Abstract:
A hallow light tube for LED lighting comprises an inner surface, an outer surface and at least one end surface. At least one LED is placed on at least one end surface to provide edge illumination. The rays emitting from edge LEDs are fed into the light tube along the longitudinal directions. The inner surface and the outer surface can be aligned in different ways to meet different lighting requirements. The inner, outer and end surfaces can be textured. The texture includes a smooth surface, a diffusive surface, a surface with micro structures, a surface with gratings, a surface with grooves, a random scattering surface, and a surface of photonics crystal.

Description:
BACKGROUND 
       [0001]    The description relates to LED light tubes. 
         [0002]    In some examples, the replacement of fluoresce light tube with light source of LEDs mainly uses an array of LED chips lining up along the axial direction of the light tube. In order to reach the uniformity of lighting intensities, a diffusive transmission cover is placed on the light tube to produce smooth illumination. One of the drawbacks of such a design is that the diffusive cover will cause a significant back reflection light inside the tube such that the power of transmission light is often less than 85% of the original illuminating power. 
         [0003]    In the present invention, a design of light tube featuring side illumination with LEDs will, first simplify the light tube structure and, second improve the transmission efficiency to save more lighting power. 
       SUMMARY 
       [0004]    One object of this invention is to provide a LED light tube, wherein the light emitting from LEDs is diffracted and reflected through a hollow light tube into free space. The intensity distributions in the free space get smoothed and broadened by multiple diffractions and reflections inside the light tube. 
         [0005]    In one aspect, a LED light tube includes a hollow tube and at least one LED. The hollow tube includes an inner surface, an outer surface, a first end surface and a second end surface. The inner surface encloses a hollow region. The outer surface encloses the inner surface coaxially along the longitudinal direction of the tube. The first end surface connects the inner and outer surfaces. The second end surface opposite to the first surface connects the inner and outer surfaces. The LED is placed on the first end surface of the light tube, wherein the LED emits light into a region between the inner and outer surfaces. 
         [0006]    In one embodiment, the inner and outer surfaces of the light tube contain unsmooth surface structures. 
         [0007]    In one embodiment, the first and second end surfaces of the light tube contain unsmooth surface structure. 
         [0008]    In one embodiment, a radial distance between the inner and outer surfaces of the light tube is a spatial function along the axis of the light tube. 
         [0009]    In one embodiment, the shapes of the inner and outer surfaces of the light tube are two surface functions along the axis of the light tube. 
         [0010]    In one embodiment, at least one, LED is attached to the first end surface that connects the inner and outer surfaces of the light tube to provide edge illumination. 
         [0011]    In another aspect, a LED light tube includes a hollow tube and at least one LED. The hollow tube includes an inner surface, an outer surface, and an end surface. The inner surface encloses a hollow region. The outer region encloses the inner surface coaxially along the longitudinal direction of the tube. The end surface connects the inner and outer surfaces. The LED is placed on the end surface of the light tube, wherein the LED emits light into a region between the inner and outer surfaces and, or into the hallow region enclosed by the inner surface. 
         [0012]    In one embodiment, the inner surface is tapered along the longitudinal direction and the outer surface extends straightly along the longitudinal direction toward the end of the tube where the inner surface and outer surface intersect to form an inclination angle of the inner surface from the outer surface on a plane containing the axis. 
         [0013]    Advantage of the present light tube is to provide omnidirectional illumination around an axis of a long tube with attached LEDs as side emitting light sources. The configuration of the light tube is simple and can be easily fabricated. Further objects and advantages of this invention will be apparent from the following detailed description with accompanied drawings. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0014]      FIG. 1  is one example of light tube with one edge illumination. 
           [0015]      FIG. 2  is the cross-section view of light tube in  FIG. 1 . 
           [0016]      FIG. 3  illustrates the light propagation of the light tube in  FIG. 1 . 
           [0017]      FIG. 4  is one example of light tube with two edge illuminations. 
           [0018]      FIG. 5  is one example of non-parallel light tube. 
           [0019]      FIG. 6  is one example of unsmooth inner and outer surfaces of a light tube. 
           [0020]      FIG. 7  is one example of light tube with two edge illuminations. 
           [0021]      FIG. 8  is one example of tapered light tube. 
           [0022]      FIG. 9  is one example of light tube with one edge illumination. 
           [0023]      FIG. 10  is another example of light tube with one edge illumination 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  shows one example of a hollow light tube  100  with one edge illumination. This light tube  100  has inner surface  102 , outer surface  104 , end surface  106  and end surface  108 . The end surfaces  106  and  108  are bounded by the inner and outer surfaces  102  and  104 . The inner and outer surfaces  102 ,  104  and two end surfaces  106 ,  108  enclose a cylindrical region  110 . The inner surface  102  encloses a hollow region  112  with a light tube axis  113 . A set of several LEDs  200 ,  202 ,  204 ,  206  are placed on the end surface  106  for one edge illumination.  FIG. 2  shows the cross-sectional view of light tube  100 , the end surface  106  bounded by the inner surface  102  and outer surface  104  for one edge illumination. 
         [0025]    As shown in  FIG. 1  and  FIG. 2 , a distance  115  between the inner surface  102  and the outer surface  104  measured radially from the axis  113 , which can vary along the axial direction, is a spatial function selected from a group of geometric functions consisting of a straight line, a slant line, a curve, a parabola, a saw-like function, a sinusoidal function, a wave-like function, a repetitive triangular bump function, a repetitive round bump function, a repetitive square bump function, or any combination thereof. In this embodiment, the distance  115  is, including but not limited to, a constant spatial function along the axis  113 . 
         [0026]    The inner surface  102  may include a first shell of a material corresponding to a material of plastics, a glass, a metal, or a material with index of refraction greater than 1. Each of the outer surface  104  and the end surfaces  106  and  108  includes a second shell of a transparent material corresponding to a material of plastics, a glass, or a material with index of refraction greater than 1. 
         [0027]    The bounded region  110  between the inner surface  102 , the outer surface  104 , the end surface  106  and the end surface  108  includes a transparent material corresponding to air, a glass, a plastics, a liquid, or a material with index of refraction greater than 1. The shape of the cross-section of the inner surface  102  is selected from a group consisting of a circle, an ellipse, a triangle, a square, a pentagon and a polygon. The shape of the cross-section of the outer surface  104  is selected from a group consisting of a circle, an ellipse, a triangle, a square, a pentagon and a polygon. Each of the inner surface  102 , the outer surface  104 , and the end surface  108  has a texture corresponding to a smooth structure, a diffusive structure, a grating structure, a grooving structure, a structure of random gratings, an irregular grooving structure, a random scattering structure, a photonics crystal structure, a periodic structure, a non-periodic structure, or any combination thereof. The end surface  106  may also have a texture corresponding to a smooth structure, a diffusive structure, a grating structure, a grooving structure, a structure of random gratings, an irregular grooving structure, a random scattering structure, a photonics crystal structure, a periodic structure, a non-periodic structure, a reflective structure, or any combination thereof. 
         [0028]      FIG. 3  illustrates the working principle of light tube  100 . In this illustration, for example, the LED  200  emits ray  300  in the region  110  and subsequently hits the unsmooth inner surface  102 . Part of the ray  300  becomes the reflected the ray  302  and part of the ray  300  becomes the transmitted the ray  306  in the region  112 . The ray  302  propagates outward to the unsmooth outer surface  104  and transmits rays  304  into the air. The ray  306  propagates in the hollow region  112  to the unsmooth inner surface  102  and transmits the ray  308  in the region  110 . The ray  308  propagates outward to the unsmooth outer surface  104  and transmits the rays  310  in the air. Because of the nature of the unsmooth surfaces  102  and  104 , the ray  304  and  310  exhibit the property of diffusive light. Therefore, the outgoing rays  304  and  310  have wide and uniform distribution of light intensity in the air. On the other hand, ray  312  emitting from LED  116  hits the unsmooth end surface  108  and transmits the rays  314  into the air. The rays  314  possess the same property of diffusive light. The rays  304  and  310  here are considered as side illumination, as contributed from the side surface  104 . The rays  314  here are considered as forward illumination, as contributed from the end surface  108  with attached LEDs  200 ,  202 ,  204 ,  206  shining in the forward direction. 
         [0029]      FIG. 4  shows one example of a hollow light tube  400  with two edges illumination. The inner surface  402 , outer surface  404 , end surface  406  and end surface  408  constitute the light tube  400 . The inner surface  402  encloses a hallow region  412 . This example of light tube  400  with two edge light sources, the set LEDs  500  placed on the end surface  406  and the set LEDs  502  placed on the end surface  408 , provide the light tube  400  for side illumination in the free space. The working principle is similar to the light tube  100  except the part of forward illumination from the end surface  108 . One example of the light propagation is that ray  600  emitting from LED  504  hits the inner surface  402 , reflects the ray  602  outward and transmits the ray  604  inward. The ray  602  passes through the outer unsmooth surface  404  and becomes the rays  606  in the air. The ray  604  propagates inside the region  412 , passes through the inner unsmooth surface  402  and becomes ray  608  in the region  410 . The ray  608  then passes through outer unsmooth surface  404  and becomes the rays  610  in the air. In another example, the side illumination contributed from the LEDs set  502  placed on the end surface  408  follows the same manner. Ray  612  emitting from one LED  506 , part of ray  612  becomes the reflected ray  614 , and part of ray  612  becomes the transmitted rays  616  in the air. The ray  614  then subsequently becomes the transmitted rays  618 ,  620 , finally  622  in the air. The rays  606 ,  610 ,  616  and  622  are the examples of the side illumination light emitting from the light tube  400 . 
         [0030]    To have wide illumination distributed in certain free space, the inner and the outer surfaces of light tube can be designed in different configurations. One example is illustrated in  FIG. 5 . The light tube  700  has a tapered structure of inner surface  702  and a straight outer surface  704  along the longitudinal direction and one end surface  706  with a set of LEDs  800 . The inner surface  702  and the end surface  706  enclose a hollow region  708  with an axis  709 . The inclination angle a  710  of the inner surface  702  from the outer surface  704  on a plane containing the axis  709  is determined to enhance the backward illumination. That is, a distance  707  between the inner surface  702  and the outer surface  704  measured radially from the axis  709  of the light tube  700  is, including but not limited to, a linear function along the axis  709  of the light tube  700  in this example. As an illustration, the ray  900  emitting from the LED  802  hits the inner surface  702  and reflects the ray  902  backward to the outer surface  704 . The backward ray  902  becomes the diffusive rays  904  in the air. In the design of light tube  700 , the inclination angle a  710  will cause some light, like ray  906 , to have total internal reflection such that the reflected ray  908  has identical intensity of ray  906  without loss to enhance the outward side illumination. The LED  804  is placed at the center of the end surface  706  to provide the complimentary illumination in the forward direction like the ray  910 . 
         [0031]    Unsmooth surface structure can reflect or transmit light with diffusive property because of diffraction or random propagation of light. This is one of the working principles of the present invention of light tube for wide illumination.  FIG. 6  illustrates one example of unsmooth inner surface  1002  and outer surface  1004  of a light tube  1000  with one edge LEDs  2000  placed on one end surface  1006 . A hollow region  1010  is enclosed by the inner surface  1002 . The inner, outer and end surfaces  1002 ,  1004 ,  1006  and  1008  bound a region  1012 . One end surface  1008  with uneven texture  1014  is for forward diffusive illumination. Ray  3000  emitting from the LED  2002  will mainly first propagate in the region  1012  between the inner surface  1002  and outer surface  1004 . The saw-like inner surface  1002  will diffract ray  3000  in the region  1012  and becomes ray  3002  to have much more light scattered in the transverse direction to enhance side illumination. When part of ray  3000  and ray  3002  are diffracted to the outer surface of rings of micro-lens  1004 , the outgoing rays  3004  will be diverged to wide region in the air. 
         [0032]      FIG. 7  shows an example of different configuration of LEDs  5000  and  5002  that are attached to a light tube  4000 . Similar to the previous examples, there are inner surface  4002 , outer surface  4004 , two end surfaces  4006 ,  4008  constituting the light tube  4000 . The inner surface  4002  encloses a hollow region  4010 . Two rings of LEDs  5000  and  5002  are placed on the end surfaces  4006  and  4008  respectively for edge illuminations. The material in region  4012  bounded by the surfaces  4002 ,  4004 ,  4006  and  4008  can be chosen from a lot substances. For example, we can use plastics like PMMA or PC, or a liquid with the index of refraction greater than 1 to make the region  4012 . In the easiest way, we can use plastic material PC to make the whole tube, i.e., the surfaces  4002 ,  4004 ,  4006 ,  4008  and the region  4012  are all made of PC. 
         [0033]      FIG. 8  shows another example similar to light tube  700  in the  FIG. 5 . In  FIG. 8 , light tube  6000  is constituted by inner surface  6002 , outer surface  6004  and end surface  6006 . End surface  6006  is a round area that has the same diameter  6007  of the outer surface  6004 . The inner surface  6002  includes a cylindrical tapered structure  60021  and a bottom circular area  60022  of diameter  6011 , together enclosing a hollow region  6008  with an axis  6009 . The inner surface  6002  has a tapered structure  60021  with an inclination angle a  6010  from the outer surface  6004  on a plane containing an axis  6009 . The substance in the region  6012  bounded by the inner surface  6002 , outer surface  6004  and end surface  6006  is a material with the index of refraction greater than 1. A round LED chip  7000  is placed on the end surface  6006 , which is larger than the bottom area  60022  of the inner surface  6002 . Part of the ray  8000  emitting from LED  7000  hits the inner surface  6002  and becomes the reflected ray  8002  and later becomes the transmitted ray  8004  in the air to provide side illumination. Part of the ray  8006  emitting from LED  7000  propagates directly into the hollow region  6008  to provide forward illumination. 
         [0034]      FIG. 9  shows another example of a light tube  9000 . Similar to the example in  FIG. 7 , there are inner surface  9002 , outer surface  9004 , two end surfaces  9006 ,  9008  constituting the light tube  9000 . One ring of LEDs  9100  and one reflector  9101  are placed on the end surfaces  9006  and  9008  respectively for edge illuminations. Ray  9200  emitting from ring LED  9100  incidents into region  9012  bounded by the surfaces  9002 ,  9004 ,  9006  and  9008 . Ray  9200  hits the inner surface  9002  and becomes ray  9201 . Ray  9201  hits reflector  9101  and reflects the ray  9202 . Ray  9202  hits surface  9004  and becomes the transmitted ray  9203  in the air. This design of light tube  9000  with reflector  9101  consider to use only one high power LED ring  9100  to provide enough edge illumination instead of using two LED rings  5000  and  5002  as in  FIG. 7 , to simplify the light tube structure. 
         [0035]      FIG. 10  shows another example of a light tube  10 . An inner surface  12 , an outer surface  14  and one end surface  16  constitute the light tube  10 . The inner surface  12 , outer surface  14  and end surface  16  bound a region  20 , which is made of a transparent material with refractive index greater than 1. The inner surface  12  is a parabolic surface symmetric about a tube axis  17  and encloses a hollow region  18 . A round LED chip  30  is placed on the end surface  16 . Ray  40  emitting from LED  30  provides side illumination and Ray  42  emitting from LED  30  provides forward illumination. The design of light tube  10  illustrates another application in this invention, for example, that the light tube  10  can be used in the field of down lighting. 
         [0036]    It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims.