Lens and LED using the lens to achieve homogeneous illumination

#1. Field of Invention

#The invention relates to a lens and a light-emitting diode (LED) using the lens for illumination systems and, in particular, to an LED with homogeneous illumination.

#2. Related Art

#The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

#The invention will become more fully understood from the detailed description given hereinbelow illustration only, and thus are not limitative of the present invention, and wherein:

#FIG. 1A is a schematic view of a conventional LED and its light-emitting style.

#In observation of the fact that the conventional LED usually has stronger light intensity around its optical axis, the disclosed lens and the LED using the disclosed lens diverge light in the vicinity of the optical axis. The first embodiment of the invention is shown in FIGS. 2 and 3. It contains a substrate 21, an LED chip 22, and a lens 23. The LED chip 22 is installed on the substrate 21 and has an optical axis 24. The lens 23 is connected to the substrate 21 by packaging to cover the LED chip 22. On the surface of the lens 23 and in the vicinity of the optical axis 24 is formed with a concave part as a divergent surface 25. The divergent surface 25 is surrounded by a convergent surface 26 with the optical axis 24 as a center. The divergent surface 25 is recessed towards the optical axis 24. The height difference from the divergent surface 25 to the bottom of the LED chip 22 increases from the optical axis outwards. The height difference from the convergent surface 26 to the bottom of the LED chip 22 decreases from the maximum outward. The upper action surface of the lens 23 is a continuous curved surface. The action surface referred herein means the surface above the lens 23 for the light emitted by the LED chip 22 to deflect. With this action surface, one is able to obtain a large-area and homogeneous beam of light. Therefore, the action surface does not necessarily mean the whole upper surface of the lens 23. It can be only a part of the upper surface. The size of the action surface is determined by the width and height of the lens 23, and type of the LED chip 22. The light emitted by the LED chip 22 and going through the divergent surface 25 is deflected away from the optical axis 24, whereas the light emitted by the LED chip 22 and going through the convergent surface 26 is deflected toward the optical axis 24. Therefore, the light intensity within a certain range becomes more homogeneous. The light intensity distribution is shown in FIG. 3. As one can see, the maximum intensity region is shifted outward away from the optical axis 24. The overall light-emitting region is larger and more homogeneous. In particular, the distance to the maximum light intensity region can be adjusted according to the distance d1 from the highest point on the surface of the lens 23 to the optical axis 24 and the height difference d2 from the lowest point of the divergent surface 25 to the highest point. A common design is that the lens 23 is a cylinder symmetric about the optical axis 24. Therefore, the intersection between the divergent surface 25 and the optical axis 24 is the lowest point. The distance d1 and the height difference d2 can be adjusted according to the refractive index, temperature coefficient, thickness, and height of the lens, the LED chip, and the desired homogeneous light-emitting area.

#Since the divergent surface 25 is used to diverge the light near the optical axis 24, it is preferably to use a concave surface. However, it can be a mixture of concave and convex surfaces. The convergent surface 26 is used to converge light with large emission angles. Therefore, it is preferably to be a convex surface. As shown in FIG. 4, when projecting light on a screen 70 at a distance of H, the disclosed LED 20 has a larger and more homogeneous light-emitting range, in comparison with the conventional LED 10.

#With reference to FIGS. 9A and 9B, one sees that the homogeneous light-emitting area is about 33 mm from the optical axis according to the first experimental data set. The LED chip has a distance of 30 mm. Therefore, we obtain a subtending angle of 47.7 degrees. Likewise, the subtending angle in FIGS. 10A and 10B is 53.8 degrees, that in FIGS. 11A and 11B is 67.4 degrees, and that in FIGS. 12A and 12B is 72.3 degrees. We therefore see that the subtending angle is enlarged to 45 to 75 degrees using the invention.