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WO2003062755A1 - Illumination device - Google Patents

Illumination device Download PDF

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Publication number
WO2003062755A1
WO2003062755A1 PCT/NL2003/000042 NL0300042W WO03062755A1 WO 2003062755 A1 WO2003062755 A1 WO 2003062755A1 NL 0300042 W NL0300042 W NL 0300042W WO 03062755 A1 WO03062755 A1 WO 03062755A1
Authority
WO
WIPO (PCT)
Prior art keywords
mirrors
lamps
lens
leds
parallel
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/NL2003/000042
Other languages
French (fr)
Inventor
Rowland De Rodde
Leopold Cornelis Petrus Keizer
Gerardus Wilhelmus Adrianus Maria Van Der Heijden
Gerrit Polder
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Plant Research International BV
Original Assignee
Plant Research International BV
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Plant Research International BV filed Critical Plant Research International BV
Publication of WO2003062755A1 publication Critical patent/WO2003062755A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/09—Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for
    • G02B27/0938—Using specific optical elements
    • G02B27/0994—Fibers, light pipes
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21V—FUNCTIONAL FEATURES OR DETAILS OF LIGHTING DEVICES OR SYSTEMS THEREOF; STRUCTURAL COMBINATIONS OF LIGHTING DEVICES WITH OTHER ARTICLES, NOT OTHERWISE PROVIDED FOR
    • F21V2200/00—Use of light guides, e.g. fibre optic devices, in lighting devices or systems
    • F21V2200/40—Use of light guides, e.g. fibre optic devices, in lighting devices or systems of hollow light guides
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F21—LIGHTING
    • F21Y—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES F21K, F21L, F21S and F21V, RELATING TO THE FORM OR THE KIND OF THE LIGHT SOURCES OR OF THE COLOUR OF THE LIGHT EMITTED
    • F21Y2115/00—Light-generating elements of semiconductor light sources
    • F21Y2115/10—Light-emitting diodes [LED]

Definitions

  • the present invention relates to a device for illuminating a (three dimensional) object in a measuring device.
  • halogen lamps for illuminating the object in imaging spectrographs, often in combination with glass fibres and line arrays (glass fibre bundle in which all glass fibres are positioned adjacently) .
  • Halogen lamps have the drawback of the spectral emission in the range between 400 and 450 nm being very low. For various uses, for instance the measuring of flowers (ornamental plants), it is desirable to measure the reflection in this spectral range.
  • LEDs Light Emitting Diodes emitting these wavelengths are available.
  • the intensity of LEDs is very low, however.
  • One LED can only evenly illuminate a very small object.
  • the use of a row of LEDs does not result in an even illumination.
  • a device for illuminating a (three-dimensional) object in a measuring device comprising a row of several lamps, a mirror cavity comprising two plane-parallel mirrors, the one mirror being placed above the other and the reflecting surfaces of the mirrors facing each other, and a cylindrical lens, wherein the row of lamps is placed at the rear edge of the mirrors between the mirrors and the lens is placed parallel near the front edge of mirrors, such that the light of the lamps reflected by the plane-parallel mirrors is directed by the lens as a virtually parallel beam of light on the object to be illuminated.
  • an illumination having an equalised intensity is achieved.
  • the achieved illumination has an evenly running intensity distribution in the three dimensions x, y and z, the z- direction being the direction of the beam coming from the device and the x- and the y-direction being perpendicular to each other and in a plane perpendicular to the direction of the light beam.
  • the y-direction is perpendicular to a plane parallel to the parallel mirrors.
  • the device according to the invention enables to combine a number of relatively weak lamps such that an illumination having sufficient intensity is achieved.
  • the term lamp refers to a device serving to illuminate.
  • preferably light emitting diodes (LEDs) are used.
  • LEDs light emitting diodes
  • the cylindrical lens to be used in the device according to the invention is a positive lens, that means a lens which converges the incident rays.
  • cylindrical lens does not only refer to single-axis spherical lenses but also to single-axis a-spherical lenses.
  • the lens used in the device according to the invention can also be a part of a cylinder.
  • the cylindrical lens of the device according to the invention is a positive lens having at least one refracting surface that is a part of a cylindrical surface wherein a cylindrical surface refers to a surface described by straight lines that each are parallel to a straight line and pass through a certain curve. Said curve is not limited to circular curves.
  • the mirror cavity and the axis of the cylindrical lens will be a little larger than the focal distance of the lens.
  • the optimal position of the lens that means the position providing a beam which is as parallel as possible, can very easily be established by experiments.
  • FIG. 1 schematically shows a cross-section of an embodiment of a device according to the invention.
  • 1 refers to a LED of a row of LEDs clamped in between an upper mirror 2 and a lower mirror 3, which have been provided at the lower and upper side, respectively, with a reflecting surface and which together form a mirror cavity.
  • the intensity distribution of the light coming from the lamps has been equalised in the x- and y-direction.
  • the light leaving the mirror cavity is guided by a rod lens (cylindrical lens) 4, the focus of which is situated outside the mirror cavity, to form a parallel beam so that an even intensity distribution is also achieved in the z-direc- tion.
  • the mirrors form the upper and lower walls of the mirror cavity.
  • the front side of the mirror cavity is open.
  • the rear side of the cavity is closed off by the row of lamps.
  • the side walls of the mirror cavity preferably are closed.
  • the surface of the side walls preferably is not reflecting. Most preferably the side walls are frosted black.
  • the mirrors generally have a rectangular shape. The length of the mirror, the distance between lamps and front side, is considerably larger than the height of the mirror cavity, the dis- tance between the mirrors.
  • the width of the mirror depends on the wanted width that has to be illuminated. When a larger illumination surface is wanted, the number of
  • LEDs in the row can be increased.
  • the height of the mirror cavity is determined by the diameter of the LEDs.
  • the effect of the mirror cavity is halved. In general it is desirable then to make the mirror cavity twice as long. Increasing the height of the mirror cavity also has consequences for the lens diameter, object distance and degree of parallelism of the beam.
  • High-intensity LEDs having a very small diameter therefore are preferred.
  • an equalised intensity distribution over a broad wavelength range can be achieved.
  • a number of devices having LEDs with a contiguous emission spectrum can also be combined.
  • the nature of the object is in fact unlimited. Due to the equalised intensity distribution of the light beam obtained with the device according to the invention, it is not necessary that the object is flat.
  • the present invention can for instance be used for illuminating fruits, plants, flowers or seeds, for instance in an industrial sorting device.
  • a mirror cavity consisting of two plane-parallel mirrors placed at a distance of 5 mm from each other and having a width of 1 25 mm made of 1 mm thick material
  • 50 bright blue light emitting LEDs (by Agilent, type HLMP-DB25-P0000) having an intensity of 100 mcd and an opening angle of 25° and a length of 8.71 mm cm were placed, wherein the centres of the LEDs were situated at a distance of 50 mm from the front edge of the mirrors.
  • a rod lens in the shape of a plastic (perspex) cylinder having a diameter of 50 mm and a length of 1 30 mm was mounted, such that the axis of the cylinder ran parallel to the front edge of the mirror cavity and was situated in a plane parallel to the mirrors.
  • the mirrors and the lens were mounted in a plastic box.
  • Figure 2 shows the intensity distribution obtained with the above-mentioned example of a device according to the invention.
  • the reflection values on a white background were measured by means of a digital camera.
  • the reflection pattern obtained with the device according to the invention is shown at the bottom.
  • the reflection pattern of a single row of LEDs is shown at the top.
  • Figure 3 shows a graphical depiction of the intensity distribution obtained with the above example of a device according to the invention measured by means of a digital camera.
  • the x- and y-axis are spatial axes in a plane placed perpendicular in the beam and show pixels (image dots). The image has not been calibrated, but 1 pixel approximately corresponds to 1 mm 2 .
  • the z-axis represents the intensity in grey values.
  • the intensity distribution obtained with the device according to the example is indicated by a, whereas b refers to the intensity distribution of a single row of LEDs.
  • Figure 4 shows the intensity distribution of figure 3 in contour lines. The intensity has not been calibrated, but has been shown in grey values, 40 grey values per step.

Landscapes

  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Investigating Materials By The Use Of Optical Means Adapted For Particular Applications (AREA)

Abstract

The invention relates to a device for illuminating an object comprising a row of several lamps, a mirror cavity comprising two plane-parallel mirrors placed above each other and a positive cylindrical lens, wherein the row of lamps is placed at the rear edge of the mirrors between the mirrors and the lens is placed parallel to the front edge of mirror cavity, such that the light of the lamps reflected by the mirror cavity is directed with an equalised intensity distribution on the object to be illuminated.

Description

Illumination device
The present invention relates to a device for illuminating a (three dimensional) object in a measuring device.
Several measuring devices are known in which an object is illuminated and the radiation reflected by the object is analysed or the reflected image is examined. Analysis of the reflected radiation means in particular that it is determined which wavelengths are absorbed by the object. An example of a device in which the radiation reflected by an object is analysed is an imaging spectrograph.
It is known to use halogen lamps for illuminating the object in imaging spectrographs, often in combination with glass fibres and line arrays (glass fibre bundle in which all glass fibres are positioned adjacently) . Halogen lamps, however, have the drawback of the spectral emission in the range between 400 and 450 nm being very low. For various uses, for instance the measuring of flowers (ornamental plants), it is desirable to measure the reflection in this spectral range.
LEDs (Light Emitting Diodes) emitting these wavelengths are available. The intensity of LEDs is very low, however. One LED can only evenly illuminate a very small object. The use of a row of LEDs does not result in an even illumination. Sometimes frosted glass is placed in front of a row of LEDs, however this has the drawback of light being absorbed.
Therefore there is a need for a device providing an illumination having an equalised intensity of an object having a surface area of up to for instance 10 x 2 cm.
According to the invention that need is met by means of a device for illuminating a (three-dimensional) object in a measuring device, comprising a row of several lamps, a mirror cavity comprising two plane-parallel mirrors, the one mirror being placed above the other and the reflecting surfaces of the mirrors facing each other, and a cylindrical lens, wherein the row of lamps is placed at the rear edge of the mirrors between the mirrors and the lens is placed parallel near the front edge of mirrors, such that the light of the lamps reflected by the plane-parallel mirrors is directed by the lens as a virtually parallel beam of light on the object to be illuminated.
By using the device according to the invention an illumination having an equalised intensity is achieved. The achieved illumination has an evenly running intensity distribution in the three dimensions x, y and z, the z- direction being the direction of the beam coming from the device and the x- and the y-direction being perpendicular to each other and in a plane perpendicular to the direction of the light beam. The y-direction is perpendicular to a plane parallel to the parallel mirrors.
The device according to the invention enables to combine a number of relatively weak lamps such that an illumination having sufficient intensity is achieved.
The term lamp refers to a device serving to illuminate. In the device according to the invention preferably light emitting diodes (LEDs) are used. Based on his knowledge a person skilled in the art will know or realise which types of lamps are suitable for use in the invention. The cylindrical lens to be used in the device according to the invention is a positive lens, that means a lens which converges the incident rays. In the present description and claims, cylindrical lens does not only refer to single-axis spherical lenses but also to single-axis a-spherical lenses. The lens used in the device according to the invention can also be a part of a cylinder. In other words, the cylindrical lens of the device according to the invention is a positive lens having at least one refracting surface that is a part of a cylindrical surface wherein a cylindrical surface refers to a surface described by straight lines that each are parallel to a straight line and pass through a certain curve. Said curve is not limited to circular curves.
When using a cylindrical lens in general the distance between the end of
, the mirror cavity and the axis of the cylindrical lens will be a little larger than the focal distance of the lens. The optimal position of the lens, that means the position providing a beam which is as parallel as possible, can very easily be established by experiments.
Figure 1 schematically shows a cross-section of an embodiment of a device according to the invention. In figure 1 , 1 refers to a LED of a row of LEDs clamped in between an upper mirror 2 and a lower mirror 3, which have been provided at the lower and upper side, respectively, with a reflecting surface and which together form a mirror cavity. After a number of reflections in the mirror cavity the intensity distribution of the light coming from the lamps has been equalised in the x- and y-direction. The light leaving the mirror cavity is guided by a rod lens (cylindrical lens) 4, the focus of which is situated outside the mirror cavity, to form a parallel beam so that an even intensity distribution is also achieved in the z-direc- tion.
The mirrors form the upper and lower walls of the mirror cavity. The front side of the mirror cavity is open. The rear side of the cavity is closed off by the row of lamps. The side walls of the mirror cavity preferably are closed. The surface of the side walls preferably is not reflecting. Most preferably the side walls are frosted black. The mirrors generally have a rectangular shape. The length of the mirror, the distance between lamps and front side, is considerably larger than the height of the mirror cavity, the dis- tance between the mirrors.
The width of the mirror depends on the wanted width that has to be illuminated. When a larger illumination surface is wanted, the number of
LEDs in the row can be increased.
The height of the mirror cavity is determined by the diameter of the LEDs.
It is possible to use several rows of LEDs placed above one another.
However, when the height is doubled, the effect of the mirror cavity is halved. In general it is desirable then to make the mirror cavity twice as long. Increasing the height of the mirror cavity also has consequences for the lens diameter, object distance and degree of parallelism of the beam.
High-intensity LEDs having a very small diameter therefore are preferred.
By combining the device according to the invention with halogen il- lumination, an equalised intensity distribution over a broad wavelength range can be achieved. A number of devices having LEDs with a contiguous emission spectrum can also be combined.
The nature of the object is in fact unlimited. Due to the equalised intensity distribution of the light beam obtained with the device according to the invention, it is not necessary that the object is flat.
The present invention can for instance be used for illuminating fruits, plants, flowers or seeds, for instance in an industrial sorting device.
Based on his general knowledge the person skilled in the art will realise for which other illumination purposes the device according to the invention can be used.
Example
Between a mirror cavity consisting of two plane-parallel mirrors placed at a distance of 5 mm from each other and having a width of 1 25 mm made of 1 mm thick material, 50 bright blue light emitting LEDs (by Agilent, type HLMP-DB25-P0000) having an intensity of 100 mcd and an opening angle of 25° and a length of 8.71 mm cm were placed, wherein the centres of the LEDs were situated at a distance of 50 mm from the front edge of the mirrors. At a distance of 20 mm from the front edge of the mirrors a rod lens in the shape of a plastic (perspex) cylinder having a diameter of 50 mm and a length of 1 30 mm was mounted, such that the axis of the cylinder ran parallel to the front edge of the mirror cavity and was situated in a plane parallel to the mirrors. The mirrors and the lens were mounted in a plastic box.
Figure 2 shows the intensity distribution obtained with the above-mentioned example of a device according to the invention. The reflection values on a white background were measured by means of a digital camera. The reflection pattern obtained with the device according to the invention is shown at the bottom. For comparison purposes the reflection pattern of a single row of LEDs is shown at the top.
Figure 3 shows a graphical depiction of the intensity distribution obtained with the above example of a device according to the invention measured by means of a digital camera. The x- and y-axis are spatial axes in a plane placed perpendicular in the beam and show pixels (image dots). The image has not been calibrated, but 1 pixel approximately corresponds to 1 mm2. The z-axis represents the intensity in grey values. The intensity distribution obtained with the device according to the example is indicated by a, whereas b refers to the intensity distribution of a single row of LEDs. Figure 4 shows the intensity distribution of figure 3 in contour lines. The intensity has not been calibrated, but has been shown in grey values, 40 grey values per step.

Claims

Claims
1 . A device for illuminating a (three-dimensional) object in a measuring device, comprising a row of several lamps, a mirror cavity comprising two plane-parallel mirrors, the one mirror being placed above the other and the reflecting surfaces of the mirrors facing each other, and a cylindrical lens, wherein the row of lamps is placed at the rear edge of the mirrors between the mirrors and the lens is placed parallel to the front edge of mirrors, such that the light of the lamps reflected by the plane-parallel mirrors is directed by the lens as a virtually parallel beam on the object to be illuminated.
2. A device according to claim 1 , wherein the lens is a cylindrical lens.
3. A device according to claim 1 , wherein the lamps are LEDs.
4. A device according to claim 3, wherein the LEDs are bright blue LEDs.
5. A measuring device comprising a device according to any one of the claims 1 -4.
6. A measuring device comprising a device according to any one of the claims 1 -4 and a halogen illumination.
7. A measuring device comprising several devices according to any one of the claims 1 -4 wherein the LEDs of the various devices have different emission spectra.
8. A measuring device according to any one of the claims 5-7 which is an imaging spectrograph.
9. A method for illuminating an object in a measuring device, wherein the object is illuminated using a device according to any one of the claims 1 -4.
10. A method according to claim 9, wherein the object comprises plants or plant material, such as seeds, fruits and flowers.
PCT/NL2003/000042 2002-01-23 2003-01-21 Illumination device Ceased WO2003062755A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
NL1019823 2002-01-23
NL1019823A NL1019823C2 (en) 2002-01-23 2002-01-23 Lighting device.

Publications (1)

Publication Number Publication Date
WO2003062755A1 true WO2003062755A1 (en) 2003-07-31

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ID=27607204

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/NL2003/000042 Ceased WO2003062755A1 (en) 2002-01-23 2003-01-21 Illumination device

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NL (1) NL1019823C2 (en)
WO (1) WO2003062755A1 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0691552A2 (en) * 1994-06-28 1996-01-10 Corning Incorporated Apparatus for uniformly illuminating a light valve
WO1999058959A1 (en) * 1998-05-11 1999-11-18 Pioneer Hi-Bred International, Inc. Near infrared spectrometry for real time analysis of substances
US6036328A (en) * 1995-05-23 2000-03-14 Sharp Kabushiki Kaisha Plane-shaped lighting device and a display using such a device

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0691552A2 (en) * 1994-06-28 1996-01-10 Corning Incorporated Apparatus for uniformly illuminating a light valve
US6036328A (en) * 1995-05-23 2000-03-14 Sharp Kabushiki Kaisha Plane-shaped lighting device and a display using such a device
WO1999058959A1 (en) * 1998-05-11 1999-11-18 Pioneer Hi-Bred International, Inc. Near infrared spectrometry for real time analysis of substances

Also Published As

Publication number Publication date
NL1019823C2 (en) 2003-07-25

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