Light source with LED and optical protrusions

A light source with LED and optical protrusions is provided. It comprises an optical panel and at least one optical plate. The light source can be used together with a heat sink or an optical element to enhance its performance. The optical panel forms an optical surface having plural optical protrusions to reflect and mix lights emitted from the LEDs. The optical plate is inserted into at least one slot on the optical panel, and it comprises a heat dissipation core plate and at least one electric circuit layer. The electric circuit layer comprises LEDs and at least one control circuitry. The electric circuit layer can be attached to either single side or both sides of the heat dissipation core plate. The invention achieves good uniformity and high intensity of the combined lights with desired chromaticity.

FIELD OF THE INVENTION

The present invention generally relates to a light emitting diode (LED) lighting system, and more specifically to a light source with LED and optical protrusions.

BACKGROUND OF THE INVENTION

A light source for illuminating an information source is often required in many applications. In particular, liquid crystal displays (LCDs) have become more and more popular in many electronic media. LCDs are commonly adopted in various applications, such as laptop computers, display monitors, video cameras, automatic teller machine displays, displays in avionics, televisions etc. In general, a backlight module is required for the LCDs to illuminate the information to be displayed. There are various kinds of light sources used in a backlight module of an LCD, e.g., fluorescent lamps and LEDs. While the fluorescent lamps are inexpensive and do not need a complex control circuitry, they are sometimes inadequate for certain applications that require good color quality and long lamp life. LEDs have been proposed for use as light sources, such as LCD backlight modules, for many reasons. These advantages of LED light sources include long life, ease of replacement, robust mechanical property, and better color quality than fluorescent lamps. Certain applications (e.g., avionics) require a specific chromaticity of light emitted from the LCD backlight module. However, most commercially available LEDs are made with a limited number of chromaticity choices and their chromaticity may change over time.

An LED light source with a raised LED100, as shown inFIG. 1, to improve the chromaticity of a combined light was disclosed in U.S. Pat. No. 6,666,567. The raised LED100includes an LED diode101encased in a package102which is raised above the floor103of optical cavities. The raised structure permits light to be emitted from the base of the LED. Additionally, reflective protrusions may be placed beneath the raised LED to aid in redirecting the light trajectory. A combination of fluorescent lamps and LEDs were also proposed to form a hybrid light source. However, all these schemes increase the complexity and cost of the light source.

As shown inFIG. 2andFIG. 3, an LCD backlight200, which includes a first LED array201that provides light with a first chromaticity and a second LED array202that provides light with a second chromaticity, was disclosed in another U.S. Pat. No. 6,608,614. The lights emitted from these two LED arrays201and202are combined through a combining element301(e.g., a wave guide) and then projected towards an LCD stack302. The LED chip normally emits light in a direction which is approximately perpendicular to the chip surface. The directions of light emitted from the first and the second LED arrays are approximately perpendicular and parallel to the panel surface, respectively. A separate combining element301is required in this light source. The chromaticity of the combined light can only be adjusted by changing the chromaticity of the second LED array202through a control system (not shown). Therefore, there is a limited flexibility for chromaticity adjustment.

According to another prior art, a Luxeon side-emitter having packaged LED chips was disclosed, as shown inFIG. 4. The side-emitter may provide good uniformity of combined light but the light intensity is poor. In addition, packaged LED chips normally occupy a much larger area than the bare chips scheme of the present invention.

It is known that the majority of lights emitted from LED chips travel in a direction approximately perpendicular to the chip surface. Therefore, the LED chips need to be arranged in a way such that the lights emitted from different LED chips have a chance to be combined and mixed in order to achieve desired chromaticity before they reach a display screen. It is the main objective of the present invention to use a low complexity and low cost system to achieve high intensity and good color quality.

SUMMARY OF THE INVENTION

The present invention has been made to achieve the advantages of a practical LED light source. The primary object is to provide a light source with LED and optical protrusions. It eliminates the need of a package for encasing an LED chip, and thus reduces cost and space. The high intensity is also achieved due to a high LED packaging density.

In the first embodiment of the invention, the LED light source comprises an optical panel and at least one optical plate. This LED light source can be used together with a heat sink to enhance its performance. The optical panel forms an optical surface having plural optical protrusions to reflect and combine lights that are emitted from the LED. The optical plate is inserted into at least one slot on the optical panel. The optical plate comprises a heat dissipation core plate and at least one electric circuit layer. One electric circuit layer comprises at least one LED and at least one control circuitry which is designed to control the operation of the bare LED chips.

In the second embodiment, the LED light source further includes an optical element that is used to guide said combined light towards a display screen. The optical element may be a light diffuser or a wave guide.

The optical plate includes a heat dissipation core plate and two electric circuit layers. One electric circuit layer is attached to each side of the heat dissipation core plate. Alternatively, the optical plate includes a heat dissipation core plate and one electric circuit layer. The electric circuit layer is attached to single side of the heat dissipation core plate.

According to the invention, the LEDs are attached to an electric circuit layer via a flip chip or wire bonding. The LEDs are attached in a way such that their chip surfaces face the optical protrusions. Therefore, the emitted lights from different LEDs have a chance to be reflected and combined on the optical surface in order to achieve desired chromaticity before they reach a display screen. These LEDs can be encapsulated with a transparent material to prevent the LEDs from reacting with air. The control circuitry is used to power up the LEDs, to control the brightness of the LEDs, to provide electrostatic discharge protection for the LEDs, and to adjust the chromaticity of the combined light to meet desired applications. The control circuitry may be stacked or printed on the electric circuit layer.

Simulation results indicate that good uniformity and high intensity of combined lights with desired chromaticity are achieved. The combined lights can be further directed towards a light diffuser or a wave guide. Moreover, the heat dissipation core plates are normally connected to a heat sink to enhance dissipation of heat, and thus enhance the performance and increase the life time of the light source. The LED light source of this invention can be used as a backlight module for a liquid-crystal display.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5AandFIG. 5Bdepict a preferred embodiment of a light source500with LED and optical protrusions according to the present invention. Referring toFIG. 5A, the light source500comprises an optical panel501and at least one optical plate505. The optical panel501forms an optical surface having plural optical protrusions503to reflect and combine lights that are emitted from LEDs504and travel approximately in parallel to the surface of the optical panel501. The optical plate505is inserted into at least one slot509on the optical panel501. The slot may span from one panel edge to another. This light source500can be used together with a heat sink to enhance its performance. For example, a heat sink (shown in dotted line)502is attached to the optical panel501to enhance heat dissipation.

As shown inFIG. 5B, the optical plate505further comprises a heat dissipation core plate508and at least one electric circuit layer which is attached to the heat dissipation core plate508. One electric circuit layer506further comprises at least one LED504and at least one control circuitry507which is designed to control the operation of the bare LED chips504.

The combined lights can be further directed towards a light diffuser or a wave guide (not shown). Moreover, the heat dissipation core plates508are usually connected to the heat sink502to enhance the dissipation of heat, and thus enhance the performance and increase the life time of the light source500. The light source500of this invention can be used as a backlight module for a liquid-crystal display. The light source500eliminates the need of a package for encasing an LED chip, and thus reduces cost and space. However, this light source do not prohibit using packaged LED lamps and should not be limited to the use of bare LED chips only.

One electric circuit layer506is attached to each side of the heat dissipation core plate508, and the LEDs504on the electric circuit layer506are exposed on the optical surface to emit lights. The LEDs504are attached to the electric circuit layer506in a way such that their chips surfaces face the optical protrusions503. Therefore, the majority of lights are emitted towards the optical protrusions503, which are then reflected and combined by the optical protrusions503on the optical surface. Alternatively, only single side of the heat dissipation core plate508is attached with an electric circuit layer506. Adjacent LEDs are allowed to emit lights of different or same colors depending on desired applications.

The control circuitry507is used to power up the LEDs504, to control the brightness of the LEDs504, to provide electrostatic discharge protection for the bare LED chips504, and to adjust the chromaticity of the combined light to meet desired applications. The control circuitry507may be stacked or printed on the electric circuit layer506.

FIG. 6shows a second embodiment of a light source600with LED and optical protrusions according to the present invention, wherein an optical element601is placed in between a display screen602and the light source500shown inFIG. 5A. The optical element601is used to guide the combined light towards the display screen602such as an LCD stack. The optical element601may be a light diffuser or a wave guide.

According to desired applications, the optical protrusions can be formed in any suitable manner and shape and made of any suitable material. The shape of the optical protrusions can be, but not limited to, pyramidal or conic or parabolic or semispherical. The electric circuit layer is made of an insulating layer, such as printed circuit board (PCB), oxide and ceramic material. These LEDs can be encapsulated with a transparent material to prevent the LEDs from reacting with air. Furthermore, total reflection can be avoided if the refractive index of the transparent material is properly selected. The transparent material can be chosen from the group of, but not limited to, epoxy and silicone. The heat dissipation core plate can be made of a material chosen from the group of a dielectric material, an electrical conductor, and a thermal conductor.

According to the invention, the LEDs are attached to the electric circuit layer via a flip chip or wire bonding.FIG. 7Ashows a flip chip bonding, wherein an LED chip701is bonded onto a substrate (i.e., electric circuit layer506) with paste or solder. The flip chip bonding eliminates the need of a conventional wire bonding which is used to electrically connect the chip to an external circuitry. The bonding pads of a flip chip are also served as electrical connections to the control circuitry. The flip chip bonding is often adopted for applications that require a small form factor or have a high density of bonding pads. The wire bonding further includes edge wire bonding and center wire bonding.FIGS. 7B and 7Cshow an edge wire bonding and a center wire bonding, respectively. Wherein an LED chip702or703is first bonded onto a substrate (i.e., electric circuit layer506) with paste or solder, and then metal wire bonding is followed to complete the electrical connections to the control circuitry.

In a simulated RGB color map of a combined light at a screen surface, it shows that the chromaticity of the combined light using the light source with LED and optical protrusions according to the invention well matches a targeted white color. The light intensity is also higher than that can be achieved with the conventional schemes.FIG. 8further shows the intensity of the combined light from left/bottom to right/top of the screen surface. The horizontal axis represents the location on the screen. The solid line represents the horizontal component of the light intensity and the dashed line represents the vertical component of the light intensity. The results indicate that good uniformity and high intensity of the combined lights with desired chromaticity are achieved in both horizontal and vertical directions.