GB2457296A

GB2457296A - Optical device e.g. radiant-power-transferring light engine

Info

Publication number: GB2457296A
Application number: GB0802441A
Authority: GB
Inventors: David Steven
Original assignee: APTICOL Ltd
Current assignee: APTICOL Ltd
Priority date: 2008-02-09
Filing date: 2008-02-09
Publication date: 2009-08-12
Also published as: GB0802441D0

Abstract

The optical device 3 has an input face 9 and an output face 11. A first surface 13 is provided for reflecting light from a light source 5 and a second surface 15 is provided for reflecting light reflected from said first surface 13 towards the output face 11. The light reflected from the first surface 13 is convergent. The present invention also relates to an illumination system 1 comprising one or more of the optical devices 3. Also claimed is an optical system comprising a first optical device for converging light from a light source and outputting substantially collimated light. A second optical device converges light output from the first optical device and outputs substantially collimated light.

Description

OPTICAL DEVICE

The present invention relates generally to an optical device. More particularly, the present invention relates to a radiant power transferring, light engine.

Light engines according to the present invention may be employed in a range of applications, but they are particularly suitable for use in lighting and projection systems.

In many commercial applications using light, which require a target component (1) to be illuminated by a beam of a certain size, there is a physical separation between the source (S) and the target (T). The light source itself can be one, or a combination of sources which can be operated continually or pulsed, can be coherent, incoherent or partially coherent. In general they can be driven by AC or DC voltage, by chemical methods, by microwave heating or the like.

Generally, the light from the source will require to be reformatted such that it is usable by the target in terms of spectral efficiency and in particular the spatial and angular matching of source to target. Most commonly, the formatting required will be in terms of beam area (cross-sectional), intensity distribution, intensity level (both maximum and minimum), incident angle when reaching target, propagation direction, spectral content and spectral distribution. These parameters can be affected by various optical components such as colour wheels (cw), light guides (LG), Polarization Converters (PC), etc. and the overall system layout can affect the overall light throughput of the system. Each individual component can be described as an effective or intermediate target component when describing the system.

The light rays which are not incident on a given target are considered to be wasted and can have undesired effects on the system such as heating of certain elements, and causing undesired reflections and stray light within the system. It is useful to mask these rays or use suitable light sinks' to alleviate any problem with stray light rays. It is therefore desirable for any system used for the purpose such as the invention stated here that as much of the source light is utilised by the target as is physically possible.

A Light Engine (LE) as defined here can be described as an apparatus that collects light from a given source or sources and reformats that light so that it can be utilised elsewhere in a given system. It is typically made up of multiple optical components that together have at least two or three major tasks. The first task is to collect light from a source S. The second task is to deliver some of the collected light to the target T. The third, and often optional, task is to reformat the light beam to enhance the usable content of the light delivered to the target T. At least in preferred embodiments, the light engine efficiently collects light from a source or sources and reformats the light so that it can be utilised efficiently.

The optical parameters called etendue E, etendue efficiency EE, throughput efficiency TE and delivery efficiency DE are important in better understanding this invention and are defined and discussed below. The etendue E is a measure of both the spatial and angular confinement of a light beam. The throughput efficiency TE and etendue efficiency EE are related parameters and measure in different ways how efficiently a given optical system reformats a given input beam compared to an ideal performing optical system. The delivery efficiency DE parameter measures both the fulfilment of the target formatting requirements and the throughput efficiency of a LE for a given target T, i.e. measured the amount of both collectable and usable light by a given target T. Light engines are used in many applications and the references given here show the different methods for collection and distribution of light rays within a light engine.

U.S. Patent No. 5,491,765 to Matsumoto (1996) describes a typical Light Engine design where a parabolic, sealed short arc reflector lamp, in combination with a focusing lens, is used to deliver collected energy to the entrance surface of a round fiber optic Light Guide and U.S. Pat. No. 5,574,328 to Okuchi (1996) discusses a light engine which has a double concave reflector forming a light engine collection system with the source axis of a gas discharge arc lamp aligned co-linear with the optical axis of the collection system. U.S. Pat. No. 5,491,620 to Winston et. all (1994) has a double concave reflector system as the light engine and a light guide collecting the re-concentrated light.

These types of light engine are standard formats which are used extensively in lighting apparatus, car headlamps etc and do not allow for multiple sources to be used in an efficient manner.

Prior art Projection Light Engines (PLE's), which are designed to illuminate a projection screen by illuminating first a Light Valve or Light Modulator, are even more complex and optically demanding than the above-discussed prior art light engines. The selection of particular optical key components for a PLE often introduces additional design constraints.

U.S. Pat. No. 5,592,188 to Doherty (1997) describes a typical PLE for a single digital micro mirror device (DMD) type reflective light valve. The light discussed in this patent is very similar to the one discussed in U.S. Pat. No. 5,491,765. However, instead of illuminating a light guide, this system focuses the collected source energy onto a colour wheel, which creates a time sequenced colour beam. This application also uses only one source. The use of the colour wheel has a marked effect on the efficiency of the overall system.

U.S. Pat. No. 5,098,184 to van den Brandt and Timmers (1992) describe lens array designs for the spatial beam intensity homogenization in a PLE that illuminates a liquid crystal type light modulator. This type of light engine again uses a single source and reflector but uses lens arrays to increase efficiency.

In order to increase efficiency of a light engine, it is important that the light from the source is collected and redirected in such a manner that a high percentage of the source light is incident on the image forming component of the system, as is suggested here for use in a projector.

US Patent 6674576B1 show a method for use in telescopic communications which uses a general mirror arrangement. GB03851 04A, GB0474039A and US 635639081 show the use of an array of light sources in an annular configuration.

It is therefore an object of the present invention, at least in preferred embodiments, to provide a method for designing efficient light engines for a broad range of etendue-limited targets T. It is still a further object of the present invention, at least in preferred embodiments, to provide improved cost/performance ratio of Light Engine's for given primary and/or intermediate target demands due to reduced or minimised component count.

It is still a further object of the present invention, at least in preferred embodiments, to provide improved PLE's and new types of projection display systems for truly portable projection systems.

It is still a further object of the present invention, at least in preferred embodiments, to change the manufacturing of related component to improve their usability for manufacturing high efficiency light engines.

It is still another object of the present invention, at least in preferred embodiments, to provide methods for reducing the size of related components and projection systems while increasing or maximizing the delivery efficiency of a related light engine.

Viewed from a first aspect, the present invention relates to an optical device comprising an input face, an output face, a first surface for reflecting light from a light source, and a second surface for reflecting light reflected from said first surface towards said output face; wherein light reflected from the first surface is convergent. In use, light passes through the input face and, preferably, is reflected by the first surface so as to converge on a longitudinal axis or a central point of the optical device. The convergent light is reflected by the second surface towards the output face. Thus, at least in preferred embodiments, the optical device according to the present invention may provide a robust means for concentrating light from a light source. Moreover, a plurality of the optical devices may be arranged in series.

The light reflected from the first surface may converge on an axis of the optical device. Alternatively, the first surface may be configured such that the reflected light converges on a point. Equally, the first surface may be configured such that the reflected light converges on a plane.

The light reflected from the second surface may be substantially collimated.

Preferably, the light reflected from the second surface is substantially parallel to the longitudinal axis of the optical device.

The optical device may be an optical element comprising the input face, the output face, the first surface and the second surface. Preferably, the optical element is formed in one piece.

The first surface is preferably convex and the second surface is preferably concave. The first and second surfaces may be substantially parallel.

The first surface preferably tapers away from the input face. Preferably, the first surface tapers towards a longitudinal axis of the optical device. The first surface is preferably substantially conical. In preferred embodiments, the first surface is defined by a first circular or elliptical cone which may be truncated. Alternative arrangements of the optical device may comprise a first surface defined by a cone having a polygonal base.

The optical device may, for example, comprise or consist of a cone or truncated cone having a triangular, quadrilateral, pentagonal, hexagonal, heptagonal or octagonal base.

The first surface may define at least part of the outside of the optical device.

The second surface is preferably substantially conical. In preferred embodiments, the second surface is defined by a second circular or elliptical cone which may be truncated. Alternatively, the optical device may comprise a second surface defined by a second cone having a polygonal base. The second cone may define at least part of the inside of the optical device. For example, a conical recess may be formed in the optical device to define the second surface. The optical device may comprise a second surface defined by a cone having a polygonal base.

The first and second surfaces are preferably arranged concentrically. Preferably, the first and second surfaces may be arranged co-axially with the longitudinal axis of the optical device.

In use, the reflection of light by the first surface and/or the second surface preferably occurs internally. Preferably, the first surface andlor the second surface is/are adapted to provide substantially total internal reflection. Thus, at least in preferred embodiments, the first surface and/or the second surface are arranged such that incident light is at an angle greater than the critical angle, measured with respect to a normal of the respective surfaces. The critical angle being the angle at which light would be reflected from the surface.

Rather than utilise internal reflection, a reflective or mirrored element may be provided on the first surface and/or the second surface. The reflective or mirrored element may be a coating or layer applied to the optical device. Of course, a combination of internal reflection and reflection off a reflective or mirrored element may be utilised.

The input face is preferably substantially planar and may be arranged substantially perpendicular to the longitudinal axis of the optical device. The input face is preferably substantially annular. The second surface is preferably defined by a recess formed in the optical device. The recess is preferably formed in the middle of the input face. Furthermore, a lens, such as a piano-convex lens, may be provided in the recess.

The output face is preferably circular or annular. The output face may be planar or convex.

The optical device is made of an at least partially transparent material. The optical device may, for example, be made of glass or a plastics material.

Viewed from a further aspect, the present invention relates to an optical device comprising a first surface for converging light from a light source, and a second surface for reflecting convergent light from said first surface towards an output face of the optical device.

Preferably the optical device described herein is formed in a single piece. For example, the optical device may be a one-piece moulding.

Viewed from a still forther aspect, the present invention relates to an optical element comprising an input face, an output face, a first surface for reflecting light from a light source, and a second surface for reflecting light reflected from said first surface towards said output face. The optical element may comprise or consist of an at least partially hollow cone. The first and second surfaces may, for example, be defined by inner and outer faces of said at least partially hollow cone. The cone may have a circular, elliptical or polygonal base. The cone may be truncated.

Viewed from a still further aspect, the present invention relates to an illumination system comprising at least one optical device as described herein.

The illumination system may comprise a plurality of said optical devices arranged coaxially. Preferably, the optically elements are arranged in series such that light passes through the optical devices sequentially.

The optical devices preferably have different diameters. The optical devices are preferably arranged such that the diameters of the optical devices increase or decrease in size along the illumination system. Preferably, the illumination system comprises at least first optical device having a first diameter and a second optical device having a second diameter, wherein said first diameter is greater than the second diameter.

The illumination system may include a light source. The light source may comprise a plurality of Light Emitting Diodes (LEDS). The LEDS may, for example, be arranged in a ring.

A collimator is preferably provided for collimating light. The collimator is preferably arranged to collimate light emitted from a light source. In use, the collimated light may be incident on the input face. Preferably, the collimated light is substantially parallel with the longitudinal axis of the optical device.

Viewed from a yet further aspect, the present invention relates to an optical system comprising a first optical device for converging light from a light source and outputting substantially collimated light; and a second optical device for converging light output from said first optical device and outputting substantially collimated light. Thus, the optical system may reduce the cross-section of a light beam in a stepwise manner.

The first and second optical devices may comprise or consist of optical elements of the types described herein.

The term convergent used herein means that the reflected light tends towards a central point, axis or plane.

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: Figures 1A and 1 B show an optical device for an illumination system in accordance with a first embodiment of the present invention; Figure 2 shows a perspective view of the optical device according to Figure 1; Figure 3 shows a second embodiment of the optical device according to the present invention; Figure 4 shows a third embodiment of the optical device according to the present invention; Figure 5 shows two optical devices in accordance with the present invention arranged in series; Figure 6 shows an exploded view of an optical device according to a fourth embodiment of the present invention; Figure 7 shows a side view of the assembled optical element of Figure 6; Figure 8 shows an array comprising two optical devices according to the fourth embodiment of the present invention arranged in series; and Figure 9 shows an array comprising three optical devices according to the fourth embodiment of the present invention arranged in series.

The present invention relates to an illumination system I comprising an optical device 3. A first embodiment of the optical device 3 in accordance with the present invention is illustrated in Figures 1A, 1 B and 2. The optical device 3 according to the first embodiment consists of an optical element 4 made of a transparent material, such as plastics or glass. The optical device 3 has a longitudinal axis X and a transverse axis V arranged perpendicular to each other.

The illumination system I comprises an array 5 of light sources 7 such as Light Emitting Diodes (LEDs). The light sources 7 are arranged in a ring in the present embodiment, but alternative arrangements are also envisaged. The light sources 7 may each be collimated or an optical collimation device (not shown) may be coupled to the array 5 to collimate the light emitted from the light sources 7.

The optical element 4 comprises a planar input face 9, a planar output face 11, a first surface 13 and a second surface 15. The input face 9 and the output face 11 are parallel to each other and arranged substantially perpendicular to the longitudinal axis X of the optical device 3. The input face 9 is in the shape of a torus and corresponds generally to the ringed arrangement of light sources 7 in the array 5. The output face 11 is circular and is defined by a cylindrical portion of the optical element 4.

The first surface 13 is defined by an outer surface of the optical element 4 in the shape of a first truncated cone. The second surface 15 is defined by an inner surface of the optical element 4 formed by a recess 17. The first and second surfaces 13, 15 correspond to the surfaces of first and second truncated cones arranged concentrically having a common axis coincident with the longitudinal axis X of the optical element 4.

The first surface 13 is inclined at a first angle a (alpha) relative to the transverse axis X of the optical element 4. The first angle a (alpha) is selected such that the collimated light from the array 5 strikes the first surface 13 at an angle 81, measured with respect to a normal of the first surface 13, which is greater than the critical angle. The critical angle being the angle at which light would be reflected from the first surface 13.

The critical angle varies for different materials having different refractive indexes. For example, if the optical element 4 is made of acrylic having a refractive index of 1.49, the critical angle is 42.15° and light striking at an angle greater than this will be reflected.

As shown in Figure 1 B, the second surface 15 is inclined at a second angle (beta) relative to the transverse axis X of the optical element 4. The second angle fi (beta) is selected such that the convergent light reflected from the first surface 13 strikes the second surface 15 at an angle 02, measured with respect to a normal of the second surface 15, which is greater than the critical angle. The critical angle being the angle at which light would be reflected from the second surface 15.

The first and second angles a (alpha) and S (beta) are preferably equal such that the first and second surfaces 13, 15 are parallel to each other. In the present embodiment the first and second angles a (alpha) and fi (beta) are both 47.50° when measured relative to the transverse axis Y. The operation of the illumination system 1 will now be described with reference to Figure 1. The light generated by the light sources 7 is collimated in a conventional manner. As illustrated by arrow A, the collimated light enters the optical element 4 substantially perpendicular to the input face 9. The light travels through the input face 9 and strikes the first surface 13 of the optical element 4. Since the refractive index on the other side of the first surface 13 is lower, substantially total internalreflection occurs.

The light is reflected radially inwardly towards the longitudinal axis X of the optical element 4, as illustrated by arrow B. Thus, the light reflected by the first surface 11 is convergent.

The convergent light strikes the second surface 15 at an angle greater that the critical angle. Since the refractive index on the other side of the second surface 15 is lower, substantially total internal reflection occurs. The light reflected from the second surface 15 exits through the output surface 11, as illustrated by the arrow C. Advantageously, the light exiting the optical element 4 may be substantially parallel to the longitudinal axis X. Of course, by varying the first angle a (alpha) and/or the second angle fi (beta) the light exiting the optical element 4 may be made convergent or divergent, as required.

Rather than utilise internal reflection, a reflective coating or layer may be provided on the first and second surfaces 11, 13 of the optical element 4. For example, a mirrored coating may be provided to reflect incident light. In such an arrangement, the first and second angles a (alpha) and 8 (beta) may be varied since it is not a requirement that the incident light strikes the first and second surfaces 11, 13 at an angle greater than the critical angle. Of course, an arrangement utilising a combination of internal reflection and a reflective coating may be utilised.

It will be appreciated that the light sources 7 can be a single colour or can be a combination of colours, typically red, green and blue (RGB), to allow mixing of different colours.

A second embodiment of an optical device 3' in accordance with the present invention is illustrated in Figure 3. The optical device 3' according to this embodiment corresponds generally to the first embodiment described herein and like reference numerals have been used for like components.

The second embodiment of the optical device 3' comprises a first optical element 4' and a second optical element 19. In the present embodiment, the second optical element 19 is a pIano-convex lens 19 mounted in the recess 17' formed in the optical element 4'. The pIano-convex lens 19 may converge light emitted from the light sources 7 towards the longitudinal axis X; or reduce the divergence of said light before it enters the optical device 3 through said second surface 15'.

A third embodiment of the optical device 3" is illustrated in Figure 4. This embodiment corresponds closely to the second embodiment described above and, again, like reference numerals have been used for like components.

The optical device 3" comprises a first optical element 4" and a second optical element 4" which is again a piano-convex lens. The output face 11" of the optical element 4" according to the third embodiment is convex (rather than planar) such that light exiting the optical device 3" converges, as illustrated by the arrow D. An external lens (riot shown) may be provided in series with the optical device 3" to re-direct the light after it has exited through the output face 11".

As illustrated in Figure 5, first and second optical devices 3a, 3b in accordance with the present invention may be arranged in series. The optical devices 3a, 3b are arranged co-axially such that light passes through the first optical device 3a before entering the second optical device 3b. In the illustrated arrangement, the first optical device 3a corresponds to the third embodiment of the optical device 3" described herein comprising an optical element 4" having a piano-convex lens 19" provided in the recess 17" formed therein and a convex output face 11". The second optical device 3b corresponds to a modified version of the third embodiment of the optical device 3" comprising a first optical element 4" having a convex output face 11". However, the the piano-convex lens 19" of the second optical device 3b has been omitted. The passage of light through the first and second optical devices 3 is illustrated by the arrows E in Figure 5.

The first and second optical devices 3a, 3b are illustrated as having the same diameter. However, the skilled person will understand that this is not essential. For example, the second optical device 3 may have a smaller diameter than the first optical device 3.

An optical device 101 in accordance with a fourth embodiment of the present invention is illustrated in Figures 6 and 7. The optical device 101 comprises an inner optical element 102 and an outer optical element 103 made of a transparent medium, such as glass or plastic. The inner and outer elements 102, 103 are shown separated from each other in Figure 6, but in use the inner optical element 102 is mounted at least partially inside the outer optical element 103 as described below.

The outer element 103 comprises a planar input face 105, a planar output face 107, a first reflective surface 109 and a second reflective surface 111. The input face and the output face 107 are substantially parallel to each other and are arranged substantially perpendicular to a longitudinal axis X of the outer element 103. A first circular aperture 113 is formed in the input face 105 and a second circular aperture 115 is formed in the output face 107. Thus, the input face 105 and the output face 107 are both torus-shaped.

The first surface 109 is defined by an outer surface of the outer element 103.

The second surface 111 is defined by an inner surface of the outer element 103 formed by a recess 117 in the input face 105. The first and second surfaces 109, 111 correspond to the surfaces of first and second truncated cones arranged concentrically having a common axis coincident with the longitudinal axis X of the outer element 103.

The arrangement of the first and second surfaces 109, 111 corresponds to that of the first and second surfaces 13, 15 of the optical device 3 according to the first embodiment described herein. Thus, the first and second surfaces 109, 111 are inclined relative to the transverse axis Y at first and second angles a (alpha) and fi (beta) respectively such that there is substantially total internal reflection of incident light. The first and second angles a (alpha) and,8 (beta) are equal such that the first and second surfaces 109, 111 are substantially parallel.

The inner element 102 is generally conical and, as shown in Figure 7, is mounted in the recess 117 formed in the outer element 103. The inner element 102 is designed such that the conditions for total internal reflection are not met. Rather, light is refracted through the inner element 102 into the outer element 103 and out through the outlet face 107. The angles of refraction are such that the light is passed through the second circular aperture 115.

The outer surface of the inner element 102 is inclined at an angle y (gamma) relative to the transverse axis Y. The angle y (gamma) is less than the angle fi (beta) such that a tapered aperture 119 is formed between the inner element 102 and the outer element 103. This arrangement may help reduce the divergence of light entering the outer element 103 The inner element 102 in the present embodiment is conical, but could be convex or any other shape suitable for refracting the light at the angle required for entering the outer element 103 of the optical device 101 to achieve efficient light transmission through the exit aperture of the system.

A plurality of optical devices 101 according to the fourth embodiment of the present invention may be arranged in series along the longitudinal axis X. The optical devices 101 arranged in series may have different diameters.

As shown in Figure 8, first and second optical devices lOla, lOib may be arranged coaxially in series. The first and second optical devices lOla, lOib correspond to the optical device 101 according to the fourth embodiment of the present invention. The optical devices lOla, lOib are illustrated spaced apart from each other along the longitudinal axis X, but preferably they abut each other. The second optical device 101 b has an input face 105' and an output face 107' smaller than the diameters of the corresponding input face 105 and output face 107 of the first optical device lOla.

The input face 105' of the second optical device 101 b has the same diameter as the output face 107 of the first optical device lOla and this may help reduce the loss of light at the junction. The output face 107' of the second optical device lOib is smaller than the input face 105'.

The first optical device lOla may be provided with a flange or projection suitable for at least partially surrounding the input face 105' of the second optical device 101 b.

Alternatively, the second optical device 101 b may be provided with a flange or projection for at least partially surrounding the output face 107 of the first optical device lOla.

A further arrangement is illustrated in Figure 9 comprising three optical devices lOla, bib, lOlc in accordance with the fourth embodiment of the present invention.

The optical devices lOla, bib, lOic are illustrated spaced apart from each other along the longitudinal axis X. Preferably, the adjacent optical devices lOla, lOib, lOic in the series abut each other. The optical devices lOla, bib, lOic are arranged coaxially such that the output face 107 abuts the input face 105 of the adjacent optical device 101 in the series.

It will be appreciated that various changes and modifications may be made to the illumination system 1 and the optical devices 3 described herein without departing from the spirit and scope of the present invention. -13-

Claims

CLAIMS: 1. An optical device comprising an input face, an output face, a first surface for reflecting light from a light source, and a second surface for reflecting light reflected from said first surface towards said output face; wherein light reflected from the first surface is convergent.
2. An optical device as claimed in claim 1, wherein said first surface is convex.
3. An optical device as claimed in claim I or claim 2, wherein said second surface is concave.
4. An optical device as claimed in any one of claims 1, 2 or 3, wherein said first surface is substantially conical.
5. An optical device as claimed in claim 4, wherein said first surface is defined by a first truncated cone.
6. An optical device as claimed in any one of claims 1 to 5, wherein said second surface is substantially conical.
7. An optical device as claimed in claim 6, wherein said second surface is defined by a second truncated cone.
8. An optical device as claimed in any one of claims 4 to 7, wherein said first and second surfaces are arranged concentrically.
9. An optical device as claimed in any one of the preceding claims, wherein the first surface and/or the second surface is/are adapted to provide substantially total internal reflection.
10. An optical device as claimed in any one of the preceding claims, wherein a reflective coating is provided on said first surface and/or said second surface.
II. An optical device as claimed in any one of the preceding claims, wherein said input face is annular.
12. An optical device as claimed in any one of the preceding claims, wherein said second surface is defined by a recess formed in the optical device.
13. An optical device as claimed in claim 12 further comprising an optical element mounted in said recess.
14. An optical device as claimed in claim 13, wherein said optical element is a piano-convex lens.
15. An optical device as claimed in any one of the preceding claims, wherein the output face is planar or convex.
16. An optical device comprising a first surface for converging light from a light source, and a second surface for reflecting convergent light from said first surface towards an output face of the optical device.
17. An optical device as claimed in any one of the preceding claims, wherein the optical device is formed in a single piece.
18. An optical element comprising an input face, an output face, a first surface for reflecting light from a light source, and a second surface for reflecting light reflected from said first surface towards said output face.
19. An illumination system comprising at least one optical device as claimed in any one of the preceding claims.
20. An illumination system as claimed in claim 19 comprising a plurality of said optical devices arranged coaxially.
21. An illumination system as claimed in claim 19 or claim 20, comprising at least a first optical device having a first diameter and a second optical device having a second diameter, wherein said first diameter is greater than the second diameter.
22. An illumination system as claimed in any one of claims 19, 20 or 21 further comprising a light source.
23. An illumination system as claimed in any one of claims 19 to 22 further comprising a collimator for collimating light.
24. An optical system comprising a first optical device for converging light from a light source and outputting substantially collimated light; and a second optical device for converging light output from said first optical device and outputting substantially collimated light.
25. An optical device substantially as herein described with reference to the accompanying Figures.
26. An illumination system substantially as herein described with reference to the accompanying Figures.