG. 4A , and  FIG. 4B , when the LED structure  200  is operating in a normal condition, in which the correlated color temperature of the light emitted is lower than 9000 K and the corresponding temperature of the LED chip  10  is lower than about 150° C., which is typical of the L70 threshold, the thermosensitive material  60  is colorless and transparent or is white. 
     However, referring to  FIG. 8A  and  FIG. 8B , when the LED structure  200  starts to operate in an abnormal condition such that the correlated color temperature of the light emitted approaches or exceeds 9000 K and the corresponding temperature of the LED chip  10  is about to reach or has reached the L70 threshold (i.e., being about 150° C. or above), the thermochromics material  60  changes from colorless and transparent or white to a hue which is neither colorless and transparent nor white (e.g., black, red, or yellow). As a result, light (including blue light) that can pass through the encapsulation element  20 ′ is substantially reduced. 
     This significant reduction in light permeability not only protects the user from overexposure to blue light and consequently from associated eye injuries, but also serves to remind the user in an unambiguous manner that the light source of illumination is damaged or has shown signs of damage and needs replacing. 
     The interaction between the LED chip  10  and the thermochromics material  60  while the LED chip  10  passes the L70 threshold is further illustrated with reference to  FIG. 5  and  FIG. 6 , which respectively plot the correlated color temperatures and luminous fluxes of an LED structure without the thermochromics material  60  and an LED structure of the present invention (i.e., with the thermosensitive material  60 ) against time. 
     As shown in  FIG. 5 , a common white LED (without the thermochromics material  60 ) having reached the L70 threshold (i.e., with a correlated color temperature of 9000 K) or about to reach the L70 threshold (i.e., with a correlated color temperature approaching 9000 K) generates and releases a considerable amount of heat such that a significant leakage of blue light occurs. In consequence, the correlated color temperature (represented by the thicker black line in  FIG. 5 ) rises precipitously. 
     However, referring to  FIG. 6 , when the thermochromics material  60  is incorporated into the encapsulation element  20 ′, the large amount of blue light generated immediately before the L70 threshold is reached is blocked by the thermochromics material  60 , which by that time has turned into a non-colorless, non-transparent, and non-white hue such as black, red, or yellow. As a result, the correlated color temperature plummets (as shown by the thicker black line in  FIG. 6 ), which dims the light rapidly and thereby notifies the user that this light source needs replacing. 
       FIG. 9  shows the blue light leakage-suppressing LED structure  300  in yet another embodiment of the present invention, wherein the LED structure  300  is configured to emit white light and includes at least one blue LED chip  310 , a fluorescent powder layer  320 , an isolation region  330 , an optical fuse layer  340 , and a light output lens  350 . 
     The blue LED chip  310  in  FIG. 9  is configured to emit blue light and is electrically connected to and fixedly provided on a substrate  380 . 
     As shown in  FIG. 9 , the fluorescent powder layer  320  is provided on a light output surface  311  of the blue LED chip  310 . The blue light emitted by the blue LED chip  310  reacts with the fluorescent powder layer  320  to produce white light. 
     The isolation region  330  in  FIG. 9  surrounds and covers the blue LED chip  310  and the fluorescent powder layer  320  on the substrate  380 . The isolation region  330  can be a space filled with nothing but air or be filled with silicone, epoxy, or both silicone and epoxy. 
     The optical fuse layer  340  in  FIG. 9  is formed of a mixture of a thermochromics material  60  and silicone and covers the isolation regions  330 , the blue LED chip  310 , and the fluorescent powder layer  320  in a sealing manner. 
     Like its counterparts in the LED structures  100  and  200 , the thermochromics material  60  used in the LED structure  300  may be cellulose, a thermochromic paint, a thermochromic ink, a thermochromic pigment, PVP, or a mixture of at least two of the foregoing. 
     Furthermore, the thermochromics material  60  is colorless and transparent or is white when at a temperature lower than 150° C. and turns into a hue which is neither colorless and transparent nor white when at a temperature not lower than 150° C. 
     The large amount of blue light generated in the LED structure  300  immediately before or after the L70 threshold is reached will turn the thermochromics material  60  into a hue which is neither colorless and transparent nor white (e.g., black, red, or yellow), in order for the thermochromics material  60  to block the passage of light and reduce the luminous flux of the LED structure  300  significantly. The correlated color temperature of the LED structure  300  will drop as a result, and the light will dim accordingly, which serves to notify the user that the light source needs to be replaced. 
     The embodiments described above are intended only to demonstrate the technical concept and features of the present invention so as to enable a person skilled in the art to understand and implement the contents disclosed herein. It is understood that the disclosed embodiments are not to limit the scope of the present invention. Therefore, all equivalent changes or modifications based on the concept of the present invention should be encompassed by the appended claims.