Patent Publication Number: US-2015077993-A1

Title: Lighting apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-194112, filed on Sep. 19, 2013; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a lighting apparatus. 
     BACKGROUND 
     A lighting apparatus using a light emitting diode (LED) as the light source, such as a downlight and a spotlight, is in practical use. 
     The lighting apparatus using a light emitting diode as the light source has a long lifetime and allows power consumption to be reduced. 
     However, the lighting apparatus using a light emitting diode as the light source has the problem that the heat generation amount in the light source and a control unit is large. 
     Furthermore, in view of replacement with an existing incandescent lamp, halogen lamp, or the like, there is a constraint on the external dimensions. 
     Hence, it is difficult to increase the external dimensions to enhance cooling effect by natural air cooling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view for illustrating an external appearance of a lighting apparatus  1  according to the embodiment; 
         FIG. 2  is a schematic perspective view for illustrating a cross section of the lighting apparatus  1  according to the embodiment; 
         FIG. 3  is a schematic cross-sectional view for illustrating the opening area ratio and the measurement position of the flow velocity; 
         FIG. 4  is a graph for illustrating heat dissipation effect; 
         FIG. 5  is a schematic cross-sectional view for illustrating a lighting apparatus  11  according to another embodiment; 
         FIGS. 6A to 6C  are diagrams for illustrating the effect of the protrusion  13   a;    
         FIGS. 7A and 7B  are diagrams for illustrating the effect of the protrusion  13   a;    
         FIG. 8  is a schematic perspective view for illustrating a cross section of a lighting apparatus  21  according to another embodiment; and 
         FIG. 9  is a schematic perspective view for illustrating a cross section of a lighting apparatus  31  according to another embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In general, according to one embodiment, a lighting apparatus includes a plurality of light emitting units, a plurality of optical elements, a first housing, a control unit and a second housing. 
     The plurality of light emitting units includes a light emitting element. 
     The plurality of optical elements is provided individually for the plurality of light emitting units. 
     The first housing houses the plurality of light emitting units and the plurality of optical elements and having a hole penetrating between a first surface and a second surface opposing the first surface. 
     The control unit is configured to supply electric power to the plurality of light emitting units. 
     The second housing is provided on the second surface side of the first housing via a space and housing at least part of the control unit. 
     The lighting apparatus satisfies the following formula. 
         B/A≧ 0.3 
     where A is an opening area of an opening of the space facing an outside of the lighting apparatus and B is an opening area of an opening of the hole facing an outside of the lighting apparatus. 
     Hereinbelow, embodiments are illustrated with reference to the drawings. In the drawings, like components are marked with the same reference numerals, and a detailed description is omitted as appropriate. 
       FIG. 1  is a schematic view for illustrating an external appearance of a lighting apparatus  1  according to the embodiment. 
       FIG. 2  is a schematic perspective view for illustrating a cross section of the lighting apparatus  1  according to the embodiment. 
     As shown in  FIG. 1  and  FIG. 2 , the lighting apparatus  1  includes a main body  2 , a main body  3 , a connection unit  4 , a light emitting module  5 , a cover  6 , a feeder unit  7 , and a control unit  8 . 
     The main body  2  includes a housing  2   a  (corresponding to an example of a first housing), a hole  2   b , and a heat dissipation portion  2   c.    
     The planar shape of the housing  2   a  is a ring shape. 
     The cross-sectional shape of the housing  2   a  in a plane including the central axis  1   a  of the lighting apparatus  1  is a concave shape. One end of the housing  2   a  is opened. The light emitting module  5  is housed in the housing  2   a.    
     The hole  2   b  penetrates through a central portion of the housing  2   a  in the thickness direction (the direction of the central axis  1   a ). 
     That is, the hole  2   b  penetrates between a first surface  2   a   1  of the housing  2   a  and a second surface  2   a   2  opposing the first surface  2   a   1 . 
     The cross-sectional dimension of the hole  2   b  in a direction orthogonal to the central axis  1   a  of the lighting apparatus  1  in the neighborhood of an opening  2   b   2  on the side of a space  1   b  increases gradually toward the space  1   b  side. 
     Thereby, the flow of air flowing through the hole  2   b  by natural convection can be made smooth. 
     An opening  2   b   1  of the hole  2   b  facing the outside of the lighting apparatus  1  has a shape along parts of the outer edges of a plurality of optical elements  5   c . Parts of the outer edge of the opening  2   b   1  are provided on the outside of a circle inscribed in the outer edges of the plurality of optical elements  5   c , for example. When four optical elements  5   c  are provided, the planar shape of the opening  2   b   1  may be substantially a cross shape. 
     Thereby, a flow of air flowing between light emitting units  5   b  by natural convection can be formed. 
     The heat dissipation portion  2   c  includes a ring-like portion  2   c   1  and a support  2   c   2 . 
     The ring-like portion  2   c   1  is in a ring shape, and is provided so as to surround an end portion on the opening side of the housing  2   a . A space is provided between the ring-like portion  2   c   1  and the outside surface of the housing  2   a.    
     The support  2   c   2  protrudes from the outside surface of the housing  2   a.    
     The support  2   c   2  is provided in plural at prescribed intervals. 
     The plurality of supports  2   c   2  are provided radially around the central axis  1   a.    
     One end of the support  2   c   2  is connected to the ring-like portion  2   c   1 . 
     The housing  2   a , the hole  2   b , and the heat dissipation portion  2   c  may be molded integrally. 
     There are no particular limitations on the material of the housing  2   a , the hole  2   b , and the heat dissipation portion  2   c.    
     However, from the viewpoint of heat dissipation performance, the housing  2   a , the hole  2   b , and the heat dissipation portion  2   c  are preferably formed of a material with a high thermal conductivity. As the material with a high thermal conductivity, a metal such as aluminum and magnesium alloy, an inorganic material such as a ceramic (for example, aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), etc.), an organic material such as a high thermal conductivity resin, or others may be given, for example. 
     The main body  3  includes a housing  3   a  (corresponding to an example of a second housing) and a heat dissipation portion  3   b . The housing  3   a  is provided on the second surface  2   a   2  side of the housing  2   a  via the space  1   b . When the housing  2   a  and the housing  3   a  are made apart, heat dissipation performance can be improved. 
     Details of heat dissipation performance are described later. 
     An opening is provided in an end surface of the housing  3   a  on the opposite side to the side where the housing  2   a  is provided. 
     The housing  3   a  is in a box shape. At least part of the control unit  8  may be provided in the housing  3   a.    
     The length of the housing  3   a  in a direction orthogonal to the central axis  1   a  is shorter than the length of the housing  2   a  in a direction orthogonal to the central axis  1   a.    
     The heat dissipation portion  3   b  is in a plate shape, and protrudes from the outside surface of the housing  3   a.    
     The heat dissipation portion  3   b  is provided in plural at a prescribed intervals. 
     The length of the end of the heat dissipation portion  3   b  in a direction orthogonal to the central axis  1   a  (protrusion length) is longer on the main body  2  side than on the feeder unit  7  side. 
     The plurality of heat dissipation portions  3   b  are provided radially around the central axis  1   a.    
     In a planar view, each of the plurality of heat dissipation portions  3   b  is provided in a position overlapping with each of the plurality of supports  2   c   2 . 
     That is, in a planar view, the support  2   c   2  is not provided between heat dissipation portions  3   b . As described above, a space is provided between the ring-like portion  2   c   1  and the outside surface of the housing  2   a.    
     Therefore, the possibility that the flow of air flowing in the direction of the central axis  1   a  along the outside surface of the lighting apparatus  1  (the flow of air by natural convection) will be disordered is reduced. 
     There are no particular limitations on the material of the housing  3   a  and the heat dissipation portion  3   b.    
     However, from the viewpoint of heat dissipation performance, the housing  3   a  and the heat dissipation portion  3   b  are preferably formed of a material with a high thermal conductivity. The material with a high thermal conductivity may be similar to those described above, for example. 
     The connection unit  4  is in a columnar shape, and is provided between the main body  2  and the main body  3 . The connection unit  4  connects the main body  2  and the main body  3 . 
     The connection between the connection unit  4 , and the main body  2  and the main body  3  can be made using an engaging member such as a screw, or can be made using a bonging member such as an adhesive. 
     The connection unit  4  is provided in plural. There are no particular limitations on the number of connection units  4 , but it is preferable to provide three or more connection units  4 . When three or more connection units  4  are provided, the rigidity of the structure formed of the main body  2 , the main body  3 , and the connection unit  4  can be enhanced. 
     At least one of the plurality of connection units  4  is provided with a hole  4   a  penetrating in the axial direction of the connection unit  4 . An interconnection electrically connecting the light emitting module  5  and the control unit  8  can be passed through the hole  4   a  penetrating in the axial direction of the connection unit  4 . 
     That is, an interconnection electrically connecting the light emitting unit  5   b  and the control unit  8  is provided in at least one of the plurality of connection units  4 . 
     The light emitting module  5  includes a substrate  5   a , the light emitting unit  5   b , and the optical element  5   c.    
     The light emitting module  5  is provided in the housing  2   a.    
     The substrate  5   a  is in a plate shape, and its surface is provided with a not-shown interconnection pattern. 
     The planar shape of the substrate  5   a  may be a ring shape, for example. The substrate  5   a  may be provided for each of the plurality of light emitting units  5   b.    
     There are no particular limitations on the material of the substrate  5   a , but a material that is low in thermal expansion and good in heat dissipation performance and heat resistance is preferably used. The substrate  5   a  is preferably formed of a thermally conductive substrate based on a metal such as aluminum (MCPCB; metal core printed circuit board) or an inorganic material such as a ceramic, for example. 
     When the substrate  5   a  is formed of a material that is low in thermal expansion and good in heat dissipation performance and heat resistance, heat generated in the light emitting unit  5   b  can be transferred to the housing  2   a  and further to the heat dissipation portion  2   c  with good efficiency. 
     The light emitting unit  5   b  is provided in plural on the substrate  5   a . The plurality of light emitting units  5   b  are provided around the hole  2   b.    
     There are no particular limitations on the number of light emitting units  5   b , but providing three or more light emitting units  5   b  allows the direction dependence regarding light distribution to be reduced. 
     The plurality of light emitting units  5   b  may be provided in positions rotationally symmetric about the central axis  1   a , for example. 
     By arranging the plurality of light emitting units  5   b  in this way, the direction dependence regarding light distribution can be further reduced. 
     At least one light emitting element is provided in the light emitting unit  5   b.    
     The light emitting element may be a light emitting diode, a laser diode, or the like, for example. The light emitting element is mounted on the substrate  5   a . The light emitting element can be mounted by the COB (chip on board) method or the SMT (surface mount technology) method, for example. 
     The light emitting element may be covered with a resin containing a fluorescent substance to obtain a desired luminous color. 
     The optical element  5   c  is provided in plural. Each of the plurality of optical elements  5   c  is provided on each of the plurality of light emitting units  5   b . Thus, the arrangement of the plurality of optical elements  5   c  is made the same as the arrangement of the plurality of light emitting units  5   b . That is, the plurality of optical elements  5   c  may be provided in positions rotationally symmetric about the central axis  1   a.    
     The optical element  5   c  and the cover  6  may be molded integrally. 
     The optical element  5   c  controls the light distribution angle of the light applied from the light emitting unit  5   b . The optical element  5   c  may be a lens illustrated in  FIG. 2 , or a reflector, for example. When a lens is used as the optical element  5   c , the material of the optical element  5   c  may be the same as the material of the cover  6 , for example. 
     The cover  6  is in a plate shape, and covers the opening of the housing  2   a . When the opening of the housing  2   a  is covered with the cover  6 , the entry of the outside air, water, foreign substances, etc. into the housing  2   a  can be suppressed. Consequently, the degradation of the light emitting element, the interconnection pattern, etc. provided in the light emitting module  5  can be suppressed. 
     There are no particular limitations on the material of the cover  6  to the extent that it is a material having transmissivity to the light applied from the light emitting unit  5   b . However, in view of sealing performance in the housing  2   a , a material with low gas permeability is preferably used. The material of the cover  6  may be an acrylic resin or the like, for example. 
     The feeder unit  7  is in a cylindrical shape with one end opened and the other end closed. 
     The end on the opening side of the feeder unit  7  is provided at the periphery of the opening of the housing  3   a . Thus, the internal space of the feeder unit  7  is connected to the internal space of the housing  3   a.    
     The feeder unit  7  may be molded integrally with the housing  3   a.    
     Part of the control unit  8  may be provided in the feeder unit  7 . 
     A terminal  7   a  protrudes from the end on the closed side of the feeder unit  7 . The terminal  7   a  is electrically connected to the control unit  8 . 
     The feeder unit  7  has also a function as a base. For example, as illustrated in  FIG. 1  and  FIG. 2 , the feeder unit  7  may be configured to be a plug-in type base having a pin-like terminal made of a metal. As the plug-in type base, GU5.3, GU10, and the like provided in the International Electrotechnical Commission (IEC) standard may be given, for example. 
     However, the configuration of the base is not limited to those illustrated but may be altered as appropriate. 
     For example, also a screw type base such as E11 provided in the Japanese Industrial Standards (JIS) is possible. 
     A not-shown external power source etc. are electrically connected to the terminal  7   a . Thus, the control unit  8  is electrically connected to the not-shown external power source etc. via the terminal  7   a.    
     The control unit  8  includes a substrate  8   a  and various electronic parts  8   b.    
     The control unit  8  includes a lighting circuit, for example. The lighting circuit is for supplying electric power to the light emitting unit  5   b  of the light emitting module  5 . Thus, the control unit  8  can supply electric power to the light emitting unit  5   b  of the light emitting module  5 . 
     The control unit  8  may further include a light control circuit, for example. The light control circuit is for performing the light control of the light emitting unit  5   b  of the light emitting module  5 . Thus, the control unit  8  can perform also the light control of the light emitting unit  5   b  of the light emitting module  5 . 
     Next, heat dissipation performance in the lighting apparatus  1  is further illustrated. 
     In view of replacement with an existing incandescent lamp, halogen lamp, or the like, there is a constraint on the external dimensions of the lighting apparatus  1 . Hence, it is desired for the lighting apparatus  1  to increase the light emission amount (to achieve high power) while suppressing the increase in the external dimensions. 
     If it is attempted to increase the light emission amount in a state where the mounting density of electronic parts mounted in the light emitting module  5  and the control unit  8  is not changed in order to suppress the increase in the external dimensions, the heat generation density is increased. If the heat generation density is increased, the performance of the lighting apparatus  1  may be degraded or the lifetime may be shortened. For example, if the light emitting element provided in the light emitting unit  5   b  is used at a higher temperature than the standard, a decrease in light emission luminance and a decrease in lifetime will be caused. Furthermore, if the electronic parts provided in the control unit  8  are used at a higher temperature than the standard, a degradation in performance and a decrease in lifetime will be caused. 
     To suppress the increase in the external dimensions, it is necessary to shorten the distance between the light emitting module  5  and the control unit  8 . Consequently, the light emitting module  5  and the control unit  8  are affected by each other&#39;s heat, and the temperature of the light emitting module  5  and the control unit  8  is likely to be increased. 
     Thus, if it is attempted to suppress the increase in the external dimensions of the lighting apparatus  1 , the temperature of the lighting apparatus  1  is likely to be increased. 
     In this case, when heat dissipation fins in a parallel flat plate form are provided on the side surface of the lighting apparatus, heat dissipation performance can be improved. 
     However, in the heat dissipation fin in a parallel flat plate form, the direction in which air flows is mainly the direction in which the heat dissipation fin extends. Consequently, it is feared that heat dissipation effect by natural convection will become significantly poor, depending on the direction of installation of the lighting apparatus  1  etc. 
     Here, the light emitting module  5 , which is a heat generating source, is provided in the housing  2   a  of the main body  2 . The control unit  8 , which is a heat generating source, is provided in the housing  3   a  of the main body  3 . 
     In view of this, the lighting apparatus  1  according to the embodiment is configured such that the main body  2  and the main body  3  are made apart to provide the space  1   b  between the main body  2  and the main body  3 . That is, by forming a layer of air between the main body  2  and the main body  3 , the thermal interference between the light emitting module  5  and the control unit  8  is lessened. 
     Furthermore, by making the main body  2  and the main body  3  apart, the heat dissipation area can be increased. 
     The space  1   b  is opened on the lateral side of the lighting apparatus  1 . The space  1   b  and the hole  2   b  are connected together. 
     Therefore, a flow of air flowing in the direction of the central axis  1   a  of the lighting apparatus  1  and in a direction orthogonal to the central axis  1   a  can be formed. 
     That is, in the lighting apparatus  1 , heat dissipation by natural convection can be made. Consequently, it is possible to suppress the increase in the external dimensions of the lighting apparatus  1  and at the same time improve heat dissipation performance. 
     Even when the direction of installation of the lighting apparatus  1  is changed, the flow of air by natural convection in the lighting apparatus  1  can be maintained. Thus, even when the lighting apparatus  1  is installed on the ceiling, the surface of a wall, or the surface of the floor, a certain heat dissipation performance can be maintained, for example. 
     Next, heat dissipation effect in the lighting apparatus  1  according to the embodiment is illustrated. 
       FIG. 3  is a schematic cross-sectional view for illustrating the opening area ratio and the measurement position of the flow velocity. 
     As shown in  FIG. 3 , when the opening area of an opening  1   b   1  facing the outside of the space  1   b  between the main body  2  and the main body  3  is denoted by A and the opening area of the opening  2   b   1  facing the outside of the hole  2   b  of the main body  2  is denoted by B, the opening area ratio can be expressed by B/A. 
     The opening area A is the area in a direction parallel to the central axis  1   a  of the lighting apparatus  1 . 
     The opening area B is the area in a direction orthogonal to the central axis  1   a  of the lighting apparatus  1 . 
     The flow velocity S of air in the space  1   b  is defined as the flow velocity in the neighborhood of the opening  2   b   2 , which is located at the center of the space  1   b  and faces the outside. 
       FIG. 4  is a graph for illustrating heat dissipation effect. 
     T1 in  FIG. 4  is the case where the main body  2  side of the lighting apparatus  1  faces downward in the gravity direction. For example, T1 is the case where the lighting apparatus  1  is installed on the ceiling. 
     T2 is the case where the main body  2  side of the lighting apparatus  1  faces upward in the gravity direction. For example, T2 is the case where the lighting apparatus  1  is installed on the surface of the floor. 
     As can be seen from  FIG. 4 , when the opening area ratio B/A is set to 0.3 or more, the flow velocity S of air in the hole  2   b  can be made high. When the opening area ratio B/A is 0.3 or more, the flow velocity S of air in the hole  2   b  is almost constant. 
     Here, the flow of air by natural convection in the space  1   b  forms a flow of air that flows near the light emitting unit  5   b . Therefore, when the flow velocity S of air in the space  1   b  is increased, heat generated in the light emitting unit  5   b  can be dissipated with good efficiency. 
     Consequently, as shown in  FIG. 4 , the temperature of the light emitting unit  5   b  can be lowered effectively. As can be seen from T2 in  FIG. 4 , even when the direction of installation of the lighting apparatus  1  is changed, heat dissipation performance can be maintained. 
       FIG. 5  is a schematic cross-sectional view for illustrating a lighting apparatus  11  according to another embodiment. 
       FIG. 5  is the case where the central axis  11   a  of the lighting apparatus  11  is directed in a direction orthogonal to the gravity direction. For example, it is the case where the lighting apparatus  11  is installed on the surface of a wall. 
       FIG. 5  is drawn by omitting some components provided in the lighting apparatus  11  to avoid complication. 
     As shown in  FIG. 5 , the lighting apparatus  11  includes the main body  2 , a main body  13 , the connection unit  4 , the light emitting module  5 , the cover  6 , the feeder unit  7 , and the control unit  8 . 
     The main body  13  includes the housing  3   a  and the heat dissipation portion  3   b , similarly to the main body  3  described above. 
     The main body  13  further includes a protrusion  13   a  (corresponding to an example of a first protrusion). That is, the main body  13  is the case where the main body  3  described above is provided with the protrusion  13   a.    
     The protrusion  13   a  protrudes into the space  1   b.    
     The protrusion  13   a  has a shape in which the cross-sectional area in a direction orthogonal to the central axis  11   a  decreases gradually toward the main body  2  side. The protrusion  13   a  may have a shape such as a cone, a pyramid, a truncated cone, and a truncated pyramid, for example. 
     When the protrusion  13   a  having such a shape is used, a turbulent eddy can be generated in the flow of air in the space  1   b , and therefore the flow of air by natural convection from the space  1   b  toward the hole  2   b  can be strengthened. 
     Consequently, the flow velocity of air in the hole  2   b  can be increased, and thus heat generated in the light emitting unit  5   b  can be dissipated with good efficiency. 
     The cross-sectional dimension D1 in a direction orthogonal to the central axis  11   a  of the protrusion  13   a  is shorter than the cross-sectional dimension D2 in a direction orthogonal to the central axis  11   a  of the opening  2   b   2  on the space  1   b  side of the hole  2   b . When the protrusion  13   a  having such a dimension is used, the possibility that the flow of air by natural convection in the space  1   b  will be inhibited by the protrusion  13   a  is reduced. 
       FIGS. 6A to 6C  are diagrams for illustrating the effect of the protrusion  13   a.    
       FIG. 6A  is the case where the protrusion  13   a  is not provided. 
       FIG. 6B  is the case where a protrusion  130   a  having a cross-sectional dimension longer than the cross-sectional dimension of the opening  2   b   2  of the hole  2   b  is provided. 
       FIG. 6C  is the case where the protrusion  13   a  described above is provided. 
     In  FIGS. 6A to 6C , the distribution of the flow velocity of air is shown by light and shade of a monotone color. In this case, the drawings are illustrated such that the higher the flow velocity of air is, the lighter the color is; and the lower the flow velocity of air is, the darker the color is. 
       FIGS. 6A to 6C  are the case where the central axis  1   a  is directed in a direction orthogonal to the gravity direction. For example, they are the case where the lighting apparatus is installed on the surface of a wall. 
     As can be seen from  FIG. 6B , when the protrusion  130   a  having a cross-sectional dimension longer than the cross-sectional dimension of the opening  2   b   2  of the hole  2   b  is provided, the flow of air by natural convex in the space  1   b  is inhibited. 
     As can be seen from  FIGS. 6A to 6C , when the protrusion  13   a  described above is provided, the flow velocity of air in the hole  2   b  can be increased. Consequently, heat generated in the light emitting unit  5   b  can be dissipated with good efficiency. 
       FIGS. 7A and 7B  are diagrams for illustrating the effect of the protrusion  13   a.    
       FIG. 7A  is the case where the protrusion  130   a  having a cross-sectional dimension longer than the cross-sectional dimension of the opening  2   b   2  of the hole  2   b  is provided. 
       FIG. 7B  is the case where the protrusion  13   a  described above is provided. 
     In  FIGS. 7A and 7B , the distribution of the flow velocity of air is shown by light and shade of a monotone color. In this case, the drawings are illustrated such that the higher the flow velocity of air is, the lighter the color is; and the lower the flow velocity of air is, the darker the color is. 
       FIGS. 7A and 7B  are the case where the main body  2  side faces upward in the gravity direction. For example, they are the case where the lighting apparatus is installed on the surface of the floor. 
     As can be seen from  FIG. 7A , when the protrusion  130   a  having a cross-sectional dimension longer than the cross-sectional dimension of the opening  2   b   2  of the hole  2   b  is provided, the flow of air by natural convex in the space  1   b  is inhibited. 
     As can be seen from  FIG. 7B , when the protrusion  13   a  described above is provided, the flow velocity of air in the hole  2   b  can be increased. Consequently, heat generated in the light emitting unit  5   b  can be dissipated with good efficiency. 
     That is, the effect of the protrusion  13   a  can be maintained even when the direction of installation of the lighting apparatus  1  is changed. 
       FIG. 8  is a schematic perspective view for illustrating a cross section of a lighting apparatus  21  according to another embodiment. As shown in  FIG. 8 , the lighting apparatus  21  includes the main body  2 , a main body  23 , the connection unit  4 , the light emitting module  5 , the cover  6 , the feeder unit  7 , and the control unit  8 . 
     The main body  23  includes the housing  3   a  and the heat dissipation portion  3   b , similarly to the main body  3  described above. 
     The main body  23  further includes a protrusion  23   a  (corresponding to an example of a fourth protrusion). That is, the main body  23  is a structure in which the main body  3  described above is provided with the protrusion  23   a.    
     The protrusion  23   a  is in a cylindrical shape with one end closed and the other end opened. 
     The protrusion  23   a  protrudes from a surface of the housing  3   a  on the main body  2  side. The protrusion  23   a  extends through the hole  2   b  in the direction of the central axis  21   a . The end surface on the closed side of the protrusion  23   a  is flush with the surface of the cover  6 . 
     When the protrusion  23   a  is provided in the hole  2   b , a flow of air by natural convection can be formed in the hole  2   b.    
     Part of the control unit  8  is provided in the protrusion  23   a.    
     When part of the control unit  8  is provided in the protrusion  23   a , the length in the direction of the central axis  21   a  of the lighting apparatus  21  can be shortened. 
       FIG. 9  is a schematic perspective view for illustrating a cross section of a lighting apparatus  31  according to another embodiment. As shown in  FIG. 9 , the lighting apparatus  31  includes a main body  32 , a main body  33 , the connection unit  4 , the light emitting module  5 , the cover  6 , the feeder unit  7 , and the control unit  8 . 
       FIG. 9  is drawn by omitting some components provided in the lighting apparatus  31  to avoid complication. 
     The main body  32  includes the housing  2   a , the hole  2   b , and the heat dissipation portion  2   c , similarly to the main body  2  described above. 
     The main body  32  further includes a protrusion  32   a  (corresponding to an example of a third protrusion). That is, the main body  32  is a structure in which the main body  2  described above is provided with the protrusion  32   a.    
     The protrusion  32   a  protrudes from the second surface  2   a   2  of the housing  2   a  into the space  1   b.    
     The protrusion  32   a  is provided in plural. The plurality of protrusions  32   a  are provided radially around the central axis  31   a  at prescribed intervals. In this case, part of the plurality of protrusions  32   a  may be made to protrude into the hole  2   b.    
     When the protrusion  32   a  is provided, the heat dissipation area can be increased, and therefore heat dissipation performance can be improved. 
     When the plurality of protrusions  32   a  are provided radially, the possibility that the flow of air by natural convection in the space  1   b  will be inhibited by the protrusion  32   a  is reduced. 
     The main body  33  includes the housing  3   a  and the heat dissipation portion  3   b , similarly to the main body  3  described above. 
     The main body  33  further includes a protrusion  33   a  (corresponding to an example of a second protrusion). That is, the main body  33  is a structure in which the main body  3  described above is provided with the protrusion  33   a.    
     The protrusion  33   a  protrudes from a surface of the housing  3   a  on the main body  2  side into the space  1   b.    
     The protrusion  33   a  is provided in plural. The plurality of protrusions  33   a  are provided radially around the central axis  31   a  at prescribed intervals. 
     When the protrusion  33   a  is provided, the heat dissipation area can be increased, and therefore heat dissipation performance can be improved. 
     When the plurality of protrusions  33   a  are provided radially, the possibility that the flow of air by natural convection in the space  1   b  will be inhibited by the protrusion  33   a  is reduced. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. Moreover, above-mentioned embodiments can be combined mutually and can be carried out.