Directional light source

Abstract

At least one embodiment in the disclosure describes a high efficiency directional light engine. The light engine comprises a light emitter emitting light and a collimation lens. The collimation lens has a cone-shaped sidewall, a base surface and a curved top surface. The height of the cone-shaped sidewall is at least three times more than the diameter of the base surface. The light emitter is optically coupled to and disposed in close proximity to the base surface. One or more first reflection images of the light emitter result from first reflection of the light off a surface of the cone-shaped sidewall. The diameter of the light emitter is substantially close to the diameter of the base surface so that the light emitter and the first reflection images form a virtual point light source with minimal gap(s) or without any gap between the light emitter and the first reflection images.

What is claimed is: 
     
         1 . A method for output directional light, comprising:
 emitting a light from a light emitter;   reflecting at least a portion of the light by a cone-shaped mirror, wherein the cone-shaped mirror has a top opening and a base opening, the cone-shaped mirror further has a reflective inside surface and an axis passing through a center of the base opening and a center of the top opening, and the intersection of any plane containing the axis and the reflective inside surface of the cone-shaped mirror has a profile with a constant slope; and   adjusting an optical beam divergence angle of the light by a focusing optical device placed at a top opening of the cone-shaped mirror, wherein the focusing optical device is large enough so that substantially all light exiting from the top opening of the cone-shaped mirror reaches the focusing optical device, and wherein a focal point of the focusing optical device is in close proximity of a base opening of the cone-shaped mirror.   
     
     
         2 . The method of  claim 1 , wherein the cone-shaped mirror has a half-cone angle of at least 30 degrees. 
     
     
         3 . The method of  claim 1 , wherein the cone-shaped mirror has a height at least three times more than a diameter of the base opening. 
     
     
         4 . The method of  claim 1 , wherein the cone-shaped mirror has a horizontal cross-section with a circular shape or a polygonal shape or an oval shape or a rectangular shape or a triangular shape. 
     
     
         5 . The method of  claim 1 , wherein the focusing optical device is configured so that light emitted from the focusing optical device has a beam angle of less than 15 degrees. 
     
     
         6 . A light emitting device, comprising:
 a light emitter;   a cone-shaped mirror having a top opening and a base opening, wherein the cone-shaped mirror further has a reflective inside surface and an axis passing through a center of the base opening and a center of the top opening, and the intersection of any plane containing the axis and the reflective inside surface of the cone-shaped mirror has a profile with a constant slope, and wherein a height of the cone-shaped mirror is at least three times more than a diameter of the base opening; and   a focusing optical device placed at the top opening of the cone-shaped mirror, wherein the focusing optical device is large enough so that substantially all light exiting from the top opening of the cone-shaped mirror reaches the focusing optical device, and wherein a focal point of the focusing optical device is in close proximity of the base opening of the cone-shaped mirror;   wherein the light emitter occupies a substantial portion of the base opening so that the light emitter and the first reflection images form a virtual point light source with minimal gap(s) between the light emitter and the first reflection images.   
     
     
         7 . The light emitting device of  claim 6 , wherein the cone-shaped mirror has a half-cone angle of at least 30 degrees. 
     
     
         8 . The light emitting device of  claim 6 , wherein the light emitter includes at least one light emitting diode (LED). 
     
     
         9 . The light emitting device of  claim 6 , wherein the cone-shaped mirror has a half-cone angle of less than or equal to 45 degrees. 
     
     
         10 . The light emitting device of  claim 6 , wherein the cone-shaped mirror has a top opening with a shape different than the bottom opening shape. 
     
     
         11 . The light emitting device of  claim 6 , wherein the cone-shaped mirror has a horizontal cross-section with a circular shape or a polygonal shape or an oval shape or a rectangular shape or a triangular shape. 
     
     
         12 . The light emitting device of  claim 6 , wherein the focusing optical device has a focus in close proximity of the light emitter. 
     
     
         13 . The light emitting device of  claim 6 , wherein the smallest possible beam angle of the light engine θ beam  is determined by
   θ beam =2×tan −1   [H ′(2 s ′)]=2×tan −1   [H /(2 s )];
 
 wherein H is a diameter of the virtual point light source, s is a distance between the virtual point light source and the focusing optical device, H′ is a diameter of an image of the virtual point light source formed by light traveling through the focusing optical device, and s′ is a distance between the image of the virtual point light source and the focusing optical device. 
 
     
     
         14 . An apparatus, comprising:
 a cone-shaped mirror having a top opening and a base opening, wherein the cone-shaped mirror further has a reflective inside surface and an axis passing through a center of the base opening and a center of the top opening, and the intersection of any plane containing the axis and the reflective inside surface of the cone-shaped mirror has a profile with a constant slope; and   a focusing optical device placed at a top opening of the cone-shaped mirror, wherein the focusing optical device is large enough so that substantially all light exiting from the top opening of the cone-shaped mirror reaches the focusing optical device, and wherein a focal point of the focusing optical device is in close proximity of a base opening of the cone-shaped mirror.   
     
     
         15 . The apparatus of  claim 14 , wherein the top opening has a shape different from a shape of the bottom opening. 
     
     
         16 . The apparatus of  claim 14 , wherein the cone-shaped mirror has a horizontal cross-section with an asymmetric shape. 
     
     
         17 . The apparatus of  claim 14 , wherein the focusing optical device has a surface coated with an anti-reflection coating. 
     
     
         18 . The apparatus of  claim 14 , wherein the focusing optical device is disposed in close proximity of the top opening of the cone-shaped mirror. 
     
     
         19 . The apparatus of  claim 14 , wherein the focusing optical device is disposed at a distance from the top opening of the cone-shaped mirror. 
     
     
         20 . The apparatus of  claim 14 , wherein the focusing optical device includes a bi-convex spherical lens, a plano-convex spherical lens, a concave-convex lens, a bi-convex aspheric lens, a plano-convex aspheric lens, a Fresnel lens, a binary lens, a gradient-index lens, a spherical interface between different media, or an aspheric interface between different media. 
     
     
         21 . The apparatus of  claim 14 , wherein the cone-shaped mirror has a half-cone angle of less than or equal to 45 degrees.