Patent Application: US-201514710627-A

Abstract:
an integrated led structure and a method of adjusting the emission spectrum of an integrated led structure , for photobiological process . the structure comprises a substrate ; a plurality of optically isolated and electrically non - independent light emission areas integrated on the substrate ; a light emitting semiconductor source of a first type mounted in the emission area ; a light emitting semiconductor source of a second type mounted in the emission area ; an electrical circuit layer for connecting the said light emitting semiconductor sources in serial fashion for each emission area ; and wavelength conversion materials . the emission areas are controlled with a common electrical drive current , and the emission output can be tuned by adjusting the common current value , to enable use of one luminaire for a large variety of biomass growing applications .

Description:
the following descriptions are merely non - limiting examples and it will be appreciated by one skilled in the art that specific details of the examples may be changed without departing from the spirit of the invention . it is an aspect of certain embodiments to provide an integrated led structure comprising ; a substrate , at least one or a plurality of isolated emission areas , and an electrical two wire control interface . in one embodiment , the isolated emission areas comprise one or multiple led semiconductor diodes as light emitters to provide light emission . in preferred embodiments the emitters are of different type and have emission peaks between 365 to 440 nm . the light emitters are electrically connected in series to enable a common current drive scheme . the control interface has at least one wire for providing the common drive current and least one ground wire to close the current path back to power supply . one or multiple isolated emission areas comprise wavelength conversion materials to provide means for light emission with wider bandwidth . one or plurality of isolated emission areas can comprise in some preferred embodiment more than one type of wavelength conversion materials layered vertically upon each other . in preferred embodiments the wavelength conversion material is a narrow band phosphor based e . g . on nitridoaluminates materials providing emission spectrum with full width half maximum of 40 to 80 nm . the isolated emission areas can be formed as buried shallow cavities on the top surface of the said substrate . alternatively , the isolated emission areas can be formed by manufacturing an optically opaque mesa structure between the emission areas . in some preferred embodiments the led structure can comprise both buried shallow cavities and isolated emission areas surrounded by opaque mesa structure . in some preferred embodiments the led structure can comprise several emission areas in buried cavities of different heights . the emission spectrum is formed of emissions from different emission areas at wavelength bands with at least some of them in blue ( 365 - 440 nm ) and red ( 600 - 780 nm ) bands and optionally having one or multiple emission bands in wavelength bands of ultra - violet ( uv ), green , red and near - infra red to complement the emission spectrum . in some embodiments the emission side of the integrated led structure can be equipped optionally with a polarizer to provide polarized light depending again the lighting and application requirements . the said polarizer can cover all or some of the emissions areas . an embodiment comprises using an integrated led structure , which has two different type of semiconductor emitters coupled in series and which is driven with a common current signal . the light emitters have different current - to - light conversion due to different thermal characteristics . this results in asymmetric excitation of the wavelength conversion material with high current values due to elevated operating temperature . in more detail , the asymmetric excitation can be explained as follows : in a nominal operation point the current is e . g . 350 ma and the emission spectrum has a characteristic quadruple structure with blue emissions e . g . at 425 nm and 435 nm , and one red ( red1 ) emission peak at 630 nm and another red ( red2 ) emission peak at 660 nm . the said intensity ratio between the blue1 : blue2 : red1 : red2 is in low current state close to e . g . 1 : 1 : 2 : 2 . in another set point of operation , also known as the “ high current state ”, the current is tuned up to e . g . 700 ma . now the other light emitter , namely the sapphire based light emitter shows reduced emission efficiency with relative to vertical type emitter and the characteristic quadruple peak structure changes so that the intensity ratio of the four peaks become close to 2 : 1 . 5 : 4 : 3 . such spectrum tuning is beneficial for optimizing the artificial lighting conditions for different growth phases of various plants in greenhouse . in one embodiment , the intensity ratio between a peak in the range of 620 to 640 nm and a corresponding peak in the range from 650 to 670 nm is in the range from about 0 . 8 : 1 to 3 : 1 . in another embodiment , the intensity ratio between said peaks is in the range from about 0 . 5 to 1 . 1 : 1 as a low value of intensity and in the range from about 1 . 2 to 3 : 1 at a high value of intensity . in general the isolated emission areas can be driven via the control interface intermittently to turn on and off , also called later as activation , to provide a light energy pulse of required length . a turn off time , also called later as a delay time or deactivation time , with no light emitting from the emission area can be controlled via the multiple wire control interface . furthermore , the current control allows deactivation of the emission area for longer periods . also the current control allows setting of emission frequency of emission area to provide the required spectral density , as required by arbitrary biomass growing application . appropriate electrical current control sequence via the control interface allows generating emission spectrum which is varying in time . in one preferred embodiment the integrated led structure provides built - in spectrum adjustability based on a common drive current of asymmetric excitation arrangement . the integrated led structure is formed of two isolated emission areas in a way that the emission from the first emission area does not influence the emission from the other emission area . in such arrangement of two emission areas the first emission area applies the first type of excitation source and the first type of wavelength conversion material . consistently , the second emission area applies the second type of excitation source and the second type of wavelength conversion material . the asymmetric excitation is thus achieved by applying two different types of excitation sources , buried under the wavelength conversion materials in the two isolated emission areas , and connected electrically in series with each other to be able to control them simultaneously with a common drive current . in a typical case the first wavelength conversion material is a wide band phosphor with excitation maximum near 420 nm and emission maximum near 630 nm , and fwhm of about 100 nm and the second first wavelength conversion material is a wide band phosphor with excitation maximum near 435 nm and emission maximum near 660 nm , and fwhm of about 100 nm . the first type of the excitation source is a so called vertical light emitting semiconductor diode operating e . g . at 420 nm , and the second type of excitation source is a sapphire based light emitting semiconductor diode operating e . g . at 435 nm . the two types of the semiconductor diodes have different thermal behavior , and their light output varies independently as a function of junction temperature , which on the other hand depends of the drive current . typically the sapphire based semiconductor diode &# 39 ; s light output drops faster as a function of rising junction temperature while the vertical semiconductor diode structure is relatively insensitive to junction temperature , as long as the junction temperature is kept within preferred operating range i . e . typically between 45 to 90 ° c . in a nominal situation the combination of the two semiconductor diode types is driven with a common 300 ma current producing an excitation spectrum at blue wavelengths of 425 and 435 nm ( fig4 ) with a 1 : 1 intensity ratio between 420 nm and 435 nm . this results in nearly equal emission peaks at 630 and 660 nm from the two phosphors . as the current is increased to 700 ma the efficiency of the sapphire led drops and the output spectrum changes accordingly while changing the intensity ratio of blue excitation to roughly 1 : 0 . 75 . this in turn results in an emission intensity ratio of 630 nm and 660 nm to change to 1 : 0 . 75 . this characteristic behavior can be applied also gradually by tuning the current continuously or stepwise between 300 ma and 700 ma , thus enabling the adjustment of the said ratio of excitation intensities at 420 nm and 435 nm wavelengths from 1 : 1 to 1 : 0 . 75 and adjusted spectrum of red wavelength bands , following the excitation intensities . so any wanted intensity ratio can be set in a flexible way by adjusting the common drive current . in another preferred embodiment the integrated led structure provides built - in spectrum adjustability by applying narrow band phosphors matching the absorption spectrum of chlorophyll a and chlorophyll b . in one case there are two emission areas , which have different wavelength conversion materials , for example the first emission area has a narrow band phosphor of the first type providing peak output at 630 nm with and the second emission area has a narrow band phosphor of the second type providing peak output at 660 nm ( fig5 ). such narrow band phosphors could be of e . g . nitridoaluminates based material providing emissions with full width half maximum of typically only 50 nm and their emission spectrum suits particularly well for the excitation of the chlorophyll molecules . in such case the first emission area applies vertical type led chip and the second emission area applies a sapphire based led chip . now it becomes straightforward to adjust the ratio of 630 and 660 nm emission of the integrated led structure by simply tuning the common drive current . narrow bandwidth red phosphors are used for red wavelength area selective excitation of chlorophyll a and chlorophyll b in order to minimize chlorophyll a and chlorophyll b bands over lapping as well to maximize individual chlorophyll a and chlorophyll b absorption band coverage . narrow bandwidth red phosphor should have emission peak between 600 - 700 nm and peak &# 39 ; s full width half maximum value less than 50 nm but more 25 nm or more preferably less than 50 but more than 35 nm . the asymmetric excitation and the common current drive method can be applied also in case there is a plurality of isolated emission areas . in such case the number of different type of excitation sources and the number of different type of wavelength conversion materials is not necessarily two . furthermore the asymmetric excitation and the common current drive methods can be applied in case there is only one emission area . in such case the number of different type of excitation sources can be e . g . two and the emission area comprises one type of wavelength conversion material . turning next to the embodiment shown in fig2 to 5 , the following can be noted : the led structure is comprised of a substrate 100 , two optically non - interacting isolated emission areas 101 , and 102 , and a two wire control interface 103 , see fig2 . the first emission area 101 comprises the first type of led semiconductor chip 104 emitting at 425 nm , and wavelength conversion material 105 having its peak emission at 630 nm and having a full width half maximum ( fwhm ) emission of about 50 nm . the second emission area 102 comprises a second type of led semiconductor chip 106 emitting at 438 nm , and wavelength conversion material 107 having its peak emission at 660 nm and having a full width half maximum ( fwhm ) emission of about 50 nm . the first led chip is of vertical type and the second one is of sapphire based led chip . the control interface is having a two wire structure and is to enable common control of the said two isolated emission areas . the two emitter diodes are connected in series to enable a common drive current control . thus the cathode of the first emitter diode , located in the first emission area , is connected to the anode of the second emitter diode , located in the second emission area . one electrical contact point of the control interface is electrically connected to the anode of the first emitter diode in the first emission area , and the other electrical contact point is electrically connected to the cathode of the second emitter diode in the second emission area . thus a close current loop is formed with the said two emitter diodes in series , enabling a common current drive for applying the asymmetric excitation scheme . the optically independent operation of the two isolated emission areas is achieved by isolating the said first emission area from the second emission area with an optically opaque mesa structure 113 , which prevents light emission from the led emitter 104 located inside of the first emission area 101 to excite the wavelength conversion material 107 ] inside the said second emission area . the mesa structure 113 a is shown in fig3 in the cross section view of the said led structure . the first emission area and the second emission areas provide two red wavelength bands centered at 630 and 660 nm and contribute to the total emission spectrum . the emission band centered at 630 nm is used for the excitation of chlorophyll b and emission band centered at 660 nm is used for the excitation of chlorophyll a . the emission spectrum is adjustable and can be controlled by tuning of the common continuous drive current so that the ratio of the 630 and 660 nm intensities vary in scale of 1 : 1 to 1 : 0 . 75 . such magnitude of change can be expected with a current tuning range of 350 ma to 700 ma . the integrated led structure described in the previous embodiment can be optionally powered by pulsed source to optimize the excitation of the chlorophyll molecules associated with plants &# 39 ; photosynthesis process . the said led structure is driven alternately with a pulsed current sequence with a pulse on time period being 0 . 1 ms and off - time being 2 to 10 ms . fig4 a , 4 b , 5 a and 5 b were already referred to above . in summary it can be noted that fig4 a and 4 b show the nominal emission spectra of led module with two isolated emission areas comprised of asymmetric excitation emitters at 425 nm and 435 nm driven at common current of 350 ma ( left ) and 700 ma ( right ). emission areas comprise wide band phosphor material with fwhm of about 100 nm . red emissions are not summed for visualization purposes . fig5 a and 5 b show the nominal emission spectrum of led module with two isolated emission areas comprised of asymmetric excitation emitters at 425 nm and 435 nm driven at common current of 350 ma ( left ) and at 700 ma ( right ). emission areas comprise narrow band phosphor material with fwhm & lt ; 60 nm . red emissions at 630 and 660 nm are not summed for visualization purposes . it is to be understood that the embodiments of the invention disclosed are not limited to the particular structures , process steps , or materials disclosed herein , but are extended to equivalents thereof as would be recognized by those ordinarily skilled in the relevant arts . it should also be understood that terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting . reference throughout this specification to “ one embodiment ” or “ an embodiment ” means that a particular feature , structure , or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention . thus , appearances of the phrases “ in one embodiment ” or “ in an embodiment ” in various places throughout this specification are not necessarily all referring to the same embodiment . as used herein , a plurality of items , structural elements , compositional elements , and / or materials may be presented in a common list for convenience . however , these lists should be construed as though each member of the list is individually identified as a separate and unique member . thus , no individual member of such list should be construed as a de facto equivalent of any other member of the same list solely based on their presentation in a common group without indications to the contrary . in addition , various embodiments and example of the present invention may be referred to herein along with alternatives for the various components thereof . it is understood that such embodiments , examples , and alternatives are not to be construed as de facto equivalents of one another , but are to be considered as separate and autonomous representations of the present invention . furthermore , the described features , structures , or characteristics can be combined in any suitable manner in one or more embodiments . in the following description , numerous specific details are provided , such as examples of lengths , widths , shapes , etc ., to provide a thorough understanding of embodiments of the invention . one skilled in the relevant art will recognize , however , that the invention can be practiced without one or more of the specific details , or with other methods , components , materials , etc . in other instances , well - known structures , materials , or operations are not shown or described in detail to avoid obscuring aspects of the invention . while the forgoing examples are illustrative of the principles of the present invention in one or more particular applications , it will be apparent to those of ordinary skill in the art that numerous modifications in form , usage and details of implementation can be made without the exercise of inventive faculty , and without departing from the principles and concepts of the invention . accordingly , it is not intended that the invention be limited , except as by the claims set forth below . the present arrangements and methods can be used for providing artificial grow light in greenhouses as well as in other objects in agriculture , horticulture and in biomass growing industry , in particular for meeting the needs of different plants to achieve optimal growth . klueter et al ., 1980 , transactions of the asabe . 23 ( 2 ): 0437 - 0442 yeh , et al . 2009 , renewable and sustainable energy reviews 13 : 2175 - 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