Patent Publication Number: US-2022228724-A1

Title: Plant growth lighting systems

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of and claims priority to U.S. application Ser. No. 16/095,643, filed on Oct. 22, 2018, which is a U.S. National Phase application of International Application No. PCT/US2017/028971, filed on Apr. 21, 2017, which claims benefit under 35 U.S.C. § 119(e)( 1 ) of U.S. Provisional Application No. 62/326,633, filed on Apr. 22, 2016, and of U.S. Provisional Application No. 62/341,577, filed on May 25, 2016, all of which are incorporated by reference herein. 
    
    
     FIELD OF THE TECHNOLOGY 
     The present technology relates to horticulture and more specifically to lighting systems for plant growth systems. The present technology is related to plant and biological growth systems with characteristics that can enhance yield and the expression of certain nutritional, pharmacological or commercial properties of plants, bacteria, algae and other life forms. 
     BACKGROUND OF THE TECHNOLOGY 
     Research has shown that plants and other biological systems may have certain properties enhanced by the manipulation of certain lighting conditions that change the wavelength, and the timing of certain lighting spectral qualities. For example, certain wavelengths of light can stimulate growth while others may trigger flowering. 
     Historically lighting for plant growth systems has typically been delivered by natural daylight in the open or within greenhouses where lighting can be supplemented by artificial light sources such as High Pressure Sodium (HPS), Metal Halide (MH), and more recently, solid-state or semiconductor light sources including Light Emitting Diodes (LEDs), laser diodes and other types of semiconductor light emitting devices which will hereinafter be referred to as Light Emitting Elements or LEE&#39;s. 
     LEDs and lasers typically are narrow band emitters and can be used in combination with light conversion elements such as quantum dots or other phosphors, which in turn can generate light of broader spectral composition. Many LEE&#39;s are orders of magnitude smaller in physical dimensions than conventional light sources such as HPS and MH. 
     The evolution of plant and biological life on earth has occurred under light that has widely varying conditions throughout the day and time of year and plants have highly sensitive mechanisms for harnessing light to express certain biological properties. While researchers study effects of spectral composition and timing, what is distinctly lacking in the field are lighting systems which can favorably impact the spatial control of light with practical and complementary lighting fixture designs and delivery mechanisms that can be adjusted to provide properly mixed and distributed light that is useful for plant growth. 
     SUMMARY OF THE TECHNOLOGY 
     The present technology is directed to lighting systems that leverage the scale of LEEs and that can improve plant growth factors such as size, yield, substance expression and other aspects of artificially illuminated plants. Specifically, the instant technology aims to enable a spatial dimension of light to be harnessed from new lighting apparatus designs that can be located in new and advantageous positions within a plant-growth environment. The present technology provides lighting systems that can mimic diurnal, seasonal and weather dependent lighting conditions both in spectral and spatial aspects. Furthermore, the present technology can be configured to control plant growth beyond variations of mimicry of natural lighting conditions and influence certain forces in plant growth to express substances that can help advance human health, and nutritional and commercial produce value. The present technology can be used to control spatial and temporal distribution of the light provided for plant growth and the spectral composition of the provided light in various ways. Moreover, direction, timing and spectral composition of the provided light can be controlled to adjust to plant size during growth. 
     According to an embodiment of the present technology, there is provided a plant growth lighting system comprising a plant support configured to hold one or more plants; and a light guide luminaire module comprising at least one LEE, a light guide arranged to receive light emitted by the at least one LEE at a first end of the light guide and guide the received light in a forward direction to a second end thereof, and an extractor arranged to receive light from the second end of the light guide and configured to output light, the light guide luminaire module disposed relative to the plant support such that at least a portion of the light output by the extractor impinges on the plants in predetermined directions. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some implementations, the extractor can be configured to output backward light within a range of directions having a component antiparallel to the forward direction. In some cases, the extractor additionally can output forward light within a range around the forward direction. Optionally, the forward light has a forward spectrum and the backward light has a backward spectrum different from the forward spectrum. Here, the extractor can include a chromatic filter configured to provide a forward spectrum different from the backward spectrum. 
     In some implementations, the plant growth lighting system can include a shifting system configured to translate the light guide luminaire module relative to the plant support along a direction of growth of the plants. Here, the plant growth lighting system can further include a sensor system configured to monitor growth of the plants, the sensor system operatively coupled with a control system configured to control translation of the light guide luminaire module via the shifting system. 
     In some implementations, the light guide luminaire module can include a tertiary reflector arranged to redirect at least a portion of the light directly output by the extractor and is configured to direct at least a portion of the light in a predetermined manner. 
     In some implementations, the plant growth lighting system can include a reflector system spaced apart from the light guide luminaire module and arranged to receive at least a portion of light output by the extractor, the reflector system configured to direct the reflected light towards the plants. In some cases, the reflector system and the plant support can have the same dimensions perpendicular to the forward direction. In some cases, the reflector system can include two reflector elements arranged on either side of the light guide luminaire module and have translational symmetry along a direction perpendicular to the forward direction. 
     In some implementations, the plant growth lighting system can include two light guide luminaire modules configured to output light having different spectral power density distributions (SPDs) and to output the output light with the different SPDs in different directions. 
     In some implementations, the plant growth lighting system can include a control system operatively coupled with and configured to control the one or more LEEs. In some cases, the one or more LEEs can be configured to generate light having different spectral power density distributions (SPDs) and the control system can be configured further to control the SPD of the light output by the light guide luminaire module. 
     According to another embodiment of the present technology, there is provided an indirect plant growth lighting system with a primary narrow light distribution angle in at least one plane that is optically matched to a reflective surface to provide a desired distribution of light to plants. 
     The foregoing and other embodiments can each optionally include one or more of the following features, alone or in combination. In some implementations, the primary narrow distribution of light can have a full width half-maximum intensity distribution of less than 30 degrees. In some implementations, the reflective surface can exhibit both specular and diffuse reflectance characteristics. In some implementations, the components of reflectance can be at least 5% of the total light reflectance. 
     In some implementations, the lighting system can provide mixing of individual LEE source spectral content. In some implementations, the mixing of adjacent LEE sources at primary emission location can be higher than 90%. 
     In some implementations, the lighting system has a plurality of LEE spectral distributions. In some cases, the plurality of LEE spectral distributions can be controlled independently. 
     In some implementations, the timing and relative mixed spectral content is controlled by one of desired plant growth data or data representative of at least one desired plant growth characteristic. In some cases, the plant growth data can be derived from one of spectral reflectance information or spectral transmission information. 
     In some implementations, plant growth data can be obtained from chemical analysis of at least part of the plant or its byproducts as contained in the soil, water or air surrounding or having come into contact with the plant. In some implementations, plant growth data can be obtained from plant physical characteristics. In some implementations, the reflective surface substantially can reflect only predetermined spectral components of impinging light. 
     According to yet another embodiment of the present technology there is provided a second plant growth lighting system. A plurality of narrow light distributions of the second plant growth lighting system are each narrow in at least one plane optically matched to reflective surfaces of the second plant growth lighting system to provide a desired distribution of light to plants. 
     According to yet another embodiment of the present technology there is provided a third plant growth lighting system. A primary light emitting device of the third plant growth lighting system is in a remote location relative to a secondary light reflecting system of the third plant growth lighting system. 
     The details of one or more implementations of the technologies described herein are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the disclosed technologies will become apparent from the description, the drawings, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is the typical total solar spectrum for light reaching the earth at sea level. 
         FIG. 1B  is the typical spectrum for blue sky. 
         FIG. 1C  is the range in solar spectrum variations due to cloud cover, haze and time of day. 
         FIG. 2A  is an elevation view of a typical plant in nature with constituent light components. 
         FIG. 2B  is a schematic of solar radiation interactions in atmosphere and ground. 
         FIG. 3A  is a typical tubular lamp lighting fixture. 
         FIG. 3B  is a typical high intensity discharge lamp fixture. 
         FIG. 3C  is a typical Light Emitting Diode type light fixture. 
         FIG. 3D  is a typical Lambertian radiation profile. 
         FIG. 3E  is a projection of a Lambertian radiation profile in terms of illumination obeying the inverse square law on a horizontal surface. 
         FIG. 4  is a typical prior art lighting system as used in horticulture lighting. 
         FIG. 5A  is a first embodiment of the disclosed technologies with side firing optical extractors and reflective surfaces underneath the adjacent tray. 
         FIG. 5B  is a second embodiment of the disclosed technologies with a plurality of side firing optical extractors and redirection features above the plant canopy. 
         FIG. 5C  shows a luminance plot associated with the first embodiment of the disclosed technologies. 
         FIG. 6A  is a third embodiment of the disclosed technologies with embedded vertical waveguides and extractors penetrating below the growth trays. 
         FIG. 6B  shows how the third embodiment of the disclosed technologies is configured to support newly germinated plants. 
         FIG. 6C  shows how the third embodiment of the disclosed technologies can be configured to support mature plants. 
         FIG. 6D  shows a fourth embodiment of the disclosed technologies that shows how the disclosed technologies are configured to provide indirect and direct light from within the plant environment. 
         FIG. 6E  shows a light intensity plot associate with the third and fourth embodiments of the disclosed technologies. 
         FIGS. 7A-7B  show aspects of light guide luminaire modules. 
         FIG. 8  shows aspects of an adjustable illumination device that includes a light guide luminaire module and a sliding mechanism. 
         FIGS. 9A-9B  show aspects of an embodiment of the sliding mechanism of the adjustable illumination device of  FIG. 8 . 
         FIGS. 10A-10C, 11A-11C and 12A-12C  show aspects of a fully extended, partially extended and fully retracted, respectively, light guide luminaire module of the adjustable illumination device of  FIG. 8 . 
         FIGS. 13A-13B  show aspects of a configuration of the third embodiment of the disclosed technologies. 
         FIGS. 14A-14F and 15  show aspects of components of the configuration of the third embodiment of the disclosed technologies. 
         FIGS. 16A-16B  show aspects of a configuration of the fourth embodiment of the disclosed technologies. 
     
    
    
     Reference numbers and designations in the various drawings indicate exemplary aspects, implementations of particular features of the present disclosure. 
     DETAILED DESCRIPTION 
     Radiation that reaches the earth&#39;s surface includes an ever-changing composite of wavelengths of light coming from many different directions depending on time, season and weather, for example. Biological organisms have evolved under this scenario and it is known that the efficacy of plant growth and the optimization of certain characteristics can be enhanced by artificially manipulating certain attributes of the light. Much research is underway on changing the spectrum, timing, ambient gas composition, temperature, nutrient mix and humidity, to improve yields and develop specific recipes for certain crops. However, prior art systems for the lighting component typically employ high output static light placement points far away from the crops to ensure that the infrared radiation and localized heating is not detrimental to plant health. For example, conventional HPS, MH or fluorescent fixtures are typically placed well above the plant canopy to avoid thermal damage and to leverage a wider distribution of the light. This requires lots of space between the plant canopy and the light mounting points and generally increases the volumetric requirement for the plant growth area. Many plant growth illumination systems are also static in terms of their directional illumination and temporally uniform in their spectral content. Similarly, newer LED systems often consist of fixed large banks of mixed LED sources that have relatively wide distribution patterns that are close to Lambertian and that also need to be placed a distance from the plant canopy to avoid uneven spatial distribution and mutual plant shadowing from leaves, stems or other plant parts. There is a clear need to develop new lighting systems that are significantly more space efficient in terms of mounting location and light distribution. 
       FIG. 1A  illustrates the typical combined solar spectrum for radiation reaching the Earth&#39;s surface at sea level. Notably the spectrum starts in the ultraviolet region and climbs upwards into the middle region of the visible light spectrum near 550 nanometers where it begins to taper off into the red and finally the infrared. This spectrum represents the typical combined daylight spectrum from the direct sunlight and blue sky.  FIG. 1B  illustrates the isolated blue sky spectrum component without direct sunlight. This spectrum is delivered by the blue sky dome and as such represents light that comes from all directions of the sky.  FIG. 1C  shows the variation in spectral power of various daylight components at various atmospheric conditions during daylight hours. The various spectra are normalized to 100% at about 460 nm. Notably, the blue sky components are generally fully diffused and reach the ground from all directions. 
       FIG. 2A  is an elevation view of a typical plant  2200  in nature with constituent light components including direct sunlight  2201  provided by the sun  2210 , atmospherically scattered light  2203  scattered by the atmosphere  2202 , light  2206  from clouds  2207  and light  2209  from the ground, light  2208  received at ground level, and light  2205  received by clouds  2207 .  FIG. 2B  is a schematic of solar radiation interactions in atmosphere and ground. 
       FIG. 3A  shows a sectional view, e.g., in the (y,z) plane, of a typical tubular lamp lighting fixture  300  extending into the page, along the x-axis, and having a housing, ballast  307 , and multiple light-emitting tubes  301 . The fixture  300  has a reflective surface facing the tubes  301 . The fixture  300  can emit direct light  304  directly emitted from the tubes and indirect light  303  reflected from the reflective surface.  FIG. 3B  shows a sectional view, e.g., in the (y,z) plane, of a typical high intensity discharge lamp fixture including a reflector  306 , a bulb  305  and a ballast  307 .  FIG. 3C  schematically shows a typical linear LED-based fixture  309  including multiple LEDs  308  in an elongate arrangement (e.g., extending along the x-axis) and drive electronics  307 . 
       FIG. 3D  shows a typical Lambertian radiation profile  321  relative to a surface  311  with surface normal  312 .  FIG. 3E  shows a projection of a Lambertian radiation profile  321  from a Lambertian emitter  320  onto a plane coplanar with plane  311 . The illumination in the coplanar plane obeys an inverse square law with a respective illuminance dropping from a maximum with axial distance, for example at points  323 ,  324  and  325 , from the zenith  322 . 
       FIG. 4  schematically shows a typical plant growth system including plants  502  grown in and located between growth trays  503  (also referred to as plant support(s)) separated by a height  507  from light fixtures  501 . The light fixtures  501  are located such that heat  505  from the fixtures can be used to warm trays, water or other substances. 
       FIG. 5A  shows a side view, e.g., in the (y,z) plane, of a plant growth lighting system  500 , in short referred to as lighting system, for a plant-growth container according to an embodiment of the present technology. In this example, the lighting system  500  includes side-emitting, light guide luminaire modules  501 . Each light guide luminaire module  501  includes a base supporting light emitting elements (LEEs)  510 , light guide  521  and extractor  512 , and a reflector  515  underneath the adjacent tray  503  with multiple trays spaced vertically by a vertical distance  508 . In some implementations, the light guide luminaire modules are elongated along the x-axis. Examples of respective light guide luminaire modules and reflectors are described below in connection with  FIGS. 7A-7B, 13 and 17A-17B , for instance. The reflector  515  can be shaped to illuminate plants  502  with a predetermined horizontal uniformity, e.g., as described below in connection with  FIG. 5C . Good horizontal uniformity may improve certain plant growth factors. 
     Generally, the reflector  515  can have a curved shape (as indicated in  FIG. 5A ), be planar or otherwise shaped. Other shapes can include structures of sizes that are about one or more orders of magnitude smaller than the lateral extension of the reflector. Examples include macroscopic and microscopic shape variations including Fresnel reflectors. 
     According to an embodiment, the reflector  515  and the light guide luminaire modules  501  are configured to provide a high degree of spatially uniform illumination from grazing incident light. Such uniformity may occur in direction, lateral extension of the reflector  515  or both. Grazing incidence allows for compact systems with low overall height. Such systems may be stackable and as such improve economics from reduced foot print requirements. 
     According to another embodiment, the reflector  515  is configured to reflect different spectral components of incident light in different directions. Such a system further may be configured to control spectral composition of plant illumination by varying the spectral composition of the light provided by the light guide luminaire module  501 , for example. 
     The reflector  515  may be configured to alter the spectral composition via selective reflection, absorption, conversion and/or other processes. For example, the reflector  515  may include chromatic filters such as interference filters or (remote) phosphor conversion substances so that it can filter certain spectral components of light when indirectly illuminating plants. This may be combined with spectral engineering of light at the source level, for example, at the LEEs  510 . 
     Components of the lighting system  500  can be configured to form part of a plant-growth container. For example, reflector  515  can be configured to form part a cap of the plant-growth container or it can be attached to the bottom of the cap. 
       FIG. 5B  shows a side view of a lighting system  500 B according to another embodiment of the present technology with a side-emitting, light guide luminaire module  501 A located on the left and arranged to emit light to the right towards reflector  516  and another side-emitting, light guide luminaire module  501 B located on the right and arranged to emit light to the left towards reflector  516  above the plant canopy. Examples of respective light guide luminaire modules  501 A,  501 B and reflectors  516  are described below in connection with  FIGS. 7B and 17A-17B , for instance. 
       FIG. 5C  shows a luminance (x,y)-contour plot  522  measured looking upward, as “seen” by the plants  502  along the z-axis, at light reflected towards the plants by reflectors  515  of the lighting system  500 . The dotted-line rectangle overlaid onto the luminance (x,y)-contour plot  522  indicates a footprint of reflectors  515  of the lighting system  500 , for a light guide luminaire module  501  disposed between a pair of reflectors.  FIG. 5C  also shows a y-axis cross-section  524  that represents first variation of the luminance of the lighting system  500  across a first reflector  515 , the bottom of the extractor  512  of the light guide luminaire module  501  and the second reflector  515  of the lighting system. The dotted lines overlaid onto the y-axis cross-section  524  indicate edges of the reflectors  515  of the illumination system  500 . Additionally,  FIG. 5C  shows an x-axis cross-section  526  that represents second variation of the luminance of the illumination system  500  along the bottom of the extractor  512  of the light guide luminaire module  501  of illumination system  500 . The dotted lines overlaid onto the x-axis cross-section  526  indicate edges of the reflectors  515  of the illumination system  500 . 
     The results summarized in plots  522 ,  524  and  526  of  FIG. 5C  indicate that the choice of shapes and relative orientations of the redirecting surfaces and the backward output surfaces of the optical extractor  512  and of the reflective surface of the reflectors  515  that was made for designing the illumination system  500  led to a ratio of maximum luminance to minimum luminance across each of the reflectors  515  that is lower than 3:1. In this manner, each of the reflectors  515  appears to be uniformly lit, free of dark regions and/or hot spots, when “viewed” by the plants  502  from directly underneath the optical extractor  512 . 
     Additionally, the results summarized in plots  522 ,  524  and  526  of  FIG. 5C  further indicate that (i) the choice of diffusive coatings applied on the transmissive backward output surfaces of the optical extractor  512  of the light guide luminaire module  501  and reflective surface of the reflectors  515 —which influences, at least in part, a total amount of indirect light visible by the plants  502  underneath the illumination system  500 —and (ii) the other choice of diffusive coatings applied on the transmissive forward output surfaces of the optical extractor  512 —which influences, at least in part, a total amount of direct light visible by the plants  502  underneath the illumination system—that were made for designing the illumination system led to another ratio of maximum luminance to minimum luminance across each of the reflectors  515  and the bottom side of the optical extractor  512  that is lower than 15:1. These designs will be described below in detail, in connection with  FIGS. 14A-14F and 15 . 
       FIG. 6A  shows a side view, e.g., in the (y,z) plane, of a plant growth lighting system  600 , in short referred to as lighting system, according to another embodiment of the present technology including height-adjustable or otherwise movable (indicated by shifting mechanism  603 ) light guide luminaire modules  601  configured to slide below a growth tray  611  (also referred to as a plant support) and configured to emit light  604 ,  605  from an extractor  606  sideways for direct illumination of plants  602 . The extractor  606  is optically coupled with light guide  620 .  FIG. 6B  schematically illustrates how a light guide luminaire module  601  can be recessed in a lower configuration to provide light close to the growth tray  611  for newly germinated plants  602 .  FIG. 6C  schematically illustrates how a light guide luminaire module  601  can be raised to provide light for mature plants  602 . The plant growth lighting system  600  can optionally include a sensor system  613  configured to monitor growth of the plants that is operatively coupled with a control system  623  that is configured to control the translation of one or more of the light guide luminaire modules  601  via the shifting system  603 . Such control may be fully automated to follow the plant growth in a predetermined manner. 
       FIG. 6D  schematically illustrates a lighting system  600 D according to another embodiment of the present technology. In lighting system  600 D, the luminaire modules  601  are configured to provide light  608  to a reflector  607  for indirect lighting  609  in addition to providing light  604 ,  605  directly to plants. Each of the luminaire modules  601  includes one or more LEEs  610 . A single luminaire module  601  can include multiple LEEs  610  configured to generate light of like or different spectral power density distributions (SPDs). The lighting system  600 D includes a control system  631  operatively coupled with and configured to control the LEEs  610  in the luminaire modules  601  during operation. Depending on the implementation, the lighting system  600 D may be configured to allow control of the amount of the light, the SPD of the light output per luminaire module or across different luminaire modules, or combinations thereof via the control system  631 . 
     Examples of respective light guide luminaire modules  601  are described below in connection with  FIGS. 7A-7B, 8 and 9A-9B . 
     In general, the light intensity distribution provided by light guide module  601  reflects the symmetry of the light guide luminaire module&#39;s structure about the y-z plane. For example, referring to  FIG. 6E , light  605  output in a first backward angular range corresponds to the first output lobe  145   a  of the far-field light intensity distribution  690 , light  604  output in second backward angular range corresponds to the second output lobe  145   b  of the far-field light intensity distribution  690  and light  608  output (leaked) in third forward angular range corresponds to the third output lobe  145   c  of the far-field light intensity distribution  690 . In general, an intensity profile of light guide luminaire module  601  will depend on the configuration of an optical coupler, the light guide  620  and the optical extractor  606 . For instance, the interplay between the shape of the optical coupler, the shape of a redirecting surface of the optical extractor  606  and the shapes of the output surfaces of the optical extractor can be used to control the angular width and prevalent direction (orientation) of the output first  145   a  and second  145   b  lobes in the far-field light intensity profile  690 . Additionally, a ratio of an amount of light in the combination of first  145   a  and second  145   b  output lobes and light in the third output lobe  145   c  is controlled by reflectivity and transmissivity of the redirecting surfaces of the optical extractor  606 . For example, for a reflectivity of 90% and transmissivity of 10% of the redirecting surfaces, 45% of light can be output in the first backward angular range corresponding to the first output lobe  145   a,  45% light can be output in the second backward angular range  145 ″ corresponding to the second output lobe  145   b , and 10% of light can be output in the third forward angular range corresponding to the third output lobe  145   c.    
     It is noted that luminaire modules  501 ,  601  as noted above may be configured as elongate edge-coupled edge-emitting elements. Such elements can be made substantially as narrow as the employed LEEs and also use a transport light guide that is transparent. Also, the noted luminaire modules have light sources (e.g., LEEs) disposed remote from the light-emitting extractor thereby displacing the heat producing light sources in a better location remote from temperature sensitive plants and thereby aid in thermal management of the whole plant growth system. 
     Because the light guides  521 ,  621  are transparent, light can flow through the luminaire modules  501 ,  601 , so they do not shadow light from adjacent light sources. 
     Plant shadowing of natural daylight in greenhouses by conventional electric lighting fixtures is noted as a problem in the current state of the art. Designs for light guide-based lighting fixtures of lighting systems  500 ,  500 B,  600 ,  600 D can be placed such that they minimize the shadowing effect because light can transmit through more than 60 to 70% of the light fixture. 
     The light guide luminaire modules  501 ,  601  can be placed through the growth trays  503 ,  611  and translated vertically to provide the optimal light for the various growth stages. 
     Small enough light guide luminaire modules  501 ,  601  can be placed much closer to the plants  502 ,  602  and yet provide very uniform illumination since it is not as impacted by inverse square law. 
     Under leaf lighting becomes possible as the light guide luminaire modules  501 ,  601  can be situated below the plants  502 ,  602  and radiate upwards towards the leaves. As the plant grows  502 ,  602 , it is also possible to extend or retract the light guide luminaire modules  501 ,  601  so that the light is placed in the most optimal position. 
     If the light guide luminaire modules  501 ,  601  are placed at the side of the growth trays  503 ,  611 , they can send sheets of light out across the bottom of the growth trays above the plants  502 ,  602  where it can be reflected in a prescribed pattern of uniform illumination to the plants below. 
     Light guide luminaire modules  501 ,  601  can be designed to be very small and even designed to become part of the growth environment infrastructure such as trays, holders and fluid delivery systems so that they are in closer proximity to the plants  502 ,  602 . 
     Spectral content of the upward light vs the downward light components can be modified via adjacent extraction systems with different spectral content LEDs. Thus the underleaf light spectral mix (due to light  604 ,  605 ) can be different from the over leaf spectral mix (due to light  609 ), thereby fine-tuning the lighting to the plant&#39;s needs. 
     The bottom of the upper growth tray  503 ,  611  becomes part of the prescribed reflecting surface above the target growth tray. 
     The highly asymmetric lighting distribution from light guide luminaire modules  501 ,  601  on either side of the growth tray  503 ,  611  is matched to a surface profile of the tray which provides for uniform diffuse illumination from above. 
     The light guide luminaire modules  501 ,  601  are placed on either one or both sides of the growth plane and can be moved up/down depending upon crop and lifecycle. 
     The light guide luminaire modules  501 ,  601 , on one or both sides, can have their LEE cooling and heat removal advantageously conveyed by having the lighting system  500 ,  500 B,  600 ,  600 D include the fluid flow for nutrients within the housing. As water and nutrients flow through the conduit, heat can be coupled directly and will warm the fluid, which can either be harnessed for other purposes, in a heat exchanger, or exhausted, to manage the working air temperature of the enclosure. 
     By combining electronic spatial tuning with light guides that have a plurality of light distributions that can be electronically selected, it is possible to modify the light distribution during the maturation of the plant  502 ,  602 . By combining this feature with spectral tuning and mixing, the plant  502 ,  602  is able to go through an efficient process of absorption and relaxation that may stimulate increased growth. 
     Mixing and modulating the light of different spectral capabilities in the system  500 ,  500 B,  600 ,  600 D can be done at high frequencies, which may increase the productive efficiency of certain desirable plant characteristics. 
     Using the disclosed systems  500 ,  500 B,  600 ,  600 D with feedback techniques, such as chemical analysis, (hyper) spectral analysis and other measurements of plant growth dynamics, by both direct and indirect means, the systems  500 ,  500 B,  600 ,  600 D can be electronically and/or mechanically adapted to increase the productivity of the plant growth environment. 
     The use of multi-lobed light distributions (e.g.,  690 ), offers the opportunity to modulate the balance between direct and indirect lighting for the plant canopy. As in nature, the combinations of light received by plants  502 ,  602  consists of many different spectral and spatial components that vary throughout the day. This electro-optical system is capable of emulating the important properties of natural daylighting, or even improving upon natural sources of light and its respective components effective in growth and maturation of plant materials. This can fine-tune the plant properties, which are noted in research as being highly plastic to changes in light content/direction/duration recipes. 
     The use of light guide luminaire modules  501 ,  601  in lighting systems  500 ,  500 B,  600 ,  600 D as described herein can help mitigate the impact of fixture “shadowing” on plants  502 ,  602  grown in greenhouses where artificial lighting is provided with traditional fixtures. The light guide transparency and compact emitting surfaces may be useful in this respect. Moreover, plant illumination is not necessarily concerned with glare, which is an important aspect in the lighting of human occupied spaces. Additionally, diffuse-transmitting greenhouse windows and/or panels may be used to spread sunlight or artificial light and provide Lambertian-emitting surfaces. 
     Examples of light guide luminaire modules  601  used in lighting systems  600 ,  600 D are described next. 
     Referring to  FIG. 7A , a light guide luminaire module  201  (or simply a light guide module) includes a substrate  205  having a plurality of LEEs  210  distributed along a first surface of the substrate  205 . The mount with the LEEs  210  is disposed at a first (e.g., upper) edge  231  of a light guide  230 . Once again, the positive z-direction is referred to as the “forward” direction and the negative z-direction is the “backward” direction. Sections through the light guide module  201  parallel to the x-z plane are referred to as the “cross-section” or “cross-sectional plane” of the light guide module. Also, light guide module  201  extends along the y-direction, so this direction is referred to as the “longitudinal” direction of the light guide module. Implementations of light guide modules can have a plane of symmetry parallel to the y-z plane, and can be curved or otherwise shaped. This is referred to as the “symmetry plane” of the light guide module. 
     Multiple LEEs  210  are disposed on the first surface of the substrate  205 , although only one of the multiple LEEs  210  is shown in  FIG. 7A . For example, the plurality of LEEs  210  can include multiple white LEDs. The LEEs  210  are optically coupled with one or more optical couplers  220  (only one of which is shown in  FIG. 7A ). An optical extractor  240  is disposed at second (e.g., lower) edge  232  of light guide  230 . 
     Substrate  205 , light guide  230 , and optical extractor  240  extend a length L along the y-direction, so that the light guide module is an elongated light guide module with an elongation of L that may be about parallel to a display panel. Generally, L can vary as desired. Typically, L is in a range from about 1 cm to about 200 cm (e.g., 20 cm or more, 30 cm or more, 40 cm or more, 50 cm or more, 60 cm or more, 70 cm or more, 80 cm or more, 100 cm or more, 125 cm or more, or, 150 cm or more). 
     The number of LEEs  210  on the substrate  205  will generally depend, inter alia, on the length L, where more LEEs are used for longer light guide modules. In some implementations, the plurality of LEEs  210  can include between 10 and 1,000 LEEs (e.g., about 50 LEEs, about 100 LEEs, about 200 LEEs, about 500 LEEs). Generally, the density of LEEs (e.g., number of LEEs per unit length) will also depend on the nominal power of the LEEs and illuminance desired from the light guide module. For example, a relatively high density of LEEs can be used in applications where high illuminance is desired or where low power LEEs are used. In some implementations, the light guide module  201  has LEE density along its length of 0.1 LEE per centimeter or more (e.g., 0.2 per centimeter or more, 0.5 per centimeter or more, 1 per centimeter or more, 2 per centimeter or more). The density of LEEs may also be based on a desired amount of mixing of light emitted by the multiple LEEs. In implementations, LEEs can be evenly spaced along the length, L, of the light guide module. In some implementations, the substrate  205  can be attached to a housing  202  configured as a heat-sink to extract heat emitted by the plurality of LEEs  210 . A surface of the substrate  205  that contacts the housing  202  opposes the side of the substrate  205  on which the LEEs  210  are disposed. The light guide module  201  can include one or multiple types of LEEs, for example one or more subsets of LEEs in which each subset can have different color or color temperature. 
     Optical coupler  220  includes one or more solid pieces of transparent optical material (e.g., a glass material or a transparent plastic, such as polycarbonate or acrylic) having surfaces  221  and  222  positioned to reflect light from the LEEs  210  towards the light guide  230 . In general, surfaces  221  and  222  are shaped to collect and at least partially collimate light emitted from the LEEs. In the x-z cross-sectional plane, surfaces  221  and  222  can be straight or curved. Examples of curved surfaces include surfaces having a constant radius of curvature, parabolic or hyperbolic shapes. In some implementations, surfaces  221  and  222  are coated with a highly reflective material (e.g., a reflective metal, such as aluminum or silver), to provide a highly reflective optical interface. The cross-sectional profile of optical coupler  220  can be uniform along the length L of light guide module  201 . Alternatively, the cross-sectional profile can vary. For example, surfaces  221  and/or  222  can be curved out of the x-z plane. 
     The exit aperture of the optical coupler  220  adjacent upper edge of light guide  231  is optically coupled to edge  231  to facilitate efficient coupling of light from the optical coupler  220  into light guide  230 . For example, the surfaces of a solid coupler and a solid light guide can be attached using a material that substantially matches the refractive index of the material forming the optical coupler  220  or light guide  230  or both (e.g., refractive indices across the interface are different by 2% or less.) The optical coupler  220  can be affixed to light guide  230  using an index matching fluid, grease, or adhesive. In some implementations, optical coupler  220  is fused to light guide  230  or they are integrally formed from a single piece of material (e.g., coupler and light guide may be monolithic and may be made of a solid transparent optical material). 
     Light guide  230  is formed from a piece of transparent material (e.g., glass material such as BK7, fused silica or quartz glass, or a transparent plastic, such as polycarbonate or acrylic) that can be the same or different from the material forming optical couplers  220 . Light guide  230  extends length L in the y-direction, has a uniform thickness T in the x-direction, and a uniform depth D in the z-direction. The dimensions D and T are generally selected based on the desired optical properties of the light guide (e.g., which spatial modes are supported) and/or the direct/indirect intensity distribution. During operation, light coupled into the light guide  230  from optical coupler  220  (with an angular range  125 ) reflects off the planar surfaces of the light guide by TIR and spatially mixes within the light guide. The mixing can help achieve illuminance and/or color uniformity, along the x-axis, at the distal portion of the light guide  232  at optical extractor  240 . The depth, D, of light guide  230  can be selected to achieve adequate uniformity at the exit aperture (i.e., at end  232 ) of the light guide. In some implementations, D is in a range from about 1 cm to about 20 cm (e.g., 2 cm or more, 4 cm or more, 6 cm or more, 8 cm or more, 10 cm or more, 12 cm or more). 
     In general, optical couplers  220  are designed to restrict the angular range of light entering the light guide  230  (e.g., to within +/−40 degrees) so that at least a substantial amount of the light (e.g., 95% or more of the light) is optically coupled into spatial modes in the light guide  230  that undergoes TIR at the planar surfaces. Light guide  230  can have a uniform thickness T, which is the distance separating two planar opposing surfaces of the light guide. Generally, T is sufficiently large so the light guide has an aperture at first (e.g., upper) surface  231  sufficiently large to approximately match (or exceed) the exit aperture of optical coupler  220 . In some implementations, T is in a range from about 0.05 cm to about 2 cm (e.g., about 0.1 cm or more, about 0.2 cm or more, about 0.5 cm or more, about 0.8 cm or more, about 1 cm or more, about 1.5 cm or more). Depending on the implementation, the narrower the light guide the better it may spatially mix light. A narrow light guide also provides a narrow exit aperture. As such light emitted from the light guide can be considered to resemble the light emitted from a one-dimensional linear light source, also referred to as an elongate virtual filament. 
     While optical coupler  220  and light guide  230  are formed from solid pieces of transparent optical material, hollow structures are also possible. For example, the optical coupler  220  or the light guide  230  or both may be hollow with reflective inner surfaces rather than being solid. As such material cost can be reduced and absorption in the light guide can be mitigated. A number of specular reflective materials may be suitable for this purpose including materials such as 3M Vikuiti™ or Miro IV™ sheet from Alanod Corporation where greater than 90% of the incident light can be efficiently guided to the optical extractor. 
     Optical extractor  240  is also composed of a solid piece of transparent optical material (e.g., a glass material or a transparent plastic, such as polycarbonate or acrylic) that can be the same as or different from the material forming light guide  230 . In the example implementation shown in  FIG. 7A , the optical extractor  240  includes redirecting (e.g., flat) surfaces  242  and  244  and curved surfaces  246  and  248 . The flat surfaces  242  and  244  represent first and second portions of a redirecting surface  243 , while the curved surfaces  246  and  248  represent first and second output surfaces of the light guide module  201 . 
     Surfaces  242  and  244  are coated with a reflective material (e.g., a highly reflective metal such as aluminum or silver) over which a protective coating may be disposed. For example, the material forming such a coating may reflect about 95% or more of light incident thereon at appropriate (e.g., visible) wavelengths. Here, surfaces  242  and  244  provide a highly reflective optical interface for light having the angular range  125  entering an input end of the optical extractor  232 ′ from light guide  230 . As another example, the surfaces  242  and  244  include portions that are transparent to the light entering at the input end  232 ′ of the optical extractor  240 . Here, these portions can be uncoated regions (e.g., partially silvered regions) or discontinuities (e.g., slots, slits, apertures) of the surfaces  242  and  244 . As such, some light is transmitted in the forward direction (along the z-axis) through surfaces  242  and  244  of the optical extractor  240  in a third forward angular range  145 ′″. In some cases, the light transmitted in the third forward angular range  145 ′″ is refracted. In this way, the redirecting surface  243  acts as a beam splitter rather than a mirror, and transmits in the third forward angular range  145 ′″ a desired portion of incident light, while reflecting the remaining light in angular ranges  138 ″ and  138 ′. 
     In the x-z cross-sectional plane, the lines corresponding to surfaces  242  and  244  have the same length and form an apex or vertex  241 , e.g. a v-shape that meets at the apex  241 . In general, an included angle (e.g., the smallest included angle between the surfaces  244  and  242 ) of the redirecting surfaces  242 ,  244  can vary as desired. For example, in some implementations, the included angle can be relatively small (e.g., from 30° to 60°). In certain implementations, the included angle is in a range from 60° to 120° (e.g., about 90°). The included angle can also be relatively large (e.g., in a range from 120° to 150° or more). In the example implementation shown in  FIG. 7A , the output surfaces  246 ,  248  of the optical extractor  240  are curved with a constant radius of curvature that is the same for both. In an aspect, the output surfaces  246 ,  248  may have optical power (e.g., may focus or defocus light.) Accordingly, light guide module  201  has a plane of symmetry intersecting apex  241  parallel to the y-z plane. 
     The surface of optical extractor  240  adjacent to the lower edge  232  of light guide  230  is optically coupled to edge  232 . For example, optical extractor  240  can be affixed to light guide  230  using an index matching fluid, grease, or adhesive. In some implementations, optical extractor  240  is fused to light guide  230  or they are integrally formed from a single piece of material. 
     The emission spectrum of the light guide module  201  corresponds to the emission spectrum of the LEEs  210 . However, in some implementations, a wavelength-conversion material may be positioned in the light guide module, for example remote from the LEEs, so that the wavelength spectrum of the light guide module is dependent both on the emission spectrum of the LEEs and the composition of the wavelength-conversion material. In general, a wavelength-conversion material can be placed in a variety of different locations in light guide module  201 . For example, a wavelength-conversion material may be disposed proximate the LEEs  210 , adjacent surfaces  242  and  244  of optical extractor  240 , on the exit surfaces  246  and  248  of optical extractor  240 , and/or at other locations. 
     The layer of wavelength-conversion material (e.g., phosphor) may be attached to light guide  230  held in place via a suitable support structure (not illustrated), disposed within the extractor (also not illustrated) or otherwise arranged, for example. Wavelength-conversion material that is disposed within the extractor may be configured as a shell or other object and disposed within a notional area that is circumscribed between R/n and R*(1+n2)(−½), where R is the radius of curvature of the light-exit surfaces ( 246  and  248  in  FIG. 7A ) of the extractor  240  and n is the index of refraction of the portion of the extractor that is opposite of the wavelength-conversion material as viewed from the reflective surfaces ( 242  and  244  in  FIG. 7A ). The support structure may be a transparent self-supporting structure. The wavelength-conversion material diffuses light as it converts the wavelengths, provides mixing of the light and can help uniformly illuminate a surface of the ambient environment. 
     During operation, light exiting light guide  230  through end  232  impinges on the reflective interfaces at portions of the redirecting surface  242  and  244  and is reflected outwardly towards output surfaces  246  and  248 , respectively, away from the symmetry plane of the light guide module. The first portion of the redirecting surface  242  provides light having an angular distribution  138  towards the output surface  246 , the second portion of the redirecting surface  244  provides light having an angular distribution  138 ′ towards the output surface  248 . The light exits optical extractor  240  through output surfaces  246  and  248 . In general, the output surfaces  246  and  248  have optical power, to redirect the light exiting the optical extractor  240  in first and second backward angular ranges  145 ′,  145 ″, respectively. For example, optical extractor  240  may be configured to emit light upwards (i.e., towards the plane intersecting the LEEs and parallel to the x-y plane), downwards (i.e., away from that plane) or both upwards and downwards. In general, the direction of light exiting the light guide module through surfaces  246  and  248  depends on the divergence of the light exiting light guide  230  and the orientation of surfaces  242  and  244 . 
     Surfaces  242  and  244  may be oriented so that little or no light from light guide  230  is output by optical extractor  240  in certain directions. In implementations where the light guide module  201  is attached to a ceiling of a room (e.g., the forward direction is towards the floor) such configurations can help avoid glare and an appearance of non-uniform illuminance. 
     In general, the light intensity distribution provided by light guide module  201  reflects the symmetry of the light guide module&#39;s structure about the y-z plane, as described above in connection with  FIG. 6E . Referring to both  FIGS. 6E and 7A , the orientation of the output lobes  145   a ,  145   b  can be adjusted based on the included angle of the v-shaped groove  241  formed by the portions of the redirecting surface  242  and  244 . For example, a first included angle results in a far-field light intensity distribution  690  with output lobes  145   a ,  145   b  located at relatively smaller angles compared to output lobes  145   a ,  145   b  of the far-field light intensity distribution  690  that results for a second included angle larger than the first angle. In this manner, light can be extracted from the light guide module  201  in a more forward direction for the smaller of two included angles formed by the portions  242 ,  244  of the redirecting surface  243 . 
     Furthermore, while surfaces  242  and  244  are depicted as planar surfaces, other shapes are also possible. For example, these surfaces can be curved or faceted. Curved redirecting surfaces  242  and  244  can be used to narrow or widen the output lobes  145   a ,  145   b . Depending of the divergence of the angular range  125  of the light that is received at the input end of the optical extractor  232 ′, concave reflective surfaces  242 ,  244  can narrow the lobes  145   a ,  145   b  output by the optical extractor  240  (and illustrated in  FIG. 6E ), while convex reflective surfaces  242 ,  244  can widen the lobes  145   a ,  145   b  output by the optical extractor  240 . As such, suitably configured redirecting surfaces  242 ,  244  may introduce convergence or divergence into the light. Such surfaces can have a constant radius of curvature, can be parabolic, hyperbolic, or have some other curvature. 
     In general, the geometry of the elements can be established using a variety of methods. For example, the geometry can be established empirically. Alternatively, or additionally, the geometry can be established using optical simulation software, such as Lighttools™, Tracepro™, FRED™ or Zemax™, for example. 
     In general, light guide module  201  can be designed to output light into different first and second backward angular ranges  145 ′,  145 ″ from those shown in  FIG. 7A . In some implementations, illumination devices can output light into lobes  145   a ,  145   b  that have a different divergence or propagation direction than those shown in  FIG. 6E . For example, in general, the output lobes  145   a ,  145   b  can have a width of up to about 90° (e.g., 80° or less, 70° or less, 60° or less, 50° or less, 40° or less, 30° or less, 20° or less). In general, the direction in which the output lobes  145   a ,  145   b  are oriented can also differ from the directions shown in  FIG. 6E . The “direction” refers to the direction at which a lobe is brightest. In  FIG. 6E , for example, the output lobes  145   a ,  145   b  are oriented at approx. −130° and approximately +130°. In general, output lobes  145   a ,  145   b  can be directed more towards the horizontal (e.g., at an angle in the ranges from −90° to −135°, such as at approx. −90°, approx. −100°, approx. −110°, approx. −120°, approx. −130°, and from +90° to +135°, such as at approx. +90°, approx. +100°, approx. +110°, approx. +120°, approx. +130°. 
     The light guide modules can include other features useful for tailoring the intensity profile. For example, in some implementations, light guide modules can include an optically diffuse material that can diffuse light in a controlled manner to aid homogenizing the light guide module&#39;s intensity profile. For example, surfaces  242  and  244  can be roughened or a diffusely reflecting material, rather than a specular reflective material, can be coated on these surfaces. Accordingly, the optical interfaces at surfaces  242  and  244  can diffusely reflect light, scattering light into broader lobes than would be provided by similar structures utilizing specular reflection at these interfaces. In some implementations these surfaces can include structure that facilitates various intensity distributions. For example, surfaces  242  and  244  can each have multiple planar facets at differing orientations. Accordingly, each facet will reflect light into different directions. In some implementations, surfaces  242  and  244  can have structure thereon (e.g., structural features that scatter or diffract light). 
     Surfaces  246  and  248  need not be surfaces having a constant radius of curvature. For example, surfaces  246  and  248  can include portions having differing curvature and/or can have structure thereon (e.g., structural features that scatter or diffract light). In certain implementations, a light scattering material can be disposed on surfaces  246  and  248  of optical extractor  240 . 
     In some implementations, optical extractor  240  is structured so that a negligible amount (e.g., less than 1%) of the light propagating within at least one plane (e.g., the x-z cross-sectional plane) that is reflected by surface  242  or  244  experiences TIR at light-exit surface  246  or  248 . For certain spherical or cylindrical structures, a so-called Weierstrass condition can avoid TIR. A Weierstrass condition is illustrated for a circular structure (i.e., a cross section through a cylinder or sphere) having a surface of radius R and a concentric notional circle having a radius R/n, where n is the refractive index of the structure. Any light ray that passes through the notional circle within the cross-sectional plane is incident on the surface of the circular structure and has an angle of incidence less than the critical angle and will exit the circular structure without experiencing TIR. Light rays propagating within the spherical structure in the plane but not emanating from within the notional surface can impinge on the surface of radius R at the critical angle or greater angles of incidence. Accordingly, such light may be subject to TIR and won&#39;t exit the circular structure. Furthermore, rays of p-polarized light that pass through a notional space circumscribed by an area with a radius of curvature that is smaller than R/(1+n2)(−½), which is smaller than R/n, will be subject to small Fresnel reflection at the surface of radius R when exiting the circular structure. This condition may be referred to as Brewster geometry. Implementations may be configured accordingly. 
     Referring again to  FIG. 7A , in some implementations, all or part of surfaces  242  and  244  may be located within a notional Weierstrass surface defined by surfaces  246  and  248 . For example, the portions of surfaces  242  and  244  that receive light exiting light guide  230  through end  232  can reside within this surface so that light within the x-z plane reflected from surfaces  242  and  244  exits through surfaces  246  and  248 , respectively, without experiencing TIR. 
     In the example implementations described above in connection with  FIG. 7A , the light guide module  201  is configured to output light into first and second backward angular ranges  145 ′ and  145 ″ and in third forward angular range  145 ′″. In other implementations, the light guide-based light guide module  201  is modified to output light into a single backward angular range  145 ′.  FIG. 7B  shows such light guide-based light guide module  201 * configured to output light on a single side of the light guide is referred to as a single-sided light guide module. The single-sided light guide module  201 * is elongated along the x-axis like the light guide module  201  shown in  FIG. 7A . Also like the light guide module  201 , the single-sided light guide module  201 * includes a substrate  205  and LEEs  210  disposed on a surface of the substrate  205  along the x-axis to emit light in a first angular range. The single-sided light guide module  201 * further includes optical couplers  220  arranged and configured to redirect the light emitted by the LEEs  210  in the first angular range into a second angular range  125  that has a divergence smaller than the divergence of the first angular range at least in the x-z cross-section. Also, the single-sided light guide module  201 * includes a light guide  230  to guide the light redirected by the optical couplers  220  in the second angular range  125  from a first end  231  of the light guide to a second end  232  of the light guide. Additionally, the single-sided light guide module  201 * includes a single-sided extractor (denoted  240 *) to receive the light guided by the light guide  230 . The single-sided extractor  240 * includes a redirecting surface  244  to redirect some of the light received from the light guide  230  into a third angular range  138 ′, like described for light guide module  201  with reference to  FIG. 7A , and an output surface  248  to output the light redirected by the redirecting surface  244  in the third angular range  138 ′ into a first backward angular range  145 ′. Also as described in  FIG. 7A , the redirecting surface  244  is configured to leak some the light received from the light guide  230  into a third forward angular range  145 ′″. 
     A light intensity profile of the single-sided light guide module  201 * is represented in  FIG. 6E  as the first output lobe  145   a  and the third output lobe  145   c . The output lobe  145   a  corresponds to light output by the single-sided light guide module  201 * in the first backward angular range  145 ′ and the output lobe  145   c  corresponds to light output by the single-sided light guide module  201 * in the third forward angular range  145 ″. 
     In general, light guide modules like the light guide module  201 * can be combined with a single tertiary reflector to provide (i) indirect illumination to a first portion of a target surface from light output by the light guide module in the first backward angular range  145 ′ and redirected by the tertiary reflector to a first forward angular range  155 ′, and (ii) direct illumination to a second, different portion of the target surface from light output by the light guide module in the third forward angular range  145 ″. Further, light guide modules like the light guide module  201 * can be combined with a pair of tertiary reflectors to provide, as shown, e.g., in  FIG. 1 , (i) indirect illumination to first and second different portions of a target surface from light output by the light guide module in the respective first and second backward angular ranges  145 ′,  145 ″ and respectively redirected by the tertiary reflectors to first and second forward angular ranges  155 ′,  155 ″, and (ii) direct illumination to a third portion of the target surface, different from the first and second portions, from light output by the light guide module in the third forward angular range  145 ″. An example of the latter combination is described below. 
     The light guide module  201  or  201 * can be used in an upright configuration where the LEEs are positioned underneath the optical extractor  240 .  FIG. 8  shows a cross-section of an adjustable illumination device  800  that can be implemented in lighting system  600 ,  600 D, for instance. In this example, the adjustable illumination device  800  includes an embodiment of a light guide luminaire module, such as light guide luminaire module  201  described above in connection with  FIG. 7A , and a sliding mechanism  805  (the latter represented by two anti-parallel arrows). Further in this example, a position of the light guide luminaire module  201  can be adjusted by the sliding mechanism  805  relative to a housing  811  to which the light guide luminaire module is coupled. 
     As described above in connection with  FIG. 7A , the light guide luminaire module  201  can output light in backward angular ranges  145 ′ and  145 ″. In this example, the light output in backward angular ranges  145 ′ and  145 ″ illuminates a target space (e.g., a tray  611  that support plants  602  in lighting systems  600 ,  600 D, for instance). In some implementations, the light guide luminaire module  201  is configured to also output light in forward angular range  145 ′″, as described above in connection with  FIG. 7A . In this example, the light output in forward angular range  145 ″ illuminates a remote space (e.g., the reflector  607  lighting system  600 D.) 
     As described herein, the light guide luminaire module  201  includes a substrate  205  and multiple LEEs  210 . The LEEs  210  can be coupled with the substrate  205 . The light guide luminaire module  201  includes optical couplers  220  corresponding to the LEEs  210 , the light guide  230 , and the optical extractor  240 . A portion of the light that is guided by the light guide  230  in a collimated angular range to the optical extractor  240  is redirected by a first portion  242  of a redirecting surface and then output from the optical extractor  240  through a first output surface  246 . 
     Another portion of the light received at the optical extractor  240  in the collimated angular range is redirected by a second portion  244  of the redirecting surface and then output from the optical extractor  240  through a second output surface  248 . A mounting frame and attachment brackets can be used to position/attach the optical couplers inside the housing  811  to couple the light guide luminaire module  201  to the sliding mechanism  805 . 
     In general, the mounting structure that allows for adjustment of the position of the luminaire module relative to the ceiling (or other background area) can be configured in different ways. An example of a mounting structure for an elongate luminaire module is shown in  FIGS. 9A-9B . Here, an adjustable illumination device  900  includes a housing  911  that allows for mounting the adjustable illumination device to a ceiling. The adjustable illumination device  900  includes a luminaire module  901  (e.g., having a structure similar to luminaire module  201 ), the housing  911 , and a sliding mechanism  905  for adjusting an extension of the luminaire module  901  relative to the housing  911 . The luminaire module  901  can be moved relative to the housing  911  (e.g., the luminaire module can be slid back and forth in the housing to extend or retract the luminaire module.) In some implementations, one or more tools  950  can be used to push/pull the luminaire module  901  into and out of the housing  911 . The one or more tools  950  can be permanently or removably coupled with the luminaire module at one or more locations. For example, such tools can be arranged at opposite ends with respect to the length of the light guide and/or in the center of the light guide proximate the optical extractor. The tool can comprise a tab handle, hook, a spring, or alike. One end of the housing  911  includes a flange that sits flush with the ceiling when the adjustable illumination device is installed in a room. This end includes an opening into which the luminaire module is inserted. 
     The sliding mechanism  905  includes guide rails  925 , guide blocks  942  and  944 , spring loaded bolts  946  and openings  912 . The openings  912  are configured to allow partial mating with respective spring loaded bolts  946 . The spring loaded bolts  946  can have rounded ends for protruding beyond a face of the respective guide blocks  942 . The guide block  944  can have an opening  948  that can be configured to receive a screw  914  for securing the luminaire module  901  and limiting its translational movement relative to the housing  911 . 
     The sliding mechanism can be configured such that the spring loaded bolts  946  resiliently engage with the openings  912  when the luminaire module  901  is inserted in the housing  911 . Release from the resilient engagement can be achieved by exerting a minimum pull/push force between the luminaire module  901  and the housing  911 . Force can be exerted via the removable tool  950 , by an electric motor, or any other means suitable to traverse the luminaire module  901 . 
     The guide rails  925  can be located between the guide blocks  942  when the luminaire module  901  is inserted in the housing  911 . The fit between the guide blocks  942  and the guide rails  925  can be configured to provide sufficient tolerances and allow for an amount of force imbalance between the removable tools  950  that are located on opposite ends of the luminaire module  901  to avoid jamming during up/down movement. In some implementations, the openings  912  can have a circular, an elongate (parallel to horizontal) or other shape to allow reproducible interlocking even when an offset between the spring loaded bolts  946  and the openings  912  occurs. The guide blocks  942  and  944  can be attached to a rail  945 , which can be configured to hold and secure the upper edge of the luminaire module  901 . 
     While in the present example the luminaire module is manually slid relative to the housing in discrete steps, other implementations are also possible. For example, in some embodiments, adjusting the luminaire module  901  (i.e., sliding the luminaire module into and out of the housing) can be performed using a mechanical or electromechanical or other actuator, for example. The actuator can be based on analog or digital control and configured to slide the luminaire module relative to the housing. Such actuators can be configured to allow for remote control of the position of the luminaire module  901 . Example actuators can include leadscrews and stepper motors in which the stepper motor drives the leadscrew which then translates rotational movement into a linear movement. To mitigate seizing in long linear systems, multiple actuators and/or extended actuator mechanisms may be disposed along the length of the illumination device, which may be electrically or mechanically synchronized via suitable control signals or one or more synchronization belts, for example. 
     Furthermore, different luminaire modules can have different heights, i.e., the maximum (and minimum) extension relative to the housing  911  depends on the height of the respective luminaire module. 
       FIG. 10A  is a contour plot of a simulated intensity distribution in a plane of the housing  811  that corresponds to the configuration of the adjustable illumination device  800  shown in  FIG. 8  (i.e., full extension of the luminaire module, e.g., at z=Z 1 ) and the intensity profile shown in  FIG. 6E . The x-axis of the plot shown in  FIG. 10A  refers to the illumination distribution in the longitudinal direction of the adjustable illumination device  800  (x-axis in  FIG. 7A or 8 ) and the y-axis of the plot refers to the illumination distribution in the transverse direction of the adjustable illumination device  800  (y-axis in  FIG. 7A or 8 .)  FIG. 10B  is a cross section plot of the intensity distribution from  FIG. 10A  in the transverse direction (y-axis) of the adjustable illumination device  800  at x=0. The second axis of the plot shown in  FIG. 10B  refers to illuminance (lux) in the transverse direction of the adjustable illumination device  800 . In this example, the illuminance between a distance of −1,000 and +1,000 mm from the adjustable illumination device in transverse direction reaches up to 3,500 lux.  FIG. 10C  is a cross section plot of the intensity distribution from  FIG. 10A  in the longitudinal direction (x-axis) of the adjustable illumination device  800  at y=0. The second axis of the plot shown in  FIG. 10C  refers to illuminance (lux) in the longitudinal direction of the adjustable illumination device  800 . In this example, the illuminance between a distance of −400 and +400 mm from the adjustable illumination device along the longitudinal direction reaches up to 2,250 lux. 
       FIG. 11A  is a contour plot of a simulated intensity distribution in a plane of the housing  811  that corresponds to the configuration of the adjustable illumination device  800  shown in  FIG. 8  (i.e., partial extension of the luminaire module, e.g., at z=Z 2 ) and the intensity profile shown in  FIG. 6E . The x-axis of the plot shown in  FIG. 11A  refers to the illumination distribution in the longitudinal direction of the adjustable illumination device  800  (x-axis in  FIG. 7A or 8 ) and the y-axis of the plot refers to the illumination distribution in the transverse direction of the adjustable illumination device  800  (x-axis in  FIG. 7A or 8 ).  FIG. 11B  is a cross section plot of a simulated intensity distribution in the transverse direction (y-axis) of the adjustable illumination device  800 . The second axis of the plot shown in  FIG. 11B  refers to illuminance (lux) in the transverse direction of the adjustable illumination device  800 . In this example, the illuminance between a distance of −900 and +900 mm from the adjustable illumination device in transverse direction reaches up to 4,750 lux.  FIG. 11C  is a cross section plot of a simulated intensity distribution in the longitudinal direction (x-axis) of the adjustable illumination device  800 . The second axis of the plot shown in  FIG. 11C  refers to illuminance (lux) in the longitudinal direction of the adjustable illumination device  800 . In this example, the illuminance between a distance of −375 and +375 mm from the adjustable illumination device along the longitudinal direction reaches up to 2,400 lux. 
       FIG. 12A  is a contour plot of a simulated intensity distribution in a plane of the housing  811  that corresponds to the configuration of the adjustable illumination device  800  shown in  FIG. 8  (i.e., full retraction of the luminaire module, e.g., at z=Z 3 ) and the intensity profile shown in  FIG. 6E . The x-axis of the plot shown in  FIG. 12A  refers to the illumination distribution in the longitudinal direction of the adjustable illumination device  800  (x-axis in  FIG. 7A or 8 ) and the y-axis of the plot refers to the illumination distribution in the transverse direction of the adjustable illumination device  800  (y-axis in  FIG. 7A or 8 .)  FIG. 12B  is a cross section plot of a simulated intensity distribution in the transverse direction (y-axis) of the adjustable illumination device  800 . The second axis of the plot shown in  FIG. 12B  refers to illuminance (lux) in the transverse direction of the adjustable illumination device  800 . In this example, the illuminance between a distance of −600 and +600 mm from the adjustable illumination device in transverse direction reaches up to 7,500 lux.  FIG. 12C  is a cross section plot of a simulated intensity distribution in the longitudinal direction (x-axis) of the adjustable illumination device  800 . The second axis of the plot shown in  FIG. 12C  refers to illuminance (lux) in the longitudinal direction of the adjustable illumination device  800 . In this example, the illuminance between a distance of −350 and +350 mm from the adjustable illumination device along the longitudinal direction reaches up to 2,500 lux. 
       FIGS. 10C, 11C, and 12C  show that the illumination of the plane of the housing  811  remains substantially above 2000 lux along the elongate dimension of the adjustable illumination device  800  (i.e., the length of the adjustable illumination device  800  defined by the X coordinate) even though the extension of the luminaire module (i.e., the distance of the optical extractor  240  to the plane of the housing  811 ) varies. However, the illumination of the plane of the housing  811  along the Y coordinate varies dependent on the extension of the luminaire module. For example, as shown in  FIG. 10B , the adjustable illumination device  800  with a fully extended luminaire module illuminates the plane of the housing  811  at above 500 lux to about 600 mm in the Y direction from the adjustable illumination device  800 . In comparison, as shown in  FIG. 12B , the adjustable illumination device  800  with a fully retracted luminaire module illuminates the plane of the housing  811  at above 500 lux to about 400 mm in the Y direction from the adjustable illumination device  800 . 
     Examples of light guide luminaire modules  501 ,  501 A,  501 B and reflectors  515 ,  516  used in lighting systems  500 ,  500 B are described next. 
       FIGS. 13A-13B  show a side view and a perspective view, respectively, of an example lighting system  1300  including a light guide module  1301  and tertiary reflectors  1570 ′,  1570 ″. Lighting system  1300  can be used as the lighting system  500  described above, where the light guide module  1301  and the tertiary reflectors  1570 ′,  1570 ″ correspond to the light guide module  501  and reflector  515 , respectively. Solid state light sources, optical couplers and a light guide of the light guide module  1301  can be implemented like the corresponding components of the light guide module  201  described above in connection with  FIG. 7A . An optical extractor  1440  of the light guide module  1301  is mirror symmetric relative to the z-axis (which coincides with the optical axis of the light guide module  1301 ) and can be implemented as described below in connection with  FIGS. 14A-14F . Respective “front faces” (referred to as reflective surfaces) of the tertiary reflectors  1570 ′,  1570 ″, that face the light guide module  1301 , can be implemented as described below in connection with  FIG. 15 , while “rear faces” can be implemented as a solid block or can have other forms/shapes. Note that while the plurality of solid state light sources and the optical couplers of the light guide module  1301  are housed within a housing  1302 , the light guide of light guide module protrudes from the housing to lower the optical extractor  1440  of light guide module by a distance D along the z-axis comparable to a sag of the tertiary reflectors  1570 ′,  1570 ″ in the (y,z) plane. The light guide module  1301  and the tertiary reflectors  1570 ′,  1570 ″ are elongated along the x-axis and can have a length L of about 2′ or 4′, corresponding to the size of conventional fluorescent light luminaires. 
     In this implementation, output surfaces of the optical extractor  1440  of the light guide module  1301 , and corresponding reflective surfaces of the tertiary reflectors  1570 ′,  1570 ″ are shaped and arranged with respect to one another such that each of the tertiary reflectors  1570 ′,  1570 ″ appears to be uniformly lit to plants disposed directly in front, and along an optical axis, of the optical extractor. For example, a ratio of maximum luminance to minimum luminance across each of the tertiary reflectors  1570 ′,  1570 ″ can be lower than 5:1, 4:1 or 3:1. In this manner, the observer can view a fully lit surface of each of the tertiary reflectors  1570 ′,  1570 ″ free of dark regions and/or hot spots. 
       FIG. 14A  is a cross-section in the (y-z) plane of an example implementation of the optical extractor  1440  of the light guide module  1301 . The optical extractor  1440  is formed from a solid material (with refractive index n&gt;1). For example, the material can be glass with a refractive index of about 1.5. As another example, the material can be plastic with a refractive index of about 1.5-1.6. In this implementation, the optical extractor  1440  includes an input surface  1441  centered on the optical axis of the light guide (here, the z-axis); a first backward output surface  1442   a  and a second backward output surface  1442   b  arranged to mirror each other relative to the z-axis; a first forward output surface  1443   a  and a second forward output surface  1443   b  arranged to mirror each other relative to the z-axis; a first redirecting surface  1444   a  and a second redirecting surface  1444   b  arranged to mirror each other relative to the z-axis; and a third forward output surface  1445  centered on the z-axis and opposing the input surface. Note that the first/second backward output surface  1442   a / 1442   b  intersects the first/second forward output surface  1443   a / 1443   b  at edge  1446   a / 1446   b . Additionally, the first/second redirecting surface  1444   a / 1444   b  intersects the first/second forward output surface  1443   a / 1443   b  at vertex  1447   a / 1447   b.    
     The input surface  1441  is formed from a first input interface  1441   a  (also referred to as the 1st interface), which is represented above the z-axis in this example, and a second input interface  1441   b  (also referred to as the 2nd interface), which is represented below the z-axis in this example.  FIG. 14B  is a cross-section in the (y-z) plane of the 1st interface  1441   a —the z and y axes have different scaling. Coordinates of a polyline corresponding to the 1st interface  1441   a  are given in Table 1. Coordinates of another polyline corresponding to the 2nd interface  1441   b  have sign-opposite y-values and same z-values as the coordinates given in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 1 st  interface 1441a 
               
            
           
           
               
               
               
            
               
                 Point 
                 z (mm) 
                 y (mm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 0 
                 0 
               
               
                 2 
                 0 
                 4.45 
               
               
                 3 
                 −1.25 
                 4.45 
               
               
                 4 
                 −1.25 
                 4.50 
               
               
                   
               
            
           
         
       
     
     The input surface  1441  of the optical extractor  1440  can be bonded to an output end of the light guide of the light guide module  1401  (e.g., as described above in connection with  FIG. 7A ). In such case, an anti-reflective coating may be disposed between the output end of the light guide and optical extractor  1440 . If the material of the optical extractor  1440  is different from the material from which the light guide is formed, for example an index-matching layer may be disposed between the output end of the light guide and optical extractor  1440 . In other cases, the light guide and the optical extractor  1440  can be integrally formed. 
       FIG. 14C  is a cross-section in the (y-z) plane of the 1st backward output surface  1442   a . Coordinates of nodes for a fitted curve, e.g., a spline, corresponding to the first backward output surface  1442   a  are given in Table 2. Coordinates of another spline corresponding to the 2nd backward output surface  1442   b  have sign-opposite y-values and same z-values as the coordinates given in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 1 st  backward output surface 1442a 
               
            
           
           
               
               
               
            
               
                 Point 
                 z (mm) 
                 y (mm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 −1.25 
                 4.5 
               
               
                 2 
                 −1.11 
                 5.02 
               
               
                 3 
                 −0.94 
                 5.54 
               
               
                 4 
                 −0.72 
                 6.04 
               
               
                 5 
                 −0.44 
                 6.50 
               
               
                 6 
                 −0.09 
                 6.92 
               
               
                 7 
                 0.30 
                 7.29 
               
               
                 8 
                 0.72 
                 7.64 
               
               
                 9 
                 1.15 
                 7.97 
               
               
                 10 
                 1.56 
                 8.31 
               
               
                 11 
                 1.99 
                 8.65 
               
               
                 12 
                 2.34 
                 9.01 
               
               
                 13 
                 2.79 
                 9.39 
               
               
                 14 
                 3.19 
                 9.75 
               
               
                 15 
                 3.60 
                 10.11 
               
               
                 16 
                 4.03 
                 10.44 
               
               
                 17 
                 4.48 
                 10.74 
               
               
                 18 
                 4.95 
                 11.02 
               
               
                 19 
                 5.43 
                 11.27 
               
               
                 20 
                 5.92 
                 11.51 
               
               
                 21 
                 6.41 
                 11.74 
               
               
                 22 
                 6.91 
                 11.95 
               
               
                 23 
                 7.43 
                 12.10 
               
               
                 24 
                 7.97 
                 12.15 
               
               
                 25 
                 8.51 
                 12.11 
               
               
                 26 
                 9.05 
                 12.00 
               
               
                 27 
                 9.57 
                 11.87 
               
               
                 28 
                 10.09 
                 11.71 
               
               
                 29 
                 10.60 
                 11.54 
               
               
                 30 
                 11.11 
                 11.35 
               
               
                 31 
                 11.62 
                 11.16 
               
               
                   
               
            
           
         
       
     
     Here, the first/second backward output surface  1442   a / 1442   b  of the optical extractor  1440  is convex and, along with the first/second redirecting surface  1444   a / 1444   b  and a reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″, plays a major role in determining the luminance uniformity across the first/second tertiary reflector. Note that point  31  of the first/second backward output surface  1442   a / 1442   b  corresponds to the edge  1446   a / 1446   b  where the first/second backward output surface intersects the first/second forward output surface  1443   a / 1443   b . In some implementations, the first/second backward output surface  1442   a / 1442   b  is uncoated. In other implementations, an anti-reflective coating may be provided on the first/second backward output surface  1442   a / 1442   b  such that light reflected by the first/second redirecting surface  1444   a / 1444   b  can transmit with minimal back reflection. In other implementations, the first/second backward output surface  1442   a / 1442   b  is coated with a diffusive coating (e.g., BrightView M PRO5™ or BrightView M PR10™). In such cases, the light reflected by the first/second redirecting surface  1444   a / 1444   b  can diffuse upon transmission through the first/second backward output surface  1442   a / 1442   b.    
       FIG. 14D  is a cross-section in the (y-z) plane of the 1st forward output surface  1443   a . Coordinates of a polyline corresponding to the first forward output surface  1443   a  are given in Table 3. Coordinates of another polyline corresponding to the 2nd forward output surface  1443   a  have sign-opposite y-values and same z-values as the coordinates given in Table 3. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 1 st  forward output surface 1443a 
               
            
           
           
               
               
               
            
               
                 Point 
                 z (mm) 
                 y (mm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 11.62 
                 11.16 
               
               
                 2 
                 11.62 
                 7.97 
               
               
                   
               
            
           
         
       
     
     Here, the first/second forward output surface  1443   a / 1443   b  of the optical extractor  1440  is flat (or has a curvature that varies around zero). Note that point  1  of the first/second forward output surface  1443   a / 1443   b  corresponds to the edge  1446   a / 1446   b  where the first/second forward output surface intersects the first/second backward output surface  1442   a / 1442   b ; point  2  of the first/second forward output surface  1443   a / 1443   b  corresponds to the vertex  1447   a / 1447   b  where the first/second forward output surface intersects the first/second redirecting surface  1444   a / 1444   b . In some implementations, the first/second forward output surface  1443   a / 1443   b  is uncoated. In other implementations, an anti-reflective coating may be provided on the first/second forward output surface  1443   a / 1443   b  such that guided light provided through the input surface  1441  that reaches the first/second forward output surface can transmit there through with minimal back reflection. In other implementations, the first/second forward output surface  1443   a / 1443   b  is coated with a diffusive coating (e.g., BrightView M PRO5™ or BrightView M PR10™). In such cases, guided light provided through the input surface  1441  that reaches the first/second forward output surface  1443   a / 1443   b  can diffuse upon transmission there through. 
       FIG. 14E  is a cross-section in the (y-z) plane of the 1st redirecting surface  1444   a . Coordinates of nodes for a fitted curve, e.g., a spline, corresponding to the first redirecting surface  1444   a  are given in Table 4. Coordinates of another spline corresponding to the 2nd redirecting surface  1444   b  have sign-opposite y-values and same z-values as the coordinates given in Table 4. 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 1 st  redirecting surface 1444a 
               
            
           
           
               
               
               
            
               
                 Point 
                 z (mm) 
                 y (mm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 11.62 
                 7.97 
               
               
                 2 
                 11.35 
                 7.62 
               
               
                 3 
                 11.09 
                 7.28 
               
               
                 4 
                 10.82 
                 6.93 
               
               
                 5 
                 10.56 
                 6.58 
               
               
                 6 
                 10.29 
                 6.23 
               
               
                 7 
                 10.03 
                 5.88 
               
               
                 8 
                 9.78 
                 5.52 
               
               
                 9 
                 9.53 
                 5.17 
               
               
                 10 
                 9.27 
                 4.81 
               
               
                 11 
                 9.02 
                 4.45 
               
               
                 12 
                 8.76 
                 4.10 
               
               
                 13 
                 8.49 
                 3.76 
               
               
                 14 
                 8.23 
                 3.41 
               
               
                 15 
                 7.96 
                 3.06 
               
               
                 16 
                 7.71 
                 2.70 
               
               
                 17 
                 7.49 
                 2.32 
               
               
                 18 
                 7.29 
                 1.94 
               
               
                 19 
                 7.05 
                 1.57 
               
               
                 20 
                 6.81 
                 1.20 
               
               
                 21 
                 6.60 
                 0.82 
               
               
                   
               
            
           
         
       
     
     Here, the first/second redirecting surface  1444   a / 1444   b  of the optical extractor  1440  is flat (i.e., has a curvature that varies around zero) or it is concave and, along with the first/second backward output surface  1442   a / 1442   b  and a reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″, plays a major role in determining the luminance uniformity across the first/second tertiary reflector. Note that point  1  of the first/second redirecting surface  1444   a / 1444   b  corresponds to the vertex  1447   a / 1447   b  where the first/second redirecting surface intersects the first/second forward output surface  1443   a / 1443   b . In some implementations, the first/second redirecting surface  1444   a / 1444   b  is uncoated. In such cases, guided light from the input surface  1441  that impinges on the first/second redirecting surface  1444   a / 1444   b  at angles beyond a critical angle θ=arcsine(1/n) relative to the respective surface normal reflects off the first/second redirecting surface via total internal reflection (TIR) towards the first/second backward output surface  1442   a / 1442   b . In other implementations, the first/second redirecting surface  1444   a / 1444   b  is coated with a reflective coating. In such cases, guided light from the input surface  1441  that impinges on the first/second redirecting surface  1444   a / 1444   b  reflects off via specular reflection or diffuse reflection or a combination thereof towards the first/second backward output surface  1442   a / 1442   b.    
       FIG. 14F  is a cross-section in the (y-z) plane of a portion  1445   a  of the third forward output surface  1445 . Coordinates of nodes for a fitted curve, e.g., a spline, corresponding to the portion  1445   a  of the third forward output surface  1445  are given in Table 5. Coordinates of another spline corresponding to portion  1445   b  of the third forward output surface  1445  have sign-opposite y-values and same z-values as the coordinates given in Table 5. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 portion 1445a of third forward output surface 1445 
               
            
           
           
               
               
               
            
               
                 Point 
                 z (mm) 
                 y (mm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 6.60 
                 0.81 
               
               
                 2 
                 6.56 
                 0.74 
               
               
                 3 
                 6.51 
                 0.66 
               
               
                 4 
                 6.46 
                 0.58 
               
               
                 5 
                 6.42 
                 0.50 
               
               
                 6 
                 6.37 
                 0.42 
               
               
                 7 
                 6.33 
                 0.34 
               
               
                 8 
                 6.30 
                 0.26 
               
               
                 9 
                 6.27 
                 0.17 
               
               
                 10 
                 6.26 
                 0.09 
               
               
                 11 
                 6.25 
                 0 
               
               
                   
               
            
           
         
       
     
     Here, the third forward output surface  1445  of the optical extractor  1440  is concave. Note that slope  1448   a  (and  1448   b —not shown in  FIG. 14A or 14F ) is continuous at the intersection of the portion  1445   a / 1445   b  of third forward output surface  1445  with the first/second redirecting surface  1444   a / 1444   b . In this manner, there are no vertices between the third forward output surface  1445  and the adjacent first and second redirecting surfaces  1444   a ,  1444   b . Also note that the third forward output surface  1445  intersects the z-axis with a slope parallel to the y-axis. In some implementations, the third forward output surface  1445  is uncoated. In other implementations, an anti-reflective coating may be provided on the third forward output surface  1445  such that guided light provided through the input surface  1441  that reaches the third forward output surface can transmit there through with minimal back reflection. In other implementations, the third forward output surface  1445  is coated with a diffusive coating (e.g., BrightView M PRO5™ or BrightView M PR10™). In such cases, guided light provided through the input surface  1441  that reaches the third forward output surface  1445  can diffuse upon transmission there through. 
     Note that a total depth of the optical extractor  1440  in the forward direction (e.g., along the z-axis) is less than 14 mm (or about 0.5″), and a total width of the optical extractor in an orthogonal direction (e.g., along the y-axis) is about 24 mm (or less than 1″). 
       FIG. 15  is a cross-section in the (y-z) plane of the reflective surface of the second tertiary reflector  1570 ″. Coordinates of nodes for a fitted curve, e.g., a spline, corresponding to the reflective surface of the second tertiary reflector  1570 ″ are given in Table 6. Coordinates of another spline corresponding to the reflective surface of the first tertiary reflector  1570 ′ have sign-opposite y-values and same z-values as the coordinates given in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 reflective surface of second tertiary reflector 1570″ 
               
            
           
           
               
               
               
            
               
                 Point 
                 y (mm) 
                 z (mm) 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 0 
                 0 
               
               
                 2 
                 9.5 
                 0 
               
               
                 3 
                 19.0 
                 0 
               
               
                 4 
                 28.5 
                 0 
               
               
                 5 
                 38.0 
                 0 
               
               
                 6 
                 47.5 
                 0 
               
               
                 7 
                 57.0 
                 0 
               
               
                 8 
                 66.5 
                 0 
               
               
                 9 
                 76.0 
                 0 
               
               
                 10 
                 85.5 
                 0 
               
               
                 11 
                 95.0 
                 0 
               
               
                 12 
                 104.5 
                 0 
               
               
                 13 
                 114.0 
                 0 
               
               
                 14 
                 123.5 
                 0 
               
               
                 15 
                 133.0 
                 0 
               
               
                 16 
                 142.5 
                 0 
               
               
                 17 
                 152.0 
                 −0.01 
               
               
                 18 
                 161.5 
                 0.41 
               
               
                 19 
                 171.0 
                 1.19 
               
               
                 20 
                 180.5 
                 2.49 
               
               
                 21 
                 190.0 
                 4.42 
               
               
                 22 
                 199.5 
                 7.03 
               
               
                 23 
                 209.0 
                 10.33 
               
               
                 24 
                 218.5 
                 14.27 
               
               
                 25 
                 228.0 
                 18.78 
               
               
                 26 
                 237.5 
                 23.77 
               
               
                 27 
                 247.0 
                 29.10 
               
               
                 28 
                 256.5 
                 34.67 
               
               
                 29 
                 266.0 
                 40.40 
               
               
                 30 
                 275.5 
                 46.28 
               
               
                 31 
                 285.0 
                 52.39 
               
               
                   
               
            
           
         
       
     
     Here, the reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″ is concave and, along with the first/second redirecting surface  1444   a / 1444   b  and the first/second backward output surface  1442   a / 1442   b  of the optical extractor  1440 , plays a major role in determining the luminance uniformity across the first/second tertiary reflector. In this embodiment of the first/second tertiary reflector  1570 ′/ 1570 ″ a portion of the reflective surface adjacent to the housing is flat and a remaining portion of the reflective surface that is remote from the housing  1402  is concave. The reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″ is coated with a reflective coating. In such cases, light from the first/second backward output surface  1442   a / 1442   b  of the optical extractor  1440  that impinges on the reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″ reflects off via specular reflection or diffuse reflection or a combination thereof towards the first/second backward output surface  1442   a / 1442   b . An example of diffusive coatings that can be used to cover the reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″ is WhiteOptics White 98 F16™ (high angle diffusive film). 
     Note that a sag in the forward direction (e.g., along the z-axis) of the first/second tertiary reflector  1570 ′/ 1570 ″ is less than 55 mm (or about 2″), and a span in an orthogonal direction (e.g., along the y-axis) of the first/second tertiary reflector is 285 mm (or about than 11″). The latter dimension of the first/second tertiary reflector  1570 ′/ 1570 ″ and a thickness (along the y-axis) of order less than 1″ for the housing  1402  that supports the light guide module  1401  and the first and second tertiary reflectors causes the lighting system  1300  to have a total span (along the y-axis) of 23-24″. The forward output surfaces  1443   a/b  of the extractor in this example are located at about 90% of the sag that is at z˜47 mm. The forward output surfaces  1443   a/b  of the extractor may be located between 70% to 95% of the sag, that is between about z˜36 mm to z 50 mm with varying effects on the uniform appearance of respective lighting systems. 
     The above-described combination of shapes and relative orientations of the first/second redirecting surface  1444   a / 1444   b  and the first/second backward output surface  1442   a / 1442   b  of the optical extractor  1440  and of the reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″ was used to design the lighting system  1300  for which a ratio of maximum luminance to minimum luminance across each of the tertiary reflectors  1570 ′,  1570 ″ is lower than 3:1, as shown above in connection with  FIG. 5C . 
     Moreover, (i) a choice of diffusive coatings applied on the transmissive first/second backward output surface  1442   a / 1442   b  of the optical extractor  1440  of the light guide module  1401  and reflective surface of the first/second tertiary reflector  1570 ′/ 1570 ″—which influences, at least in part, a total amount of indirect light visible by an observer in front of the lighting system  1300 —and (ii) another choice of diffusive coatings applied on the transmissive first/second forward output surface  1443   a / 1443   b  and third forward output surface  1445  of the optical extractor—which influences, at least in part, a total amount of direct light visible by the observer in front of the lighting system—were made to design the lighting system  1300  for which another ratio of maximum luminance to minimum luminance across each of the tertiary reflectors  1570 ′,  1570 ″ and the bottom side of the optical extractor is lower than 15:1, as shown above in connection with  FIG. 5C . 
     Other lighting systems that use a light guide module and only a single tertiary reflector also can be designed to satisfy specified luminance uniformities, as described below. 
       FIG. 16A  shows a side view of an example lighting system  1600  that includes a light guide module  1601  and a single tertiary reflector  1670 . Lighting system  1600  can be used as (a portion of) the lighting system  500 B described above, where the light guide module  1601  and the tertiary reflector  1670  correspond to either of the light guide modules  501 A,  501 B and reflector  516 , respectively. Solid state light sources, optical couplers and a light guide of the light guide module  1601  can be implemented like the corresponding components of the light guide module  201 * described above in connection with  FIG. 7B . An optical extractor  1640  of the light guide module  1601  lacks mirror symmetry relative to the optical axis of the light guide module  1601  (parallel to the z axis) and can be implemented as described below in connection with  FIG. 16B . A “front face” (referred to as a reflective surface) of the tertiary reflector  1670 , that faces the light guide module  1601 , can be implemented in a manner similar to the one described above in connection with  FIG. 16A , while a “rear face” can be implemented as a solid block or can have other forms/shapes. Note that while the plurality of solid state light sources and the optical couplers of the light guide module  1601  are housed within the housing  1602 , the light guide of light guide module protrudes from the housing to lower the optical extractor  1640  of light guide module by a distance D along the z-axis comparable to a sag of the tertiary reflector  1670  in the (y,z) plane. The light guide module  1601  and the tertiary reflector  1670  are elongated along the x-axis (e.g., as shown in  FIG. 7B ) and can have a length L of about 2′ or 4′, corresponding to the size of conventional fluorescent light luminaires. 
     In this implementation, output surfaces of the optical extractor  1640  of the light guide module  1601 , and the reflective surface of the tertiary reflector  1670  are shaped and arranged with respect to one other such that the tertiary reflector  1670  appears to be uniformly lit when “viewed” by plant  502  associated with the lighting system  500 B implemented as  1600  from directly in front, and along an optical axis, of the optical extractor. For example, a ratio of maximum luminance to minimum luminance across the tertiary reflector  1670  can be lower than 5:1, 4:1 or 3:1. In this manner, the observer can view a fully lit surface of the tertiary reflector  1670  free of dark regions and/or hot spots. 
       FIG. 16B  is a cross-section in the (y-z) plane of an example implementation of the optical extractor  1640  of the light guide module  1601 . Note that the optical extractor  1640  is a single-sided optical extractor like the optical extractor  240 * described above in connection with  FIG. 7B . The optical extractor  1640  is formed from a solid material (with refractive index n&gt;1). For example, the material can be glass with a refractive index of about 1.5. As another example, the material can be plastic with a refractive index of about 1.5-1.6. In this implementation, the optical extractor  1640  includes an input surface  1641  centered on the optical axis of the light guide (here, the z-axis); a forward output surface  1643  opposing the input surface  1641 ; a backward output surface  1642  extending from the input surface  1641  to the forward output surface  1643 ; and a redirecting surface  1644  extending from the input surface  1641  to the forward output surface  1643  and opposing the backward output surface  1642 . Note that the backward output surface  1642  intersects the forward output surface  1643  at edge  1646 . Additionally, redirecting surface  1644  intersects the forward output surface  1643  at vertex  1647 . 
     The input surface  1641  of the optical extractor  1640  can be bonded to an output end of the light guide of the light guide module  1601  (e.g., as described above in connection with  FIG. 7B ). In such case, an anti-reflective coating may be disposed between the output end of the light guide and optical extractor  1640 . The light guide and the optical extractor  1640  can be integrally or separately formed, for example. If the optical extractor  1640  and the light guide are formed as separate components from like materials, an index matching layer may be disposed between the output end of the light guide and optical extractor  1640 . 
     The backward output surface  1642  of the optical extractor  1640  is convex and, along with the redirecting surface  1644  and the reflective surface of the tertiary reflector  1670 , plays a major role in determining the luminance uniformity across the tertiary reflector. In some implementations, the backward output surface  1642  is uncoated. In other implementations, an anti-reflective coating may be provided on the backward output surface  1642  such that light reflected by the redirecting surface  1644  can transmit with minimal back reflection. In other implementations, the backward output surface  1642  is coated with a diffusive coating (e.g., BrightView M PRO5™ or BrightView M PR10™). In such cases, the light reflected by the redirecting surface  1644  can diffuse upon transmission through the backward output surface  1642 . 
     The forward output surface  1643  of the optical extractor  1640  is flat (or has a curvature that varies around zero). In some implementations, the forward output surface  1643  is uncoated. In other implementations, an anti-reflective coating may be provided on the forward output surface  1643  such that guided light provided through the input surface  1641  that reaches the forward output surface can transmit there through with minimal back reflection. In other implementations, the forward output surface  1643  is coated with a diffusive coating (e.g., BrightView M PRO5™ or BrightView M PR10™). In such cases, guided light provided through the input surface  1641  that reaches the forward output surface  1643  can diffuse upon transmission there through. 
     The redirecting surface  1644  of the optical extractor  1640  has a complex shape and, along with the backward output surface  1642  and the reflective surface of the tertiary reflector  1670 , plays a major role in determining the luminance uniformity across the tertiary reflector. For example, the redirecting surface  1644  is flat (i.e., has a curvature that varies around zero) over a portion adjacent the forward output surface  1643  and convex over another portion adjacent the input surface  1641 . As another example, the redirecting surface  1644  has an inflection point, i.e., is concave over a portion adjacent the forward output surface  1643  and convex over another portion adjacent the input surface  1641 . In some implementations, the redirecting surface  1644  is uncoated. In such cases, guided light from the input surface  1641  that impinges on the redirecting surface  1644  at angles beyond a critical angle θ=arcsine(1/n) relative to the respective surface normal reflects off the first/second redirecting surface via total internal reflection (TIR) towards the backward output surface  1642 . In other implementations, the redirecting surface  1644  is coated with a reflective coating. In such cases, guided light from the input surface  1641  that impinges on the redirecting surface  1644  reflects off via specular reflection or diffuse reflection or a combination thereof towards the backward output surface  1642 . 
     Referring again to  FIG. 16A , the reflective surface of the tertiary reflector  1670  is concave and, along with the redirecting surface  1644  and the backward output surface  1642  of the optical extractor  1640 , plays a major role in determining the luminance uniformity across the tertiary reflector. The reflective surface of the tertiary reflector  1670  is coated with a reflective coating. In such cases, light from the backward output surface  1642  of the optical extractor  1640  that impinges on the reflective surface of the tertiary reflector  1670  reflects off via specular reflection or diffuse reflection or a combination thereof towards the first/second backward output surface  1442   a / 1442   b . An example of diffusive coating that can be used to cover the reflective surface of the tertiary reflector  1670  is WhiteOptics White 98 F16™ (high angle diffusive film). 
     The above-described combination of shapes and relative orientations of the redirecting surface  1644  and the backward output surface  1642  of the optical extractor  1640  and of the reflective surface of the tertiary reflector  1670  can be used to design the lighting system  1600  for which a ratio of maximum luminance to minimum luminance across the tertiary reflector  1670  is lower than a first specified uniformity ratio, e.g., 3:1. 
     Moreover, (i) a choice of diffusive coatings applied on the transmissive backward output surface  1642  of the optical extractor  1640  of the light guide module  1601  and the reflective surface of the tertiary reflector  1670 —which influences, at least in part, a total amount of indirect light visible by a plant  502  in front of the lighting system  500 B implemented as lighting system  1600 —and (ii) another choice of diffusive coatings applied on the transmissive forward output surface  1642  of the optical extractor—which influences, at least in part, a total amount of direct light visible by the observer in front of the lighting system—can be made to design the lighting system  1600  for which another ratio of maximum luminance to minimum luminance across the tertiary reflector  1670  and the bottom side of the optical extractor is lower than a second specified uniformity ratio, e.g., 15:1. 
     Samples of the lighting system  1300 , described above in connection with  FIGS. 13A-13B, 14A-14F and 15 , have been fabricated and experiments have been conducted to evaluate their respective performance. Some of these experiments are summarized above in connection with  FIG. 5C . 
     The preceding figures and accompanying description illustrate example methods, systems and devices for illumination. It will be understood that these methods, systems, and devices are for illustration purposes only and that the described or similar techniques may be performed at any appropriate time, including concurrently, individually, or in combination. In addition, many of the steps in these processes may take place simultaneously, concurrently, and/or in different orders than as shown. Moreover, the described methods/devices may use additional steps/parts, fewer steps/parts, and/or different steps/parts, as long as the methods/devices remain appropriate. 
     In other words, although this disclosure has been described in terms of certain aspects or implementations and generally associated methods, alterations and permutations of these aspects or implementations will be apparent to those skilled in the art. Accordingly, the above description of example implementations does not define or constrain this disclosure. Further implementations are described in the following claims.