Patent Application
20060285332
Current Light Emitting Diode (“LED”) packages have a general wide or narrow field of view (“FOV”). To achieve this currently, a lens is used to collimate the light from the light source/die. This normally adds additional height and area to the LED package. Current problems include an undesirable dome shape caused by an optical lens since a flat-sided and oblong shape is preferred for manufacturability and pick-and-place setups. Additionally, use of an optical lens adds height and size to the overall package thickness.
Increased height and size are marked problems for big chip LED's, for example, a 1 watt LED of 0.9 mm×0.9 mm, as big chip LED's require big lenses to collimate the emitted light for increased brightness. Increased brightness results from decreasing the FOV of the LED, but with a taller package. Similarly, in a smaller LED package of 1-2 mm but with space restraints on the packaging, an LED with a lens presents design problems due to the lens height. If a reflector cup is used, be it a punched cup or a drilled cup, additional space is required.
What is needed is a way to increase brightness of a LED package with a smaller size.
One aspect of the present invention provides a light emitting diode system including a housing including a light emission opening and a light emitting diode disposed within the housing. A first film layer covers the light emission opening and includes a uniaxial collimating film configured to direct light from the light emitting diode along a first axis.
Another aspect of the present invention provides a method of collimating light. The method includes receiving light in a first collimating layer and directing a first portion of the received light through a second collimating layer along a first axis.
Another aspect of the present invention provides a system for collimating light. The system includes means for receiving light in a first collimating layer.
In one embodiment, base 215 includes a mirror-finish layer attached to the housing 205, such that light emitting diode 210 rests upon the mirror-finish layer. A mirror-finish layer is any reflective surface, such as a mirror or other similarly reflective surface. In one embodiment, the mirror-finish layer includes a grooved surface configured to direct incoming light toward a first and second film layer 230, 240 covering the light emission opening 208.
Light emitting diode 210 emits light 220 at a plurality of angles. The light 220 is then refracted by the first and second film layers 230, 240. θ illustrates the critical angle associated with Snell's law: if the angle of the light entering a medium, such as first film layer 230, is greater than θ, then the light has total internal reflection (“TIR”); and if the angle is less than θ, the light is refracted. Additionally, Snell's law posits that if medium A is denser than medium B, light traveling from A into B is focused closer to the normal of the plane between medium A and medium B.
A first and second film layer 230, 240 is disposed over at least a portion of the opening of the housing 205 and the light emission opening 208. In one embodiment, the first and second film layers cover the entire opening, while in other embodiments, the first and second film layers cover only a portion of the opening. In embodiments wherein the first and second film layers cover only a portion of the opening, the first and second film layers may cover the same portion, or at least partially different portions of the opening. The first and second film layers 230, 240 include a uniaxial collimating film configured to direct light emitted from the light emitting diode 210 along a first and second axis, respectively. Thus, light received by the first film layer 230 is directed along a first axis, while light received by the second film layer 240 can be directed along a second axis. The second axis is offset from the first axis. In one embodiment, the first axis is the x-axis, and the second axis is the y-axis. In one embodiment, the uniaxial collimating film is attached to the light emission opening 208. The uniaxial collimating film may be attached to the light emission opening 208 using any appropriate technique, such as a transparent adhesive or optical gel.
In one embodiment, the uniaxial collimating film is implemented as Vikuiti Brightness Enhancement Film (BEF) III-10 T, available from 3M of St. Paul, Minn. In one embodiment, the uniaxial collimating film comprises a transmissive film with a grooved surface. For example, the grooved surface features prismatic properties in certain embodiments. It is preferred that the film is configured to concentrate approximately 40 to approximately 70 percent of the light generated by the light emitting diode to a center, although other configurations are anticipated. It is further preferred that the film is configured to resist deforming on exposure to environmental factors. Environmental factors include, without limitation, heat, cold, dust, and humidity. Maintaining the film in a clean and debris-free state helps to maximize light extraction, and brightness of the emitted light.
Collimating the light in this fashion helps to reduce the FOV of the light emitting diode, and maximize the brightness within the effective FOV.
Light beam 583 is illustrated entering one portion of the first film layer, and being refracted to re-enter the first film layer at a different location. Such refraction will tend to increase light emitted in the desired direction, as a greater portion of the light being emitted will refract at desirable angles, minimizing light loss. For example, upon re-entering the first film layer, light beam 583 may be refracted in a desirable direction (depending on the angle), or light beam 583 may be refracted toward a reflective surface that supports the light emitting diode, or another reflective surface. Other times, even after the refraction, light beam 583 may result in a lost light beam, but at least some light beams 583 will be collimated toward the desired direction.
Reflector 695 is any surface configured to reflect a substantial portion of incident light. In one embodiment, reflector 695 is a mirror. In another embodiment, reflector 695 is a mirror-finish layer. In yet another embodiment, reflector 695 comprises a grooved surface. In one embodiment, reflector 695 is a sloped reflector. In one embodiment, reflector 695 is a flat surface disposed along a lower surface 601 of the housing 205. In another embodiment, reflector 695 features a smaller opening at the bottom and a larger opening at the top 602, with a sloped surface connecting the bottom and top, termed a “sloped reflector.” In yet another embodiment, reflector 695 is a cup, either drilled or punched, into the housing.
A first portion of the received light is directed through a second collimating layer along a first axis at step 720. In one embodiment, the second collimating layer is implemented as second film layer 240. The second collimating layer receives the light refracted by the first collimating layer and directs at least a portion of the light away from the source of the light.
A second portion of the received light is directed through the second collimating layer along a second axis offset from the first axis at step 730. In one embodiment, the first axis is the x-axis. In one embodiment, the second axis is the y-axis. In other embodiments, other axes are chosen for the first and second axis, such as an embodiment where it is desirable to collimate light off-angle from the light emitting diode emitting the light. Directing the received light through the first and second collimating layers collimates the light, increasing the brightness of the light emitted from the light emitting diode as perceived by a viewer.
A third portion of the received light is directed toward a reflective surface at step 840. In one embodiment, the third portion of the received light is reflected back toward the housing. For example, the third portion of the received light is reflected toward the mirror-surface layer in one embodiment. In another embodiment, the third portion of the received light is reflected toward a grooved surface.
In one embodiment, receiving light in the first collimating layer includes generating light. In another embodiment, directing the first portion of the received light includes transmitting the received light when the received light has a predetermined angle. In another embodiment, directing the second portion of the received light includes reflecting the received light when the received light does not have the predetermined angle.
Light is reflected from a mirror-surface layer toward the first and second collimating layers at step 940. In one embodiment, the mirror-surface layer is a flat surface supporting the light emitting diode. In another embodiment, the mirror-surface layer is sloped. In yet another embodiment, the mirror-surface layer is a cup supporting the light emitting diode.
The directed light is diffused with at least one of a liner and a light guide at step 1040. The liner and/or light guide may be placed between the light emitting diode and the first collimating layer, between the first and second collimating layers, or outside the light emitting diode package.
Directing light through the first and second collimating layers, as described with respect to methods 700, 800, 900 and 1000, results in collimating the light received by the first and second collimating layers. Such collimation optimally results in a reduced FOV for a light source directing light beams toward the first and second collimating layers, and an increased effective brightness based on the reduced FOV.
While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the scope of the invention. The scope of the invention is indicated in the appended claims and all changes that come within the meaning and range of equivalents are intended to be embraced therein.
