DE102005022175A1 - Multispectral lighting unit - Google Patents

Abstract

The present invention relates to a lighting unit with which objects can be illuminated as homogeneously as possible with white light or light of another defined wavelength. DOLLAR A The multispectral illumination unit according to the invention is based on a spectrometer arrangement in which, instead of the photodetector, a linear arrangement of LEDs (4) emitting light of different wavelengths and driven individually by current regulators is present. DOLLAR A emitted by the spectrally arranged according to their peak wavelength LEDs (4) light is coupled by a spectrally selective component in an optical fiber (1) and / or illumination optics and mixed in this, so that emerges at the output spectrally and laterally homogeneous light. DOLLAR A The lighting unit according to the invention is in principle applicable anywhere where spectrally adjustable, homogeneous light sources are required, the lighting conditions can be changed extremely quickly and accurately. Possible applications include microscopy and endoscopy. With the arrangement of a very compact, electronically spectrally adjustable and almost arbitrarily switchable multispectral lighting unit is provided.

Description

The The present invention relates to a lighting unit with which Objects with white Light or light of another defined wavelength possible can be illuminated homogeneously. The change the lighting conditions can be extremely fast and precise, without any, mechanically moving parts done.

The conventional light sources known in the art emit characteristic spectra according to the type of light generation. Thus, halogen lamps, which are considered Planckian emitters, emit spectrum, depending on change from the applied electric current, whereby the spectrum at higher currents to lower wavelength shifts. While High-pressure steam lamps an emission spectrum of discrete lines radiate, have the essentially continuous spectra xenon mercury lamps have pronounced local peaks. From Laser sources monochromatic light of high coherence is generated.

Around with the known lighting systems any spectral distribution either filter systems or spectrometers for selection are to be generated single wavelengths required.

The Combination of multiple sources leads usually to an inhomogeneous illumination of the examination object, the usually complicated and difficult to adjust optical Systems must be balanced.

The Disadvantages of conventional lighting sources are, for example in a limited spectral diversity, an inertia in the Changing the lighting conditions as well as the quite considerable thermal load.

When in the EP 120 01 179 B1 described white light source with light-emitting diodes for endoscopes, the light source of at least two light-emitting diodes, which emit light in different, preferably mutually complementary spectral regions, so that spectrally additive mixed light emerges from the illumination system. In an advantageous embodiment, three light emitting diodes are used as the white light source, which emit light of high light intensity, preferably in the blue, green and red spectral range. Light emitting diodes (LED's) offer the advantage due to their small size that they are usually integrated into the device and can be dispensed with an external lighting unit. LEDs are now available with high brightness, so they are sufficiently bright for many applications. The LEDs can be pulsed as well as continuously, individually or jointly controlled. LEDs also have the advantage that in the case of the application of colored light, the color quality of light of a light emitting diode is better than when a white light source is used with a color filter.

The US 5,489,771 A describes a standard LED light source as a calibration system for photo and video microscopy. The standard LED light source can be used to determine the performance of the microscope optics or to calibrate the microscope system. Selectable light intensities are generated by controlling the energy supplied to the LEDs. In order to homogenize the preferably green, yellow and red light emitted by the LEDs, the LEDs are encapsulated in a diffuser. A portion of the light from the LEDs is scattered to the side and strikes a photodiode arranged there, the signal of which is provided to a control circuit to control the light intensity of the LEDs. This method of regulation automatically takes into account changes in the performance of the LEDs. The targeted activation of a defined Lichhtspektrum, for example, monochromatic light can be generated that can be both continuous and pulse-modulated.

A variable, multi-color LED lighting system for ophthalmic applications will be available in the US 6,183,086 B1 described whose color of the emitted light can be varied. Compared to conventional ophthalmic lighting systems, less heat is emitted from the LEDs and a much longer life is achieved. The system consists of three LEDs of different colors, whose radiated light is mixed by a device and passed through an optical fiber to the ophthalmic device. Preferably, the color combinations: red-blue-green or red-blue-yellow are used. In addition to the white light produced by mixing the light components, the system can also be used to generate specific colored light for lighting through targeted control.

An LED based lighting unit for a surveillance system is used in the US 6,624,597 B2 described. For the lighting system, the use of different colored LED's is provided, which are driven by a processor accordingly to produce white or colored light. Since previous, monochrome monitoring systems were essentially only suitable for determining size and shape, it is possible with color systems to control significantly more properties of the object to be monitored. The monitoring system described is based on a camera, a lighting unit and a processor that controls the lighting of the object to be analyzed accordingly. The control can be done for example by modulation of pulse width, intensity or other parameters. By creating a variety of colors, the lighting can be adapted to the particular object, the environment and the camera to provide optimal results. In addition to continuous illumination, strobe effects can also be realized with the system, which are used in particular on conveyor belts to make changes visible immediately. The LED-based lighting unit even allows monitoring in the ultraviolet or infrared spectral range. While many articles fluoresce under UV light and thus can easily be labeled, monitoring under IR light takes place in the non-visible spectral range. Lighting conditions can be changed almost instantaneously to provide a fast system response.

Of the present invention, the object is based on a simple and compact lighting system with a spectrally adjustable light source to develop, with which an object field illuminated as homogeneously as possible can be. The lighting system should be characterized by a high spectral diversity, a low inertia and low thermal problems.

According to the invention Problem solved by the features of the independent claims. preferred Further developments and embodiments are the subject of the dependent claims.

The Lighting unit according to the invention basically everywhere can be used where spectrally controllable, homogeneous light sources are required whose lighting conditions are changed extremely quickly and precisely can. Possible Applications include microscopy and endoscopy.

The Invention will be described below with reference to an embodiment. Show this

1 : the basic structure of an MMS spectrometer,

2 : a selection of LED spectra (between 370 nm and 960 nm),

3 a spectrometric multi-spectral illumination unit according to the invention,

4 : a programmable circuit arrangement for LED control and

5 a multispectral illumination unit based on a monochromator arrangement according to the invention.

at the spectrometer-based, multispectral Lighting unit is a linear instead of the photodetector Arrangement of LEDs, emit the light of different wavelengths and individually via current regulator be driven, the LED's according to their emitted peak wavelength spectral are ordered. Their emitted light is emitted by a spectrally selective Component coupled in an optical fiber and / or illumination optics and mixed in this, so that at its output spectral and lateral homogeneous light emerges.

To clarify the inventive solution shows 1 the basic structure and beam path of an MMS spectrometer.

The measuring light reflected by the object is transmitted via an optical fiber 1 coupled and serving as a spectrally selective device spectrometer crystal 2 split into its spectral components and on the photodetector 3 displayed. The simultaneously registered spectral components of the measuring light are evaluated accordingly.

Replacing the photodiode array with a linear arrangement of several LED's, one can use this arrangement as a source of illumination. The LEDs emit a narrowband light spectrum with a clear peak wavelength. 2 shows a selection of LED spectra (between 370 nm and 960 nm). It can be seen that LED's can produce light of a variety of wavelengths.

By the, according to their peak wavelength spectrally ordered LED's one achieves that emitted by the LEDs Light to a great extent is coupled into the optical fiber and / or illumination optics. In this the light is mixed so that spectrally at its output and lateral homogeneous light emerges.

Due to the small size of the individual LEDs of about 300 microns, it is possible to provide a plurality of LED spectrally sorted according to their peak wavelength, so that a large part of the emitted light is coupled into the optical fiber and / or illumination optics. The larger this proportion becomes, the lower the ene which occur ergieverluste. Likewise, it is also possible to use LEDs with a size of z. B. 1 mm to increase the intensity of the source accordingly.

A multispectral illumination unit based on a spectrometer arrangement is disclosed in US Pat 3 shown. It is instead of the photodetector 3 (in 1 ) a linear array of LEDs 4 , which emit light of different wavelengths and individually controlled by current regulator, available. By according to their peak wavelength spectrally ordered LED's 4 it is ensured that the emitted light from the serving as a spectrally selective device spectrometer crystal 2 to a large extent in the optical fiber 1 or lighting optics is coupled. Since the real, acting as a spectrally selective device spectrometer crystal 2 a flat contact surface for the photodetector 3 there is no problem, there is an applied on a support board LED's 4 to adapt.

In order to increase the efficiency of the lighting, one gets the diameter of the optical fiber 1 or increase illumination optics with respect to the spectrometer arrangement. That of the applied LEDs 4 emitted light is from the spectrometer crystal 2 in the optical fiber 1 coupled and mixed in this, so that emerges at the output spectrally and laterally homogeneous light.

The LEDs are individually controlled by current regulators, which makes it possible to set a desired spectrum very flexibly. 4 shows an electronic circuit for controlling the LED's. In the example shown, the control takes place via a CAN bus, with the 24 Channels with regard to current flow and time behavior (pulse mode) can be programmed as required.

In a second exemplary embodiment, the spectrally selective component is a diffraction grating 5 used. Again, the spectrometer arrangement, according to 5 used with reversed beam path. The emitted light of the spectrally ordered LEDs according to their peak wavelength 4 is via the diffraction grating 5 is coupled to a large extent in an optical fiber or lighting optics. By using so-called imaging grating (English: "imaging grating"), it is possible to unite the LEDs in a "virtual source". Again, the LEDs are 4 individually controlled via current controller. Advantage over the execution according to 3 is the larger aperture angle captured by the overall system. Depending on the size of the diffraction grating 5 and the desired spectral splitting a high collection efficiency can be achieved. diffraction grating 5 Nowadays, they can be optimally adapted to the task to be solved.

By individually controllable via current regulator LEDs, the spectral composition of the light arriving at the output of the optical fiber and / or illumination optics light can be influenced in a very effective manner. According to the 2 In principle, any wavelength can be generated by LEDs in the spectral range between 370 nm and 960 nm.

The inventive multispectral Lighting unit is based on a spectrometer with a spectrometer crystal or a diffraction grating as a spectrally selective Component which is operated with reverse beam path. Instead of the photodetector is a linear array of LEDs, the light of different wavelength emit and singly over Current controller can be controlled, available.

With the inventive arrangement becomes a very compact, electronically spectrally adjustable and nearly any switchable multispectral lighting unit provided, the principle everywhere can be used where spectrally controllable, homogeneous light sources are required are. The lighting conditions can be changed very quickly and precisely.

Claims (4)

Multispectral illumination unit based on a spectrometer arrangement in which instead of the photodetector a linear array of LEDs ( 4 ), which emit light of different wavelengths and are individually controlled by current regulators, is present, whereby the LEDs ( 4 ) spectrally ordered according to their peak wavelength whose emitted light from a spectrally selective component in an optical fiber ( 1 ) and / or illumination optics is coupled and mixed in this, so that exits at the output spectrally and laterally homogeneous light. Multispectral illumination unit according to Claim 1, in which a spectrometer crystal is used as the spectrally-selective component ( 2 ) or a diffraction grating ( 5 ) Is used. Multispectral illumination unit according to at least one of Claims 1 and 2, in which the optical fiber ( 1 ) and / or illumination optics with respect to a spectrometer arrangement has a larger diameter. Multispectral illumination unit according to at least one of the preceding claims, in which by the individually controllable via current regulator LED's ( 4 ) the spectral composition of the light arriving at the output of the optical fiber and / or illumination optics can be influenced.