SYSTEMS AND METHODS FOR ILLUMINATING AN OBJECT FIELD DURING A PROCESSING PROCESS OF A LIGHT CURING PLASTIC

Abstract

Presented herein is an optical filter system for visible light, which has a first average transmittance T.sub.1 between a limit wavelength λ.sub.G and a wavelength of 700 nm and a second average transmittance T.sub.2 between a wavelength of 380 nm and the limit wavelength λ.sub.G. In this case: 410 nm<λ.sub.G<520 nm and 0.05

[00001]$<\frac{T_1}{T_2}<0.60.$

Claims

1. Optical filter system for visible light, which in a wavelength range of 380 nm to 700 nm has the following transmission characteristic: a transmission range between a limit wavelength λ.sub.G and a wavelength of 700 nm, wherein the transmission range between the limit wavelength λ.sub.G and the wavelength of 700 nm has a first average transmittance T.sub.1; and a dimming range between a wavelength of 380 nm and the limit wavelength λ.sub.G, wherein the dimming range between the wavelength of 380 nm and the limit wavelength λ.sub.G has a second average transmittance T.sub.2; where: $410<{\lambda }_G<520.Math.\mathrm{nm},.Math.\mathrm{and}$ $0.05<\frac{T_2}{T_1}<0.60;$

2. Optical filter system according to claim 1, wherein the transmission characteristic of the filter system has a transition range that extends between a first wavelength λ.sub.1 and a second wavelength λ.sub.2, wherein: 380 nm<λ.sub.1<λ.sub.G<λ.sub.2<700 nm; λ.sub.2−λ.sub.1>20 nm $T_{\mathrm{soll}}\left(\lambda \right)=\frac{T\left({\lambda }_2\right)-T\left({\lambda }_1\right)}{{\lambda }_2-{\lambda }_1}.Math.\left(\lambda -{\lambda }_1\right)+T\left({\lambda }_1\right)$ $\mathrm{and}$ $.Math.T\left(\lambda \right)-T_{\mathrm{soll}}.Math.<0.15.Math..Math.\mathrm{for}.Math..Math.\mathrm{all}.Math..Math.\lambda .Math..Math.\mathrm{with}.Math..Math.{\lambda }_1\le \lambda \le {\lambda }_2;$ wherein T(λ) is a wavelength-dependent transmittance of the filter system.

3. Optical filter system according to claim 1, wherein: $\frac{{\int }_S.Math.T\left(\stackrel{.fwdarw.}{r}\right).Math.\stackrel{.fwdarw.}{r}.Math.\mathrm{dr}.Math.}{{\int }_S.Math.T\left(\stackrel{.fwdarw.}{r}\right).Math.\mathrm{dr}.Math.}.Math.\stackrel{.fwdarw.}{R}$ $\mathrm{and}$ $.Math.\stackrel{.fwdarw.}{W}-\stackrel{.fwdarw.}{R}.Math.\le 0.3;$ wherein T(r) is a wavelength-dependent transmittance of the filter system in the colour space of the CIE(1931) colour system; {right arrow over (r)} are coordinates in the colour space of the CIE(1931) colour system; S is the spectral colour line in the colour space of the CIE(1931) colour system; and {right arrow over (W)} is the white point in the colour space of the CIE(1931) colour system.

4. Optical illumination system for illuminating an object field with visible light in a wavelength range of 380 nm to 700 nm, wherein the illumination system comprises at least one light source and has the following irradiation characteristic in a plane at a distance of 30 cm from the illumination system: an illumination range between a limit wavelength λ.sub.G and a wavelength of 700 nm, wherein over the illumination range a first average spectral irradiance E.sub.1 is radiated by the illumination system onto the plane; a dimming range between a wavelength of 380 nm and the limit wavelength λ.sub.G, wherein over the dimming range a second average spectral irradiance E.sub.2 is radiated by the illumination system onto the plane; where: $410<{\lambda }_G<520.Math.\mathrm{nm}$ $\mathrm{and}$ $0.05<\frac{E_2}{E_1}<0.60.$

5. Optical illumination system according to claim 4, wherein: $I_1=E_1.Math.\left(700.Math..Math.\mathrm{nm}-{\lambda }_G\right)$ $\mathrm{and}$ $I_1>10.Math.\frac{W}{m^2},$ and in particular $I_1>50.Math.\frac{W}{m^2}$ $\mathrm{or}$ $I_1>150.Math.\frac{W}{m^2}.$

6. Optical illumination system according to claim 4, wherein the irradiation characteristic of the illumination system has a transition range that extends between a third wavelength λ.sub.3 and a fourth wavelength λ.sub.4, wherein: 380 nm<λ.sub.3<λ.sub.G<λ.sub.4<700 nm; λ.sub.4−λ.sub.3>20 nm $E_{\mathrm{soll}}\left(\lambda \right)=\frac{E\left({\lambda }_4\right)-E\left({\lambda }_3\right)}{{\lambda }_4-{\lambda }_3}.Math.\left(\lambda -{\lambda }_3\right)+E\left({\lambda }_3\right)$ $\mathrm{and}$ $.Math.E\left(\lambda \right)-E_{\mathrm{soll}}.Math.<0.15.Math.\frac{W}{m^2.Math.\mathrm{nm}}.Math..Math.\mathrm{for}.Math..Math.\mathrm{all}.Math..Math.\lambda .Math..Math.\mathrm{with}.Math..Math.{\lambda }_3\le \lambda \le {\lambda }_4;$ E(λ) is a wavelength-dependent spectral irradiance with which the plane is irradiated by the illumination system.

7. Optical illumination system according to claim 4, wherein $\frac{{\int }_S.Math.E\left(\stackrel{.fwdarw.}{r}\right).Math.\stackrel{.fwdarw.}{r}.Math.\mathrm{dr}.Math.}{{\int }_S.Math.E\left(\stackrel{.fwdarw.}{r}\right).Math.\mathrm{dr}.Math.}.Math.\stackrel{.fwdarw.}{R}$ $\mathrm{and}$ $.Math.\stackrel{.fwdarw.}{W}-\stackrel{.fwdarw.}{R}.Math.\le 0.3;$ wherein E({right arrow over (r)}) is a wavelength-dependent spectral irradiance in the colour space of the CIE(1931) colour system, with which the plane is irradiated by the illumination system; {right arrow over (r)} are coordinates in the colour space of the CIE(1931) colour system; S is the spectral colour line in the colour space of the CIE(1931) colour system; and {right arrow over (W)} is the white point in the colour space of the CIE(1931) colour system.

8. Optical illumination system according to claim 4, wherein the illumination system comprises a plurality of light sources whose emission spectra differ from one another, wherein first light sources whose greatest part of the respective emission spectrum is in the dimming range and not in the illumination range in one operating mode radiate onto the plane with an irradiance that is at most 20 percent of the irradiance with which the plane is irradiated by way of second light sources whose greatest part of the respective emission spectrum is in the illumination range and not in the dimming range.

9. Optical illumination system according to claim 4, wherein the illumination system is configured such that in a plane at a distance of 30 cm from the illumination system: $I_2={\int }_{380.Math..Math.\mathrm{nm}}^{{\lambda }_G}.Math.E\left(\lambda \right).Math.d.Math..Math.\lambda$ $\mathrm{and}$ $I_2<15.Math.\frac{W}{m^2},$ and in particular $I_2<10.Math.\frac{W}{m^2}.Math..Math.\mathrm{or}.Math..Math.I_2<6.Math.\frac{W}{m^2},$ wherein λ is a wavelength; and E(λ) is a wavelength-dependent spectral irradiance with which the plane is irradiated by the illumination system.

10. Optical illumination system according to claim 4, furthermore comprising a controller that is configured to set the illumination system into two different operating modes, wherein in a first operating mode in the plane at the distance of 30 cm from the illumination system: $I_2<15.Math.\frac{W}{m^2},$ and in particular $I_2<10.Math.\frac{W}{m^2}.Math..Math.\mathrm{or}.Math..Math.I_2<6.Math.\frac{W}{m^2},$ and in a second operating mode in the plane at the distance of 30 cm from the illumination system: $I_2>15.Math.\frac{W}{m^2},$ and in particular $I_2>30.Math.\frac{W}{m^2}.Math..Math.\mathrm{or}.Math..Math.I_2>50.Math.\frac{W}{m^2}.$

11. Optical illumination system according to claim 10, further comprising an actuator that is configured to arrange filters of the illumination system in an illumination beam path between the light source and the plane during the first operating mode, and to remove the filters of the illumination system from the beam path between the light source and the plane during the second operating mode, wherein the controller is configured to control the actuator.

12. Optical illumination system according to claim 10, wherein the illumination system comprises a plurality of light sources whose emission spectra differ from one another, wherein irradiances from first light sources whose greatest part of the respective emission spectrum is in the dimming range and not in the illumination range are reduced by at least 80 percent during operation in the first operating mode as compared to operation in the second operating mode, wherein the controller is configured to control the reduction in the respective irradiances of the first light sources.

13. Use of the optical illumination system according to claim 4 for illuminating an object field during processing of a light curing plastic in the object field, wherein the light curing plastic comprises in particular Lucirin TPO and/or phenyl propanedione and/or Ivocerin and/or camphorquinone, and wherein the light curing plastic is attached in particular to a tooth.

14. Use according to claim 13, wherein: $I_{2;\mathrm{eff}}={\int }_{380.Math..Math.\mathrm{nm}}^{{\lambda }_G}.Math.A\left(\lambda \right).Math.E\left(\lambda \right).Math.d.Math..Math.\lambda$ $\mathrm{and}$ $I_{2,\mathrm{eff}}<6.Math.\frac{W}{m^2};$ wherein λ is a wavelength; E(λ) is a wavelength-dependent spectral irradiance with which the object field is irradiated by the illumination system; and A(λ) is a wavelength-dependent absorbance of a light curing plastic located in the object field.

15. Use according to claim 13, wherein: $D_{2;\mathrm{eff}}=t.Math.I_{2;\mathrm{eff}}={\int }_{380.Math..Math.\mathrm{nm}}^{{\lambda }_G}.Math.A\left(\lambda \right).Math.E\left(\lambda \right).Math.d.Math..Math.\lambda$ $\mathrm{and}$ $D_{2,\mathrm{eff}}<360.Math.\frac{J}{m^2};$ wherein A is a wavelength; t is a period of the illumination of the object field with the illumination system; E(λ) is a wavelength-dependent spectral irradiance with which the object field is irradiated by the illumination system; and A(λ) is a wavelength-dependent absorbance of a light curing plastic located in the object field.

16. Optical observation system, comprising: an imaging optical unit for imaging an object field; a light source for illuminating the object field; and an optical filter system according to claim 1, wherein the optical filter system is arranged in a beam path between the light source and the object field.

17. Optical observation system, comprising: an imaging optical unit for imaging an object field; a light source for illuminating the object field; and an optical illumination system according to claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Exemplary embodiments of the invention are explained in more detail below on the basis of figures:

[0069] FIG. 1 shows an exemplary configuration of an optical observation system in accordance with one embodiment of the invention;

[0070] FIG. 2 shows graphs that represent an emission spectrum of a broadband light source and a transmission characteristic of a filter system;

[0071] FIGS. 3A to 3D show absorption curves of frequently used photoinitiators;

[0072] FIG. 4 shows a representation of the colour space of the CIE(1931) colour system;

[0073] FIGS. 5A and 5B show exemplary transmission characteristics of filter systems in accordance with embodiments of the invention;

[0074] FIGS. 6A and 6B show exemplary transmission characteristics of filter systems in accordance with embodiments of the invention; and

[0075] FIG. 7 shows graphs that represent the emission spectra of different light sources and a transmission characteristic of a filter system.

[0076] The present disclosure is susceptible to various modifications and alternative forms, and some representative embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the inventive aspects are not limited to the particular forms illustrated in the drawings. Rather, the disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.

DETAILED DESCRIPTION OF ILLUSTRATED EXAMPLES

[0077] FIG. 1 shows an exemplary embodiment of the invention as an observation system. The exemplary observation system here comprises an illumination system 11 and an imaging optical unit 23. The illumination system is directed at teeth 7 in the head 3 of a patient, on which a light curing plastic for processing is placed. An object plane 8, in which the teeth 7 of the patient are located, has a distance d along a beam path 17 from a component of the illumination system 11 that is located closest to the object plane 8, here configured as a transmission filter 19, that in the present example is 30 cm. A light source 13 emits light which is shaped into a light beam 17 via a parabolic reflection mirror 15 and directed onto the object plane 8. In the present example, the light source is in the form of a xenon light source, wherein other light sources having sufficiently strong emission in the visible spectrum can also be used as the light source. A transmission filter 19 is arrangeable, with the aid of an actuator 20, in a beam path from the light source 13 to the object field 8, which is indicated by way of a double-headed arrow 16, to filter the light coming from the light source 13 before it is incident on the object field 8. In order to facilitate handling of the illumination system 11, the illumination system 11 is attached to a stand 21 that is fixed to the ceiling or the floor of the treatment room. The illumination system 11 can be brought into a desired orientation with respect to the object field via the stand and be ultimately fixed therein. The observation system has the imaging optical unit 23 for observing the object field. A treating person can then observe the object field 8 through an eyepiece 27 of the imaging optical unit 23. Similarly to the illumination system 11, the imaging optical unit 23 is also fixed to the ceiling or the floor of the treatment room using a stand 25.

[0078] In the example shown, the imaging optical unit 23 and the observation system 11 are housed in separate housings, which are supported by separate stands. However, it is also possible for the imaging optical unit and the observation system to be housed in a common housing, which is supported on a single stand.

[0079] So as now to be able to observe the object field 8 with sufficient brightness and colour fidelity, without bringing about premature curing of the light curing plastic, the illumination system 11 could be configured as follows.

[0080] FIG. 2 shows an exemplary emission characteristic E.sub.Bel(λ) of the light source 13 and an exemplary transmission characteristic T(λ) of the transmission filter 19 in the form of graphs, which show a spectral irradiance E in

[00010]$\frac{W}{m^2.Math.\mathrm{nm}}$

and respectively, a transmittance T (dimensionless) as a function of the wavelength λ in nm. Also shown is a spectral irradiance E(λ) with which the object field would ultimately be irradiated by the exemplary illumination system 11.

[0081] The emission characteristic E.sub.Bel(λ) has an approximately constant value for the wavelengths from 420 nm to 705 nm. Under direct illumination of the object field by way of the light source, this would, due to a significant irradiation with light of short wavelengths, which generally results in curing of a light curing plastic, result in fast curing of the light curing plastic. In order to prevent this, a wavelength-dependent transmittance T(λ) of the transmission filter 19 has a first transmittance T.sub.1 in a transmission range between a limit wavelength λ.sub.G and a wavelength of 700 nm, and a second transmittance T.sub.2 in a dimming range between 380 nm and the limit wavelength λ.sub.G. Here, the limit wavelength λ.sub.G is selected such that light having wavelengths below the limit wavelength λ.sub.G causes curing of the light curing plastic, and light having wavelengths above the limit wavelength λ.sub.G does not cause curing of the light curing plastic. In addition, the second transmittance T.sub.2 having an exemplary value of 0.2 is significantly smaller than the first transmittance T.sub.1, which has an exemplary value of 1.0, and is still significantly greater than zero. If the transmission filter 19 is now, as described, arranged in the beam path between the light source 13 and the object plane 8, short-wave light having wavelengths from the dimming range of the transmission filter reaches the object plane only with a significantly reduced spectral irradiance, while light having wavelengths from the illumination range of the transmission filter still has a very high irradiance in the object field. Light having a spectral irradiance illustrated in graph E(λ) thus still arrives in the object plane. On the one hand, due to the comparatively low irradiance E(λ) in the dimming range (as compared to the illumination range) that is received in the object field, no significant curing of the light curing plastic is brought about yet. On the other hand, the comparatively high irradiance E(λ) in the illumination range allows for a high illuminance in the object field, which is necessary for detailed observation of the object field. A distortion of a colour impression on the object that would be caused by the comparatively high irradiance in the illumination range is here compensated for as much as possible by the remaining irradiance E(λ) that is radiated over the dimming range (cf. T.sub.2=0.2), which allows a largely colour-neutral illumination of the object field.

[0082] It is thus possible for the object field and thus the light curing plastic to be illuminated in the object field with sufficient brightness and colour neutrality, without bringing about substantial curing of the light curing plastic.

[0083] In order to achieve the best possible illumination, the limit wavelength λG must be adapted as well as possible to the respective light curing plastic to be processed in the object field.

[0084] FIGS. 3A to 3D show absorption curves of a number of photoinitiators that are common in dentistry and are used in light curing plastics for activating polymerization in the form of graphs that indicate a relative intensity I.sub.rel (dimensionless) as a function of the wavelength λ in nm. While a suitable limit wavelength λG for Lucirin TPO (cf. FIG. 3A) could be, for example, 430 nm, a suitable limit wavelength λG for phenyl propanedione (cf. FIG. 3B) could be approximately 490 nm, for camphorquinone (cf. FIG. 3C) approximately 510 nm and for Ivocerin (cf. FIG. 3D) approximately 450 nm.

[0085] With the colour space of the CIE(1931) colour system, FIG. 4 shows an alternative to the CRI for assessing colour neutrality (or colour rendering) of a system. In order to be able to perform the corresponding assessment, an x-coordinate and a y-coordinate of a colour point {right arrow over (R)} of an illumination system (or of a filter system) in the colour space of the CIE(1931) colour system must be ascertained by way of integration and subsequent normalization of a wavelength-dependent spectral irradiance (or a transmittance) along a spectral colour line S in the colour space of the CIE(1931) colour system:

[00011]$\frac{{\int }_S.Math.E\left(\stackrel{.fwdarw.}{r}\right).Math.\stackrel{.fwdarw.}{r}.Math.\mathrm{dr}.Math.}{{\int }_S.Math.E\left(\stackrel{.fwdarw.}{r}\right).Math.\mathrm{dr}.Math.}.Math.\stackrel{.fwdarw.}{R};$

wherein
E({right arrow over (r)}) is the wavelength-dependent spectral irradiance E(λ) in the colour space of the CIE(1931) colour system, with which an object plane is irradiated by the illumination system;
{right arrow over (r)} are coordinates in the colour space of the CIE(1931) colour system; and
S is the spectral colour line in the colour space of the CIE(1931) colour system.

[0086] A distance of the colour point {right arrow over (R)} that is thus obtained from the white point {right arrow over (W)} in the colour space of the CIE(1931) colour system then shows how colour neutral the illumination system (or the filter system) is. If the distance is less than 0.3 or less than 0.2 or even less than 0.1, a significant colour neutrality of the illumination system (or of the filter system) can be assumed.

[0087] In order to meet specific requirements of average transmittances T.sub.1 and T.sub.2 of filter systems, wavelength-dependent transmittances T(λ) can be formed in various manners. Similar is true here also for wavelength-dependent spectral irradiances of illumination systems

[0088] FIGS. 5A and 5B and FIGS. 6A and 6B show transmission curves T(λ) of examples of filter systems in the form of graphs, which show a transmittance T (dimensionless) as a function of the wavelength λ in nm. It should be noted that the term “transmission curve” is not a limitation on a component-related realization of the filter system, and the filter system can also easily comprise reflection filters or the like.

[0089] The wavelength-dependent transmittance T(λ) from FIG. 5A starts at a wavelength of 380 nm with a value of approximately 0.35 and then approaches a significantly lower value of approximately 0.14 with increasing wavelength. At the limit wavelength λG, a jump of the wavelength-dependent transmittance T(λ) to a significantly higher value of approximately 0.78 occurs. Starting from this higher value, the wavelength-dependent transmittance T(λ) continues to increase with greater wavelengths and finally approaches a still higher value of approximately 0.95. Transmission filters of this type could, for example, be advantageous when working with light curing plastics having camphorquinone (cf. FIG. 3C), because at wavelengths of 380 nm to 430 nm for which camphorquinone has only a lower absorbance, an increased (as compared to the wavelengths of 430 nm to 490 nm) spectral irradiance is radiated into the object field and thus colour rendering in the object field can be significantly improved, without bringing about significant curing of the light curing plastic in the object field.

[0090] FIG. 5B shows a further wavelength-dependent transmittance T(λ), wherein here the transmittance T(λ) continuously increases with the wavelength up to a wavelength of approximately 550 nm. At wavelengths of greater than 555 nm, significant fluctuations of the wavelength-dependent transmittance T(λ) occur. Such a profile is conceivable in filter systems, in which an exact profile of the transmittance T(λ) in the short-wave range up to, for example, 555 nm is very important, and a profile of the transmittance T(λ) in the long-wave range of greater than, for example, 555 nm does not need to be as well defined.

[0091] FIG. 6A shows a further exemplary, highly idealized wavelength-dependent transmittance T(λ), which has a transition range between a first wavelength λ.sub.1 and a second wavelength λ.sub.2. It should be noted that the limit wavelength λ.sub.6 that separates a transmission range (above the limit wavelength) from a dimming range (below the limit wavelength) lies between the first wavelength λ.sub.1 and the second wavelength λ.sub.2. A corresponding filter system here has a first average transmittance T.sub.1 over the transmission range, which is significantly greater than a second average transmittance T.sub.2 of the dimming range. In the transition range, the wavelength-dependent transmittance T(λ) is very steep and is linear with respect to the wavelength, as a result of which a relatively abrupt and well-defined transition from the dimming range to the transmission range is achieved.

[0092] FIG. 6B shows a further wavelength-dependent transmittance T(λ), wherein here the two wavelengths λ.sub.1 and λ.sub.2 are significantly further apart than in FIG. 6A. This results in a relatively broad transition range. In the transition range between the first wavelength λ.sub.1 and the second wavelength λ.sub.2, the wavelength-dependent transmittance T(λ) shown here does not follow exactly a linear profile, which is indicated by the graph T.sub.soll(λ), wherein:

[00012]$T_{\mathrm{soll}}\left(\lambda \right)=\frac{T\left({\lambda }_2\right)-T\left({\lambda }_1\right)}{{\lambda }_2-{\lambda }_1}.Math.\left(\lambda -{\lambda }_1\right)+T\left({\lambda }_1\right).$

[0093] However, all values T(λ) lie within a narrow corridor around the linear graph T.sub.soll(Δ):

|T(λ)−T.sub.soll(λ)|<0.15 for all λ with λ.sub.1≦λ≦λ.sub.2;

(indicated by way of the dot-dash line), as a result of which the wavelength-dependent transmittance T(λ) over the transition range can be approximated, for the sake of simplicity, as being linearly increasing with the wavelength λ. It is also important to note here that the limit wavelength λ.sub.G is between the first limit wavelength λ.sub.1 and the second limit wavelength λ.sub.2 and separates a transmission range with a first average transmittance T.sub.1≈0.8 from a dimming range with a second average transmittance T.sub.2≈0.18, wherein the first average transmittance T.sub.1 is considerably greater than the second average transmittance T.sub.2, and the second average transmittance T.sub.2 is still considerably greater than zero.

[0094] In addition to the exemplary transmission curves shown, many other transmission curves are conceivable which still fall within the spirit of the invention.

[0095] FIG. 7 shows emission curves (R, G, B) of three different light sources and average spectral irradiances (E1 und E2) of an illumination system according to a further embodiment of the invention in the form of graphs, which indicate a relative spectral irradiance E.sub.rel (dimensionless) or a spectral irradiance E in

[00013]$\frac{W}{m^2.Math.\mathrm{nm}}$

as a function of the wavelength λ in nm. A first light source is a red LED, the relative spectral irradiance of which is indicated by the graph R. A second light source is a green LED, the relative spectral irradiance of which is indicated by the graph G. The red LED and the green LED radiate with approximately the same maximum spectral irradiance so as to be able to provide in each case approximately the same irradiance in an object field. A third light source is a blue LED, the relative spectral irradiance of which is indicated by the graph B. A maximum spectral irradiance of the blue LED is here significantly reduced as compared to the spectral irradiances of the red and the green LEDs, which can be achieved, for example, by dimming the blue LED. As a combination of the three different light sources, the illumination system (consisting of the three LEDs) has in an illumination range from a limit wavelength λG to a wavelength of 700 nm a first average spectral irradiance E1. Here, this first average spectral irradiance E.sub.1 is provided primarily from light from the red and the green LED. Over a dimming range from 380 nm to the limit wavelength λG, a second average spectral irradiance E2 is obtained. It should be noted here that this second average spectral irradiance is provided substantially via light of the blue LED. The second average spectral irradiance E.sub.2 is significantly smaller than the first average spectral irradiance E.sub.1, as a result of which curing of a light curing plastic is delayed, while a bright and colour neutral illumination of an object field is made possible. The limit wavelength λ.sub.6 is here, as already described above, adapted to a light curing plastic that is to be illuminated.

[0096] Such an illumination system, which consists of three or more different and separately controllable light sources, has significant advantages. First, the spectral irradiances radiated by the red LED and the green LED into an object field can be chosen to be so high that the object field is illuminated with a sufficiently high illuminance. In addition, the blue LED can be dimmed, independently of these two other LEDs, to an extent such that curing of the light curing plastic that is to be illuminated is delayed, and additionally a total colour impression that is similar to white light is brought about in the object field. It is not necessary here to develop a specific filter system or adapt it to individual light curing plastics, since adapting a respective light curing plastic takes place merely by way of adapting the irradiances of the individual light sources (R, G, B). Such an illumination system can have a plurality of operating modes, wherein the blue LED radiates, for example, with the same maximum irradiance onto the object field as the red and the green LED in one operating mode, while it is dimmed in another operating mode by at least 80% in order to radiate onto the object field with an irradiance of less than 20% of the irradiance with which the red and the green LED radiate onto the object field.