Abstract:
A spotlight for generating an output light beam ( 9 ) of variable width, including a light source ( 1 ) having a selected focal length, and an aperture ( 3 ) for directing light from said light source to a first lens ( 5 ), said first lens ( 5 ) being movable to adjust the width of said output light beam ( 9 ), wherein the first lens ( 5 ) is moveable to a position closely adjacent to said aperture ( 3 ) and substantially about or at said selected focal length (FL) to minimize said output light beam width.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to a spotlight, especially a spotlight for generating an output light beam of variable width. The invention is of particular application to the fields of search and rescue operations, the entertainment industry, security and law enforcement.  
       BACKGROUND OF THE INVENTION  
       [0002]     Spotlights are presently used in a wide variety of applications for the purpose of illuminating objects at night, especially distant objects. For example, spotlights are used in search and rescue operations to find missing persons. Spotlights are also used in the entertainment industry to illuminate performers on stage or entertainment venues. In these and other applications, spotlights are usually required to produce sufficient and consistent illumination at varying distances. This requires the output light beam to be adjustable in width while maintaining the intensity of the output light beam to be constant across the beam width.  
         [0003]     Present prior art spotlights usually employ a parabolic-mirror in conjunction with a light source to generate a light beam which is then collimated to produce an output light beam of approximately 200-500 millimeters in diameter. The intensity of the output light beam from such spotlights is generally around 4 kW/m 2 . Such intensities are often insufficient to meet the requirements for the application in hand, especially during night operations. In addition, the output light beam tends to focus at one part of the light beam width, thus producing a beam of uneven intensity. This type of beam has variations in brightness resulting in a variable intensity, structured beam, profile.  
         [0004]     Filters are often used in conjunction with spotlights to produce a particular desired lighting effect. For example, a filter may be used to produce light of a particular colour or to produce a light beam with a range of wavelengths. Filters are ordinarily placed in the expanded output light beam path of the spotlight. That is, past the focal point of the light source. This is because standard filters cannot withstand the heat generated from the light source at closer distances. Another disadvantage with the prior art is that the filters are non-adjustable; that is, filters are usually installed mechanically through a slot or located at the front of the lens in the spotlight, meaning that a filter must be physically replaced with another filter by opening the spotlight assembly.  
         [0005]     Thus, there is a need for producing spotlights which are able to adjust the width of the beam while maintaining a required intensity. There is also a need for a simple filter arrangement employed with spotlights which is more convenient and easily allows the substitution of filters when required.  
       SUMMARY OF THE INVENTION  
       [0006]     Accordingly, one aspect of the present invention provides a spotlight for generating an output light beam of variable width, including a light source having a selected focal length, and an aperture for directing light from said light source to a first lens, said first lens being movable to adjust the width of said output light beam, wherein the first lens is moveable to a position closely adjacent to said aperture and substantially about or at said selected focal length to minimise said output light beam width.  
         [0007]     Positioning the moveable first lens closely adjacent to the aperture substantially about or at the selected focal length means that most, if not all, of the light from the light source is collected by the first lens and the moveability of the first lens adjusts the output beam width while retaining the same intensity output. Thus, the spotlight is able to produce output light beams of variable width while maintaining a sufficiently high intensity required for spotlight applications.  
         [0008]     Preferably, the selected light focal length is such that the spotlight has an f number of between 1 and 1.6. Most preferably, the f number is at least 1.3.  
         [0009]     It is preferred that the positioning of the first lens substantially at or about the selected focal length maximises the intensity of the output light beam. The intensity of the output light beam, at the focal point of the spotlight, preferably ranges between 2 megawatt/m 2  to 16 megawatts/m 2 .  
         [0010]     According to another aspect of the invention, the spotlight, in addition to the features of the first aspect, includes a selectively variable filter housing having two or more filters, said filter housing being rotatable to selectively interpose one of the said filters between said light source and said aperture to filter light from said light source.  
         [0011]     The inclusion of a selectively variable filter housing allows for more than one filter to be fitted to the housing and enables a filter to be substituted by another filter easily and conveniently.  
         [0012]     The filter housing preferably includes a portion to selectively interpose one of said filters, rotatable relative to the filter housing. In a preferred embodiment, the rotatable portion is a filter wheel.  
         [0013]     It is preferred that the filter housing has at least one chamber for receiving one of the filters. Preferably, the at least one chamber is formed in the rotatable portion. The chambers are preferably radially offset in the filter housing from the rotational axis of the filter housing for selective interposition between the light source and the aperture.  
         [0014]     At least one of the filters preferably includes multiple filter elements. The multiple filter elements can be formed in a stack in at least one chamber. The stack may include four to ten filter elements. The filter elements can be coated on one or both sides. The filters preferably filter light of different wavelengths.  
         [0015]     In one embodiment, the filter wheel has at least one chamber. Preferably, the chambers are radially offset in the rotatable portion from the rotational axis of the rotatable portion.  
         [0016]     The rotational axis of the filter housing or the rotatable portion is preferably parallel to and laterally disposed from the longitudinal axis of the spotlight.  
         [0017]     The filter housing may be formed integrally with the aperture. It is preferred that the aperture is located in a recess portion of the filter housing and a portion of the first lens, when positioned closely adjacent to the aperture, nests in the recess portion. The recess portion may be correspondingly shaped to the shape of the portion of said first lens. The aperture may be radially located in the filter housing to be aligned with at least one chamber. In a preferred embodiment, the aperture is located on the opposite side of the filter housing to said at least one chamber. In a further preferred embodiment, the filter housing has a plurality of chambers and a plurality of apertures.  
         [0018]     Preferably, a second lens is provided which is moveable relative to the first lens so as to collimate the output light beam at different distances. The first lens and second lens are preferably located on a lens mounting for simultaneous movement. The first lens and second lens may move at different linear rates, thus maintaining a crisp-edged, even beam profile at various distances from the spotlight output. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]     Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings of which:  
         [0020]      FIG. 1  is a cross-sectional view of a spotlight according to a preferred embodiment of the invention;  
         [0021]      FIG. 2A  is a schematic diagram illustrating the principles of operation of the preferred embodiment of the invention;  
         [0022]      FIG. 2B  is a schematic diagram illustrating an alternative embodiment;  
         [0023]      FIG. 3  is a perspective view of the filter housing used with the spotlight according to  FIG. 1 ;  
         [0024]      FIG. 4  is a perspective view of the filter housing of  FIG. 1 ;  
         [0025]      FIG. 5  is an exploded view of the filter housing of  FIG. 1  with multiple filter elements;  
         [0026]      FIG. 6  is a cross-sectional view of the filter housing of  FIG. 1 ;  
         [0027]      FIG. 7  is a cross-sectional view of a filter housing of another embodiment;  
         [0028]      FIG. 8A  is an exploded view of a lens mounting and a filter housing according to a preferred embodiment;  
         [0029]      FIG. 8B  is a perspective view of the assembled lens mounting and filter housing;  
         [0030]      FIG. 9A  is an exploded view of the lens mounting and filter housing of  FIGS. 8A and 8B  with a light source; and  
         [0031]      FIG. 9B  is a perspective view of the assembled lens mounting, filter housing and light source of  FIG. 9A . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0032]     A spotlight according to a preferred embodiment of the invention is shown in  FIG. 1 . The spotlight has a light source  1 , an aperture  3  and convex lens  5 . The light source  1  has a selected focal length FL and a focal point F, as shown more clearly in  FIG. 2A . The light source also generates a light beam angle α.  
         [0033]     The lens  5  is moveable along the longitudinal axis X of the spotlight. Lens  5  is moveable along axis X so as to vary the width of the output light beam  9 . In the position illustrated in  FIG. 1 , the lens  5  is located closely adjacent to aperture  3  substantially at the focal length FL and the focal point F of light source  1 .  
         [0034]     As can be seen in  FIG. 2A , the spotlight operates by light from light source  1  passing through aperture  3  to the lens  5 . By placing the lens  5  at the selected focal length FL of light source  1 , the width of the output light beam  9  is minimised. In addition, the light generated by the light source  1  is substantially collected by lens  5  and therefore maximises the intensity of the output light beam  9 .  
         [0035]     It has been found that by choosing the appropriate light source having a focal length FL of between 25-40 mm, the f number of the spotlight ranges between 1 and 1.6 with intensities of 2 MWatt/m 2  to 16 MWatt/m 2 . In a particularly preferred embodiment, using an elliptical lamp with a selected focal length FL=32.5 mm, the resultant spotlight has an f number of 1.3 with an output light beam having an intensity of 2.6 MWatts/m 2 . For a 1500 Watt xenon lamp, intensities of up to 16 Mwatt/m 2  can be obtained. Generally, the longer the focal length FL, the higher the intensity of the light beam, measured at a distance of 20 metres from the output.  
         [0036]     In the embodiment shown in  FIG. 2A , lens  5  is convex so as to collimate the output light beam  9 . In another embodiment shown in  FIG. 2B , a second (plano-convex) lens  7  is positioned after convex lens  5  to collimate the output light beam  9 . The lens and second lens  7  can be convex, plano-convex, or any other shape to collimate output light bean  9 .  
         [0037]     The preferred embodiment as described is unique to the field of spotlights as it is quite difficult in the prior art to achieve the desirable relatively small beam width at large distances while maintaining the intensity of the output light beam.  
         [0038]      FIG. 1  also shows a further aspect in that the spotlight has a selectively variable filter housing  10 . The filter housing  10  has a filter wheel  12 , which contains two or more filters  14 . Referring to  FIGS. 1 and 3 , the filter wheel  12  is driven by stepping motor  16 , operable by a control unit  18  in conjunction with a positioning microswitch  20 .  
         [0039]     Referring to  FIG. 1 , the filter wheel  12  is rotatable about axis R relative to filter housing  10 . The rotational axis R is parallel to and laterally displaced from longitudinal axis X of the spotlight. The motor  16  employs a drive gear  22  to selectively rotate filter wheel  12  so as to change the filter  14  interposed between the light source  1  and the aperture  3 .  
         [0040]     The filters  14  are held on filter wheel  12  via chambers  24  which are formed within the filter wheel  12 . As shown in more detail in  FIG. 4 , the chambers  24  in filter wheel  12  are radially offset from rotational axis R to facilitate selective interposition of one of the filters  14  between the light source  1  and the aperture  3 .  
         [0041]     Selection and positioning of the filter  14  within the light path is determined by microswitch  20 . Microswitch  20  is located in a recess in the circumference of filter wheel  12 . Each chamber  24  is associated with at least one and preferably two recess locating points on the filter wheel  12  for selection and positioning by microswitch  20 .  
         [0042]     Each filter  14  may be composed of one or more individual filter elements  15 . As shown in  FIGS. 1 and 5 , the filters  14  include a stack of separate filter elements  15  in each chamber  24 . The number of filter elements  15  may vary between each filter  14  from four filter elements up to ten filter elements  15  (see  FIG. 5 ) at a time. Moreover, the filter elements  15  can be coated on one or both of their sides.  FIG. 5  also shows the filter wheel  12  in more detail, the filter wheel  12  having an end plate  28  which holds the filter elements  15  within chambers  24  via screws  29 .  
         [0043]     The filter housing  10  operates as follows. When a desired light effect is required for a particular spotlight application, control unit  18  activates the stepping motor  16  so as to rotate filter wheel  12  about axis R, selectively interposing one filter  14  between the light source  1  and aperture  3  to achieve the desired lighting effect. When a different light effect is required control unit  18  is activated, and as described before, filter wheel  12  rotates about axis R, selectively rotating chamber  24  until the required filter  14  is interposed between light source  1  and aperture  3 .  
         [0044]     In the embodiment shown in  FIGS. 1 and 6 , the aperture  3  is formed integrally with filter housing  10 . Generally, more than one aperture  3  may be provided so that there is an aperture  3  associated with each chamber  24 . The aperture  3  is located in the filter housing  10  so as to correspond with the chamber  24  containing filter  14 . A recessed portion  26  is provided in the filter housing  10  around aperture  3  so that the lens  5 , when positioned closely adjacent to aperture  3 , nests in the recess portion  26 . The recessed portion  26  is also shaped to correspond with the shape of the lens  5 . The aperture  3  is located on the opposite side of filter housing  10  to filter  14  (and chamber  24 ) interposed between light source  1  and aperture  3 .  
         [0045]      FIG. 7  shows another embodiment of the filter housing  10 , where there is no integrally formed aperture. Rather, a separate housing or frame can be provided in the spotlight for the aperture. Providing a separate housing for the aperture allows the aperture to be adjustable so as to vary the output light beam width. In the case of the embodiment of  FIG. 1 , an adjustable aperture may be provided by providing apertures of differing diameters associated with different chambers  24  in the filter housing  10 .  
         [0046]      FIGS. 8A and 8B  show a further preferred embodiment of the invention employing a second lens  7  as discussed in relation to  FIG. 2B . In this embodiment, filter housing  10  is connected to a lens mounting  40  via rods  42 . The lens mounting  40  has lens holders  44 ,  46  for the lens  5  and second lens  7 , respectively. An end frame  48  is provided for supporting the lens mounting  40 . Both lens holders  44 ,  46  are moveable along rods  42 , allowing the lens  5  and second lens  7  to move simultaneously. The rods  42  may be provided with helical tracks of different pitches to cause the lens holders  44 ,  46  to move at different rates. This allows for adjustment of the focus of the spotlight at different distances.  
         [0047]      FIGS. 9A and 9B  illustrate an assembled version of the preferred embodiment wherein light source  1 , filter housing  10  (with filter wheel  12 ), lens mounting  40  (holders  44 ,  46  and end frame  48 ) are connected with an end plate  50  to form a single assembly which can be installed in a spotlight housing.  
         [0048]     It is envisaged that the invention is applicable to spotlights in a variety of uses where powerful illumination is required for an output light beam of variable width. As discussed above, the invention can be applied to spotlights for search and rescue operations, security lighting, and lighting in entertainment industry.  
         [0049]     In addition, the invention may be used in conjunction with the filter housing for the entertainment industry in providing the ability to use different coloured lights from the same spotlight as well as for security or military applications in providing green light, full covert or infrared (IR) covert light for the same spotlight.  
         [0050]     The foregoing describes only one embodiment of the invention and modifications can be made without departing from the scope of the invention.