WO2008068598A2

WO2008068598A2 - Improved led illumination system, in particular for a video projector

Info

Publication number: WO2008068598A2
Application number: PCT/IB2007/003774
Authority: WO
Inventors: Renato Frison
Original assignee: Sim2 Multimedia S.P.A.
Priority date: 2006-12-07
Filing date: 2007-12-05
Publication date: 2008-06-12
Also published as: TW200825618A; WO2008068598A3; ITTO20060873A1

Abstract

A LED illumination system, in particular for a video projector, is described which comprises: a light source comprising a plurality of LED matrixes (1,2,3,40,41,42,43), in particular said matrixes (1,2,3,40,41,42,43) being adapted to emit light of a different colour; a plurality of reflecting elements (21,22,23,44,45,46,47), each of said reflecting elements (21,22,23,44,45,46,47) being coupled to one of said matrixes (1,2,3,40,41,42,43) for reflecting the light thereof; an integrator (33) adapted to receive the light reflected by said plurality of reflecting elements (21,22,23,44,45,46,47) and to convey it towards a projection system. The invention is characterized in that said reflecting elements consist of a plurality of triangular-section prisms (21,22,23,44,45,46,47) having: a first side (AC3DF5IG) comprising a reflecting surface (24,25,26), a second side (BC5EF3HI) on the surface of which a first layer of air (27,29,31) is obtained, a third side (AB5DE5GH) on the surface of which a second layer of air (28,30,32) is obtained, said first (27,29,31) and second (28,30,32) layers of air being adapted to provide a TIR (Total Internal Reflection) effect on the light emitted by said matrixes (1,2,3,40,41,42,43).

Description

IMPROVED LED ILLUMINATION SYSTEM, IN PARTICULAR FOR A VIDEO PROJECTOR

DESCRIPTION

The present invention relates to an improved LED illumination system, in particular for a video projector, according to the preamble of claim 1.

Illumination systems known in the art, in particular for video projectors, have been recently fitted with light sources consisting of one or several matrixes of LEDs (Light Emitting Diodes).

This solution eliminates some drawbacks related to the use of arc lamps, e.g. service life, because the average life of LEDs₅ which has been estimated to be about 50,000 hours, is much longer than that of a lamp.

Also, the luminous radiation produced by LEDs has a triangle of colour which is much broader than the one that can be obtained by using a normal arc lamp and the colour wheel thereof; consequently, the use of LEDs allows to obtain better chromatic results, i.e. to reproduce a greater number of colour shades.

However, LEDs emit light rays within an angle of about 180° and have a high etendue value. These features make it difficult to use them in video projection systems based on DLP (Digital Light Processing) technology, wherein the etendue is limited by the panel dimensions and by the aperture of the light beam outputted by the illumination system; it is also more difficult to find suitable optical structures which can be used for the collimation of the light beam emitted by LEDs.

It is in particular difficult to provide an illumination system which can ensure an effective collimation of the luminous radiation emitted by a plurality of differently coloured LEDs, i.e. to use an optical illumination system in order to distribute said luminous radiation evenly on a surface and within a solid angle such that an optimal coupling to said surface is ensured, thus minimizing light losses.

Figs. 1 and 2 show a known LED illumination system as described in patent WO 2004/107018, which relates to a LED illumination system comprising: a light source comprising a plurality of LED matrixes (1, 2, 3), in particular each matrix comprising LEDs of the same primary colour; a plurality of collectors (4, 5, 6), each of said collectors (4, 5, 6) being coupled to one of said LED matrixes (1, 2, 3) for conveying the light emitted by the respective LED matrixes (I₅ 2, 3) towards a respective aperture (7, 8, 9) of said collectors (4, 5, 6); a plurality of reflecting elements (10, 11, 12), each of said reflecting elements (10,

11, 12) being respectively coupled to one of said collectors (4, 5, 6) for reflecting the light coming out of said respective aperture (7, 8, 9); an integrator (17) comprising an input surface (16) adapted to receive the light reflected by said plurality of reflecting elements (10, 11, 12).

Said plurality of LED matrixes (1, 2, 3) comprises: a first matrix 1 comprising LEDs emitting blue light, said first matrix 1 being associated with a first collector 4; a second matrix 2 comprising LEDs emitting red light, said second matrix 2 being associated with a second collector 5; a third matrix 3 comprising LEDs emitting green light, said third matrix 3 being associated with a third collector 6; The blue light emitted by first matrix 1 is conveyed by first collector 4 toward a first reflecting element 10, in particular a cubic prism, through a first aperture 7.

Cubic prism 10 comprises a dichroic filter 13 which reflects blue light while letting through any light having a different wavelength. Said blue light is sent to the light integrator 17 through input surface 16. Likewise, the red light emitted by second matrix 2 is reflected off a dichroic filter 14 contained in a second reflecting element 11, or cubic prism 11. Dichroic filter 14 reflects the red light and lets through any light having a different wavelength; consequently, the red light passes through dichroic filter 13 and enters integrator 17 through the input surface 16.

Finally, the green light emitted by third matrix 3 is reflected off a dichroic filter 15 contained in a third reflecting element 12, or cubic prism 12, and, after having gone past dichroic filters 14 and 13, enters integrator 17 through input surface 16.

By observing the above-described LED illumination system, it can be clearly noticed how difficult it may be to provide dichroic filters 13, 14, 15 which can effectively reflect and/or transmit light with high angles of incidence. As known, the angle of incidence (AOI) is the angle formed by a light ray with the perpendicular of a surface.

As shown in Fig. 1, using cubic prisms 10, 11 and 12 involves the necessity of positioning the respective dichroic filters 13, 14 and 15 at 45° both with respect to the optical axes a, b and c of LED matrixes 1, 2, 3 and with respect to optical axis d, which at the same time represents the optical axis of integrator 17 and of the light reflected and/or transmitted by dichroic filters 13, 14, 15.

It follows that the blue, red and green light hits dichroic filters 13, 14, 15 with a high average AOI of approximately 45 ° .

Since, as previously mentioned, the capability of dichroic filters 13, 14, 15 of reflecting and/or transmitting the light emitted by LED matrixes 1, 2, 3 depends on the AOI of the light, the arrangement of dichroic filters 13, 14, 15 according to the above-described patent application is such that both the reflecting and transmitting actions of said dichroic filters ■ 13, 14, 15 are reduced.

In fact, the side of each of said dichroic filters 13, 14, 15 will be less sharp where the "transmitted" spectrum zone changes to the "reflected" spectrum zone. As a result, for example, dichroic filter 13 will not reflect all of the blue light emitted by first matrix 1 and will block a portion of the red and green light emitted by second matrix 2 and third matrixes 3, which should be allowed to pass through.

It is clear that this reduces the efficiency of the illumination system and, in the worst cases, may lead to a variation of the colour coordinates of the light emitted by matrixes 1, 2, 3. A further drawback of the above-described illumination system is that a portion of the light emitted by matrixes 1 , 2, 3 is lost, as shown by way of example in Fig. 2 in relation to matrix 1, which emits blue light.

In fact, this figure clearly shows that a ray e emitted by matrix 1 is reflected off a side wall of first collector 4 and is not directed towards dichroic filter 13; likewise, a ray f emitted by matrix 1 is substantially reflected off dichroic filter 13 in the direction of matrix 1, i.e. not towards integrator 17 as would be required in order to maximize the efficiency of the illumination system. Of course, a similar reasoning will also apply to the red and green light emitted by matrix 2 and matrix 3, respectively.

The general object of the present invention is to provide a LED illumination system, in particular for video projectors, so constructed as to overcome the above-mentioned drawbacks and to increase the efficiency of the system in a simple and economical manner. In order to attain said objects, the present invention provides an illumination system having the features set out in the appended claims, which are intended as an integral part of the present description. Further objects and advantages of the present invention will become apparent from the following detailed description and from the annexed drawings, which are supplied by way of non-limiting example, wherein:

Fig. 1 shows a LED illumination system, in particular for a video projector, according to the prior art; - Fig. 2 shows a detail of the illumination system of Fig. 1;

Fig. 3 shows a LED illumination system, in particular for a video projector, according to the present invention;

Figs. 4a and 4b show some details of the illumination system according to the present invention; - Figs. 5, 6 and 7 show some further details of the illumination system according to the present invention;

Figs. 8, 9, 10, 11 and 12 show a few variants of the illumination system according to the present invention.

Note that the blocks identified by the same reference numbers in the different figures perform the same functions.

Fig. 3 shows a first embodiment of an illumination system, in particular for a video projector, according to the present invention.

As already described with reference to Figs. 1 and 2, reference numbers 1, 2 and 3 refer to

LED matrixes emitting light of the three primary colours. In said first embodiment, matrix 3 emits a green light and is so positioned that its optical axis coincides with the optical axis AO of an integrator 33.

Matrix 1, which emits blue light, and matrix 2, which emits red light, comprise respective optical axes g, h forming an angle 2β smaller than 90° with the optical axis AO of integrator 3. As shown in Fig. 4a, each LED matrix 1, 2, 3 emits light from an emitting surface having a numerical aperture NA of the light beam defined as:

NA = n since where α is the half-angle of the beam, i.e. the angle formed by the outermost light ray with the optical axis q, and n is the refraction index of the medium in which the light propagates.

In general, the angular apertures of luminous radiations emitted by different LED matrixes

1, 2, 3 can differ from one another; however, as known, the apertures of the light beams that enter an optical system of a video projector must be equal, so that the light beams can be superimposed or collimated at the output of integrator 33.

To this end, as shown in Fig. 3, matrix 3 emitting green light is directly coupled to the illumination system, in particular through a coupling prism 36, whereas matrix 1 emitting blue light and matrix 2 emitting red light are coupled to the illumination system by means of respective collectors 18, 19. Said collectors 18, 19 preferably consist of a truncated pyramid, in particular having a rectangular cross-section, the function of which is to make the angular apertures of the respective light beams equal to that of matrix 3 at the input of the illumination system. Fig. 4b shows the principle according to which collectors 18, 19 must be manufactured or selected and, in substance, through which the angular apertures of the light beams are equalized.

If αl and Al respectively represent the emission half-angle and the area of a matrix 1, 2, 3 at the input of a collector 18, 19, and α2 and A2 respectively represent the emission half- angle and the area of the light beam at the output of collector 18, 19, and therefore also at the input of the illumination system, the following must be true in order to attain etendue constancy:

Alsin ²αl= A2 sin ²α2

Therefore, the dimensions of collectors 18, 19 are defined on the basis of the aperture of the light beam emitted by matrixes 1, 2, 3 and of the required aperture of the light beam at the input of the illumination system.

In the representation of Fig. 3, the blue light emitted by matrix 1 is collected by collector 18, which conveys said blue light towards a first reflecting element 21, consisting of a prism 21 having a triangular cross-section. In accordance with the present invention, said triangular-section prism 21 comprises a dichroic filter 24 on a first side AC; said dichroic filter 24 reflects the blue light emitted by matrix 1 towards integrator 33 and transmits the red and green light. In turn, integrator 33 receives the light reflected by dichroic filter 24 and conveys it towards a projection system (not shown in the drawings). Triangular prism 21 comprises a second side BC on the surface of which a first layer of air 27 a few μm thick is obtained; said first layer of air 27 separates triangular prism 21 from a coupling means, in particular a coupling prism 34, which allows triangular prism 21 to be optically coupled to integrator 33. Triangular prism 21 also comprises a third side AB on the surface of which a second layer of air 28 a few μm thick is obtained, which separates triangular prism 21 from a coupling means, in particular a coupling prism 37, which allows triangular prism 21 to be optically coupled to collector 18.

Of course, said first 27 and second 28 layers of air are parallel to said second BC and third AB sides, respectively, of triangular prism 21; furthermore, said third side AB is parallel to the optical axis AO of integrator 33 for symmetry reasons.

As already mentioned, optical axes g, h of matrixes 1 and 2 form an angle 2β of less than 90° with optical axis AO of integrator 33. It follows that output surface A2 of collector 18 is not parallel to the surface corresponding to side AB of prism 21, and that it is preferable to interpose a coupling prism 37, which has no effect on the aperture of the beam produced by collector 18.

The red light emitted by matrix 2 is collected by collector 19, which conveys said red light towards a second reflecting element 22, consisting of a triangular-section prism 22; in particular, triangular prism 22 is optically coupled to collector 19 through the interposition of a coupling prism 38.

Said triangular prism 22 comprises a dichroic filter 25 on a first side DF; said dichroic filter 25 reflects the red light emitted by matrix 2 towards integrator 3 and transmits the green light. Triangular prism 22 comprises a second side EF on the surface of which a first layer of air 29 a few μm thick is obtained; said first layer of air 29 separates triangular prism 22 from a coupling prism 35 adapted to connect together triangular prism 21 and triangular prism 22 optically.

Triangular prism 22 also comprises a third side DE on the surface of which a second layer of air 30 a few μm thick is obtained, which separates triangular prism 22 from coupling prism 38.

As in the preceding cases, said third side DE of triangular prism 22 is parallel to optical axis AO of integrator 33 for symmetry reasons.

The use of triangular prisms 21, 22 and the particular arrangement of said triangular prisms 21, 22 determining the presence of layers of air on sides BC, AB, EF, DE advantageously allow to use the TIR (Total Internal Reflection) effect in the illumination system according to the present invention.

In particular, if the light emitted by matrixes 1, 2, 3 hits one of said sides BC, AB, EF, DE with an angle of incidence AOI smaller than the critical angle, it will pass through side BC, AB, EF, DE; vice versa, if said angle of incidence AOI is greater than the critical angle, the light emitted by matrixes 1, 2, 3 will be totally reflected inwards ("TIR", Total Internal

Reflection).

In the representation of Fig. 3, matrix 3 is coupled to the illumination system through a coupling prism 36, and the green light reaches integrator 33 after passing through triangular prisms 21, 22. Of course, the optical axis of matrix 3, as well as the reflections of optical axes h and g of the red and blue light produced by dichroic filters 24 and 25, will coincide with optical axis AO of integrator 33.

It should be noted that coupling prisms 34, 35, 36, 37, 38 produce no variations in the aperture of the light emitted by matrixes 1, 2, 3, since the side surfaces thereof are parallel to respective optical axes AO, g, h.

Fig. 5 shows the advantages of the introduction of layers of air 29, 30 with reference to the red light emitted by matrix 2.

A light ray m emitted by said matrix 2 is reflected off a side surface of collector 19 and hits third side DE and the layer of air 30 with an AOI smaller than critical angle γcr (with sinγcr-1/n); consequently, ray of light m goes on to second side EF and hits layer of air 29 with an angle of incidence AOI greater than the critical angle. Therefore, on second side

EF the ray of light m undergoes a total internal reflection (TIR) and is sent to dichroic filter

25, which in turn reflects ray of light m towards integrator 33. A different ray of light n emitted by said matrix 2 is reflected off dichroic filter 25 and hits third side DE and layer of air 30 with an angle AOI greater than the critical angle, so that it undergoes a total internal reflection (TIR) and is deviated towards integrator 33.

It should be noted that the same considerations also apply to the blue light emitted by matrix 1; it is thus apparent that the insertion of an layer of air 27, 28, 29, 30 on two sides BC, AB, EF, DE of each of triangular prisms 21 and 22 advantageously allows to exploit the TIR (Total Internal Reflection) effect and to recover a portion of the light emitted by matrixes 1, 2, 3, which otherwise would be lost; the efficiency of the illumination system according to the present invention is thus improved.

In a preferred embodiment of the illumination system according to the present invention, second sides BC, EF of triangular prisms 21 and 22 are parallel to optical axes g, h of the light emitted by matrixes 1, 2, 3, so that no further variations in the angular aperture of the light emitted by said matrix will occur.

As known, in both the light transmission and reflection stages the efficiency of the dichroic filters increases as the angle of incidence of the light beam hitting them decreases. Fig. 6 shows a detail of the illumination system of Fig. 3, in particular concerning the optical path of the red light emitted by LED matrix 2; it is however clear that the following considerations will also apply to the blue light emitted by matrix 1. For simplicity, the coupling prism 38 is not shown in Fig. 6 because it is uninfluential in this regard.

In this drawing, a straight line o is perpendicular to dichroic filter 25, and angle β formed by this straight line with optical axis h of the red light emitted by matrix 2 is the angle that must be minimized in order to obtain the maximum efficiency of dichroic filter 25, provided that certain requirements due to the introduction of layers of air 29 and 30 are met.

Since optical axis h of the red light emitted by matrix 2 is reflected off dichroic filter 25 parallel to optical axis AO of integrator 33, and side DE is parallel to the same optical axis AO, the following equivalences are true: 1) γ+β =90° 2γ-δ=90° γ-δ=β θ+β =90° where γ is the angle formed by dichroic filter 25 with the second layer of air 30 (or with the third side DE) and δ is the angle formed by the perpendicular p of the first layer of air 29 with the second layer of air 30 (or with the third side DE).

Due to the equivalences defined in 1), the triangles ABC (of Fig. 5) and DEF are isosceles triangles with AB=CB=DE=EF, where γ=θ=90-β (by construction). A first requirement to be met is that the most inclined light rays of the red light emitted by matrix 2, in particular a ray r forming an angle ε with optical axis h, must be able to exit collector 19 without being subject to the TIR phenomenon on the surface of second layer of air 30 (or of third side DE), i.e. angle ω formed by ray r with the perpendicular s of layer of air 30 must be smaller than critical angle γcr, i.e.: 2) ω=δ+ε ≤ γcr where:

NA =n sinε (aperture of the beam at the output of collector 19); ε = angle between ray r and optical axis h; n = refraction index of the glass used for prisms and collectors γcr = TIR critical angle, so that sinγcr=l/n It should be pointed out that all elements of the illumination system are typically manufactured from the same glass, so that the critical angles are the same for the TIRs 27, 28, 29, 30 as well. With reference to Fig. 7, in order that ray r reflected by dichroic filter 25 can exit first layer of air 29 (and the second side EF) without undergoing a TIR reflection, angle φ formed by ray r reflected off dichroic filter 25 with perpendicular z of layer of air 29 must be smaller than γcr, i.e.:

3) φ= 90°+2δ-2γ+ε < γcr Taking into account the equivalences defined in 1), the expressions 2) and 3) become:

4) β> 45° -(γcr-ε)/2

Therefore, in order to optimize angle β and obtain the maximum efficiency of dichroic filter 25, one may use the minimum value obtained from expression 4) as a value of β .

This value of β depends on the minimum aperture NA of matrixes 1, 2, 3 and on value of n, i.e. the refraction index of the material used in the system, typically glass. In any case, the optimal value of β which provides the maximum efficiency of dichroic filter 25 turns out to be smaller than 45°.

In fact, if we consider by way of example a typical situation wherein the maximum angle

NA=O.30 and n== 1.5168 (which is the refraction index of glass, generally used for prisms), we will obtain β«30°.

Furthermore, assuming the same value of β for both the blue light and the red light, two triangles ABC and DEF turn out to be equal and the respective optical axes g and h are parallel.

This leads to a significant improvement of dichroic filters 24, 25 in both the transmission and reflection of the light emitted by LED matrixes 1, 2, 3, resulting in an increased efficiency of the whole illumination system.

The illumination system described herein may also be used to advantage in video projectors having only one active device, e.g. DMD, LCD or LCoS type, for the formation of the image to be projected. In such a case, said device separately receives the primary light beams emitted by the LED matrixes, in particular by activating said matrixes in succession.

The advantages of the illumination system, in particular for a video projector, according to the present invention are apparent from the above description.

In particular, the use of triangular prisms 21, 22 as reflecting elements for reflecting the light coming from the LED matrixes, said triangular prisms 21, 22 comprising: a dichroic filter 24, 25 on a first side AC, DF; a second side BC, EF on the surface of which a first layer of air 27, 29 a few μm thick is obtained; a third side AB, DE on the surface of which a second layer of air 28, 30 a few μm thick is obtained, advantageously allows to exploit the TIR (Total Internal Reflection) effect in the illumination system according to the present invention and, consequently, to overcome the drawbacks of prior-art illumination systems, thus increasing the efficiency thereof.

Furthermore, the particular arrangement of LED matrixes 1, 2, 3 according to which the angle of incidence AOI of the light emitted by said matrixes 1,2,3 on the dichroic filters 24, 25 (i.e. the angle formed by optical axis g, h with the perpendicular of associated dichroic filters 24, 25) is smaller than 45° allows to obtain the utmost operating efficiency of said dichroic filters 24, 25 in both the light transmission and reflection stages.

It is clear that many changes may be made to the illumination system according to the present invention without departing from the novelty spirit of the inventive idea. Among the many possible variants, LED matrix 3 generating the green light may be so arranged as to be coupled to the illumination system as shown in Fig. 3 for matrixes 1 and 2.

This variant is shown in Fig. 8, wherein it can be noticed that matrix 3 is coupled to a third reflecting element 23, in particular a triangular-section prism 23, through a coupling prism 36', which allows to keep the angular aperture of the green light unchanged. Triangular prism 23 comprises a reflecting surface 26 on a first side IG, said reflecting surface 26 being used for reflecting the green light towards integrator 33. Moreover, like triangular prisms 21 and 22, triangular prism 23 also comprises a second side HI on the surface of which there is a first layer of air 31, and a third side GH on the surface of which there is a second layer of air 32. A further variant of the illumination system, in particular for a video projector, according to the present invention is shown in Fig. 9. In particular, this variant lacks the coupling prisms referred to in the embodiment of Fig. 3 by reference numbers 37 and 38, and the coupling means which allow to obtain second layers of air 28, 30 consist of collectors 18, 19; in fact, even if the outer sides of collectors 18 and 19 are slightly misaligned relative to respective sides BC and EF of triangular-section prisms 21 and 22, the absence of the coupling prisms 37, 38 only implies a negligible discrepancy in the numerical aperture NA of the beam of light at the input of triangular-section prisms 21 and 22, resulting in a negligible error in the calculation of minimum β. In another variant of the illumination system, in particular for a video projector, according to the present invention, matrixes 1, 2 are positioned on opposite sides with respect to the optical axis AO of integrator 33, as shown in Fig. 10.

Fig. 11 shows yet another variant of the illumination system, in particular for a video projector, according to the present invention. In this variant, the collectors referred to in the embodiment of Fig. 3 by reference numbers 18 and 19 have been eliminated. Moreover, matrixes 1 and 2 are coupled to the respective triangular prisms 21 and 22 through coupling prisms 37 and 38. Such a configuration is particularly advantageous whenever the angular apertures of the light emitted by matrixes 1, 2, 3 are substantially equal. A further variant of the illumination system according to the present invention is shown in Fig. 12; in addition to matrixes 1, 2, 3 emitting light of a primary colour (i.e. blue, red and green), this variant also utilizes LED matrixes 40, 41, 42, 43 emitting light of a secondary colour.

Thus, for example, matrix 40 emits cyan light, matrix 41 emits magenta light, matrix 42 emits yellow light, and matrix 43 emits amber light, each of said LED matrixes 40, 41, 42, 43 being associated with a respective triangular prism 44,45,46 and 47.

It is clear that also the dichroic filters associated with LED matrixes 40, 41, 42, 43 must be mutually exclusive, i.e. each dichroic filter must reflect the light of the associated matrix and transmit the light emitted by the other matrixes; this is possible because the light emitted by the LED matrixes has a rather narrow Gaussian spectral profile, in particular just a few tens of nanometres.

It can be easily understood that the present invention is not limited to above-described illumination systems, but may be subject to many modifications, improvements or replacements of equivalent parts and elements without departing from the inventive idea, as clearly specified in the following claims.

* * * * * * *

Claims

1. LED illumination system, in particular for a video projector, comprising: a light source comprising a plurality of LED matrixes (1,2,3,40,41,42,43), in particular said matrixes (1,2,3,40,41,42,43) being adapted to emit light of a different colour; - a plurality of reflecting elements (21,22,23,44,45,46,47), each of said reflecting elements (21,22,23,44,45,46,47) being coupled to one of said matrixes (1,2,3,40,41,42,43) for reflecting the light thereof; an integrator (33) adapted to receive the light reflected by said plurality of reflecting elements (21,22,23,44,45,46,47) and to convey it towards a projection system, characterized in that said reflecting elements consist of a plurality of triangular-section prisms (21,22,23,44,45,46,47) having: a first side (AC₅DF₅IG) comprising a reflecting surface (24,25,26), a second side (BC₅EF₅HI) on the surface of which a first layer of air (27,29,31) is obtained, a third side (AB₃DE₅GH) on the surface of which a second layer of air (28,30,32) is obtained, said first (27,29,31) and second (28,30,32) layers of air being adapted to provide a TIR (Total Internal Reflection) effect on the light emitted by said matrixes (1,2,3,40,41,42,43).

2. LED illumination system according to claim 1, characterized in that said first (27,29,31) and second (28,30,32) layers of air separate said second (BC₅EF₅HI) and third (AB₅DE₅GH) sides from a respective coupling means (18,19; 34,35,36,36',37₅38).

3. LED illumination system according to claim 2, characterized in that said respective coupling means consists of a collector (18,19).

4. LED illumination system according to claim 2, characterized in that said respective coupling means consists of a coupling prism (34,35₅36,36',37,38).

5. LED illumination system according to claim 1, characterized in that said reflecting surface (24,25,26) consists of a dichroic filter (24,25).

6. LED illumination system according to claim 5, characterized in that said LED matrixes (1,2,3,40,41,42,43) are so positioned that the optical axis (g,h) of the light emitted by the LED matrixes (1,2,3,40,41,42,43) forms an angle (β) smaller than 45° with the perpendicular of the associated dichroic filters (24,25).

7. LED illumination system according to claim 6, characterized in that said angle (β) substantially corresponds to 45°-(γcr-ε)/2, where γcr is the critical angle for the TIR effect and ε is the aperture half-angle of the beam of light sent to the triangular prism (21,22,23,44,45,46,47).

8. LED illumination system according to claim 1, characterized by comprising a plurality of collectors (18,19), each of said collectors (18,19) being coupled to one of said matrixes (1,2,3,40,41,42,43) for conveying the light towards the respective triangular-section prism (21,22,23,44,45,46,47).

9. LED illumination system according to claim 8, characterized in that said collectors (18,19) consist of a truncated pyramid, in particular having a rectangular cross-section.

10. LED illumination system according to claim 8, characterized in that said collectors (18,19) are adapted to make the angular apertures of the respective beams of light equal to that of the matrix (1,2,3,40,41,42,43) having the smallest angular aperture in the illumination system.

11. LED illumination system according to claim 1, characterized by comprising a plurality of coupling prisms (34,35,36,36',37,38).

12. LED illumination system according to claim 11, characterized in that said coupling prisms (36 ',37,38) are adapted to send the light emitted by said matrixes (1,2,3,40,41,42,43) towards the respective triangular-section prisms (21,22,23,44,45,46,47).

13. LED illumination system according to any of claims 11 and 12, characterized in that said coupling prisms (34,35,36,36',37,38) have side surfaces which are parallel to the respective optical axes (AO,g,h,i) of the associated matrixes (1,2,3,40,41,42,43).

14. LED illumination system according to claim 1, characterized in that one matrix (3) is so positioned that its optical axis (i) is substantially parallel to the optical axis (AO) of said integrator (33).

15. LED illumination system according to claim 1, characterized in that said matrixes (1,2,3,40,41,42,43) are so arranged that their optical axes (g,h,i) are parallel to one another.

16. LED illumination system according to claim 1, characterized in that said matrixes (1,2,3,40,41,42,43) are so arranged that their optical axes (g,h,i) are positioned on opposite sides with respect to the optical axis (AO) of said integrator (33).

17. LED illumination system according to any of the preceding claims, characterized in that said matrixes (1,2,3) emit light of a primary colour.

18. LED illumination system according to any of the preceding claims, characterized in that said matrixes (40,41,42,43) emit light of a secondary colour.

19. LED illumination system according to any of the preceding claims, characterized in that said plurality of reflecting elements (21,22,23,44,45,46,47) comprises triangular prisms (21,22,23,44,45,46,47) having the same dimensions.

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