Patent Publication Number: US-2023137296-A1

Title: Illumination apparatus

Description:
TECHNICAL FIELD 
     The technical field relates to an illumination apparatus; an optical element for an illumination apparatus and a method to manufacture an illumination apparatus. Such an apparatus may be used for domestic or professional lighting, for display illumination and for general illumination purposes. 
     BACKGROUND 
     Light-emitting diodes (LEDs) formed using semiconductor growth on monolithic wafers can demonstrate significantly higher levels of efficiency compared to incandescent sources. In this specification LED refers to an unpackaged LED die (chip) extracted from a monolithic wafer, i.e. a semiconductor element. This is different from packaged LEDs which have been assembled into a package to facilitate subsequent assembly and may further incorporate optical elements such as a hemisphere which increases its size and light extraction efficiency. 
     In lighting applications, the light from the emitter is directed using a luminaire optical structure to provide the output directional profile. The angular intensity variation is termed the directional distribution which in turn produces a light radiation pattern on surfaces in the illuminated environment. Lambertian emitters flood an illuminated environment with light. Non-Lambertian, directional light sources use a relatively small source size lamp such as a tungsten halogen type in a reflector and/or reflective tube luminaire, in order to provide a more directed source. Such lamps efficiently use the light by directing it to areas of importance. These lamps also produce higher levels of visual sparkle, in which the small source provides specular reflection artefacts, giving a more attractive illumination environment. Further, such lights have low glare, in which the off-axis intensity is substantially lower than the on-axis intensity so that the lamp does not appear uncomfortably bright when viewed from most positions. 
     Directional LED elements can use reflective optics (including total internal reflective optics) or more typically catadioptric type reflectors, as described for example in US6547423. Catadioptric elements employ both refraction and reflection, which may be total internal reflection (TIR) or reflection from metallised surfaces. A known catadioptric optic system is capable of producing a 6 degree cone half angle (to 50% peak intensity) from a macroscopic LED comprising a 1 x 1 mm light emitting element, with an optical element with 20 mm final output diameter. The increase in source size arises from conservation of brightness (etendue) reasons. Further, such an optical element will have a thickness of approximately 10 mm, providing a bulky illumination apparatus. Increasing the cone angle will reduce the final device area and thickness, but also produces a less directional source. 
     The LED of this example may be replaced by a 10x10 array of LEDs each for example 0.1x0.1 mm size, providing the same emitting area. This arrangement has a number of performance advantages, including reduced junction temperature (reducing illumination apparatus cost), reduced optical element thickness (reducing illumination apparatus cost), reduced current crowding (increasing device efficiency or reducing cost for a given output luminance) and higher current density capability (increasing device luminance or reducing cost for a given output luminance). It is therefore desirable to reduce the LED size. 
     It is desirable to reduce the number of electrical connection steps in connection of such an array of LEDs, to reduce cost. It is further desirable to reduce the area of electrical connection to such LEDs, preferably at least in proportion to the reduction of area of the LED to maximise emitting area of the chip. It is further desirable to provide electrical connections to LEDs on opposite surfaces to reduce current crowding. 
     PCT/GB2009/002340 describes a method to form an illumination apparatus with an array of small LEDs by preserving the separation of the LED elements from the monolithic wafer in a sparse array and aligning to an array of optical elements. GB2463954 shows one electrical connection method to LEDs of an LED array, in which the optical input aperture is positioned between the electrical connections and output aperture of the optical elements of the array of optical elements. 
     EP1 890 343 describes LEDs positioned in reflective cups with an overcoating transparent layer. Such devices are not suitable for providing directional illumination with narrow cone angles. 
     In addition, other objects, desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background. 
     SUMMARY 
     According to an aspect of the present disclosure there is provided an illumination apparatus whose primary purpose is illumination as opposed to display, comprising: an optical element array structure: and a light emitting element structure; the optical element array structure and the light emitting element structure having been provided as respective separate structures before being assembled together; the optical element array structure comprising a plurality of optical elements, wherein the optical elements are catadioptric, reflective or refractive, and the optical elements are arranged in an array; the light emitting element structure comprising a substrate and a plurality of light emitting elements arranged on the substrate; the optical element array structure and the light emitting element structure being arranged such that the optical elements of the optical element array structure are aligned with the light emitting elements of the light emitting element structure; and wherein the optical element array structure further comprises electrodes, hereinafter referred to as optical element electrodes, arranged thereon for providing electrical connection to the plurality of light emitting elements. The optical element electrodes may be, at least in part, positioned on a part of the optical elements that has a shape profile or a material composition profile of the optical element that is related to the catadioptric, reflective or refractive characteristic of the optical element. For at least some of the plurality of light emitting elements a first electrical connection to the light emitting element may be provided by a first optical element electrode and a second electrical connection to the light emitting element may be provided by a second optical element electrode. For at least some of the plurality of light emitting elements a first electrical connection to the light emitting element may be provided by the optical element electrode and a second electrical connection to the light emitting element may be provided by a support substrate electrode. At least one optical element electrode may be formed on a substantially planar surface formed between at least two optical elements of the optical element array structure. The optical element electrodes may be, at least in part, positioned on a part of the optical elements that has a shape profile substantially arranged to provide a contact between the optical element electrodes and substrate electrodes. The part of the optical elements may comprise a transparent polymer material composition. The optical elements may comprise a wavelength conversion material. At least one of the substrate or optical array may further comprise electronic components arranged in the region between light emitting elements of the light emitting element array. The plurality of light emitting elements may cooperate to provide at least one light emitting element string comprising at least two light emitting elements connected in series and the at least one current source may be multiplexed to multiple strings of light emitting elements. 
     According to an aspect of the present disclosure there is provided a method of manufacturing an illumination apparatus whose primary purpose is illumination as opposed to display, the method comprising: providing an optical element array structure; and providing a light emitting element structure; wherein the optical element array structure and the light emitting element structure are provided as respective separate structures; the optical element array structure comprising a plurality of optical elements, wherein the optical elements are catadioptric, reflective or refractive, and the optical elements are arranged in an array; the optical element array structure further comprising electrodes, hereinafter referred to as optical element electrodes, arranged thereon for providing electrical connection to the plurality of light emitting elements; the light emitting element structure comprising a substrate and a plurality of light emitting elements arranged on the substrate; and assembling the optical element array structure with the light emitting element structure such that the optical elements of the optical element array structure are aligned with the light emitting elements of the light emitting element structure. 
     According to an aspect of the present disclosure there is provided an optical element array structure, comprising: a plurality of optical elements, wherein the optical elements are catadioptric, reflective or refractive, and the optical elements are arranged in an array; the optical element array structure being for being assembled with a light emitting element structure comprising a substrate and a plurality of light emitting elements arranged on the substrate such that the optical elements of the optical element array structure are aligned with the light emitting elements of the light emitting element structure; and wherein the optical element array structure further comprises electrodes arranged thereon for providing electrical connection to the plurality of light emitting elements when the optical element array structure and the light emitting element structure are assembled. 
     According to an aspect of the present disclosure there is provided an array of optical elements; the optical elements are catadioptric directional optical elements: the array of optical elements being adapted to be aligned with a plurality of light emitting elements arranged in an array to provide an illumination apparatus: 
     wherein: the array of optical elements comprises first electrodes, hereinafter referred to as optical element electrodes, thereon arranged for providing a first electrical connection to the plurality of light emitting elements. 
     The array of optical elements may be adapted to be aligned with the plurality of light emitting elements to provide a light output cone from the illumination apparatus with an output cone angle of less than 30 degrees. 
     According to an aspect of the present disclosure there is provided an array of catadioptric optical elements; the array of catadioptric optical elements being adapted to be aligned with a plurality of light emitting elements arranged in an array with each light emitting element positioned substantially at an input surface of a respective catadioptric optical element, to provide an illumination apparatus, wherein the catadioptric optical elements each comprise: a first section comprising a polymer material with a first refractive index; and a second section comprising a polymer material with a second refractive index greater than the first refractive index; wherein the refractive part of the catadioptric optical characteristic of each catadioptric optical element is provided by a respective interface between its first section and its second section, and the respective input surface of each optical element comprises the input surface of its first section. The reflective part of the catadioptric optical characteristic of each catadioptric optical element may be provided by a reflective surface comprised by its second section. The catadioptric optical elements may each comprise: the first section is bounded by an input surface being adapted to be substantially positioned at the light emitting elements, a wall surface and a lens surface; the second section is bounded substantially by the wall surface and the lens surface of the first section and further bounded by a reflecting surface and an output surface; such that the first and second sections are capable of cooperating to direct light from the light emitting elements to an output surface. A recess in the input surface may be adapted for alignment with a respective light emitting element of the plurality of light emitting elements. A filler polymer material may be provided between the reflecting surfaces of adjacent optical elements of the array of optical elements wherein the filler polymer material has a substantially planar surface substantially in the plane of the input surface of at least one of the array of optical elements to provide a substantially uniform thickness optical element array structure. The reflective part of the catadioptric optical characteristic of each catadioptric optical element may be provided by total internal reflection in the second section. 
     According to an aspect of the present disclosure there is provided an illumination apparatus comprising an array of catadioptric optical elements aligned with a plurality of light emitting elements, wherein the optical elements comprise: a first section comprising a polymer material with a first refractive index: and a second section comprising a polymer material with a second refractive index greater than the first refractive index; the refractive part of the catadioptric optical characteristic of each catadioptric optical element is provided by a respective interface between its first section and its second section: and wherein each light emitting element is positioned substantially at an input surface of the first section of its respective optical element. The reflective part of the catadioptric optical characteristic of each catadioptric optical element may be provided by a reflective surface comprised by its second section. 
     According to an aspect of the present disclosure there is provided a method of manufacturing an illumination apparatus; the method comprising: forming a monolithic array of light-emitting elements; selectively removing a plurality of light-emitting elements from the monolithic array by adhering them to a first adhesive substrate in a manner that preserves the relative spatial position of the selectively removed light-emitting elements; transferring the plurality of light emitting elements from the first adhesive substrate to a second adhesive substrate in a manner that preserves the relative spatial position of the selectively removed light-emitting elements; transferring the plurality of light emitting elements from the second adhesive substrate to a support substrate in a manner that preserves the relative spatial position of the selectively removed light-emitting elements; wherein the plurality of light-emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed light-emitting elements in the at least one direction. The adhesive force of light emitting elements to the second adhesive substrate may be greater than the adhesive force of the light emitting elements to the first adhesive substrate. The adhesive force of the light emitting elements to the support substrate may be greater than the adhesive force of the light emitting elements to the second adhesive substrate. The support substrate may comprise an array of optical elements and the array of light emitting elements may be aligned with the respective optical elements. The array of light emitting elements may be aligned with an optical substrate comprising an array of optical elements. The support substrate may comprise a planar substrate wherein the array of light emitting elements is aligned with an optical substrate comprising an optical element array structure. 
     According to an aspect of the present disclosure there is provided a method of manufacturing an illumination apparatus; the method comprising: forming a first monolithic array of light emitting elements; determining a first plurality of the light emitting elements which pass a functional criterion; determining a second plurality of the light emitting elements which fail the functional criterion; selectively removing a plurality of the passed light emitting elements whose relative positions in the first monolithic array correspond to desired relative positions in a desired non-monolithic array of light emitting elements, the selectively removing being performed in a manner that preserves the relative spatial position of the selectively removed passed light-emitting elements; wherein the plurality of passed light-emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed passed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of removed passed light-emitting elements in the at least one direction; and forming a non-monolithic array of light-emitting elements with the selectively removed passed light-emitting elements in a manner that preserves the relative spatial position of the selectively removed passed light-emitting elements; by virtue of which in the formed non-monolithic array of light emitting elements desired relative positions of the desired array that correspond to passed light emitting elements in the first monolithic array are occupied by passed light emitting elements and desired relative positions of the desired array that correspond to failed light emitting elements in the first monolithic array are left unoccupied. Further light emitting elements may be added to the formed non-monolithic array of light emitting elements in unoccupied desired relative positions of the desired array. The further light emitting elements may be from a second monolithic array of light-emitting elements that is different to the first monolithic array of light-emitting elements. The further light emitting elements may be from the first monolithic array of light-emitting elements. The further light emitting elements may be light emitting elements which have been determined as passing the functional criterion. The method may further comprise forming a light intensity reduction region on a surface of the monolithic array support substrate aligned with the second plurality of light emitting elements. 
     According to an aspect of the present disclosure there is provided a method of manufacturing an illumination apparatus; the method comprising: forming a non-monolithic array of light-emitting elements on a support substrate; for at least some of the light-emitting elements in a first region of the support substrate, measuring their combined spectral output; providing a first wavelength conversion layer in alignment with the respective light emitting elements of the first region, the spectral characteristic of the first wavelength conversion layer being selected dependent upon the measured combined spectral output from the measured light emitting elements of the first region; for at least some of the light-emitting elements in a second region of the support substrate, measuring their combined spectral output; and providing a second wavelength conversion layer in alignment with the respective light emitting elements of the second region, the spectral characteristic of the second wavelength conversion layer being selected dependent upon the measured combined spectral output from the measured light emitting elements of the second region. A first region average white point may be provided by virtue of providing the first wavelength conversion layer in alignment with the respective light emitting elements of the first region; a second region average white point may be provided by virtue of providing the second wavelength conversion layer in alignment with the respective light emitting elements of the second region, and wherein the first region average white point and the second region average white point are thereby more similar than they would be if the two regions had been provided with a same wavelength conversion layer. A first region average white point may be provided by virtue of providing the first wavelength conversion layer in alignment with the respective light emitting elements of the first region, a second region average white point may be provided by virtue of providing the second wavelength conversion layer in alignment with the respective light emitting elements of the second region, and wherein the first region average white point and the second region average white point may be substantially the same. The spectral characteristics of the first wavelength conversion layer may be different to the spectral characteristics of the second wavelength conversion layer. 
     According to an aspect of the present disclosure there is provided a method of manufacturing an illumination apparatus; the method comprising: forming a monolithic light-emitting layer on a first substrate; transferring the monolithic light-emitting layer to an electromagnetic wavelength band transmitting substrate; selectively removing a plurality of light-emitting elements from the monolithic light-emitting layer in a manner that preserves the relative spatial position of the selectively removed light-emitting elements, performing of the selectively removing comprising selectively illuminating the monolithic array of light-emitting elements through the electromagnetic wavelength band transmitting substrate with light in the electromagnetic wavelength band; forming a non-monolithic array of light-emitting elements with the selectively removed light-emitting elements in a manner that preserves the relative spatial position of the selectively removed light-emitting elements: and aligning the non-monolithic array of light-emitting elements with an array of optical elements. The first substrate may be an electromagnetic wavelength band absorbing substrate. 
     According to an aspect of the present disclosure there is provided a method of manufacturing an illumination apparatus; the method comprising: forming a monolithic array of light-emitting elements made of a plurality of layers on a substrate, the light emitting elements being inter-connected in the layers they are formed in; selectively illuminating a plurality of the light emitting elements with an illumination that separates, at least to an extent, the selected light emitting elements from the substrate; the illumination further breaking the connection in the layers between each selectively illuminated light emitting element and the other light emitting elements; removing the illuminated light-emitting elements from the monolithic array in a manner that preserves the relative spatial position of the removed light-emitting elements; wherein the plurality of light-emitting elements that are selectively illuminated and removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively illuminated and removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of selectively illuminated and removed light-emitting elements in the at least one direction. The method may further comprise providing a patterned support layer formed on the plurality of light emitting elements. 
     By way of comparison with a known illumination apparatus, the present embodiments advantageously provide a reduced cost electrical connection apparatus for an illumination apparatus. Advantageously the electrical connection apparatus is integrated with the optical element and substantially at the input aperture of the optical element such that light from the LED is collected efficiently. The electrical connection may provide a vertical connection path to the LED, reducing current crowding and increasing LED efficiency. The area of the electrical connection may be reduced improving light extraction efficiency. The LEDs of the array may be connected in parallel, reducing assembly time and cost and increasing device reliability. Further the optical throughput efficiency of an array of catadioptric optical elements is improved in comparison with known arrays of elements. 
     A person skilled in the art can gather other characteristics and advantages of the disclosure from the following description of exemplary embodiments that refers to the attached drawings, wherein the described exemplary embodiments should not be interpreted in a restrictive sense. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings in which: 
         FIG.  1    shows a flip chip LED with lateral electrical connections; 
         FIG.  2    shows a vertical thin film LED; 
         FIG.  3   a    shows the respective separate structures of an optical element array structure and light emitting element structure before being assembled together; 
         FIG.  3   b    shows an illumination apparatus comprising the respective structures of  FIG.  3   a    after being assembled together; 
         FIG.  4   a    shows in cross section one catadioptric optical element; 
         FIG.  4   b    shows in plan view one catadioptric optical element; 
         FIG.  5   a    shows in cross section electrical connection of a light emitting element to a catadioptric optical element; 
         FIG.  5   b    shows in plan view electrical connection of a light emitting element to a catadioptric optical element; 
         FIG.  6    shows in cross section a detail of another electrode attachment apparatus: 
         FIG.  7    shows in cross section a detail of another electrode attachment apparatus; 
         FIG.  8    shows in cross section a detail of another electrode attachment apparatus; 
         FIG.  9    shows a further illumination apparatus comprising an electrical connection apparatus integrated with an optical apparatus: 
         FIG.  10    shows a detail of an electrical connection apparatus integrated with an optical apparatus; 
         FIG.  11    shows one array of optical elements with integrated electrodes; 
         FIG.  12    shows a further array of optical elements with integrated electrodes; 
         FIG.  13    shows a further array of optical elements with integrated electrodes; 
         FIG.  14    shows a further array of optical elements with integrated electrodes; 
         FIG.  15   a    shows a method for self assembly of an LED array; 
         FIG.  15   b    shows a self assembled array of LEDs; 
         FIG.  15   c    shows a method to connect an array of optical elements with integrated electrical connections to the array of  FIG.  15   b   : 
         FIG.  16    shows in plan view one electrical connector array integrated with an array of optical elements: 
         FIG.  17    shows in plan view a further electrical connector array integrated with an array of optical elements; 
         FIG.  18    shows in plan view a further electrical connector array integrated with an array of optical elements: 
         FIG.  19    shows a detail of the LED elements of  FIG.  20    in which a redundant LED is provided: 
         FIG.  20   a    shows in plan view an array of optical elements prior to forming an electrode array; 
         FIG.  20   b    shows in plan view a mask comprising an aperture array; 
         FIG.  20   c    shows in plan view an optical array with an electrode array formed with the mask of  FIG.  20   b   ; 
         FIG.  20   d    shows in cross section the optical array of  FIG.  20   c   : 
         FIG.  20   e    shows in plan view an optical element: 
         FIG.  20   f    shows in plan view an optical element in which a first region is electrically isolated from a second region; 
         FIG.  20   g    shows in cross section an array of optical elements of  FIG.  20   f   ; 
         FIG.  20   h    shows in plan view an optical element; 
         FIG.  20   i    shows in plan view an optical element in which a first region is electrically isolated from a second region; 
         FIG.  21   a    shows a method to form an array of electrode elements on an optical element; 
         FIG.  21   b    shows a further method to form an array of electrode elements on an optical element; 
         FIG.  21   c    shows a method to form a photoresist layer on an optical element; 
         FIG.  21   d    shows the optical element of  FIG.  21   c    following an etch step; 
         FIG.  22    shows a connection apparatus for an array of LEDs: 
         FIG.  23    shows a further connection apparatus for an array of LEDs; 
         FIG.  24    shows a further connection apparatus for an array of LEDs; 
         FIG.  25    shows a further connection apparatus for an array of LEDs; 
         FIG.  26    shows a further connection apparatus for an array of LEDs; 
         FIG.  27    shows a further connection apparatus for an array of LEDs; 
         FIG.  28    shows a further connection apparatus for an array of LEDs; 
         FIG.  29    shows a further connection apparatus for an array of LEDs; 
         FIG.  30    shows a further connection apparatus for an array of LEDs; 
         FIG.  31    shows a further connection apparatus for an array of LEDs; 
         FIG.  32    shows a further connection apparatus for an array of LEDs; 
         FIG.  33    shows a further connection apparatus for an array of LEDs; 
         FIGS.  34   a - 34   d    show a method to form an array of electrode connections; 
         FIGS.  35   a - 35   c    show a further method to form an array of electrode connections; 
         FIGS.  35   d - f    show a further method to form an array of electrode connections; 
         FIGS.  35   g - i    show a further method to form an array of electrode connections; 
         FIGS.  36   a - 36   g    show a method to form an array of light emitting elements; 
         FIG.  36   h    shows a mothersheet support substrate comprising multiple arrays of light emitting elements: 
         FIGS.  36   i - 36   j    show a further method to form an array of light emitting elements; 
         FIGS.  37   a - 37   d    show a further method to form an array of light emitting elements: 
         FIGS.  38   a - 38   g    show a further method to form an array of light emitting elements with increased yield; 
         FIG.  39   a    shows schematically a string of LEDs comprising correction of light emitting element fault; 
         FIG.  39   b    shows schematically a further string of LEDs comprising correction of light emitting element fault; 
         FIG.  40    shows in plan view an array of light emitting elements: 
         FIG.  41    shows a wafer comprising an array of light emitting elements; 
         FIG.  42   a    shows a composite substrate comprising multiple arrays of light emitting elements; 
         FIGS.  42   b  and  42   c    show regions of the composite substrate: 
         FIG.  43    shows a phosphor array for use with the composite substrate of  FIG.  42   a   ; 
         FIG.  44    shows a method to form a phosphor array; 
         FIG.  45    shows a staggered electrode string; and 
         FIGS.  46   a - f    shows a method to extract an array of light emitting elements formed on a light absorbing epitaxial substrate. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. 
     A known type of flip chip LED  16  comprising one example of a light emitting element  42  with lateral configuration is shown with electrical connections in  FIG.  1   . A substrate  2  such as sapphire has epitaxial layers formed on its surface  3 . Typically a gallium nitride device comprises an n-doped layer  4 , a multiple quantum well structure  6  and a p-doped layer  8  with a p-electrode  10 . In the region  12 , a portion of the p-layer and structure  6  is removed to provide a contact electrode  14  to be formed in contact with the n-doped layer  4 . This arrangement suffers from current crowding in the region  13 , reducing the maximum light output that can be obtained from the device. Solder connections  18 ,  20  are formed on electrodes  22 ,  24  respectively, mounted on a support substrate  26 . 
     In this specification, the term solder connections refers to known electrical connections including those formed by heating or by pressure or combination of heating and pressure applied to suitable electrically conductive materials. 
       FIG.  2    shows a vertical thin film (VTF) configuration LED  17  comprising another example of a light emitting element  42  in which the n-doped layer  4  has been separated from the substrate  2 , for example by means of laser lift off. An electrode  28  is applied to the p-doped layer  8  and attached by means of a solder element  30  to an electrode  32  formed on the substrate  26 . The n-doped layer may optionally have a transparent electrode  34  formed on its surface, and a further electrode  36  to provide a solder  38  contact to an input electrode  40 . Such a VTF configuration advantageously has reduced current crowding compared to the arrangement of  FIG.  1   . 
     However, the VTF configuration needs an electrode connection on the top surface, and so often requires a wire bonding process. In the case of large arrays of small light emitting elements, this would require a large number of time consuming wire bonds to be formed. Further, wire bonding technology may have limited positional accuracy so that a large non-emitting bond pad area on electrode  36  is required to provide reliable wire bonding. For example, the wire bond pad size may be 100 micrometers in size, which may be comparable to the desirable size of the LED light emitting element  42 . However, microscopic LEDs similar to those manufactured using the method of PCT/GB2009/002340 achieve small bond pad size due to the use of photolithographically defined electrodes on large accurate arrays of small light emitting elements. 
       FIG.  3   a    shows an embodiment wherein a directional illumination apparatus prior to assembly comprises a light emitting element structure  43  comprising a substrate  67  and an array of light emitting elements  42  comprising VTF LEDs  17  arranged on the substrate  67 ; and an optical element array structure  41  comprising a plurality of optical elements  1 . 
     After assembly by aligning the structures  41 ,  43 , and translating in direction  65  such that the optical elements  1  of the optical element array structure  41  are aligned with the light emitting element  42  of the light emitting element structure  43 , an illumination apparatus as shown in  FIG.  3   b    is formed. The optical element structure  41  further comprises optical element electrodes  56  arranged thereon for providing electrical connection to the plurality of light emitting elements  42 . Further, electrical connection joints  79  are provided to facilitate connection between the two respective substrates. Joints  79  may be provided by solder (that may be eutectic solder), conductive adhesive or other known electrical connection material systems and may be arranged on one or both of the structures  41 , 43 . The light emitting elements  42  are further electrically connected by means of optical element electrode  56  and substrate electrode  64 . Optical element electrode  56  thus provides a first electrical connection to the light emitting element  42 . A connecting structure  54  is formed in or attached to the optical element  1  on which the optical element electrode  56  is formed. This provides a contact between the optical element electrode  56  and the substrate electrode  62  or substrate electrode  58 . The substrate electrode  64  provides a second electrical connection to the light emitting element  42 . Thus for at least some of the plurality of light emitting elements  42  a first electrical connection to the light emitting element is provided by the optical element electrode  56  and a second electrical connection to the light emitting element is provided by a support substrate electrode  58 .  62  or  64 . 
     The light emitting elements  42  can be operated as one or more strings of light emitting elements  42  by connecting the n-doped layer of one light emitting element  42  to the p-doped layer of an adjacent light emitting element  42 . The optical element array structure  41  and light emitting element structure  43  thus cooperate to provide at least one light emitting element string comprising at least two light emitting elements  42  connected in series. Active or passive electronic control elements  66 , for example transistors, rectifying diodes or resistors may be positioned between substrate electrodes  62  and  64 , providing some electrical control of light emitting elements  42  within the array and between adjacent optical elements. The elements  66  may form an electrical circuit with light emitting elements  42  including being in series or parallel with at least some of them. The optical element electrodes  56  are, at least in part, positioned on a part (connecting structure  54 ) of the optical elements  1  that has a shape profile substantially arranged to provide a contact between the optical element electrodes  56  and substrate electrodes  58 ,  62 . The part (connecting structure  54 ) may comprise a transparent polymer material composition. 
     The light emitting elements  42  and substrate electrodes  58 ,  62 ,  64  may be formed at least in part on a substrate  67  that may comprise an electrically insulating layer  50  and a heat conducting layer  52  which provide a heat sink function and may for example be a metal core printed circuit board. Alternatively, the layer  50  may have sufficient rigidity that it can comprise the substrate  67  without additional layer  52  during processing of the light emitting elements  42 . Substrate  67  may be typically planar and may be in the form of a mothersheet support substrate with large area to achieve the processing of many light emitting elements in parallel, reducing cost. The substrate  67  or the optical element array structure  41  may comprise electronic components  66  arranged in the region between light emitting elements  42  of the light emitting element array. The electronic components may provide additional functions to the array of light emitting elements  42  and may be non light-emitting. 
     Thus the embodiment comprises an array of optical elements  1  in which the optical elements  1  are catadioptric. Alternatively, the optical elements  1  may be reflective or refractive. The array of optical elements  1  are adapted to be aligned with a plurality of light emitting elements  42  (for example LEDs  16  or LEDs  17  ) arranged in an array to provide an illumination apparatus wherein the array of optical elements  1  comprises electrodes thereon arranged for providing electrical connection to the plurality of light emitting elements  42 . 
     Thus an illumination apparatus whose primary purpose is illumination as opposed to display, may comprise an optical element array structure  41 ; and a light emitting element structure  43 ; the optical element array structure  41  and the light emitting element structure  43  having been provided as respective separate structures before being assembled together; the optical element array structure  41  comprising a plurality of optical elements  1 , wherein the optical elements  1  are catadioptric, reflective or refractive, and the optical elements  1  are arranged in an array; the light emitting element structure  43  comprising a substrate  67  and a plurality of light emitting elements  42  arranged on the substrate; the optical element array structure  41  and the light emitting element structure  43  being arranged such that the optical elements  1  of the optical element array structure  41  are aligned with the light emitting elements  42  of the light emitting element structure  43  ; and wherein the optical element array structure  41  further comprises electrodes  56 , hereinafter referred to as optical element electrodes  56 , arranged thereon for providing electrical connection to the plurality of light emitting elements  42 . 
     Thus a method of manufacturing an illumination apparatus whose primary purpose is illumination as opposed to display, may comprise: providing an optical element array structure  41 ; and providing a light emitting element structure  43 ; wherein the optical element array structure  41  and the light emitting element structure  43  are provided as respective separate structures; the optical element array structure comprising a plurality of optical elements  1 , wherein the optical elements are catadioptric, reflective or refractive, and the optical elements  1  are arranged in an array; the optical element array structure  41  further comprising electrodes  56 , hereinafter referred to as optical element electrodes  56 , arranged thereon for providing electrical connection to the plurality of light emitting elements  42 ; the light emitting element structure comprising a substrate  67  and a plurality of light emitting elements  42  arranged on the substrate; and assembling the optical element array structure  41  with the light emitting element structure  43  such that the optical elements  1  of the optical element array structure  41  are aligned with the light emitting elements  42  of the light emitting element structure  43 . 
     Thus an optical element array structure  41 , comprises: a plurality of optical elements  1 , wherein the optical elements  1  are catadioptric, reflective or refractive, and the optical elements  1  are arranged in an array; the optical element array structure  41  being for being assembled with a light emitting element structure  43  comprising a substrate  67  and a plurality of light emitting elements  42  arranged on the substrate  67  such that the optical elements  1  of the optical element array structure  41  are aligned with the light emitting elements  42  of the light emitting element structure  43 ; and wherein the optical element array structure  41  further comprises electrodes  56  arranged thereon for providing electrical connection to the plurality of light emitting elements  42  when the optical element array structure  41  and the light emitting element structure  43  are assembled. 
     The optical elements  1  are directional optical elements arranged to convert the substantially Lambertian output of the light emitting elements  42  into a narrower cone  55  of light beams with a smaller solid angle than the Lambertian output. The cone angle of output is defined as the half angle for half of the peak intensity and may be about 6 degrees for a narrow collimation angle and may be about 45 degrees for a wide (but still with some directionality) cone angle and is typically about 30 degrees or less for directional illumination systems. By way of comparison, Lambertian output cone angle is 60 degrees. To achieve reduced cone angle of light beams  55 , directional optics that have a significant etendue varying property, requiring an output aperture size  11  that is significantly larger than light emitting element  42  size are required. For example, a catadioptric optical element arranged for use with a 100 micrometres width light emitting element  42  may have a size  11  of approximately 2 mm. Narrow cone angles in particular require non-imaging catadioptric optics . By way of comparison reflective cups such as described in EP1 890 343 are unsuitable for providing narrow cone angles due to relatively shallow depth required in order to place the LED and electrodes in the cup. This citation shows LEDs which must be placed on top of the cups and then connected in a serial (wirebonded) process to the reflective cups. The light emitting element structure therefore is not provided as a separate structure, (but as individual LEDs), before assembly to the optical element array structure 
     An array of optical elements  1  may be provided wherein the optical elements  1  are catadioptric directional optical elements; the array of optical elements  1  being adapted to be aligned with a plurality of light emitting elements  42  arranged in an array to provide an illumination apparatus; wherein: the array of optical elements  1  comprises first electrodes  56 , hereinafter referred to as optical element electrodes  56 . thereon arranged for providing a first electrical connection to the plurality of light emitting elements  42 . The array of optical elements  1  may be adapted to be aligned with the plurality of light emitting elements  42  to provide a light output cone angle of light beams  55  from the illumination apparatus with an output cone angle of less than about 45 degrees and preferably less than about 30 degrees. 
     Light emitting element  42  arrays and efficient collimating optical elements  1  of the optical element array structure  41  can be fabricated with highly precise separation, for example as described in PCT/GB2009/002340. Advantageously the present embodiments provide electrical connection to electrode  36  for each light emitting element of the array in a single step to reduce assembly cost. Further the light emitting elements are arranged as VTF configuration light emitting elements with lower current crowding effects. The position of the electrode elements can be precisely defined (for example by photolithography) so that their size can be reduced compared to that necessary for wire bonding, and so the loss of light due to shielding by the electrode can advantageously be reduced. Further, the light emitting element are sparsely separated, so that the gaps between the light emitting elements  42  on the optical elements  1  and the support substrate can be used for electrodes in addition to further electronic components including for example resistors, diodes, control signal receivers for Infra Red or RF or integrated circuits to increase device functionality. The light emitting elements may be conveniently attached to a heat sink element to reduce junction temperature and increase device efficiency, further enabling higher current densities to be used, thus providing higher efficiency. 
     The optical elements  1  may have a spacing region  72  to relieve bending stress in structure  41 , and thus provide a flat structure for uniform attachment to the light emitting element array. The array has a top surface  71  which may be planar, may be conveniently anti-reflection coated or may have a surface structure to provide some further optical function to the output ray bundle  55  such as diffuser, lenticular lens array, lens array or prism array. 
     Thus the embodiment comprises an array of optical elements  1  wherein the optical elements  1  are catadioptric. The optical elements  1  may also be reflective or refractive as will be described below. The array of optical elements  1  are adapted to be aligned with a plurality of light emitting element  42  arranged in an array to provide an illumination apparatus wherein the array of optical elements  1  comprises first optical element electrodes  56  thereon arranged for providing a first electrical connection to the plurality of LED light emitting elements  42 . Further, an illumination apparatus comprises the array of optical elements  1  aligned with a plurality of light emitting elements  42 . 
     A single catadioptric optical element  1  of array is shown in cross section in  FIG.  4   a    and plan view in  FIG.  4   b   . The optical element  1  is formed on the substrate  46  and comprises a first section  35  comprising a cavity and a polymer material with a first refractive index and a second section  49  comprising a polymer with a second refractive index greater than the first refractive index. The cavity  35  is bounded substantially by wall surface  85 , lens surface  87  and input surface  81  of size defined by the aperture  37  of the optical element  1 . The second section is bounded by the surfaces  85 ,  87  and additionally by reflecting surface  45  and output surface  83 , of size defined by the aperture  39  of the optical element  1 . Both sections comprise polymer materials, wherein the refractive index of the cavity  35  material  47  is lower than the refractive index of the second section material  49 . For example, the material  47  may be a silicone material with refractive index approximately 1.4 and the material  49  may be a cross linked UV cured polymer with refractive index 1.56. The first cavity  35  section and second reflective sections are capable of cooperating to direct light from the light emitting elements to the output surface  83  and subsequently through the substrate  46  (which may be formed in the material  49  or may for example be a glass substrate) . In particular, substantially all light emitted in a forward or lateral direction is directed through the output aperture  39  into a narrower cone angle than from the original (typically Lambertian) cone. 
     Thus an array of catadioptric optical elements  1  may be provided; the array of catadioptric optical elements being adapted to be aligned with a plurality of light emitting elements  42  arranged in an array with each light emitting element  42  positioned substantially at an input surface  81  of a respective catadioptric optical element  1 , to provide an illumination apparatus, wherein the catadioptric optical elements  1  each comprise: a first section  35  comprising a polymer material with a first refractive index; and a second section  49  comprising a polymer material with a second refractive index greater than the first refractive index; wherein the refractive part of the catadioptric optical characteristic of each catadioptric optical element is provided by a respective interface between its first section  35  and its second section  49 , and the respective input surface of each optical element comprises the input surface of its first section  81 . The reflective part of the catadioptric optical characteristic of each catadioptric optical element is provided by a reflective surface  45  comprised by its second section  49 . The first section  35  may be bounded by an input surface  81  being adapted to be substantially positioned at the light emitting elements  42 , a wall surface  85  and a lens surface  87 ; the second section  49  is bounded substantially by the wall surface  85  and the lens surface  87  of the first section and further bounded by a reflecting surface  45  and an output surface  83 ; such that the first and second sections  35 ,  49  are capable of cooperating to direct light from the light emitting elements  42  to an output surface  83 . A recess  74  in the input surface  81  may be adapted for alignment with a respective light emitting element of the plurality of light emitting elements  42 . A filler polymer material  101  may be comprised between the reflecting surfaces  45  of adjacent optical elements of the array of optical elements  1  wherein the filler polymer material  101  has a substantially planar surface  97  substantially in the plane of the input surface  81  of at least one of the array of optical elements  1  to provide a substantially uniform thickness optical element array structure  41 . The reflective part of the catadioptric optical characteristic of each catadioptric optical element  1  may be provided by total internal reflection in the second section  49 . 
     An illumination apparatus may thus comprise an array of catadioptric optical elements  1  aligned with a plurality of light emitting elements  42 . wherein the optical elements  1  comprise: a first section  35  comprising a polymer material with a first refractive index; and a second section  49  comprising a polymer material with a second refractive index greater than the first refractive index; the refractive part of the catadioptric optical characteristic of each catadioptric optical element is provided by a respective interface between its first section  35  and its second section  49 ; and wherein each light emitting element  42  is positioned substantially at an input surface  81  of the first section  35  of its respective optical element  1 . The reflective part of the catadioptric optical characteristic of each catadioptric optical element  1  may be provided by a reflective surface  45  comprised by its second section  49 . 
     Advantageously, such an arrangement provides for highly efficient coupling of light. In particular, the cavity does not comprise air and so Fresnel reflections are reduced. thus increasing output efficiency and reducing illumination apparatus cost. Further, by way of comparison with known macroscopic LED systems of thickness typically 10 mm, the low thickness of the present embodiments reduce the internal absorption in the materials  47 ,  49 . Advantageously, the low thickness reduces the amount of materials so that higher cost per unit volume materials can be used without increasing overall device cost. 
     The input surface  81  is adapted to be substantially positioned at the light emitting elements  42 . The surface  81  may be plane, or for example may comprise a recess  74  may be formed to provide a region for the light emitting element  42  to be inserted so that in operation light directed laterally from the light emitting element  42  is collected by the wall surface  45  of the optical element  1 . Typical thin film LED light emitting elements have a thickness of less than 10 micrometres. Thus for a 100 micrometre width LED device, thickness  29  may be about 1 mm, thickness  57  may be about 0.5 mm and thickness  53  may be about 50 micrometres or less. Alternatively, the recess walls may have a height to accommodate a light emitting element mounted on a support substrate, such as sapphire wafer or silicon, in which case its thickness may be greater. 
     As shown in  FIG.  4   b   , the output aperture  39  may be hexagonal in shape, or alternatively may be other shapes such as round or square for example. The optical element electrode  56  may comprise a thin strip comprising a linear feature to advantageously optimise the proportion of the reflector that uses total internal reflection, TIR rather than metallic reflection, thus increasing efficiency. The electrode  36  may be extended in an orthogonal direction to the optical element electrode  56  to reduce alignment tolerance between the two components. 
     A schematic detail of a single light emitting element  42  and aligned optical element  1  of  FIG.  3    is shown in cross section in  FIG.  5   a    and plan view in  FIG.  5   b   . For illustrative convenience, the height of the recess  74  in the input surface  81  has been increased. Electrode  56  is formed on part of the surface  81  and is thus in the region that provides an optical imaging function of the catadioptric optical element  1 . The p-doped layer  8  of LED light emitting element  42  is attached to optical element electrode  56  by means of solder  38 . Thus the optical element electrodes  56  are, at least in part, positioned on a part (such as surface  81 ) of the optical elements  1  that has a shape profile or a material composition profile of the optical element  1  that is related to the catadioptric, reflective or refractive characteristic of the optical element. The electrode  56  is positioned on part of the surface  81  of the optical elements  1  so that it is near an input aperture defined by aperture  37  in plane  61  (shown in  FIG.  4   a   ) of the optical elements  1 . That is the surface  81  is near the input aperture within less than about 10% of the thickness  29  of the optical element  1 , and preferably less than about 5% of the thickness  29  of the optical element  1 . Further the optical element electrodes  56  are positioned on part of the optical elements  1  that is between the input aperture and an output aperture of the optical elements  1 . Advantageously, as the optical element electrode  56  is on the surface  81 , the light emitting element  42  is thus arranged to be at a location from which light can be efficiently collected by the catadioptric optical element  1 . 
     The n-doped layer  4  of LED light emitting element  42  is connected by means of reflective electrode  34  and solder  30  to substrate electrode  48 . The optical element electrode  56  is connected to substrate electrode  58  by means of solder  60 . Thus the first optical element electrodes  56  are further arranged for providing an electrical connection to substrate electrode  58 . The first optical element electrodes  56  are thus at least in part, positioned on a part of the optical elements  1  (such as connecting structure  54 ) that has a shape profile substantially arranged to provide a contact between the first optical element electrodes  56  and the substrate electrodes  58 . Thus the optical elements  1  further comprise pillar regions such as structures  54  wherein the first optical element electrodes  56  are, at least in part, positioned on the pillar regions. 
     The solder attachment method may be provided (using the example of solder  38 ) by forming metal layers such as palladium or other known electrode material layers (not shown) on the optical element electrode  56  and the electrode  36 . A further metal layer such as an indium layer may be formed on one of the palladium layers. On heating for example to about 180° C. and application of pressure between the two electrodes  36 ,  56  the palladium and indium alloy, providing a mechanical, thermal and electrical joint. Such alloying step can advantageously be provided in parallel across the array of light emitting elements  42  and optical elements  1  with electrodes  56 , reducing assembly cost. The metal layers may comprise other known electrode materials including but not limited to gold, indium tin oxide, titanium, aluminium, tin, platinum and nickel. 
     For a white light source, the light emitting elements of the array may comprise separate red, green and blue LEDs. However, a wavelength conversion layer  76  for example comprising a phosphor material may be incorporated as shown in  FIG.  6    in combination with a blue emission LED  42 . The phosphor layer  76  may be formed on the surface  81  and the optical element electrode  56  positioned on the internal surface  75  of the layer  76 . Such a layer  76  remains related to the catadioptric, reflective or refractive characteristic of the optical element. The optical elements  1  thus comprise a wavelength conversion material. A further index matching material  51  may be inserted to improve optical coupling between the light emitting element and the array of optical elements  1 .  FIG.  6    further shows an alternative cross section to that shown in  FIG.  4    wherein the connecting structure  54  comprises part of the surface  81 , and optical element electrode  56  attaches to the substrate electrode  58  by means of solder  60 . Such an embodiment advantageously reduces the complexity of the optical element. A further electrically and thermally conductive pillar  80  may be incorporated to mount the light emitting element further within the cavity  35  of the optical element. 
       FIG.  7    shows an alternative cross section to that shown in  FIG.  6    wherein a wavelength conversion layer region  84  is formed after electrode connection of the light emitting element  42 . A further conductive pillar  88  may be added to the top of the light emitting element  42  or to the surface  81  to provide a connection element to increase the thickness of the region  84  above the light emitting element  42  to the optical element electrode  56 . Such embodiment provides the electrode to be formed and light emitting element  42  to be attached prior to the introduction of the phosphor layer. The material  84  could further incorporate a conductive material so as to provide electrical connection between the electrode  90  of the light emitting element  42  and electrode  56 . In this case, further dielectric layers (not shown) may be applied to the light emitting element to prevent undesirable short circuits. 
       FIG.  8    shows an embodiment wherein the optical element comprises a reflective optical element  94  in which the walls of the reflective element are a formed metal reflector. An electrode support element  96  with electrode  98  and surface  81  may be formed near the input aperture with optical element electrode  98  attached to the reflector  94  to provide a conductive path to substrate electrode  58 . The electrode support element  96  may further comprise a hemispherical output shape to optimise light output coupling efficiency. Advantageously such an optical element  94  may have a lower cost than the catadioptric optical elements described previously, although it may have lower efficiency. This arrangement may be suited to wider angle optical output, for example greater than about 30 degrees HWHM (half width half maximum),collimation compared to less than about 10 degrees HWHM possible with catadioptric optical elements. 
       FIG.  9    shows a further embodiment shown in detail in  FIG.  10    in which an array of lateral configuration LEDs  16  comprising light emitting elements  42  is used with first optical element electrodes  56  and second optical element electrodes  100 , to provide first and second connection to the light emitting elements  42 . In an LED string, the second optical element electrode  100  for one light emitting element  42  becomes the first second optical element electrode  56  for adjacent light emitting elements  42 . Both electrodes are positioned on a structure  41  comprising an array of catadioptric optical elements  1 , and provide electrical connection on part of the surface  81  in the light directing part of the catadioptric optical element  1 . Thus for at least some of the plurality of light emitting elements  42  a first electrical connection to the light emitting element  42  is provided by a first optical element electrode  56  and a second electrical connection to the light emitting element is provided by a second optical element electrode  100 . 
     The surface  45  may be coated with a reflective material  102 , and the gap between the optical elements  1  filled with a material  101 , which may be the same as material  49  to provide a uniform structure and optimise flatness for attachment of electrodes  56 ,  100  and LEDs  16 . Thus the catadioptric optical elements may further comprise a filler polymer material  101  between the reflecting surfaces of adjacent optical elements  1  of the array of optical elements  1 . The filler polymer material  101  may have a substantially planar surface  97  substantially in the plane of the surface  81  of at least one of the array of optical elements  1  to provide a substantially uniform thickness array of optical elements. Advantageously, such an embodiment may advantageously provide a flexible optical and electronic structure. 
     Thus the array of optical elements  1  comprises second optical element electrodes  100  thereon arranged for providing a second electrical connection to the plurality of light emitting elements  16 . Thus first and second electrical connections to each of the plurality of light emitting elements are provided by the respective first and second optical element electrodes. Further at least one first optical element electrode  100  is formed on a substantially planar surface  97  formed between at least two optical elements  1  of the array of optical elements  1 . 
     Further heat spreader elements  103  may be incorporated between the light emitting element  42  and support substrate  67  to advantageously reduce the thermal resistance of the mounted light emitting element  42 . The heat spreader may comprise for example a metal layer or a silicon layer. Further electronic components  66  may be arranged in the regions between the optical elements  1  of the array. Such arrangement provides a first substrate that provides electronic and optical functions and a second substrate that provides heatsinking functions. Advantageously the embodiment does not require bonding of electrodes onto the heat spreader  103 , simplifying the optical structure of the substrate  67 , thus reducing cost. In other embodiments, such heat spreaders  103  can also be used in combination with VTF configuration LEDs  17 . 
       FIG.  11    shows an optical element array structure  41  comprising an array of optical elements  1  comprising catadioptric optical elements for use in the illumination apparatus similar to that shown in  FIG.  3   . The surfaces  45  are coated with a reflective material  102  and an additional material  101  is incorporated between the optical elements  1 . 
       FIG.  12    shows a reflective compound parabolic concentrators  104  (CPC) for use in illumination apparatus. Each element may incorporate a recess for electrode attachment and insertion of the light emitting element  42 . Advantageously such an arrangement may provide lower degree of collimation than the element of  FIG.  11    with a more uniform spot profile and more defined penumbra in the output illumination beam structure. 
       FIG.  13    show reflective CPCs formed from structures  108  with a reflective coating  102  incorporating further hemispherical optics  110  into which light emitting elements  42  are inserted. Hemispherical optics advantageously couple light from the light emitting element into air efficiently and can be incorporated into the same moulding as the structures  108  or added in a secondary process. Such a structure advantageously uses less material than that shown in  FIG.  12   . Thus the part of the surface  81  of optical element  1  on which the electrodes  56  are formed comprises part of a surface of a refractive lens  110 . 
       FIG.  14    shows an alternative embodiment of optical element array structure  41  in which the cavity  35  is filled with air and hemispherical optics  110  are incorporated in the structure and have the electrode structure applied. Advantageously such a structure has a lower thickness and higher spatial density of optical elements  1  than the optical structure in  FIG.  3   . 
     To achieve high precision of separation, the plurality of light emitting elements  42  such as LEDs  16  or LEDs  17  of the present embodiments may be from a monolithic wafer with their separations preserved, and wherein the plurality of passed light-emitting elements that are selectively removed from the monolithic array may be selected such that, in at least one direction, for at least one pair of the selectively removed passed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of removed passed light-emitting elements in the at least one direction, as described in PCT/GB2009/002340. 
     Alternatively, the separation of the light emitting elements may be achieved by means of self assembly  FIG.  15   a    shows the self assembly of light emitting element into a precision array. A container  118  is filled with a liquid  120  and diced LED  122 . A substrate  124  has an array of conductive adhesive regions  126  (which may be solder regions), interspersed by non adhesive regions  128  (such as resist) formed on its surface. As shown in  FIG.  15   b   , the LEDs  122  may be coated so as to preferentially attach in a first orientation  132  with either p-doped layer up or a second orientation  130  with n-doped layer up.  FIG.  15   c    shows the alignment of the LEDs  122  with an optical element array structure  41 . In operation, the LEDs  122  of the array are typically configured with n-doped layer of a first element attached to the p-doped layer of an adjacent LED  122 . In such a self-assembled device, the orientation of the LED  122  may not be clear until the elements are tested. In this case, the electrodes may require reconfiguring to set the appropriate polarities. The orientation of the LED  122  may be determined by inspection or electrical testing. For example electrodes  134  may be cut in regions  136 , for example by means of laser cutting. Advantageously connectivity to self assembled LED  122  arrays is provided. By way of comparison, if the LEDs  122  were lateral configuration type, each LED  122  would need to have a rotational orientation so that for example the etched regions  12  in  FIG.  1    are aligned up with the relevant region in each adhesive region  126 . Advantageously in the present embodiments, the rotational orientation is not critical as the devices are VTF configuration type and connected to the electrode on the optic array. 
       FIG.  16    shows in plan view light emitting element  42 , connecting structure  54  and optical element electrode  56  for optical elements  1  of the present embodiments. Advantageously, the light emitting elements of the array may be arranged in strings to provide a number of light emitting elements to be connected in series. In this embodiment, the hexagonal output aperture  39  of  FIG.  4   b    is replaced by circular output aperture  39 . Advantageously, circular output apertures may provide more axially symmetric directionality than hexagonal elements. Further, in the present embodiments the small size of the optical elements  1  means that the detailed structure of the output apertures may not be easily resolved by observers, so that the output aperture of the whole array of apertures  39  appears substantially uniform and thus has improved cosmetic quality by way of comparison with macroscopic light emitting element arrangements. 
       FIG.  17    shows in plan view the optical element array structure  41  of  FIG.  3   b    wherein the relative position of each structure  54  is different for optical elements  1  of the array, with structures  54 ,  138 ,  140 .  142 ,  144 ,  146 ,  148  with different relative positions for a single rosette. Such an embodiment advantageously averages out over the array the loss of reflectivity in the area around the pillar so that the combined optical output is substantially uniform. Thus the optical element electrodes  56  comprise a substantially linear feature  59  and the orientation of one first optical element electrode linear feature (for example with structure  140 ) is different to the orientation of at least one other first optical element electrode linear feature (for example with structure  142 ). 
       FIG.  18    shows an arrangement in which four light emitting elements  42  comprising LEDs  150 ,  152 ,  154 , and  156  (shown in more detail in  FIG.  19    below) provide light emitting sub-elements, and are positioned in the input aperture  37  of each optical element. Such an arrangement provides compensation for short circuit loss of a single element during the lifetime of the element.  FIG.  19    shows a detailed arrangement for the connections to the LEDs in  FIG.  18   . At least one optical element  1  of the optical element array structure  41  of  FIG.  3   b    is aligned with at least two light emitting sub-elements. This provides some LED redundancy in the event of device failure. When controlled from a constant current supply, a string of LEDs produces a defined light output. If one of the LEDs  150 ,  154 ,  156  fails short circuit, the voltage drop of the respective LED is lost, but for a constant current supply the current through the remaining LEDs remains the same as opposed to increasing as would have happened with a constant voltage supply. Nevertheless the light output is reduced by the short circuit failure of one LED. In normal operation, active device  168  for example a transistor is on, effectively shorting LED  152  so that it does not emit. When short circuit failure of one of the other LEDs (150,  154 ,  156 ) is detected, then active device  168  is turned off which provides LED  152  to turn on and thereby restoring the overall output to the pre-failure value. An active semiconductor device such as transistor  168  is arranged to provide switching of at least one of the light emitting sub-elements. Other active devices such as triacs, thyristors or integrated circuits can be used in cooperation with the light emitting elements. 
     Electrode layers may be formed on optical elements  1  as described in the illustrative embodiments of  FIGS.  20  and  21   .  FIG.  20   a    shows in plan view an array of optical elements  400  comprising an input aperture  402  and an electrode support structure  404 .  FIG.  20   b    shows a mask  406  used to form electrode pattern on the array of  FIG.  20   a    comprising aperture regions  408  and shielding regions  410 .  FIG.  20   c    shows the optical elements  400  after formation of electrode  412  comprising light emitting element  42  contact region  414  and backplane contact region  416 . As shown in  FIG.  20   d    in cross section, metal material  417 , such as aluminium, gold or Indium Tin Oxide (ITO) is deposited for example sputtered onto the surface of the mask and is transmitted through apertures in the mask to provide electrode  412 . Advantageously such an arrangement can provide a high precision of electrode alignment to optical structures. 
       FIG.  20   e    shows one optical element  400  of an array of optical elements on which a metallic coating  418  is formed. In a material removal step, a region of the opaque metal material is removed through a coating such as a photoresist coating and etch steps (as well known in the art), or may be by means of laser ablation for example. As shown in  FIG.  20   f   , the region of removed material may be arranged to provide a transparent region  420  for light transmission from the light emitting element and an electrical isolation region  421  so that the contact between the light emitting element and the backplane is through electrode  422 . Advantageously the whole of the optical element  400  surface can be conveniently pre-coated with metal to provide both reflection and electrical connection properties. 
       FIG.  20   g    shows an array of the elements of  FIG.  20   f    in cross section.  FIG.  20   h    shows an alternative embodiment in which the material  418  is a transmissive conductive material such as ITO. After a metal removal step, as shown in  FIG.  20   i   , an electrical isolation region  423  and a connecting electrode region  424  are formed. Advantageously, a large contact area to the light emitting element is provided to reduce the required alignment precision of the electrode to the light emitting element. 
       FIG.  21   a    shows a further method to form the electrode regions. An array of optical elements  400  comprising supporting material  101  is selectively over-coated by means of a printing process such as ink jet (not shown) or a coating roller  425  with a conductive material  426  such as a conductive ink, to form electrode  412 . In  FIG.  21   b    as similar arrangement is used to provide electrode  412  where the structure  404  provides a platform for the coating roller and conductive material  426 . 
       FIG.  21   c    shows a further method to form the electrode regions. Array of optical structures  400  is coated with a metal layer and then a material  428  such as a photoresist or other etch resist material is selectively over-coated on the array to provide coated regions  430 . The optical element is then etched and the material in regions  430  removed to provide electrodes  432  as shown in  FIG.  21   d   . 
     An electronic control apparatus for an illumination apparatus may be provided wherein respective electrodes are arranged for connecting at least two light emitting elements of the plurality of light emitting elements. The electrical connection apparatus for the arrays of light emitting elements of the present embodiments, which may be one dimensional or two dimensional arrays, may comprise several different arrangements. Two or more of the LEDs  300  may be connected in parallel between common electrodes  301  and  302  as shown in  FIG.  22   . Light emitting diodes are shown with output light  299  emission. Electrodes  301  or  302  may take the form of a sheet electrode,  303 . This requires a low-voltage high-current supply, and this arrangement works best if all the individual LEDs are very well matched electrically. This arrangement is vulnerable to LED short circuit failure, but can tolerate open circuit failure. Thus respective electrodes are arranged for connecting a plurality of light emitting elements in parallel. 
       FIG.  23    shows that two or more of the LEDs  300  may be connected to common electrode  302  which may take the form of a sheet electrode  303 . The common electrode may be the anode or the cathode (shown). For a two dimensional array of n x m LEDs (where n and m are integers) this may be driven by n x m current sources (not shown) each connected to each of an electrode  304  of respective LED  300 . Alternatively each LED can have a series resistor (not shown) so that when the all the resistors are connected together to a constant voltage supply (not shown) the resistors promote current sharing. The resistors associated with each device may be integrated in the LED structure or external for example as shown as element  66  in  FIG.  3   . The function of a resistor for each LED may also be implemented by a uniform resistive layer (not shown), termed a ballast layer, between the LED electrodes and a common electrode. 
       FIG.  24    shows LEDs  300  connected in series strings  310 , each of which may be driven by a current source (not shown), and connected by means of electrodes  305 ,  307 . Thus respective electrodes are arranged for connecting a plurality of light emitting elements in series directionally to form a string. In series directionally means the cathode of one device is connected to the anode of the next device in series. This arrangement also reduces the number of current sources compared to  FIG.  23    and means that the current source may operate at higher voltage. Each string still functions if an individual LED fails short circuit. An open circuit failure disables only the string it is in. If required open circuit failures of an individual device can be prevented from disabling the whole string at the cost of incorporating Open Circuit Protectors (not shown) in parallel with the LED to be protected. Suitable protectors include the PLED family marketed by Littlefuse (Chicago, Illinois). To reduce components count, one Open Circuit Protector can be configured to protect for example two LEDs in series, however if only one LED fails, both will be dark. Alternatively a zener diode (not shown) can be configured in anti-parallel with each LED, or LED pairs. The zener voltage should exceed the forward voltage drop of LED(s) it is protecting. LEDS may be protected from Electro-Static Discharge (ESD) damage by incorporating ESD protection devices such as ESD diodes. These devices can be configured in parallel with one or more LEDs or connected at the external electrodes of the LED array. The individual strings  310  of LEDs  300  of  FIG.  24   , which may for example correspond to a row of n devices in the LED array, may themselves be connected in series for example by electrodes  309  to further reduce the number of drive circuits, or to raise the operating voltage to be more compatible with the available supply for example as in  FIG.  25   . The electrical arrangement discussed above can apply to a spatially different topology of the LED array for example hexagonal or square. The LEDs connected in a string need not be adjacent and may be spatially separated to promote optical uniformity in the event that a particular string fails. 
     The drive circuit for the plurality of light emitting elements may comprise at least one current source. 
     Current sources may be multiplexed to multiple strings of light emitting elements as shown schematically in the illustrative embodiment of  FIG.  26   . In operation current source  318  is connected to group of 4 parallel strings  330  of LEDs. Current sources  320 ,  322  etc. are similarly connected to strings  332 ,  334 . In a first illumination phase (phi 1) the first of the 4 parallel strings in each of groups  330 ,  332 ,  334  is connected to the respective current sources and is turned on (e.g. grounded by means of transistor  324 ). In phase two, the current sources are used to control the second string in each group. At least one current source  322  may thus be multiplexed to multiple strings of light emitting elements  42 . This system has the advantage of reduced number of current sources. Multiplexing the current sources also reduces the number of electrical connections that are needed to the array 
     The array may also have some LEDs connected in arrangements intended for AC operation.  FIG.  27    shows an AC power source  341  and a basic opposed strings  340 ,  342  each comprising one or more LEDs  300 . Each string illuminates on opposing polarity (usually half cycles) of the AC waveform. The string may contain enough devices to make the total forward diode voltages suitable to the AC voltage available. If the current is limited, for example by a resistor (not shown), then the circuit has some tolerance to short circuit failures of LEDs. Unless protected open circuit failure of a LED will disable whichever of the string  340 ,  342  the failed device is in. The strings may also further comprise a connecting link  344  as shown in  FIG.  28   . A short circuit failure in any LED also disables the LED electrically in parallel. Disadvantageously this arrangement is not tolerant to open circuit failure. 
     Some or all of the devices of the array may be configured as one or more bridge circuits e.g. half wave bridge circuits (not shown) or full wave bridge circuits as illustrated in  FIG.  29   . The arms of the bridge contain light emitting rectifying diodes. This circuit has the advantage that the centre string  346  emits on both positive and negative cycles of the AC power source  341 . Sufficient light emitting diodes are needed in the arms  348  of the bridge (two are shown for illustration in each arm) to sustain the reverse voltage of the AC waveform from the source  341 . For a typical AC waveform, these LEDs in the arms  348  only emit on half the cycles. 
       FIG.  30    illustrates another approach where the bridge is provided by non light-emitting rectifier diodes  350  in each arm that have a high reverse voltage tolerance and preferably a low forward voltage for example silicon diodes. This embodiment provides all the LEDs  300  to emit on positive and negative cycles of the AC source  341 . Such a silicon diode bridge is conveniently incorporated with the array embodiments, for example element  66  in  FIG.  3   . 
     The control circuitry associated with the above embodiments may also incorporate one or more of features such as power factor correction, current limit, over temperature and over voltage protection, as is known in the art. The control circuitry may also incorporate and Infra Red or wireless RF receiver to provide control of the functions of the lamp. 
     Strings of LEDs may be used for high voltage DC operation without needing a bridge circuit. Any reverse voltage including possible transients across the LED string  346  may be clamped with for example a silicon diode  350  and a high value (e.g. one megaohm) resistor  352  as shown in  FIG.  31   . 
     Some or the entire LED array may be connected as a cross point matrix  FIG.  32   . In this case the same electrode (say the anode) of all LED devices  300  in a row e.g.  306  are connected together; and the other LED electrodes (cathodes) in a column e.g.  304  are all connected together. When all devices are connected to their respective rows and columns, this produces a light source like a matrix display, which can be addressed one row at a time. For an n x m array only m fast, high power current sources  308  are needed as typically each device is illuminated for ⅟n of the time. With suitable control this system can be arranged to function as a display or as a signalling device as well as provide illumination. The signalling function may be performed at such a speed and/or wavelength as to be unnoticeable to humans. The plurality of light emitting elements can thus be connected in an addressable array. 
       FIG.  33    shows that a transistor  360  can be used to short circuit the voltage across a LED  300  so that ordinarily it does not operate. If greater light output is needed, for example if another element has failed, then the transistor may be switched to high resistance and LED  300  is now free to operate. The failure of a device may be detected by means of sense resistor  362  and circuitry block  364 . Different strings or parts of the array may be turned on or off in order to facilitate dimming and or lumen maintenance. Different colour LEDs may be turned on or off to facilitate a change in colour temperature or a change in colour temperature when dimming the light. 
       FIG.  34   a    shows a further embodiment for providing an array of electrode connections. Substrate  500  may comprise the array of optical elements such as item  41  in  FIG.  9    or may be a plane substrate such as a glass, silicon, metal or ceramic substrate which may further comprise additional elements such as electrodes and heat spreaders. An array of light emitting elements  502  is formed on the substrate  500  and in a first step, a shadow mask  504  is provided in alignment with the array of light emitting elements  502 . The mask  504  comprises an array of apertures  503  with size that is greater than the size of the electrode region to be provided on the upper surface of the light emitting elements  502 . The mask may comprise for example a high melting point metal or a polymer material such as polyimide. 
     In a second step as shown in  FIG.  34   b   , a coating  506  is formed on the surface of the light emitting elements  502  and mask  504 . The coating  506  may comprise metal or dielectric materials suitable for providing electrical connection to the upper surface of the light emitting elements  502  and insulation from surrounding electrical features. The coating may comprise a stack of materials of required thickness including but not limited to titanium, palladium, aluminium, gold, silver, indium, nickel and alloys thereof. The coating  506  may be formed by evaporation, sputtering, chemical vapour deposition or other known methods. Advantageously, after forming the coating  506 , the material of one or more of the coatings  506  deposited on mask  504  may be recycled. Typically the light emitting elements  502  of the present embodiments comprise relatively small devices, for example 100 micrometers width with spacing of for example 1 mm or more. Such an arrangement means that the area coverage of the light emitting elements may be less than about 1% of the total area on which the coating is formed. In this manner, the coating materials  506  may be recycled to reduce cost. 
     After the deposition step of  FIG.  34   b   , the thickness of the coating deposited through the shadow mask may be subsequently increased by an electro-deposition or plating process using the regions deposited through the mask as seed layers. 
     In a third step a lithographically patterned array of photoresist  508  may be formed on the surface of the coating  506  and light emitting elements  502  as is well known in the art. In a fourth step, etching is used to selectively remove part of the coating  506  so as to provide a small electrode region  507 . In this manner, the high precision and small size of photolithographic electrodes can be combined with the recycling capability of the lower precision shadow mask technology. Advantageously small electrodes that provide high light output can be provided at low cost. Further, the light emitting elements operate in a VTF configuration enabling higher current density with high efficiency. 
       FIGS.  35   a - c    show an alternative method for forming an array of electrodes comprising a ‘lift-off’ step. In a first step as shown in  FIG.  35   a   , a patterned photoresist layer  510  comprising aperture regions  511  is formed on the surface of the substrate  500  and light emitting elements  502 . As shown in  FIG.  35   b   , a coating  506  such as a stack of metal layers is formed on the photoresist for example by evaporation or sputtering. In a third step as shown in  FIG.  35   c    a known photoresist lift off technique is provided to remove the coating outside the desired electrode region  507 . The metal of coating  506  can be recovered from the lifted off material and advantageously recycled. 
       FIGS.  35   d - f    show an alternative method for forming an array of electrodes. In a first step as shown in  FIG.  35   d   , a substantially uniform layer  512  is provided on the surface of the substrate  500  and light emitting elements  502 . The layer  512  may comprise for example a polyimide layer. In a second step as shown in  FIG.  35   e    apertures  514  are provided for example by means of photolithography or laser patterning. In a further step as shown in  FIG.  35   f   , electrodes may be patterned on the surface, for example by means of an evaporator and shadowmask (not shown).  FIGS.  35   g - i    show a further method for forming an array of electrodes. In a first step as shown in  FIG.  35   g   , light emitting elements are arranged on an electrode array  518  and the layer  512 , for example polyimide provided. As shown in  FIG.  35   h   , via holes  520  are formed in the layer  512 , for example by means of photolithography or laser patterning. As shown in  FIG.  35   i   , electrodes are patterned on the upper surface of layer  512  to provide a VTF type electrode connection. The processes of  FIGS.  35   a - i    may be applied to planar substrates or to optical element arrays to provide first and second electrode arrays. 
       FIGS.  36   a - 36   d    show a further method to provide an array of light emitting elements. In  FIG.  36   a   , a semiconductor support substrate  520  is provided with an array  522  of light emitting elements formed on its surface separated by gaps  526  and arranged with a first adhesive substrate  524 . For example the semiconductor support substrate  520  may be sapphire, the light emitting elements may be gallium nitride and the gaps  526  may be formed by laser scribing or other known scribing, etching or ablation techniques. Ultraviolet electromagnetic radiation beams  529 ,  530 ,  531  from a homogenised excimer laser are used to illuminate patterned regions  528  in alignment with some of the light emitting elements of the array  522 . Light is transmitted through the substrate  520  and by illumination with a short pulse of light, decomposition of the semiconductor material close to the interface of the substrate  520  achieves a loss of adhesion of the light emitting element to the substrate  520 . For example, gallium nitride illuminated with a  30   nanosecond pulse of energy approximately 1 J/cm2 disassociates the gallium nitride to provide gallium metal and nitrogen gas. 
     After exposure in a separation step as shown in  FIG.  36   b   , the sandwich  520 ,  522 ,  524  may be heated above the melting point of gallium to achieve selective detachment of the light emitting elements of the array  522  from the substrate  520 . On illumination of the respective light emitting elements of the array  522 , transfer of an array of separated light emitting elements  532  to adhesive substrate  524  is thus achieved by means of laser lift off while the remaining light emitting elements of the array  522  remain attached to the substrate  520 . 
     The array  522  may advantageously be in contact with an adhesive substrate  524  as shown in  FIG.  36   c   . The adhesive substrate  524  may advantageously comprise a surface with weak adhesive properties capable of providing a temporary bond to the light emitting elements after the laser lift off step. A suitable material for the adhesive substrate may be a cross linked polydimethylsiloxane, PDMS that may be free standing or may be formed as a pre-cured adhesive layer  525  on a rigid or semi-rigid substrate  523 . The support substrate may be rigid such as glass, or may be for example a flexible polymer sheet. Alternatively the PDMS may be cured in contact with the array  522  of light emitting elements with or without a backing substrate. 
     The substrate  524  may comprise other adhesive materials with weak adhesive properties such as waxes or pressure sensitive adhesives or layers  525  with a sparse distribution of adhesive regions on a scale smaller than the light emitting elements achieving a low adhesive force and low separation energy for subsequent substrate separation steps. As shown in  FIG.  36   d   , an adhesive layer may comprise regions  527  of adhesive material  525  that may be aligned with the respective light emitting elements during the laser lift off step. Alternatively as shown in  FIG.  36   e   , the layer  525  may comprise surface relief regions  529  of adhesive material. The embodiments of  FIGS.  36   d  and  36   e    advantageously reduce the adhesion of the substrate  524  to the elements that are not removed in the laser lift off step, or the adhesion of the layer  525  to subsequent attachment substrates. 
     Advantageously, the adhesive force of the substrate  524  to the selectively removed light emitting elements may hold the selectively removed light emitting elements from the laser lift off step while releasing from light emitting elements on the semiconductor substrate  520  that were not exposed to laser illumination. 
     The adhesive material  525  may advantageously comprise a flexible layer arranged to conform with the surface of the semiconductor support substrate  520  and array  522  of light emitting elements. The substrate  520  and array  522  may be formed from materials with different thermal expansion coefficients, so that at room temperature the array  522  is warped. A rigid support substrate  523  may not be conveniently arranged in contact with all elements of the array  522 , whereas a flexible support substrate  523  can conform to the surface. Alternatively gaps  526  may be arranged to relieve the stress in the layer  522  thus enabling a planar substrate  520  and a rigid substrate  523  to be provided. 
     The separation s1 of the light emitting elements from the semiconductor support substrate  520  is substantially the same as the separation on the adhesive substrate  524 . The separation s1 may advantageously be substantially the same as the separation of the input apertures of the array of optical elements providing uniform illumination across large arrays of components, thus enabling mothersheet substrate processing. A mothersheet comprises a light emitting element support substrate of extended size, thus enabling many light emitting elements to be processed in parallel. Further the mothersheet area may be of sufficient size so that many illumination apparatuses can be processed in parallel. For example, an illumination apparatus may achieve a 10001 m output, and the mothersheet may be of sufficient size to achieve parallel processing of ten or more such devices in parallel prior to a singulation step. Advantageously such a mothersheet substrate processing approach can produce significant reduction in illumination apparatus cost. 
     In a further step as shown in  FIG.  36   f   , second regions of the array  522  are transferred from the semiconductor support substrate  520  onto a second adhesive substrate  534  to provide a second array  536  of separated light emitting elements with separation s1 as shown in  FIG.  36   g   . 
     As shown in  FIG.  36   h    in plan view, multiple substrates including  524  and  534  may be aligned onto a mothersheet support substrate  535  to produce an extended array of light emitting elements from which many illumination elements may be formed. Substrate  535  may comprise for example an optical element array structure  41  (in  FIG.  9   ) comprising optical elements  1  or may be a plane substrate such as a glass or ceramic substrate which may further comprise additional elements such as heat spreaders and electrodes. Advantageously such an arrangement achieves the alignment of multiple arrays on a single substrate. The adhesive substrate  524  may comprise a flexible substrate that can bend in conformity with both a semiconductor support substrate  520  and substrate  535 . Advantageously, such an arrangement achieves arrays of light emitting elements to be extracted from warped wafers  520  and applied to flat substrates  535 . Advantageously the arrays of light emitting elements  532 ,  536  may be aligned with lithographic precision so that the composite arrays on the substrate  535  achieve high precision of alignment with the respective optical elements. 
     The gaps  526  of  FIG.  36   a    may be provided by means of laser scribing, etching partial sawing or other know separation techniques. Alternatively, as shown in  FIG.  36   i   , the array  522  of light emitting elements may be provided with no pre prepared gaps, and is provided in layers (for example n doped and p doped layers). An optional support layer  521  which may be patterned may be formed on the array  522 . The ultraviolet electromagnetic radiation beam illumination  529 ,  530 ,  531  may be arranged so as to provide separation of the elements defined by the size of the beam providing sparse array separation as shown in  FIG.  36   j   . The step in which the gap  526  (as shown in  FIG.  36   a   ) is formed is eliminated and advantageously cost is reduced. On laser exposure of the layer  522 , defects such as cracks in the emitting layer may propagate, damaging the removed light emitting elements. 
     Thus a method of manufacturing an illumination apparatus may comprise the steps of: forming a monolithic array of light-emitting elements on a support substrate in a continuous layer; selectively removing a plurality of light-emitting elements from the monolithic array in a manner that preserves the relative spatial position of the selectively removed light-emitting elements; wherein the monolithic array of light-emitting elements are illuminated by a plurality of shaped laser beams; wherein the plurality of light-emitting elements that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed light-emitting elements in the at least one direction. A patterned support layer may be formed on the plurality of light emitting elements. 
     Thus a method of manufacturing an illumination apparatus may comprise: forming a monolithic array  522  of light-emitting elements made of a plurality of layers on a substrate  520 . the light emitting elements  532  being inter-connected in the layers they are formed in; selectively illuminating a plurality of the light emitting elements  532  with an illumination  529 ,  530 ,  531  that separates, at least to an extent, the selected light emitting elements  532  from the substrate  520 ; the illumination  529 ,  530 ,  531  further breaking the connection in the layers between each selectively illuminated light emitting element  532  and the other light emitting elements; removing the illuminated light-emitting elements  532  from the monolithic array in a manner that preserves the relative spatial position of the removed light-emitting elements  532 ; wherein the plurality of light-emitting elements  532  that are selectively illuminated and removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively illuminated and removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of selectively illuminated and removed light-emitting elements  532  in the at least one direction. Further a patterned support layer  521  may be formed on the plurality of light emitting elements  532 . 
     Advantageously, patterned or unpatterned support means  521  can be provided on the surface of the array  522  to reduce damage during the laser processing step and to provide uniform size of extracted material from the array  522 . The layer  521  may be a metal layer and may form part of the electrode structure of the device or may be some other layer such as a polymer stabilisation layer that may be removed in subsequent processing steps. The edges of the light emitting elements may be cleaned, for example by means of a laser writing or selective etch step. 
     Gallium nitride LEDs are typically grown with the n-doped side in contact with the wafer (n-down) with the p-doped side uppermost (p-up). The embodiment of  FIG.  36   h    provides n-down LEDs on the substrate  535  wherein the n doped side is in contact with the substrate. Such an arrangement requires a transparent current spreading electrode to be formed on the p doped side of the chip which reduces the optical output of the chip. It is advantageous to provide arrangements wherein the p doped side of the chip is coated with a highly reflective conductive electrode and is positioned in contact with the substrate (p-down). The higher conductivity of the n doped side of the LED means that a transparent current spreading electrode is not necessary and thus increases optical output.  FIGS.  37   a  - 37   d    show one method to achieve a p-down arrangement. After the step of extraction of the array  532  onto the receiver substrate  524  as shown in  FIG.  36   b   , a material  540  is applied to the surface of the substrate  524  and array  532  as shown in  FIG.  37   a   . The material  540  may for example be a photoresist or polyimide material. A further substrate  538  may be provided to support the material  540 . After processing of the material  540 , for example by means of heat or by UV illumination, the receiver substrate  524  is removed as shown in  FIG.  37   b   , achieving embedding of the array  532  in the material  540  with the p-doped surfaces exposed. Advantageously, the adhesive force between the adhesive material  525  of the adhesive substrate  524  to the light emitting element array  532  is lower than the adhesive force between the material  540  to the array  532 . The array  532  is then brought into contact with the substrate  535  which may comprise heat spreading, electrode and light reflecting elements  542  as shown in  FIG.  37   c   . Advantageously, the light emitting elements  532  are incorporated into a material  540  capable of withstanding process temperature required for formation of solder joint to the heat spreader and electrode elements  542 . After soldering the material  540  and substrate  538  is removed for example by immersion in a suitable solvent or by peeling at an elevated temperature as shown in  FIG.  37   d   . 
     Similarly a further light emitting element array  536  may be transferred to a separate region of the substrate  535 . Such a process advantageously preserves the separation of the light emitting elements of the respective arrays while providing p-doped side of the light emitting elements in contact with the substrate electrodes. 
     Thus a method of manufacturing an illumination apparatus comprises the steps of forming a monolithic array  522  of light-emitting elements; selectively removing a plurality of light-emitting elements from the monolithic array  522  to a first adhesive substrate  524  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements: transferring the plurality of light emitting elements from the first adhesive substrate  524  to a second adhesive substrate  538 ,  540  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements wherein the adhesive force of light emitting elements to the second adhesive substrate  538 ,  540  is greater than the adhesive force of the light emitting elements to the first adhesive substrate  524 ; transferring the plurality of light emitting elements from the second adhesive substrate  538 ,  540  to a substrate  535  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements wherein the adhesive force of the light emitting elements to the substrate  535  is greater than the adhesive force of the light emitting elements to the second adhesive substrate  538 ,  540 ; wherein the plurality of light-emitting elements that are selectively removed from the monolithic array  522  are selected such that, in at least one direction, for at least one pair of the selectively removed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed light-emitting elements in the at least one direction. 
     Thus a method of manufacturing an illumination apparatus; comprises: forming a monolithic array  522  of light-emitting elements; selectively removing a plurality of light-emitting elements  532  from the monolithic array  522  by adhering them to a first adhesive substrate  524  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements  532 ; transferring the plurality of light emitting elements from the first adhesive substrate  524  to a second adhesive substrate  538 ,  540  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements  532 : transferring the plurality of light emitting elements  532  from the second adhesive substrate  538 ,  540  to a support substrate  535  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements  532 : wherein the plurality of light-emitting elements  532  that are selectively removed from the monolithic array are selected such that, in at least one direction, for at least one pair of the selectively removed light-emitting elements  532  in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of selectively removed light-emitting elements in the at least one direction. The adhesive force of light emitting elements  532  to the second adhesive substrate  538 ,  540  may be greater than the adhesive force of the light emitting elements  532  to the first adhesive substrate  524 . The adhesive force of the light emitting elements  532  to the support substrate  535  is greater than the adhesive force of the light emitting elements  532  to the second adhesive substrate 538.540. The support substrate may comprise an array of optical elements  1  and the array of light emitting elements  532  is aligned with the respective optical elements  1 . The support substrate  535  may comprises a planar substrate wherein the array of light emitting elements  532  is aligned with an optical element array structure  41  comprising an array of optical elements  1 . 
     Errors due to scratches, pits, epitaxial errors and other effects may be present on the epitaxial wafer prior to extraction of individual light emitting elements.  FIG.  38   a    shows an embodiment in which wafer defects are present in light emitting elements of a monolithic array  522  and are characterised. For example, an element sensor  543  is used to determine the location of individual ‘passed’ light emitting elements  546  that have characteristics below a threshold tolerance of a functional criterion and ‘failed’ light emitting elements above a threshold tolerance of a functional criterion. The element sensor  543  may provide for example a functional criterion that comprises a distribution of output wavelength across the array and the defects may be due to varying thicknesses of epitaxial layers that result in differences in output wavelength. Passed devices  546  may be for example those with deviation from the target wavelength of less than or equal to +/-2 nm while failed devices  544  may have a deviation from the target wavelength of greater than +/-2nm. Alternatively the element sensor may measure a functional criterion comprising surface defect characteristics or may determine electrical characteristics of the light emitting elements. An area sensor  547  may provide measurements from groups  543  of light emitting elements, such that light emitting elements in groups  543  are classed as passed or failed light emitting elements. Pass distributions comprising the location of passed light emitting elements and fail distributions comprising the location of failed light emitting elements may thus be provided. Fail distributions will typically comprise those elements that are not in the pass distribution. It is desirable that the light emitting elements  544  in the fail distribution are not incorporated onto the substrate  500  as they may cause for example at least reduced brightness, incorrect colour, short circuit or open circuit. 
     As shown in  FIG.  38   b   , in the lift off step, the patterned UV illumination is modified so that beam  530  is absorbed, reflected or diffused by a feature  537  formed on the opposite side of the semiconductor support substrate  520  to the epitaxial layer comprising array  522  of light emitting elements. Feature  537  may for example comprise a deposited region of absorbing material in alignment with the element  544  that may be formed by an addressable printing method such as inkjet printing, a structured diffusing surface produced by laser processing or a patterned metal formed by a deposition method. On illumination, beam  530  is absorbed, diffused or reflected while beams  529 ,  531  are transmitted. If the power density at the surface of the element  544  with the semiconductor support substrate  520  falls below a threshold, then element  544  will not be lifted off and will remain attached to the semiconductor support substrate  520  as shown in  FIG.  38   c    while the passed light emitting elements  546 ,  548  are transferred onto the substrate  500  and leaving an unfilled element  547  as shown in  FIG.  38   d   . 
     In further steps shown in  FIGS.  38   e - 38   g   , regions of the substrate  500  with missing light emitting elements are filled by means of extraction of an array  558  of light emitting elements from another part of the wafer or indeed a second wafer  550  and array of light emitting elements  552 .  FIG.  38   e    shows the patterned laser lift off step and  FIG.  38   f    shows the separated elements on the adhesive substrate  554 . Adhesive substrate  554  is aligned with substrate  500  and array of elements  542  so as to provide an array of light emitting elements  546 ,  558  from respective first and second wafers on the substrate  500  as shown in  FIG.  38   g   . 
     A method of manufacturing an illumination apparatus thus comprises: forming a first monolithic array  522  of light emitting elements: determining a first plurality of the light emitting elements  546 ,  548  which pass a functional criterion; determining a second plurality of the light emitting elements  544  which fail the functional criterion; selectively removing a plurality of the passed light emitting elements  546 ,  548  whose relative positions in the first monolithic array  522  correspond to desired relative positions in a desired non-monolithic array of light emitting elements, the selectively removing being performed in a manner that preserves the relative spatial position of the selectively removed passed light-emitting elements  546 ,  548 ; wherein the plurality of passed light-emitting elements  546 .  548  that are selectively removed from the monolithic array  522  are selected such that, in at least one direction, for at least one pair of the selectively removed passed light-emitting elements  546 ,  548  in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the monolithic array between the pair of removed passed light-emitting elements in the at least one direction; and forming a non-monolithic array of light-emitting elements with the selectively removed passed light-emitting elements  546 ,  548  in a manner that preserves the relative spatial position of the selectively removed passed light-emitting elements; by virtue of which in the formed non-monolithic array of light emitting elements desired relative positions of the desired array that correspond to passed light emitting elements in the first monolithic array are occupied by passed light emitting elements  546 .  548  and desired relative positions of the desired array that correspond to failed light emitting elements in the first monolithic array are left unoccupied. Further light emitting elements  558  may be added to the formed non-monolithic array of light emitting elements in unoccupied desired relative positions of the desired array. The further light emitting elements  558  may be from a second monolithic array  552  of light-emitting elements that is different to the first monolithic array  522  of light-emitting elements. The further light emitting elements  558  may be from the first monolithic array of light-emitting elements. The further light emitting elements  558  may be light emitting elements which have been determined as passing the functional criterion. A light intensity reduction region  537  may be formed on a surface of the monolithic array support substrate  520  aligned with the second plurality of light emitting elements  544 . 
     Advantageously, elements with known poor performance are not present in the transferred array, improving the yield and achieving a reduced requirement for testing of the final light emitting element array on the substrate. Such a method can therefore reduce the cost and improve the performance of the substrate array. In some applications, particularly those requiring observers to look directly at the light engine, it may be desirable that all of the light emitting elements are functional to avoid dead spots in the output illumination. In this embodiment, further processing steps may be undertaken to prevent defects in the array  552  being transferred to substrate  500  using further wafers. 
     Alternatively as the final devices on the substrate  535  contain light emitters from a wide area of wafer, depending on the yield statistics it may be advantageous not to fully test the wafer and to transfer some defective or even all devices. The averaging effect across the mother sheet means this may achieve satisfactory performance. Alternatively only emitters identified open circuit (non emitting) may be held back from transfer. 
     Thus a method of manufacturing an illumination apparatus may comprise the steps of forming a first monolithic array  522  of light-emitting elements: characterising the first monolithic array of light emitting elements to provide a pass distribution and a fail distribution of light emitting elements; selectively removing a plurality of passed light-emitting elements  546  from the first monolithic array  522  in a manner that preserves the relative spatial position of the selectively removed passed light-emitting elements  546 ; forming a non-monolithic array of light-emitting elements with the selectively removed passed light-emitting elements  546  in a manner that preserves the relative spatial position of the selectively removed passed light-emitting elements; wherein the plurality of passed light-emitting elements that are selectively removed from the first monolithic array  522  are selected such that, in at least one direction, for at least one pair of the selectively removed passed light-emitting elements in the at least one direction, for each respective pair there is at least one respective light-emitting element that is not selected that was positioned in the first monolithic array between the pair of passed selectively removed light-emitting elements in the at least one direction; selectively removing a second plurality of light-emitting elements  558  from a monolithic array  552  of light emitting elements wherein the second plurality of light-emitting elements  558  are arranged with at least part of the fail distribution in a manner that preserves the relative spatial position of the selectively removed second plurality of light-emitting elements  558 : interspersing the second plurality of light-emitting elements  558  with the first plurality of passed light-emitting elements  546  to provide a corrected non-monolithic array of light emitting elements; and aligning the corrected non-monolithic array of light-emitting elements with an array of optical elements. 
     The method may further comprise the steps of forming a light intensity reduction region  537  on a surface of the monolithic array support substrate  520  aligned with the respective fail distribution of light emitting elements. 
     As shown schematically in  FIG.  39   a   , open circuit errors may occur for example due to attachment errors between the light emitting elements  560 ,  562 ,  564  and electrode arrangement  566 . Additional circuitry  568  can be incorporated in the region of the light emitting elements so that in the case of a diagnosed error, a conductive material can be applied in the region  570 . For example, testing may demonstrate that elements  560  and  562  are operating correctly whereas element  564  is open circuit. In this embodiment, a solder patch is applied to the region  570  to short circuit the region of the light emitting element. This embodiment achieves a greater reliability for light emitting elements connected in a series string. As shown in  FIG.  39   b    a similar defect correction can be achieved by applying a conductive layer (e.g. solder)  562  directly over the light emitting element  564 . 
       FIG.  40    shows in plan view a string of light emitting elements  560 ,  562 ,  564  connected by means of metallic heat spreaders  574 , p-electrode solder region  576 , n-electrode  578  and insulator  580 . If element  564  is diagnosed as faulty, a conductive material can be applied in the region  584  to provide a short circuit so that the electrical string can advantageously continue to operate for elements  560  and  562 . 
       FIG.  41    shows in plan view an epitaxial wafer  586  used to form an array of light emitting elements. Epitaxial growth non uniformities provide a variation of emission wavelength and forward voltage characteristics for elements across the surface of the wafer. Light emitting elements can thus be binned (i.e. placed into groups with similar properties) based on the region  588 ,  590 ,  592 ,  594 ,  596 ,  598  from which they originate on the wafer. The extraction process of for example  FIGS.  36   a - h    may be used to extract a sparse array of light emitting elements from across the entire surface of the wafer  586 . The extracted light emitting elements are arranged as a sparse array extracted from the wafer rather than from adjacent positions on the epitaxial layer on the wafer. For example, the light emitting elements may have size of 100x100 micrometres on a pitch of 2 x 2 millimetres. Light emitting elements are thus extracted from substantially all of the regions  588 ,  590 ,  592 ,  594 ,  596 ,  598  in each extraction step. 
     The sparse array may then be assembled in alignment with other sparse arrays onto a support substrate  500  (which may be a large area mothersheet) as shown in plan view in  FIG.  42   a   . Thus sparse arrays  601 ,  603 ,  605 ,  607 ,  609 ,  611  are arranged together on substrate  500 . The properties of the respective sparse arrays vary spatially across the wafer  586  and the spatial variation of properties are thus transferred to the support substrate  500 . The orientation of sparse arrays  601 ,  603 ,  605 ,  607 ,  609 ,  611  is shown in  FIG.  42   a    as being the same. The orientation of the extracted sparse arrays  601 ,  603 ,  605 ,  607 ,  609 ,  611  may alternatively be varied to advantageously provide a mixture of bin regions and so properties within any single illumination element. 
     After a singulation step, individual illumination element regions  606 ,  608  (those that are used for example in a light engine for a single lighting fixture) are extracted from the substrate after cutting along lines  604 . providing singulated illumination element regions  606 ,  608  as shown in  FIG.  42   b    and  FIG.  42   c    respectively. The singulation may be before or after alignment with optical elements and wavelength conversion layers described below. 
     Respective illumination element regions  606 ,  608  may comprise different portions of each of the respective bin regions  588 ,  590 ,  592 ,  594 ,  596 ,  598 . Alternatively, the illumination element regions  606 ,  608  may comprise mixtures of regions from different wafers, for example achieved by arranging sparse arrays from different wafers on the substrate  500 . 
     The integrated emission wavelength is an average of the emission from each of the elements within the respective illumination element regions  606 ,  608 . The integrated emission wavelength advantageously comprises light from light emitting elements arranged in multiple bins and is thus an average value between the extremes of emission wavelength for individual light emitting elements. The difference in integrated emission wavelength for illumination element regions  606 ,  608  will typically be smaller than the total deviation of wavelength within a single wafer, reducing light engine bin size and illumination element cost. 
     By way of comparison, with standard pick-and-place extraction techniques, individual light emitting elements with size for example 1x1 millimetre are extracted from single regions of the wafer and thus have the properties of the single region. Such light emitting elements thus do not have the property averaging advantages of the present embodiments. Advantageously, reduced bin size achieves a reduced variation of illumination element properties, requiring less testing and higher control of properties, thus reducing cost and improving performance. 
     Gallium nitride LEDs typically produce a blue output that is converted to white light by means of a wavelength conversion material such as a phosphor. It would be desirable to further reduce the number of bins by tuning the wavelength conversion material to match the average emission wavelength of the respective illumination element regions  606 ,  608 . As shown in  FIG.  43   , after preparation of the substrate  500  as shown in  FIG.  42   a   , the substrate  500  may further comprise at least two different phosphor coating regions  614 ,  615  tuned to the average emission of the respective illumination element regions  606 ,  608  respectively. Thus each of the white light illumination elements fabricated from blue illumination element regions  606 ,  608  and respective aligned wavelength conversion regions  614 ,  615  may have a small bin range. Advantageously, the emission wavelength, voltage and other properties of the light engine can be produced in small bins thus further reducing cost. 
     The respective phosphor for the illumination element regions  606 ,  608  may be provided after dicing of the substrate  500  and singulation of the illumination element regions  606 ,  608 . Alternatively  FIG.  44    shows an embodiment wherein a patterned phosphor layer is applied across the substrate  500  prior to dicing and singulation. In illumination element region  608 , a phosphor coating layer  612  is applied to light emitting elements  610  after measurement of the combined spectral output across the illumination element region  606 . A sensor  617 , such as a colorimeter or spectrophotometer is arranged to integrate the light from across the respective illumination element region and measure the combined spectral output of at least some of the light emitting elements  611 . The expected region average white point may be determined by measuring the blue light output from the light emitting elements  610  and determining the white point that would be provided by a standard phosphor. This can then be used to provide the properties of a suitable matched phosphor layer  618  spectral characteristic to achieve the desired target white point. In illumination element region  608 , a second phosphor layer  612  is provided, with spectral characteristic tuned to the mean emission wavelength of the light emitting elements  610 . The phosphor may printed by means of a screen or stencil  620  and doctor blade  622  across the respective region. Alternatively the phosphors may be selectively deposited by an inkjet process. In this manner, high precision printing of individual phosphor coatings tuned to each of the individual light emitting elements is avoided, thus decreasing cost for a small bin size and achieving higher performance. 
     Thus a method of manufacturing an illumination apparatus may comprise the steps of forming a non-monolithic array of light-emitting elements  611 ,  612  on a support substrate  500 ; measuring the spectral output of at least some of the light-emitting elements  611  in a first region  606  of the support substrate  500 : providing a first wavelength conversion layer  618  in alignment with the respective light emitting elements  611  of the first region  606  arranged to provide a first region average white point; measuring the spectral output of at least some of the light-emitting elements  610  in a second region  608  of the support substrate  500 ; providing a second wavelength conversion layer  612  different to the first wavelength conversion layer  618  in alignment with the respective light emitting elements  610  of the second region  608  arranged to provide a second region average while point; wherein the first and second region average white points are the same. 
     Thus a method of manufacturing an illumination apparatus may comprise the steps of forming a non-monolithic array of light-emitting elements  611  on a support substrate  500 : for at least some of the light-emitting elements  611  in a first region  606  of the support substrate  500 , measuring their combined spectral output; providing a first wavelength conversion layer  618  in alignment with the respective light emitting elements  611  of the first region  606 , the spectral characteristic of the first wavelength conversion layer  618  being selected dependent upon the measured combined spectral output from the measured light emitting elements  611  of the first region  606 ; for at least some of the light-emitting elements  612  in a second region  608  of the support substrate  500 , measuring their combined spectral output: and providing a second wavelength conversion layer  612  in alignment with the respective light emitting elements  610  of the second region  608 , the spectral characteristic of the second wavelength conversion layer  612  being selected dependent upon the measured combined spectral output from the measured light emitting elements  610  of the second region  608 . 
     A first region average white point may be provided by virtue of providing the first wavelength conversion layer  618  in alignment with the respective light emitting elements  611  of the first region  606 ; a second region average white point may be provided by virtue of providing the second wavelength conversion layer  612  in alignment with the respective light emitting elements  610  of the second region  608 , and wherein the first region average white point and the second region average white point are thereby more similar than they would be if the two regions  606 .  608  had been provided with a same wavelength conversion layer. A first region average white point is provided by virtue of providing the first wavelength conversion layer  618  in alignment with the respective light emitting elements  611  of the first region  606 , a second region average white point is provided by virtue of providing the second wavelength conversion layer  612  in alignment with the respective light emitting elements  610  of the second region  608 , and wherein the first region average white point and the second region average white point are substantially the same. The spectral characteristics of the first wavelength conversion layer  618  may be different to the spectral characteristics of the second wavelength conversion layer  612 , that is the spectrum that is output for a given light emitting element input is varied. 
     Alternatively or in combination, the white point can be adjusted by leaving some of the light emitting elements uncoated. Thus the number of light emitting elements  610 ,  611  that have a wavelength conversion layer can be used to adjust the white point of the respective regions  606 ,  608 . Thus a method of manufacturing an illumination apparatus may comprise the steps of forming a non-monolithic array of light-emitting elements  611  on a support substrate  500 ; for at least some of the light-emitting elements  611  in a first region  606  of the support substrate  500 , measuring their combined spectral output; providing a first wavelength conversion layer  618  in alignment with some of the respective light emitting elements  611  of the first region  606 , wherein the number of light emitting elements  611  of the first region  606  that are provided with the first wavelength conversion layer  618  is adjusted dependent upon the measured combined spectral output from the measured light emitting elements  611  of the first region  606 ; for at least some of the light-emitting elements  610  in a second region  608  of the support substrate  500 , measuring their combined spectral output; and providing a second wavelength conversion layer  612  in alignment with some of the respective light emitting elements  610  of the second region  608 , wherein the number of light emitting elements  610  of the second region  608  that are provided with the second wavelength conversion layer  612  is adjusted dependent upon the measured combined spectral output from the measured light emitting elements  610  of the second region  608 . The first and second wavelength conversion layers  612 ,  618  may be the same. 
     Alternatively or in combination, the white point can be adjusted by adjusting the thickness of the wavelength conversion layer. The thickness may be adjusted by varying the solvent fraction of the layers  612  and  618 , or by adjusting the thickness of the stencil  620  to be different for different regions  606 ,  608 . The thickness refers to the thickness of the layers  612 ,  618  after processing (for example after baking to remove solvent). Thus a method of manufacturing an illumination apparatus may comprise the steps of forming a non-monolithic array of light-emitting elements  611  on a support substrate  500 ; for at least some of the light-emitting elements  611  in a first region  606  of the support substrate  500 , measuring their combined spectral output; providing a first wavelength conversion layer  618  in alignment with the respective light emitting elements  611  of the first region  606 , the thickness the first wavelength conversion layer  618  being selected dependent upon the measured combined spectral output from the measured light emitting elements  611  of the first region  606 ; for at least some of the light-emitting elements  612  in a second region  608  of the support substrate  500 , measuring their combined spectral output; and providing a second wavelength conversion layer  612  in alignment with the respective light emitting elements  610  of the second region  608 , the thickness of the second wavelength conversion layer  612  being selected dependent upon the measured combined spectral output from the measured light emitting elements  610  of the second region  608 . 
       FIG.  45    shows that the light emitting elements may be provided in strings wherein the string electrodes  624 ,  626  connected to light emitting elements  610  in region  608  cover a number of bin regions within the region. Thus the deviation about the mean of the total forward voltage across the string is reduced, advantageously simplifying some types of driver design and reducing cost. 
       FIGS.  46   a - f    shows a method to form an array of light emitting elements for embodiments wherein the semiconductor epitaxial growth substrate  630  is not adequately transparent (in an electromagnetic wavelength band) to a suitable or desirable illumination wavelength for a lift off process such as a laser lift off process. Alternatively, the lift-off interaction layer may not be well suited to a desirable laser. For example, as shown in  FIG.  46   a   , the semiconductor growth substrate  630  may be silicon or silicon carbide on which a light emitting element layer  632  is grown for example by known epitaxial growth methods. Such materials are typically substantially absorbing to the ultraviolet radiation wavelength band typically used in excimer laser lift off at GaN-sapphire interfaces. Alternatively the laser lift off process may not be sensitive to electromagnetic radiation of a desirable light source. For example the interface of GaN-sapphire is not sensitive to decomposition in infra-red electromagnetic radiation in comparison with that is achieved by excimer laser illumination. Infra-red electromagnetic radiation is a preferable electromagnetic radiation source due to its lower cost compared to excimer laser sources. 
     A metallisation layer  631  may be applied to the top surface of the layer  632  to provide electrical connection to the light emitting elements following an extraction step. The metallisation layer  631  may be continuous or may be patterned. Further the metallisation may be suitable for bonding to electrodes, for example by eutectic soldering to other layers on a substrate such as a support substrate which may be a mothersheet. 
       FIG.  46   b    shows that a support substrate  520  that is transparent in an electromagnetic radiation wavelength band may be attached to the layer  632  by means of an absorbing layer  634  that is absorbing in the electromagnetic wavelength band. The layer  634  may comprise for example an ultra-violet sensitive tape (wherein adhesion strength is lowered by means of an illuminating UV laser) or may an infra-red absorber (wherein adhesion strength is lowered by means of infra-red radiation). In each case, an array of patterned electromagnetic radiation beams  529 ,  530 ,  531  is used to illuminate the layer  634  in alignment with light emitting elements  532  that are desirably removed. 
     In a further step, layer  632  is removed from substrate  630  for example by means of an etch step, a photochemical etch or known lift off techniques to provide a structure of substrate and layers as shown in  FIG.  46   c   . Further metallisation layers  633  may be applied to the opposite side of the light emitting element layer  632  compared to the metallisation layer  631 . 
     Further layers (not shown) such as silicon dioxide may be arranged between the layer  632  and substrate  630  to facilitate or improve the reliability of the separation, for example by means of wet etching or photochemical etching. The separated structure of  FIG.  46   c    may then be patterned to provide an array of light emitting elements with separation s1, as shown in  FIG.  46   d   , for example by means of laser scribing or etching. 
     As shown in  FIG.  46   e    in a similar manner to that used for  FIG.  36   a   , a patterned array of optical illumination regions  528  in the electromagnetic radiation wavelength band is provided so as to provide a patterned lift off of light emitting elements with separation s1 onto support substrate  636  as shown in  FIG.  46   f   . Residual material of layer  631  on elements  532  may be cleaned after the extraction step. 
     The substrate  636  may then be aligned with an array of optical elements, or may comprise the optical elements, for example as shown by optical element array structure  41  of  FIG.  9   ; or may comprise an intermediate transfer substrate that is used to transfer the elements  532  onto a substrate  67  or optical element array structure  41 . 
     Thus a method of manufacturing an illumination apparatus may comprise the steps of forming a monolithic light-emitting layer  632  on an electromagnetic radiation wavelength band absorbing substrate  630 ; transferring the monolithic light-emitting layer  632  to a electromagnetic radiation wavelength band transmitting substrate  520 ; selectively removing a plurality of light-emitting elements  522  from the monolithic light-emitting layer  632  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements  522  by selectively illuminating the monolithic array of light-emitting elements  522  through the electromagnetic radiation wavelength band transmitting substrate  520  with electromagnetic radiation in the electromagnetic radiation wavelength band; forming a non-monolithic array of light-emitting elements  532  with the selectively removed light-emitting elements in a manner that preserves the relative spatial position of the selectively removed light-emitting elements; and aligning the non-monolithic array of light-emitting elements with an array of optical elements. 
     Thus method of manufacturing an illumination apparatus comprises forming a monolithic light-emitting layer  632  on a first substrate  630 ; transferring the monolithic light-emitting layer  632  to an electromagnetic wavelength band transmitting substrate  520 ; selectively removing a plurality of light-emitting elements  532  from the monolithic light-emitting layer  632  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements  532 , performing of the selectively removing comprising selectively illuminating the monolithic array of light-emitting elements through the electromagnetic wavelength band transmitting substrate  520  with light in the electromagnetic wavelength band; forming a non-monolithic array of light-emitting elements with the selectively removed light-emitting elements  532  in a manner that preserves the relative spatial position of the selectively removed light-emitting elements  532 ; and aligning the non-monolithic array of light-emitting elements  532  with an array of optical elements. The first substrate  630  may be an electromagnetic wavelength band absorbing substrate. 
     Advantageously, the absorption of the material or materials forming the layer  634  may be optimised for use with the wavelength band of the electromagnetic radiation source such as a laser used to provide illumination regions  528 . For example, the laser may be an excimer laser with an ultraviolet wavelength band emission, for transmission through a substrate  520  comprising quartz or sapphire material. The material of the layer  634  may however have a wider process window than the gallium nitride to sapphire adhesion process window that may increase reliability and reduce process time. Alternatively an infra-red laser with an infra-red electromagnetic wavelength emission band may be used in combination with a substrate  520  comprising a glass or plastic substrate. Advantageously, infra-red electromagnetic radiation sources such as diode pumped solid state lasers may be provided with high power and low cost compared to excimer lasers. Thus, the throughput yield of the patterned laser lift off may be improved and the cost reduced. Further the beam uniformity requirements for illumination of layer  634  may be less tight than for UV excimer laser lift off, providing Gaussian beam exposure conditions and reduced probability of cracking of the layer  632  during the extraction step of  FIG.  46   e   . Further, the substrate  630  may advantageously have reduced cost (for example silicon) compared to the sapphire epitaxial growth substrate of  FIG.  36   a    reducing light emitting element cost. Further, the lattice constant of the epitaxial growth substrate  630  may be more closely matched to the lattice substrate of the semiconductor material of layer  632  (for example silicon carbide); thus reducing strain in the device and improving light emitting element performance. 
     While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims and their legal equivalents.