Illumination device and illumination process with measurement and display of the distance

Abstract

An illumination device (100) includes an illumination unit (1, 2) which illuminates a surface (Ob). The position and the orientation of the illumination unit (1, 2) relative to the surface (Ob) can be changed. A distance sensor (4.1, 8.2) measures an indicator of the current distance between the illumination unit (1, 2) and the surface (Ob). A signal processing control unit (10) is configured to control an output unit (6.1, 6.2) of the illumination unit (1, 2). The controlled output unit (6.1, 6.2) outputs an indication of how much the measured distance deviates from a predetermined reference distance (Ref.sub.1, Ref.sub.2).

Claims

1. An illumination device comprising: an illumination unit configured to illuminate a surface, wherein a position and orientation of the illumination unit relative to the surface is variable; a distance sensor associated with the illumination unit, wherein the distance sensor is configured to measure an indicator of a current distance between the associated illumination unit and the surface; an output unit associated with the illumination unit; and a signal processing control unit configured to control the output unit based on the indicator of the current distance and on a given reference distance between the illumination unit and the surface, wherein the controlled output unit is configured to output an indication in a form that can be perceived by a human, and wherein the indication relates to how much the measured distance between the illumination unit and the surface deviates from the given reference distance.

2. An illumination device according to claim 1, wherein the output unit comprises a first output element; a second output element; and a third output element, wherein the controlled output unit is configured to: highlight the first output element if the difference between the measured current distance and the given reference distance is within a given tolerance range around zero; highlight the second output element if the difference is greater than an upper threshold of the tolerance range; and highlight the third output element if the difference is smaller than a lower threshold of the tolerance range.

3. An illumination device according to claim 2, wherein the illumination device comprises a first illumination unit and a second illumination unit; the first illumination unit is configured to generate a greater maximal irradiance than the second illumination unit; and a given tolerance range for the first illumination unit is smaller than a given tolerance range for the second illumination unit.

4. An illumination device according to claim 1, wherein the output unit comprises: a first output element; two second output elements; and two third output elements, wherein the controlled output unit is configured to highlight the first output element if the difference between the measured current distance and the given reference distance is within a predetermined first tolerance range around zero; if the difference is greater than an upper threshold of the first tolerance range, highlight one of the second output elements and additionally or instead highlight another one of the second output elements if the difference is even increasing, highlight another of the second output elements if the difference is decreasing and highlight another one of the second output elements if the difference is even greater than an upper threshold of a given further wider tolerance range comprising the first tolerance range; and if the difference is smaller than the lower threshold of the first tolerance range, highlight one third output element and additionally or instead highlight another of the third output elements if the difference is even decreasing, highlight another of the third output elements if the difference between the measured distance and the reference distance is increasing and highlight another of the third output elements if the difference between the measured distance and the reference distance is even smaller than the lower threshold of the wider tolerance range.

5. An illumination device according to claim 1, further comprising another illumination unit and another output unit associated with the other illumination unit, wherein: the position and orientation of each illumination unit relative to each other illumination unit is variable; and the output unit is mechanically connected to the illumination unit such that the position and orientation of the associated output unit relative to the illumination unit is fixed; and the other output unit is mechanically connected to the other illumination unit such that the position and orientation of the associated other output unit relative to the other illumination unit is fixed.

6. An illumination device according to claim 1, wherein: the distance sensor is configured to scan the surface without contact and to generate a topographic profile of the surface using results of the scan; and the control unit is configured to determine the indicator of the distance between the illumination unit and the surface using the generated topographic profile.

7. An illumination device according to claim 1, wherein: the illumination unit comprises a handle; the output unit is integrated in the handle, and the controlled output unit in the handle is configured to output the indication by vibration.

8. An illumination device according to claim 1, wherein: the illumination unit comprises a plurality of light sources; and the output unit is configured to visually output the indication for the deviation between the measured distance and the reference distance using at least one light source of the plurality of light sources.

9. An illumination device according to claim 8, wherein: the output unit is configured to transfer at least one light source of the plurality of light sources from a first state to a second state, if the distance between the illumination unit and the surface measured at a first time lies within a predetermined tolerance range around the reference distance and the distance measured at a subsequent second time lies outside the reference distance; both the first state and the second state are visually perceptible by a human; and a visual perception of the second state is different from a visual perception of the first state.

10. An illumination device according to claim 9, wherein the light source being in the first state appears to a human as continuously luminous and being in the second state as flashing, or the light source of the plurality of light sources flashes in the second state with a higher frequency perceptible by a human than in the first state, or a maximum illuminance or a light field diameter or a light spectrum of the light source being in the second state is different from that with the light source being in the first state.

11. An illumination device according to claim 1, further comprising a sensor configured to detect an activating event, wherein: the activating event comprises at least one of: the illumination device is moved or touched; the illuminated surface is moved; an actuating element of the illumination device is actuated; and the deviation between the measured distance and the reference distance is above a predetermined deviation tolerance range and/or a change in deviation between the measured distance and the reference distance is above a predetermined change tolerance range; the control unit is arranged to control the output unit in response to the detection of the activating event such that the controlled output unit outputs the indication; and the control unit is further configured, if no further activating event has been detected within a specified time period after the detection of the activating event, to control the output unit such that the controlled output unit terminates the output of the indication.

12. An illumination process for illuminating a surface, the process comprising the steps of: providing an illumination device comprising an illumination unit, a distance sensor associated with the illumination unit, and an output unit associated with the illumination unit; illuminating the surface with the illumination device; and changing a position and/or an orientation of the illumination unit relative to the surface, wherein after changing the position and/or the orientation of the illumination unit, triggering and performing a sequence, wherein the sequence comprises: with the distance sensor, measuring an indication of a current distance between the associated illumination unit and the surface; controlling the output unit of the illumination unit such that the controlled output unit outputs an indication in a form perceptible by a human, wherein the indication indicates how much the measured current distance between the illumination unit and the surface deviates from a given reference distance, and wherein the sequence is triggered at least when at least one of: the illumination device is moved or touched; the illuminated surface is moved; an actuating element of the illumination device is actuated; and a position and/or orientation deviation outside a predetermined deviation tolerance range and/or a change in deviation outside a predetermined change tolerance range is detected.

13. An illumination process according to claim 12, wherein: the output unit comprises: a first output element; a second output element; and a third output element; and the step that this output unit outputs the indication comprises the controlled output unit steps of: highlighting the first output element when the difference between the measured current distance and the given reference distance is within a predetermined tolerance range around zero, highlighting the second output element when the difference is greater than the upper threshold of the tolerance range, and highlighting the third output element if the difference is smaller than the lower threshold of the tolerance range.

14. An illumination process according to claim 12, wherein: the output unit comprises: a first output element; two second output elements; and two third output elements; and the controlled output unit: highlights the first output element if the difference between the measured current distance and the given reference distance is within a predetermined first tolerance range around zero; if the difference is greater than the upper threshold of the tolerance range, highlights one of the second output elements and additionally or instead highlights another of the second output elements if the difference is even increasing, highlights another of the second output elements if the difference decreases, and highlights another of the second output elements if the difference is even greater than an upper threshold of a given further wider tolerance range comprising the first tolerance range; and if the difference is smaller than the lower threshold of the tolerance range, highlights one of the third output elements and additionally or instead highlights another of the third output elements if the difference is even decreasing, highlights another of the third output elements if the difference is increasing and highlights another of the third output elements if the difference is even smaller than the lower threshold of the wider tolerance range.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a schematic cross-sectional view of an illumination device with two illumination units and one distance sensor and one display unit per illumination unit;

(3) FIG. 2 schematically shows a measured current distance, a reference distance and two tolerance ranges;

(4) FIG. 3 is a schematic view showing two display units and two touch sensors for the two illumination devices of FIG. 1;

(5) FIG. 4 is a schematic view showing how a camera scans an illuminated surface;

(6) FIG. 5A is a schematic view showing an image from one of three different viewing directions from the same illuminated surface of FIG. 4;

(7) FIG. 5B is a schematic view showing an image from another of three different viewing directions from the same illuminated surface of FIG. 4;

(8) FIG. 5C is a schematic view showing an image from another of three different viewing directions from the same illuminated surface of FIG. 4;

(9) FIG. 6 is a schematic view showing how an indication of the deviation is output by flashing light sources.

DESCRIPTION OF PREFERRED EMBODIMENTS

(10) Referring to the drawings, in the embodiment example, the invention is used for illuminating an object Obj in the form of an operating table. On this operating table Obj a patient, not shown, lies who is being medically treated. The illumination device 100 according to the invention illuminates that surface Ob of the operating table Obj and/or of the patient on the operating table Obj wherein the illuminated surface faces the illumination device 100. The illumination device 100 generates a light field on the illuminated surface Ob. In subsequent figures, a flat surface Ob is shown for simplicity. Of course, the illuminated surface of a patient on the operating table Obj is not flat.

(11) The illumination device 100 of the embodiment comprises several illumination units which illuminate the operating table Obj vertically or obliquely from above and from several directions. FIG. 1 shows exemplarily and schematically two illumination units 1, 2 of the illumination device 100. Of course, another number of illumination units is also possible.

(12) In the embodiment, the illumination units 1, 2 are movably attached to a ceiling and can be moved independently of each other. The respective position and orientation in space of each illumination unit 1, 2 can be changed, and preferably independently of the position and orientation of the illumination unit or each other illumination unit 1, 2. In one embodiment, joints (hinges) of each illumination unit 1, 2 are configured such that the illumination unit 1, 2 does not change its position and orientation by itself, but only after a user intervention. In another embodiment, each illumination unit 1, 2 can be locked and unlocked in a desired position and orientation.

(13) FIG. 2 illustrates the reference distance. The figure is not necessarily true to scale. FIG. 2 shows the illumination unit 1, its optical center axis MA.1 and the illuminated surface Ob of the object Obj. The point Ref.sub.1 on the center axis MA.1 has a reference distance dist.sub.Ref from the illuminated surface Ob. The point Ref.sub.1 would be on that surface of the illumination unit 1 which faces to the surface Ob if the distance dist.sub.1 between the illumination unit 1 and the illuminated surface Ob were equal to the reference distance dist.sub.Ref. The measured current distance dist.sub.1, however, is greater. In addition the deviation A between the measured current distance dist.sub.1 and the reference distance dist.sub.Ref is shown. Furthermore a first, narrower tolerance range Tol.sub.1 and a further, wider tolerance range Tol.sub.w are shown. The first tolerance range Tol.sub.1 is completely comprised in the wider tolerance range Tol.sub.w. The meaning of the tolerance ranges are explained below.

(14) Various variable parameters affect the particular light field that an illumination unit 1, 2 generates on the illuminated surface Ob. These parameters include: the maximum illuminance achieved at the reference distance dist.sub.Ref or in space, the light field diameter d.sub.x, the color temperature correlated with the light spectrum of the illumination unit 1, 2, and the position and orientation of the illumination unit 1, 2, relative to the illuminated surface Ob and thus the current distance dist.sub.1, dist.sub.2 between the illumination unit 1, 2 and the surface Ob.

(15) The parameters maximum illuminance achieved and light field diameter d.sub.x have been explained above.

(16) A user can specify values for the first three parameters just mentioned, for example at an input unit with knobs (buttons), with rotary controls and/or with at least one touch-sensitive screen (touchscreen). In particular, a user can reduce the maximum achieved illuminance in space or at the reference distance dist.sub.Ref relative to the maximum achievable illuminance and thereby dim or also turn up the illumination unit 1, 2. Furthermore, the user can change the position and orientation of the illumination unit 1, 2 relative to the surface Ob, preferably by a manual intervention.

(17) As mentioned above, a user can position and orient each illumination unit 1, 2 independently of the or each other illumination unit 2, 1 in space, in particular at a respective desired distance from the surface Ob. If the actual distance dist.sub.1, dist.sub.2 between an illumination unit 1, 2 and the surface Ob deviates significantly from the reference distance dist.sub.Ref, the actual value of a parameter of the light field achieved by an illumination unit 1, 2 on the surface Ob may also deviate significantly from a desired value for this parameter. Therefore, the respective actual current distance dist.sub.1, dist.sub.2 between an illumination unit 1, 2 is measured without contact, and an indication for the deviation between the actual measured distance dist.sub.1, dist.sub.2 and the reference distance dist.sub.Ref is output in a form that can be perceived by a human.

(18) In FIG. 1 a point Ref.sub.1 on the optical center axis MA.1 is shown wherein the distance between the point Ref.sub.1 and the illuminated surface Ob, measured along the optical center axis MA.1, is equal to the reference distance dist.sub.Ref. Accordingly a point Ref.sub.2 on the optical center axis is shown wherein the distance between the point Ref.sub.2 and the surface Ob is equal to the reference distance dist.sub.Ref.

(19) In the embodiment example, the first illumination unit 1 is rotationally symmetrical to a center axis MA.1, and the second illumination unit 2 is rotationally symmetrical to a center axis MA.2. In the exemplary situation shown, the two center axes MA.1 and MA.2 are oblique on the illuminated surface Ob and lie in the drawing plane of FIG. 1. Each illumination unit 1, 2 and thus each center axis MA.1, MA.2 can also be positioned differently relative to the surface Ob.

(20) The illumination units 1, 2 each have an optical center axis. In the embodiment example, the optical center axis of the illumination unit 1 is equal to the geometric center axis MA.1, and the optical center axis of the illumination unit 2 is equal to the geometric center axis MA.2. Along the optical center axis MA.1, MA.2, the illuminance and the irradiance are maximum. More precisely, in a plane perpendicular to the optical center axis MA.1, MA.2, the illuminance and the irradiance take their maximum values at the intersection of the plane with the optical center axis MA.1, MA.2. FIG. 1 shows the intersection points S.1 and S.2 of the two optical center axes MA.1 and MA.2 with the illuminated surface Ob.

(21) The first illumination unit 1 comprises a support (carrier) 5.1 and several individual light sources 1.1, 1.2, . . . , which are fixed to the support 5.1 and are preferably arranged rotationally symmetrically about the center axis MA.1, cf. FIG. 1. A handle 9.1 is mounted on the support 5.1, namely with a lateral offset from the geometric center axis MA.1. The second illumination unit 2 comprises a support 5.2 and a plurality of individual light sources 2.1, 2.2, . . . , which are fixed to the support 5.2 and are preferably arranged rotationally symmetrically about the center axis MA.2. A handle 9.2 is mounted centered on the support 5.2. FIG. 1 shows schematically the light beams Lb.sub.1.1, Lb.sub.1.2, . . . of the light sources 1.1, 1.2, . . . as well as the light beams Lb.sub.2.1, Lf.sub.2.2, . . . of the light sources 2.1, 2.2, . . . . For illustration these light beams are dotted differently. The light sources 1.1, 1.2, . . . , 2.1, 2.2, . . . can emit light of the same color temperature or light of different color temperatures.

(22) As already explained, the respective current distance dist.sub.1, dist.sub.2 between an illumination unit 1, 2 and the surface Ob is measured without contact. Different measurement processes to measure a distance are possible, for example a time-of-flight (transit time, runtime) measurement for electromagnetic radiation, in particular infrared radiation, ultrasonic radiation, radar, laser, a measurement of how much the radiation intensity is attenuated, as well as optical processes. By way of example, some principles of distance sensors that can be used for the invention are described below.

(23) In the embodiment example, a first distance sensor 4.1, which is connected to the first illumination unit 1 and is configured as a camera, is able to measure the distance dist.sub.1 between itself and the illuminated surface Ob. A second distance sensor 8.2, which is connected to the second illumination unit 2, is able to measure the distance dist.sub.2 between itself and the illuminated surface Ob. A signal-processing control unit 10 receives a signal from each of the two distance sensors 4.1 and 8.2. The control unit 10 captures the lateral offset dist.sub.lat between the distance sensor 4.1, 8.2 and the optical center axis MA.1, MA.2 of the associated illumination unit 1, 2. This lateral offset dist.sub.lat is predetermined by the configuration of the illumination unit 1, 2 and is not variable during operation. In FIG. 1, this lateral offset dist.sub.lat is shown exaggerated. The distance sensor 4.1 is centered. Different possible configurations of the distance sensors are described below by way of example.

(24) A camera 4.1 is attached to the support 5.1 of the first illumination unit 1, which acts as a distance sensor. The camera 4.1 cannot move relative to the support 5.1 and therefore cannot move relative to the light sources 1.1, 1.2, . . . . A distance sensor 8.2 is attached to the support 5.2 of the second illumination unit 2. The distance sensor 8.2 cannot move relative to the support 5.2 and therefore also cannot move relative to the light sources 2.1, 2.2, . . . . In the example shown, the camera 4.1 is located on or near the optical center axis MA.1, while a larger lateral offset dist.sub.lat occurs between the distance sensor 8.2 and the optical center axis MA.2. In the example shown, the handle 9.1 is positioned with a lateral offset from the optical center axis MA.1. It is also possible that the handle 9.1 is positioned centered and the camera 4.1 is integrated into the handle 9.1. Accordingly, the distance sensor 8.2 can be integrated in the handle 9.2.

(25) The camera 4.1 has an autofocus function and automatically focuses on the illuminated surface Ob. The control unit 10 detects the distance at which the autofocus function has focused the camera 4.1. This distance is an estimate of the sought distance dist.sub.1 between the first illumination unit 1 and the surface Ob, and measured along the optical center axis MA.1. In one embodiment, the sought distance dist.sub.1 is derived from the estimated distance and the lateral distance between the camera 4.1 and the optical center axis MA.1.

(26) The distance sensor 8.2 emits electromagnetic radiation or also sound waves towards the surface Ob. The surface Ob reflects this electromagnetic radiation or these sound waves, and a part of it reaches the distance sensor 8.2 again. The distance sensor 8.2 measures the transit time and derives an estimate for the distance dist.sub.2 between itself and the surface Ob from it. The control unit 10 uses this estimate for as well as the invariant lateral offset dist.sub.lat between MA.2 and 8.2 to determine the distance dist.sub.2 between the illumination unit 2 and the surface Ob along the center axis MA.2.

(27) As a rule, the illuminated surface Ob does not have a flat contour. As an example, five elevations 7.1, . . . , 7.5 are shown in FIG. 1 and FIG. 4.

(28) FIG. 4 shows a different configuration. As shown in FIG. 1, a first camera 4.1 is attached to the support 5.1, whereas a second camera 4.2 is attached to the support 5.2, which camera takes the place of the distance sensor 8.2. Each camera 4.1, 4.2 is configured as a time-of-flight sensor and is capable on the one hand of generating an image of the surface Ob and on the other hand of scanning the surface Ob without contact. A topographic 3D profile is generated with the aid of a signal from the camera 4.1. Such a time-of-flight sensor is described, for example, in DE 10 2013 012 231 A1 (corresponding U.S. Pat. No. 9,491,835 (B2) is incorporated by reference) and in DE 10 2012 014 716 A1 (corresponding U.S. Pat. No. 9,504,113 (B2) is incorporated by reference). In order to generate the topographic profile, the camera 4.1, 4.2 emits electromagnetic beams which impinge on different points of the surface Ob and are reflected there. From the respective transit time of each ray, the camera 4.1, 4.2 derives the distance to the reflecting point on the surface Ob, and from the distances the camera 4.1, 4.2 generates the respective topographic profile. The camera 4.1, 4.2 thus scans the surface Ob with the five elevations 7.1, . . . , 7.5 without contact.

(29) FIG. 4 illustrates how the camera 4.2 is positioned on the second illumination unit 2 relative to the surface Ob. FIG. 5 A shows the five elevations 7.1, . . . , 7.5 are shown in a topographic profile when the optical axis of the camera 4.2 is perpendicular to the illuminated surface Ob, which is not the case for the two cameras 4.1 and 4.2 of FIG. 1, FIG. 3, and FIG. 4. FIG. 5 B shows how the five elevations 7.1, . . . , 7.5 are shown in a topographic profile of the camera 4.2 on the support 3.2 of the second illumination unit 2. FIG. 5 C shows how the five elevations 7.1, . . . , 7.5 are represented in a topographic profile of the camera 4.2. As is known, the closer an elevation 7.1, . . . , 7.5 is to the respective camera 4.1, 4.2, the larger it is displayed.

(30) It is possible that an object, for example a body part of a human or a medical instrument, gets into the area between an illumination unit 1, 2 and the illuminated surface Ob. This event is distinguished from the event that the illumination device 100 is moved to a different position relative to the surface Ob during an operation, for example, in one of the following ways: It is detected that the measured topographic profile changes abruptlythis can only be caused by an object entering the area between the illumination device 100 and the illuminated surface Ob. The topographic profile differs significantly from the profile of a patient on the operating table Obj. A given object, for example a hand or a medical instrument, is recognized.

(31) In one embodiment, the distance used is the distance that was last measured before the event that an object entered the area was detected, or averages are taken over several last measured values of the distance. If the object enters the area between the illumination unit 1, 2 and the surface Ob in such a way that the object interrupts the optical center axis MA.1, MA.2, the distance measured along the optical center axis MA.1, MA.2 also changes abruptly. Also in this case, the distance that was last measured before the event was detected is used. It is also possible that the contour of the object between the illumination unit 1, 2 and the surface Ob is determined, and the area enclosed by this contour in the topographic profile is disregarded when the current distance dist.sub.1, dist.sub.2 is determined.

(32) Preferably, the control unit 10 computationally projects the center axis MA.1, MA.2 into the topographic profile from the surface Ob generated by the camera 4.1, 4.2. The control unit 10 determines a mean distance between the illumination unit 1, 2 and the illuminated surface Ob in a region around the intersection S.1, S.2. In many cases, this average distance suitably takes into account unevenness of the surface Ob.

(33) An indication of the deviation between the reference distance dist.sub.Ref and the respective measured current distance dist.sub.1, dist.sub.2 is output in a form that can be perceived by a human. In one embodiment, the respective measured distance dist.sub.1, dist.sub.2 or an indicator for a deviation are output continuously. In another embodiment, the indicator for the deviation is output when a user touches an actuation unit of the illumination unit 1, 2. This actuation unit is, for example, a handle 9.1, 9.2, which is attached to the bottom of the support 5.1, 5.2 and makes it easier for the user to position and orient the illumination unit 1, 2 in space. The actuation unit may also comprise a push button, a switch, a slider, a touch sensitive screen (touchscreen) or a similar suitable element. The deviation between the reference distance dist.sub.Ref and the respective measured current distance is dist.sub.1, dist.sub.2 output, in particular visually, acoustically and/or haptically, and preferably by means of an output unit attached to the illumination device 1, 2 itself. The visual output is described in more detail below. An acoustic output may include a sequence of tones, where the greater the deviation between the reference distance dist.sub.Ref and the measured distance dist.sub.1, dist.sub.2, the higher the frequency in one implementation and the lower the frequency in another implementation. In a haptic output, an actuating unit, for example the handle 9.1, 9.2 described above, vibrates, with the vibration frequency preferably being the higher or also the lower the greater is the deviation.

(34) In a visual output, one of at least three different visual display elements is shown highlighted. These at least three different display elements are one embodiment of output elements according to the invention. For example, a green indicator element is shown highlighted when the deviation is within a given first tolerance range Tol.sub.1 around zero, yellow when the deviation is outside the first tolerance range Tol.sub.1 in a wider tolerance range Tol.sub.w around zero, and red when the deviation is even outside the wider tolerance range Tol.sub.w.

(35) FIG. 3 shows another embodiment of a visual output. An output unit in the form of a display unit 6.1 is assigned to the illumination unit 1 and preferably attached to the support 5.1, another output unit in the form of a display unit 6.2 is assigned to the illumination unit 2 and preferably attached to the support 5.2. In one implementation, the additional display elements 14.1, 14.2 light up when a user touches the illumination unit 1 or 2. The display unit 6.1 comprises five display elements 3.1, 3.2, 3.3a, 3.3b, the display unit 6.2 comprises five display elements 13.1, 13.2, 13.3a, 13.3b. The circular display element 3.1, 13.1 in the center functions as the first output element and indicates that the deviation is in the tolerance range Tol.sub.1 around zero. The arrow-shaped display elements 3.2a, 3.2b, 13.2a, 13.2b, 3.3a, 3.3b, 13.3a, 13.3b to the left and right of the circular display element 3.1, 13.1 each act as a second or as a third output element and indicate that the deviation is outside the first tolerance range Tol.sub.1. The eight arrow-shaped indicator elements 3.2a, 3.2b, 13.2a, 13.2b, 3.3a, 3.3b, 13.3a, 13.3b also indicate the direction in which the illumination unit 1, 2 must be moved so that the actual distance does not differ from the reference distance dist.sub.Ref by more than the first tolerance range Tol.sub.1. Thus, a single or double arrow 3.2a, 3.2b, 13.2a, 13.2b from top left to bottom right indicates that the distance must be decreased, a single or double arrow 3.3a, 3.3b, 13.3a, 13.3b from bottom left to top right indicates that the distance must be increased. A single arrow 3.2a, 13.2a, 3.3a, 13.3a indicates that the distance is slightly too large or slightly too small, respectively, a double arrow 3.2b, 13.2b, 3.3b, 13.3b indicates that the distance is considerably too large or considerably too small, respectively. More precisely, the double arrow 3.2b, 13.2b, 3.3b, 13.3b indicates that the distance is even outside a predetermined further tolerance range Tol.sub.w, which includes the first tolerance range Tol.sub.1. The single arrow 3.2a, 13.2a, 3.3a, 13.3a indicates that the distance is outside the first tolerance range Tol.sub.1 but still within the further tolerance range Tol.sub.w. In the example of FIG. 3, a simple arrow 3.2a from top left to bottom right is shown highlighted on the display unit 6.1 and a simple arrow 13.3a from bottom left to top right is shown filled in black on the display unit 6.2.

(36) FIG. 1 and FIG. 3 also each show a handle 9.1, which is mechanically connected to the support 5.1 of the first illumination unit 1, and a handle 9.2, which is mechanically connected to the support 5.2 of the second illumination unit 2. With the handle 9.1, 9.2, the illumination unit 1, 2 can be moved in space and thereby positioned and oriented.

(37) A touch sensor 11.1 is integrated in the handle 9.1, and a touch sensor 11.2 is integrated in the handle 9.2. The touch sensor 11.1 detects the event that a user has touched the handle 9.1. The touch sensor 11.2 detects the event that a user has touched the handle 9.2. The event that a touch of the handle 9.1 has been detected triggers the step of outputting the measured current distance dist.sub.1 between the first illumination unit 1 and the illuminated surface Ob in a form perceptible by a human, for example as just described on the display unit 6.1. Accordingly, the event that a touch of the handle 9.2 has been detected triggers the step of outputting the measured current distance dist.sub.2 between the second illumination unit 2 and the illuminated surface Ob. Furthermore, the event of touching a touch sensor 11.1, 11.2 triggers the step of illuminating or otherwise highlighting the corresponding display element 14.1, 14.2 on the display unit 6.1, 6.2.

(38) It is also possible that the deviation between the measured distance dist.sub.1, dist.sub.2 and the reference distance dist.sub.Ref is visually displayed in another way. For example, an indicator light flickers according to the deviation, changes its diameter or light spectrum depending on the deviation, or shows a pattern that depends on the deviation, such as a running light.

(39) FIG. 6 illustrates an example of another embodiment including an output unit to visually output an indication for the deviation between the measured distance dist.sub.1, dist.sub.2 and the reference distance dist.sub.Ref. Some light sources of the first illumination unit 1 also function as the output unit in another form of a display unit. FIG. 6 shows the illumination unit 1, wherein the optical center axis MA.1 is perpendicular to the drawing plane and the viewer looks at the illumination unit 1 from the direction of the illuminated surface Ob. In the example shown, the illumination unit 1 comprises eight assemblies each having four light sources, the four light sources being arranged in a row. As an example, the assembly Bg is marked. Each assembly consists of two light sources 1.w, which emit warm white light, and two light sources 1.c, which emit cool white light. In FIG. 6, the warm white light sources 1.w are shown hatched differently than the cool white light sources 1.c. The warm white light sources 1.w and the cool white light sources 1.c are arranged alternately. The eight assemblies are arranged radially around the center optical axis MA. In addition, the light sources 1.w, 1.c are arranged on four concentric circles around the optical center axis.

(40) As long as the deviation is in a tolerance range Tol.sub.1 or Tol.sub.w around zero, all light sources appear to a human observer as continuously illuminated. It is possible that the light sources 1.w, 1.c are operated in pulsed mode, i.e. that a pulsed electrical voltage is applied to the light sources 1.w, 1.c, such as LEDs. However, the pulse frequency is such that a user does not perceive any flickering. If, on the other hand, the deviation is outside the tolerance range Tol.sub.1, Tol.sub.w, some light sources are supplied with electrical energy in such a way that they flicker in a way that can be perceived by a human. The frequency of the flickering can be higher the further the deviation is from the tolerance range Tol.sub.1, Tol.sub.w. In FIG. 6, four light sources on the outermost circle K are represented by four black circles as an example. If the deviation is outside the tolerance range Tol.sub.1, Tol.sub.w, these four light sources flicker.

(41) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

(42) TABLE-US-00001 List of reference characters 1 First illumination unit, comprises the light sources 1.1, 1.2, . . . , the support 5.1 with the handle 9.1 and the camera 4.1, has the optical center axis MA.1 1.1, 1.2, . . . Light sources of the first illumination unit 1, generate the light beams Lb.sub.1.1, Lb.sub.1.2, . . . , are mounted on the support 5.1 1.c Cool white light source of the first illumination unit 1 1.w Warm white light source of the first illumination unit 1 2 Second illumination unit, comprises the light sources 2.1, 2.2, . . . , the support 5.2 with the handle 9.2 and the distance sensor 8.2 or the camera 4.2, has the optical center axis MA.2 2.1, 2.2, . . . Light sources of the second illumination unit 2, generate the light beams Lb.sub.2.1, Lb.sub.2.2, . . . , are mounted on the support 5.2 3.1 First display element on the display unit 6.1 3.2a, 3.2b Second display elements on the display unit 6.1 3.3a, 3.3b Second display elements on the display unit 6.1 4.1 Camera of the first illumination device 1, centered mounted on the support 5.1, has the field of view Bf.1, is able to measure the distance dist.sub.1 between itself and the surface Ob and, in one embodiment, to yield a signal for generating a topographic profile of the surface Ob 4.2 Camera of the second illumination device 2, mounted on the support 5.2, has the field of view Bf.2, is able to measure the distance dist.sub.2 between itself and the surface Ob and, in one embodiment, to yield a signal for generating a topographic profile of the surface Ob 5.1 Support of the first illumination device 1, includes the handle 9.1, carries the light sources 1.1, 1.2, . . . 5.2 Support of the second illumination device 2, includes the handle 9.2, carries the light sources 2.1, 2.2, . . . 6.1 Display unit referring to the first illumination unit 1 comprises the display elements 3.1, 3.2, 3.3a, 3.3b 6.2 Display unit referring to the second illumination unit 2 comprises the display elements 13.1, 13.2, 13.3a, 13.3b 7.1, 7.2, . . . Elevations on the object Obj 8.2 Distance sensor of the second illumination device 2, mounted on the support 5.2 with the lateral offset dist.sub.lat, is able to measure the distance dist.sub.2 between itself and the surface Ob 9.1 Handle on the support 5.1, can be used to position the first illumination unit 1, comprises the touch sensor 11.1 9.2 Handle on the support 5.2, can be used for positioning the second illumination unit 2, comprises the touch sensor 11.2 10 Signal processing control unit, receives signals from the sensors 4.1, 4.2, 8.2, 11.1, 11.2, controls the display units 6.1 and 6.2 11.1 Touch sensor on the handle 9.1, detects a touch of the handle 9.1 11.2 Touch sensor on the handle 9.2, detects a touch of the handle 9.2 13.1 First display element of the display unit 6.2 13.2a, 13.2b Second display elements of the display unit 6.2 13.3a, 13.3b Third display elements of the display unit 6.2 14.1, 14.2 Display elements on the display unit 6.1, 6.2, indicate that the assigned illumination unit 1, 2 is being touched 100 Illumination device, comprising the illumination units 1 and 2, the display units 6.1 and 6.2, and the control unit 10, is capable of illuminating the surface Ob of the object Obj Bf.1 View field of the camera 4.1 Bf.2 View field of the camera 4.2 Bg Assembly of the first illumination unit 1, includes four light sources 1.w, 1.c dist.sub.1 Current distance between the first illumination unit 1 and the illuminated surface, measured by the camera 4.1 dist.sub.2 Current distance between the first illumination unit 1 and the illuminated surface, measured by the distance sensor 8.2 dist.sub.lat Lateral offset between the distance sensor 8.2 and the optical center axis MA.2 dist.sub.Ref given reference distance between and illumination unit and an illuminated surface, is 1 m, e.g. deviation between the measured distance dist.sub.1 and the given reference distance dist.sub.Ref K Circle around the optical center axis MA, on which eight light sources of the first illumination unit 1 are arranged, four of these light sources flickering when the deviation is outside the tolerance range around zero Lb.sub.1.1, Light beams which generate the light sources 1.1, Lb.sub.1.2, . . . 1.2, . . . Lb.sub.2.1, Light beams generated by the light sources 2.1, Lb.sub.2.2, . . . 2.2, . . . MA.1 Optical and geometrical center axis of the first illumination unit 1 MA.2 Optical and geometrical center axis of the second illumination unit 2 Ob Illuminated surface of the object obj, here: of the patient on the operating table Obj Illuminated object, here: patient on the operating table Ref.sub.1 Point on the optical center axis MA.1 where the illumination unit 1 would be if it were positioned at the reference distance dist.sub.Ref from the surface Ob Ref.sub.2 Point on the optical center axis MA.2 where the illumination unit 2 would be if it were positioned at the reference distance dist.sub.Ref from the surface Ob S.1 Intersection of the center axis MA.1 with the surface Ob S.2 Intersection of the center axis MA.2 with the surface Ob Tol.sub.1 first, narrower tolerance range around Zero Tol.sub.w further, wider tolerance range, comprises and surrounds the first tolerance range Tol.sub.1