LED FLASH RING SURROUNDING CAMERA LENS
1. An illumination system, comprising:
- a light guide;
a first light emitting diode (LED) encapsulated in the light guide and configured to emit light into the light guide; and
a light extraction feature configured to direct at least a portion of the emitted light out of the light guide.
A flash system for an electronic device includes a ring-shaped light guide having a central opening. A camera lens is positioned in or behind the opening. A first light emitting diode (“LED”) is mounted on a printed circuit board (“PCB”), and the LED and PCB are encapsulated by a molded light guide of the flash system. An identical LED and PCB are encapsulated at an opposite end of the molded light guide (i.e., 180 degrees away). The back surfaces of each PCB diffusively reflects light from the LED on the other PCB. Light extraction features on the light guide surface uniformly leak out light from the LEDs. The light emission profile of the light guide has a peak axially aligned with the central opening of the light guide and rolls off to the edge of the camera'"'"'s field of view.
- 1. An illumination system, comprising:
a light guide; a first light emitting diode (LED) encapsulated in the light guide and configured to emit light into the light guide; and a light extraction feature configured to direct at least a portion of the emitted light out of the light guide.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
- 16. A method for providing illumination, the method comprising:
emitting, with a first light-emitting diode (LED) encapsulated in a light guide, light into the light guide; and extracting, with a light extraction feature positioned on the light guide, at least a portion of the emitted light out of the light guide.
- View Dependent Claims (17, 18)
- 19. An illumination system, comprising:
a light guide configured to guide light along a closed path loop, the light guide shaped to guide light in a first direction in the light guide; a first light-emitting diode (LED) encapsulated in the light guide and configured to emit light into the light guide in the first direction; a second LED encapsulated in the light guide and configured to emit light into the light guide in the first direction; and
- View Dependent Claims (20)
This application is a continuation of U.S. patent application Ser. No. 15/496,892, filed Apr. 25, 2017, which claims the benefit of U.S. Provisional Application No. 62/327,628 filed on Apr. 26, 2016, the content of which is hereby incorporated by reference herein as if fully set forth.
This disclosure relates to camera flashes that incorporate light emitting diodes (LEDs) and, in particular, to a ring-shaped camera flash that surrounds the lens of a camera.
Cameras are prevalent in smartphones and other electronic devices that are relatively compact. The flash for the camera is typically formed of one or two phosphor-converted, white-light light emitting diodes (“LEDs”). The total combined area of the LEDs typically determines the instantaneous brightness of the flash for a given driving current pulse. The bare LED die is GaN-based and emits blue light, and the phosphor (typically YAG) adds a yellow component (or red and green components). The combination of the blue light leaking through the phosphor and the light provided by the phosphor itself creates the bright white light for the flash.
The camera flash typically uses a tiny Fresnel lens or other type of molded plastic lens to collimate the light in an attempt to direct most of the light at the subject in the field of view of the camera. The flash lenses are typically small, and the LED is off to one side of the camera lens. Due to the difficulties in designing small flash units, the lighting quality produced by LED flash units is typically low. Improvements in LED flashes for small cameras are needed.
In one embodiment, a white-light LED is mounted near an end of a Metal Core Printed Circuit Board (MCPCB) in an LED assembly. Two such LED assemblies are molded into a ring-shaped light guide, the LED assemblies being 180 degrees apart within the light guide. Since the light guide material (e.g., transparent acrylic, poly(methyl methacrylate) (“PMMA”), etc.) directly encapsulates the LEDs and MCPCB, there is very good optical coupling of the LEDs to the light guide material. A small camera lens of a smartphone is positioned in or behind a center opening of the light guide. The top surface of the light guide has optical features for extracting the injected light, such as a roughened surface, prisms, and the like.
The light emitted from the two LEDs is reflected off the smooth side and bottom surfaces of the light guide by total internal reflection (“TIR”) until the light impinges on the top surface of the light guide, where the light exits. Light from one LED assembly that reaches the reflective surface of the opposite LED assembly is diffusively reflected back within the light guide. The optical features on the surface of the light guide may be tailored to uniformly leak out the light. In various embodiments, the LEDs are top-emitting LEDs or are side-emitting LEDs. The portions of the MCPCBs that protrude out from the light guide act as air-cooled heat sinks. Heat sinking is important where the LED is steadily turned on, such as for video or being used as a flash light.
Benefits of the disclosed LED light guide include production of a desired light emission profile, where light is symmetrically emitted around the camera lens, has a peak emission axially aligned with the camera lens, and rolls off toward the edges of the camera'"'"'s field of view.
Additional features and embodiments are described herein.
Elements that are the same or similar are labeled with the same numeral.
The LED 10 is mounted on a printed circuit board (“PCB”) such as a metal core printed circuit board (“MCPCB”) 24 having an insulating layer 26 and a metal pattern 28 for connecting a flash power supply to the contacts 14/16. The MCPCB 24 has a white (diffusively reflective) back surface formed by a reflective layer 30 that, in some embodiments, comprises white diffusing particles, such as TiO2. The front surface of the MCPCB 24 (opposite the back reflective surface 30) may also be coated with the reflective layer. In one embodiment, the LED 10 is about 1 mm wide or less, and the MCPCB 24 is about 1-2 mm wide so that the portion of the MCPCB 24 supporting the LED 10 can be encapsulated in a thin, acrylic ring-shaped light guide. The LED 10 is “top-emitting” because light is emitted out of the top of the LED 10 (in the “up” direction in
Two of the front-emitting LEDs 10 from
One end of the MCPCB 24 extends out from the light guide 38, and its contact pads are electrically connected to an LED flash controller 52 on another circuit board, forming part of the flash module. The LED flash controller 52 is configured to control the LED 10 brightness and illumination time in for various uses such as when generating a brief pulse for use as a camera flash or for a longer duration when used, for example, as a flashlight. The ends of the MCPCBs 24 that extend beyond the light guide 38 also sink heat away from the LEDs 10.
As shown in
Also shown in
The light guide 38 may be 1-3 mm thick to encapsulate the LED and MCPCB and sufficiently mix the light. A larger light guide 38 improves light emission uniformity around the ring. Since the height of a side emitting LED may be less than the width of the MCPCB, the thickness of the light guide 38 in
Besides the functional advantage of the ring-shaped flash, the unaesthetic yellow phosphor typically present in white color LEDs is less visible since the LEDs are mounted sideways in the light guide 38 (
While particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this disclosure in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this disclosure.