Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
HARVESTING, TRANSMISSION, SPECTRAL MODIFICATION AND DELIVERY OF SUNLIGHT TO SHADED AREAS OF PLANTS
Document Type and Number:
WIPO Patent Application WO/2015/103310
Kind Code:
A1
Abstract:
A light harvester or collector collects solar radiation from an unshaded location adjacent a growing plant. The light harvester can be either imaging (e.g., parabolic reflectors) or non-imaging (e.g., compound parabolic concentrator). The concentrated solar radiation is projected into a light transmitter that conducts the light through the plant's outer canopy and into the inner canopy to a diffuser which disperses and reradiates the light into the inner canopy. The diffused light transforms a non-productive, potentially leafless zone of the plant into a productive zone so that more fruit can be produced per volume of land surface. The system can prevent transmission of infrared into the inner canopy so that the inner canopy zone is not heated and the amount of water lost to transpiration is reduced. The system can also modify other spectral components to affect plant development and to control pests and diseases.

Inventors:
FARKAS, Daniel L. (Los Angeles, California, California, US)
BOOTH, Nicholas (Covina, California, California, US)
RAVID, Nadav (Visalia, California, California, US)
Application Number:
US2014/072837
Publication Date:
July 09, 2015
Filing Date:
December 30, 2014
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
DISPERSOLAR, LLC (201 North Robertson Blvd, Suite 102Beverly Hills, California, 90211, US)
International Classes:
G02B19/00; A01G7/04; A01G9/24; F21V7/06
Foreign References:
US4969288A1990-11-13
US20110226311A12011-09-22
US20090021934A12009-01-22
EP0875724A21998-11-04
Attorney, Agent or Firm:
KIRCHANSKI, Stefan J. (Venable LLP, P.O. Box 34385Washington, DC, 20043-9998, US)
Download PDF:
Claims:
What is claimed is:

1. A device for modifying plant growth and development by supplying light energy comprising:

a light harvester for collecting and concentrating light energy;

a light transmitter for conducting concentrated light energy from the light harvester; and

a light diffuser for receiving concentrated light energy from the light transmitter and diffusing and radiating said light energy so as to illuminate a portion of a plant to thereby modify growth and development of the plant.

2. The device according to claim 1 further comprising at least one optical component which alters the spectral quality of the light energy transmitted to the plant.

3. The device according to claim 2, wherein the at least one optical component alters the spectral quality of the light energy by permitting photosynthetically active radiation to be transmitted to the plant while preventing infrared and/or near infrared radiation from being transmitted to the plant.

4. The device according to claim 2, wherein the at least one optical component alters the spectral quality of the light energy by altering the ultraviolet, blue, yellow, red or far-red wavelengths.

5. The device according to claim 1 , wherein the light concentrator comprises a non-imaging optical system.

6. The device according to claim 5, wherein the non-imaging optical system comprises a compound parabolic concentrator.

7. The device according to claim 6, wherein the compound parabolic concentrator has a rectangular geometry.

8. The device according to claim 6, wherein the compound parabolic concentrator has a circular geometry.

9. The device according to claim 1 , wherein the light transmitter is an internally reflecting pipe-like structure.

10. The device according to claim 1 , wherein the light transmitter is a fiber optic bundle.

11. The device according to claim 1 , wherein the light transmitter is an inverse periscope.

12. The device according to claim 1 , wherein the light diffuser comprises a concave mirror.

13. The device according to claim 1 , wherein the light diffuser comprises a flexible reflective surface.

14. The device according to claim 1 , wherein the light diffuser comprises a reflector formed as a trough.

15. The device according to claim 1 , wherein the light diffuser comprises a diffusing sphere.

16. A method for improving growth and productivity of a plant comprising the steps of:

providing a device comprising a light harvester which collects and concentrates light energy, a light transmitter and a light diffuser; placing the light diffuser in proximity to the plant;

disposing the light harvester so as to receive and collect light energy- conducting the collected light energy to the light transmitter; transmitting the collected light energy by means of the light transmitter to the light diffuser; and

broadcasting the transmitted light energy by means of the light diffuser so as to illuminate a portion of a plant to thereby modify growth and development of the plant.

17. The method according to claim 16, the light transmitter transmits collected light energy through the roof, floor or wall of a structure.

18. The method according to claim 16, wherein the light harvester collects solar light energy.

19. The method according to claim 18, wherein the light harvester collects light over the full course of the day without the need for solar tracking or adaptive systems.

20. The method according to claim 18, further comprising a step of repositioning the light harvester at intervals during a growing season so as to maintain optimal reception of solar energy.

21. The method according to claim 16, wherein the light diffuser is positioned within an inner canopy of the plant.

22. The method according to claim 16 further comprising a step of adjusting a quality of the collected light energy.

23. The method according to claim 22, wherein the step of adjusting the quality of the collected light energy comprises eliminating some or all of the near infrared and/or infrared wavelengths from the collected light energy.

24. The method according to claim 22, wherein the step of adjusting the quality of the collected light energy comprises supplementing the collected light energy with light from a different light source.

25. The method according to claim 22, wherein the step of adjusting the quality of the collected light energy comprises altering the ultraviolet, blue, yellow, red or far-red wavelengths.

26. The method according to claim 25, wherein altering the ultraviolet, blue, yellow red or far-red wavelengths results in pest and disease control.

Description:
Harvesting, Transmission, Spectral Modification and Delivery of Sunlight to Shaded Areas of Plants

Cross-reference to Prior Applications

[0001] The present invention is based on and claims priority from U.S.

Provisional Patent No. 61/922,317 filed on 31 December 2013.

U.S. Government Support

[0002] Not Applicable

Background of the Invention

Field of the Invention

[0003] This invention relates to a device for improving the growth and productivity of plants by harvesting, tunneling, modifying and delivering light into the shaded areas of plants.

Description of the Background

[0004] It is well known that plant development including growth, flowering and fruit production is dependent upon and is regulated by light energy. Solar radiation provides the energy for photosynthesis, the process by which atmospheric carbon is "fixed" into sugar molecules thereby providing the basic chemical building blocks for green plants as well as essentially all life on Earth. In addition, light is involved in the natural regulation of how and where the photosynthetic products are used within the plant and in the regulation of all photomorphogenetic and photoperiodic related processes. Plants can sense the quality (i.e., color), quantity and direction of light and use such information as signals to optimize their growth and development. This includes various "blue light" responses which may depend on UVA and UVB ultraviolet wavelengths as well as traditional "blue" wavelengths. These regulatory processes involve the combined action of several photoreceptor systems, which are responsible for the detection of specific parts of the sunlight spectrum, including far- red (FR) and red (R) light, blue light, and ultra violet (UV) light. The activated photoreceptors initiate signal transduction pathways, which culminate in morphologic and developmental processes (Warrington and Mitchell, 41 ; Briggs and Lin, 12; Kasperbauer, 23). The photosynthetically active radiation (PAR) ranges between 400-700 nm, because chlorophyll-protein complexes within the chloroplasts absorb the blue as well as the red part of the light spectrum. However, chlorophyll absorbs little of the green part of the spectrum which, of course, is why photosynthetic plants generally appear green in color.

[0005] Generally, low-to-medium light intensities are sufficient to drive photomorphogenetic and photoperiodic processes, while for photosynthesis the total amount of sunlight energy is a major factor dictating plant productivity. Light is often the limiting factor for agricultural production even in sunny climates. The more light intercepted by leaves of agricultural crops, the higher the productivity of those crops. In other words, the photosynthetic capacity of plants is often not saturated by available solar energy. Generally, the plant's chloroplasts adjust to the amount of available solar energy. Photosynthesis of chloroplasts in leaves exposed to maximum levels of light will saturate only at high light fluxes. However, all of the leaves of a plant cannot all be exposed to maximum solar radiation because the leaves are arranged to form a "canopy" in which there will be minimal mutual shading by the outer leaves. Some of the light, mostly the scattered part, passes between the outer leaves to be absorbed by the inner leaves. These leaves generally receive lower levels of solar radiation and will saturate at light fluxes insufficient to saturate the outer leaves because their chloroplasts adapt to low light conditions so as to saturate at lower light fluxes.

[0006] Similarly, where plants are growing close together and shade each other, the shaded leaves will become adapted to saturate at a lower light fluence. Thus, there is excess photosynthetic capacity in the plants, and if added light can be supplied to the shaded leaves, overall productivity will increase. The spacing between individual plants significantly controls the amount of effective light reaching different parts of the plant. If the individual plants are far apart, there will be more effective irradiation of plant tissue. This may result in improved growth and productivity, but if the individual plants are too far apart, there will be no gain on a unit area basis because significant amounts of solar radiation will not be intercepted by plants. Similarly, improving irradiation of plant tissue by pruning may not have the overall benefits expected because the amount of photosynthetically active plant tissue has been decreased. [0007] Because of the efficient light absorption by chlorophyll, the light that passes through the foliage of the outer canopy arrives at the inner canopy both too low in intensity and with the wrong spectral composition. Because blue and red are preferentially absorbed by the outer canopy, mostly green light is transmitted into the inner canopy. However, green light is of little use in driving photosynthesis and as a result, fruit production, which requires a significant input of photosynthate is restricted to the external canopy. Because leaves deep within the inner parts of the canopy are unable to maintain effective levels of photosynthesis, these leaves senesce, the inner part of the canopy loses foliage and becomes non-productive. In citrus trees, for example, the productive leaf layer is estimated to be only about 100 cm deep (33). All the rest of the tree's crown is a non-productive volume that keeps increasing as the tree grows larger.

[0008] It is also known that scattered (diffused) natural light often has advantages over direct solar radiation because it partially penetrates between the leaves of the outer canopy, thereby arriving at the inner canopy essentially spectrally unmodified. In sunny climates, the outer, sun-exposed plant canopy might suffer from excessive solar radiation, which can damage (photodamage) the plant tissues and can be inhibitory (photoinhibition). That is one of the reasons for the use of horticultural "shade" cloth in such climates.

[0009] Plant pests (largely insects and arachnids) as well as fungal and bacterial diseases are also known to respond to the intensity, spectral quality and direction of sunlight. They mostly respond to the ultraviolet (UVA and UVB), blue and yellow spectral regions (2, 9). Thus, pest and disease control might be achieved by light quality and quantity manipulations.

[0010] Many horticultural and agricultural practices that have been developed through the ages have a significant effect on light interception by agricultural crops, even though in some cases this effect was not originally recognized or understood. Many of these practices are relatively inefficient and expensive due to their high labor requirements. Such practices include pruning, training and plant spacing. It is generally thought that pruning is effective because it redirects the plants growth energy and eliminates weak and/or poorly placed branches. However, in many cases (e.g., hedging, topping and removing major branches) the pruning involves the removal of vital parts of the tree. This is particularly true with "summer or green pruning" practices which remove shading foliage. These practices are both energy-wasteful (because the plant and the grower had invested a lot of energy, water and other inputs into the growth of the removed parts), and labor costly processes. One is essentially forced to sacrifice vital parts of the tree to achieve improved production by the remaining vital parts

[001 1] Plant and tree growth is largely controlled by the plant's search for light.

Numerous pruning practices were developed to enable maximal light interception. Pruning methods include mechanical topping and hedging for height and shape control, as well as manual selective removal of dead wood, weak branches, and often also vital branches. Pruning remains one of the main tools, at present, to bring light to both the internal and external parts of the canopy. Particularly in fruit trees pruning controls the position of fruit buds and prevents them from moving farther and farther from the main trunk. Pruning has a major effect on the penetration of solar energy. By removing weak and crossing branches pruning opens up the structure of the plant and allows effective (PAR) light to reach closer to the main stem. Similarly, training (such as the process of espaliering a tree or vine) positions the branches so that the leaves of one branch do not shade the leaves of another branch.

[0012] Flowering is induced by photomorphogenetic processes, and is thus light- dependent. The light regime in the inner-most-shaded canopy is often of too low fluence, and/or inadequate spectral composition for inducing flowering (flowering and other developmental processes respond to the ratio of red to far-red (near infrared) wavelengths. Physiological processes, such as pollination, fertilization, fruit- set and fruit development, all utterly depend on obtaining adequate carbohydrates from adjacent leaves. The carbohydrates required for fruit development cannot be adequately translocated from remote leaves. Thus, even if some flowering does occur in the inner canopy, the limited photosynthetic activity of the shaded foliage does not suffice for proper fruit development.

[0013] In some crops (e.g., peaches, table and wine grapes) green pruning of part of the foliage is practiced by growers a few weeks prior harvest for increasing light penetration, thereby significantly increasing fruit color and aromatic compounds— i.e., fruit quality. It is known that shading has particularly negative effects on fruit coloration. Fruit color development is controlled by light via several different routes. Light is the trigger for the metabolic pathways of pigment biosynthesis. Light also provides (via photosynthesis in the leaves adjacent to the fruit) the sugars that bind and stabilize the anthocyanin pigments in the colored tissue. Because, the three dimensional structure of fruit creates self-shading. The shaded side of the fruit does not develop optimum color. The biosynthesis of aromatic compounds in the fruit skin is similarly dependent on the exposure to sunlight. Both fruit coloration and aroma/flavor accumulation require light of relatively intense fluence.

[0014] There have been a number of modern cultural practices that seek to redistribute the amount of solar radiation without eliminating plant tissue. Covering the crop by light-scattering materials (glass, plastic film, photoselective translucent nets, reflective particle films, etc.; see, Glenn (14) and Glenn et al. (15)) is one way of ensuring that photosynthetically effective light reaches more of the plant body. Covering the soil with reflective films may reflect light into the interior portions of a plant's canopy. Supplemental artificial illumination (e.g., inter-crop LED illumination) is expensive both in energy to provide the illumination and capital to purchase the illuminating devices but may result in improvements in growth and yield. Genetic manipulation is another way to approach more efficient irradiation of the plant body. Breeding for more compact plants can have much the same effect as altering the spacing of plants, but a compact plant can be superior because it may pack a given leaf area into a smaller volume. Of course, excessively compact plants may exacerbate problems with self-shading. Plant volume and spacing of leaves can also be affected by grafting onto growth-regulating rootstocks and by application of growth-regulating agricultural chemicals.

[0015] The interception/collection of sunlight for useful purposes (mainly energy- related) is becoming a vibrant, mature field. Solar energy is collected to directly (e.g., photovoltaics) or indirectly (e.g., solar boilers) produce electricity. Solar energy is also collected to provide heat energy (e.g., solar water heaters). Strong competition in these areas has yielded advances in solar collector design and efficiency (including both cost-efficiency and overall functional efficiency). The current invention seeks to exploit these technologies and use collected light energy in new ways.

Summary of the Invention

[0016] Solar radiation is both ubiquitous and is the only agriculture resource that is free of charge. Improving the utilization of this resource for agricultural production is the goal of the present invention. To achieve enhanced plant growth modern solar collectors are used to collect, concentrate and redirect solar energy. The collected sunlight is then delivered to a (lower) sub-canopy/internal location in the chosen plant (i.e., tree, grape vine, etc.), thereby stimulating plant growth and development. Illuminating the inner, most shaded volume of plants/trees improves the physiological activity and the productivity of the otherwise non- or less- productive parts of the plant. The inner canopy portion of the plant receives insufficient solar energy; so that eventually the leaves there senesce and the inner volume becomes a leafless zone. When light is delivered to this zone before the leaves senesce, the zone retains healthy functional leaves and becomes productive. The entire volume of the plant body becomes productive, thus significantly increasing the yield from a given acreage.

[0017] The present invention provides a light harvester or collector to collect solar radiation from an unshaded location adjacent a growing plant. The light harvester is preferably placed alongside or above the growing plant. It will be appreciated that the light harvester can be placed in any convenient location. Furthermore, the number or light harvesters per plant depends on the growing conditions and size of the plant (several plants per system or one, two, three or more systems per plant). The light harvester can be either imaging (e.g., parabolic reflectors) or non-imaging (e.g., compound parabolic concentrator). The non-imaging system is preferred for its simplicity, low cost and ease of construction. The concentrated solar radiation is projected into a light transmitter (either an internally reflective light pipe, an optical arrangement much like a periscope, or a bundle of optical fibers) that conducts the light through the plant's outer canopy and into the inner canopy. The conducted light enters a diffuser, which disperses and reradiates the light into the inner canopy. The diffused light provides light to drive photosynthesis as well as light to influence multiple photomorphogenetic systems. The result is that a non-productive, potentially leafless zone of the plant is transformed into a productive zone. Thus, more fruit can be produced per volume of land surface and more carbon dioxide can be sequestered in plant material (improved carbon footprint). Also, by providing light to developing fruit the quality of the fruit can be altered and improved.

[0018] It will further be appreciated that supplemental light at the proper location on a plant results in increased productivity with enhanced induction and initiation of buds resulting in increased vegetative as well as floral (fruit) growth. The enhanced production of photosynthate results in reduced bud/fruit drop and improved flower/fruit quality including better color, improved flavor (sugar/acid ratio as well as aroma/taste), improved storage characteristics and improved nutritional value. The added light (particularly if spectral modification is employed) results in growth regulation (shape of plant, etc.) without application of growth regulating chemicals. In addition, controlling the quantity and quality of light can result in reduction of plant diseases and pests without an increase in pesticide chemical application.

[0019] Because the optical systems employed can be used to prevent the transmission of infrared and near infrared radiation into the inner canopy, the inner canopy zone is not heated and the amount of water lost to transpiration is less than would be anticipated considering the increased growth in the inner canopy zone. However, when the invention is used early in the growing season, it is simple to alter the optical system to allow infrared transmission and provide growth-promoting warmth to the inner canopy. Similar optical systems can be used to change the relative amount of light at different wavelengths, thereby having a photomorphogenic effect on plant growth and development. Rather than rejecting certain wavelengths, LEDs or similar efficient light sources can be used to supplement certain wavelengths, thus attaining photomorphogenic effects.

[0020] The inventive system can be used in any plant-growing situation. While the examples provided are primarily directed towards vineyards and orchards, the system is also applicable to nurseries, all types of field crops, landscaping, home gardens as well as greenhouses of all types, lath houses, shade houses and any other plant growing structure. In a closed building (e.g., an urban garden), the light collectors can be placed on the roof and light is "piped" into the growing area. In that case, the system provides essentially all of the light. In any of the applications some or all of the light can be supplied by artificial illumination (such as LEDs). The advantage of using the system with artificial light sources is that the sources (LEDs or metal halide lamps, for example) can be located where they will be unaffected by the water, etc. inherent in agriculture which water is likely to cause electrical failures.

Description of the Figures

[0021] FIGURE 1 shows a diagrammatic overview of one embodiment of the invention;

[0022] FIGURE 2 shows a diagrammatic representation of a simple design that is a predecessor to the current CPC design;

[0023] FIGURE 3 shows the coordinate system used in equations describing

CPC design;

[0024] FIGURE 4 shows the angle φ used in parametric equations describing the

CPC;

[0025] FIGURE 5 shows the common descriptive terms used for the parabolic

CPC;

[0026] FIGURE 6 shows several CPC designs with varying angles of collection;

[0027] FIGURE 7 is a diagram of the CPC showing heat rejection

[0028] FIGURE 8 shows an alternate rectangular embodiment of non-imaging light collectors;

[0029] FIGURE 9 shows a diagram of an imaging light harvester based on parabolic mirrors;

[0030] Fig. 10 shows a transmitter/conveyer;

[0031] FIGURE 1 1 a is convex-concave mirror combination used as a diffuser for citrus and similar tree applications;

[0032] FIGURE 1 1 b shows a ray diagram of the device of Fig. 10a;

[0033] FIGURE 12 shows a "hammock linear diffuser made from flexible reflective material;

[0034] FIGURE 13 shows a trough diffuser constructed from rigid reflective materials; Detailed Description of the Invention

[0035] The following description is provided to enable any person skilled in the art to make and use the invention and sets forth the best modes contemplated by the inventor of carrying out his invention. Various modifications, however, will remain readily apparent to those skilled in the art, since the general principles of the present invention have been defined herein specifically to provide a system to collect solar energy and deliver it to strategic locations within the canopy of a growing plant.

[0036] Fig. 1 shows a general overview of the components used in one embodiment of the present invention. The diagrammatic arrow 50 represents the daily movement of the sun relative to the harvester/collector component, a compound parabolic concentrator (CPC) reflective element 56. The lines 54 represent the acceptance limits of the CPC, and these limits define the acceptance angle 52. The CPC 56 transmits light through a light pipe 58 which penetrates the canopy 60 and projects the light onto a disperser 64 which radiates the dispersed light 62 into the inner part of the canopy. These components will now be described in more detail.

[0037] The system harvests the natural sunlight from above/beside the plant/tree/vine/bush, and transmits it through the outer, productive canopy of plant/tree, thereby delivering and scattering it throughout the inner/lower, most shaded, non-productive portions of the foliage. A direct, reflective design for this is preferred (e.g., light beams directed by mirrors, prisms, etc.). The device is composed of three principal parts. The first component is a light harvester/collector/concentrator (generally a wide angle/ compound parabolic collector, with or without a condenser system) and designed to be disposed above, or adjacent to the plants/trees.

[0038] The light harvester can comprise a number of forms, each of which could be applicable depending upon the end users agriculture needs and general environment. A preferred embodiment of the harvester design employs a reflective element known as a CPC (compound parabolic concentrator). This design has many advantages including reducing manufacturing cost, minimizing heat buildup within the system and easing installation due to its tolerance for misalignment with the sun. [0039] The light collection and dispersal systems described herein are all based on the principle of non-imaging optics. The CPC design is an evolution of a primitive form of non-imaging concentrator, the light cone or cone concentrator, has been used for many years (see, e.g., Holter et al., 21 ; Senthilkumar and Yasodha, 36). Fig. 2 shows the principle. If the cone has semi-angle γ and if θ/ ' is the extreme input angle, then the ray indicated will just pass after one reflection if 2γ = (π/2) - θ/ ' . It is easy to arrive at an expression for the length of the cone for a given entry aperture diameter. Also, it is easy to see that some other rays incident at angle θ/ ' such as the one indicated by the double arrow, will be turned back by the cone. If we use a longer cone with a larger number of reflections, we still find some rays at angle θ/ ' being turned back. Clearly, the cone is far from being an ideal concentrator. Williamson (42) and Witte (49) attempted some analysis of the cone concentrator but both restricted this treatment to meridian rays.

[0040] Descriptions of this type of optical device appeared in the literature in the mid-1960s in widely different contexts. Baranov and Melnikov (6) described the same principle in three-dimensional geometry, and Baranov (4) suggested three dimensional CPCs for solar energy collection. Baranov (3; 5) obtained Soviet patents on several CPC configurations. Axially symmetric CPCs were described by Ploke (30), with generalizations to designs incorporating refracting elements in addition to the light-guiding reflecting wall. Ploke (31 ) obtained a German patent for various photometric applications. The CPC structure was described as a collector for light from Cerenkov counters by Hinterberger and Winston (19, 20).

[0041] In other applications to light collection for applications in high-energy physics, Hinterberger and Winston (19, 20) noted the limitation to 1/sin29 of the attainable concentration, but it was not until sometime later that the theory was given explicitly (Winston, 43). In the latter publication the author derived the generalized etendue and showed how the CPC approaches closely to the theoretical maximum concentration.

[0042] The CPC in two-dimensional geometry was described by Winston (44).

Further elaborations may be found in Winston and Hinterberger (48) and Rabl and Winston (32). Applications of the CPC in 3D form to infrared collection (Harper et al., 16) and to retinal structure (Baylor and Fettiplace, 8) have also been described. The general principles of CPC design in 2D geometry are given in a number of U.S. patents (Winston, 45, 46, 47).

[0043] Fig. 3 illustrates the r— z coordinate system used in mathematical description of the CPC. Whereas Fig. 4 shows the definition of angle φ used in CPC parametric equations, and Fig. 5 illustrates the descriptive terms used with the parabolic CPC to relate the various angles to the focal point of the parabola. Fig. 6 shows diagrams of four different CPC devices with angles of acceptance ranging from 10 degrees to 25 degrees (top to bottom). The diagrams are all to the same scale and all have the same size exit apertures and illustrate how the dimension change according to angle of acceptance.

[0044] The CPC light collecting design is a highly efficient way of collecting light and is utilized in nature in many optical systems including the cones of the human retina. Utilizing a CPC for the collection of sunlight delivers a number of advantages to the system.

[0045] The first advantage of the CPC collector geometry is that it possesses a large acceptance angle or numerical aperture meaning that a fixed unit can effectively collect sunlight over a wide range of angles of incidence as the sun processes overhead during the course of the day. A typical CPC with a 45 degree acceptance angle will be able to effectively collect sunlight for 6-8 hours; hence an active tracking subsystem is not required, reducing system complexity and cost. It is also possible to use two or more CPC units with different orientations to further extend the period of maximum light collection. The straightforward design and ability to use low cost materials allow for easy industrial mass production meaning that the system could be used at the density of at least one unit per tree. The large acceptance angle also allows device setup and use by non-experts, as alignment with the sun is not critical, and means once installed the collection efficiency is not sensitive to the change in position of the sun as the seasons change.

[0046] The second advantage is that the CPC design has over an imaging optical system that must track the sun to collect sufficient light is that there is much less heat generated within the device. Imaging system designs generally require fiber optics to allow for the movement of the tracking head unit. For fiber optics to efficiently transmit the light, the collected light must be concentrated into a very small area thereby causing immense heat stress on device component parts. Such systems generally require high-cost exotic materials to prevent equipment failure.

[0047] The third advantage is the ability to vastly reduce the amount of heat entering the system and thus reduce heat stress on plants and, as a consequence, reduce plant water consumption. To enable the delivery of 'cool' light to the inner canopy the system will employ filters, such as those used in energy efficient low-E glass, at the entrance aperture of the collector as shown Fig. 7 where incoming sunlight 70 strikes a filter (dichroic) 74 covering the entry to the CPC 78. The infrared radiation 72 is rejected whereas the PAR 76 is transmitted into the CPC 78. A bonus of the overall modularity of the system is that these filters can be designed to be easily detachable. Hence, at temperate latitudes these filters could be removed in the early growing season when overall temperatures are low and the additional warmth from the collected light would be a benefit to the plants and replaced in the summer months to reduce heat stress. The fourth advantage is that imaging systems work only for clear, unobstructed sunlight, in contrast, the CPC design collects diffuse light as well as direct sunlight so that even on cloudy days extra light will be transferred to the inner canopy.

[0048] It will be appreciated that the light harvester should be located so as not to significantly shade the outer parts of the plant. Depending on the spacing of the plants, the light harvester can be placed between the rows or between the individual plants (e.g., trees) in the row, and, via the shape of the diffuser element, able to deliver light to multiple (e.g. four) trees simultaneously. To avoid shading the outer parts of the plant, the light harvester can be placed either lower than the canopy or significantly above it. If the harvester is placed significantly above the canopy, light diffraction and seasonal-diurnal movement of the harvester's shadow will avoid any significant shading of the plants. If the light harvester is placed in a low position, it will be unable to significantly shade the plants; however, the plants may significantly shade the harvester unless they are widely spaced. This militates in favor of a high location for the harvester. Because of the diffraction- movement effect mentioned above, the harvester can also be located at a distance more or less directly above the plant. The harvester will utilize the light transfer pipe as a base structural element to hold it in position. This support can be integrated with the plant itself or already existing supports (e.g., grape vine trellises).

[0049] Other embodiments of a non-imaging light harvester include geometries such as the rectangular version of Fig. 8. Harvesters with such four-fold symmetry and flat reflective surfaces offer less optical efficiency than the round CPC design. However potential advantages in modularity and the ability to flat pack (i.e., collapsibility) for transportation allow for reduced production costs. Other implementations of flat-plane designs will be obvious to those skilled in the art.

[0050] The non-imaging inventive devices described above are generally passive and operate without an additional energy source. It will be appreciated that with the exception of equatorial regions, the position of the sun in the sky changes seasonally. Therefore, for maximum efficiency solar collectors must be constantly adjusted to track the sun's position. Tracking the sun on a diurnal/continuous basis is complex and expensive due to the high cost of the technology needed. However, the seasonal changes in solar position are relatively slow; therefore, adjustment on a weekly/monthly basis by changing the collector's angle in a small number of fixed increments yields most of the advantages of daily tracking at a very low cost. A simple manual adjustment interface is provided to keep the collectors aimed in spite of seasonal change in solar position.

[0051] Fig. 9 shows an alternate embodiment on the light harvester system is based around an imaging optical system consisting of a pair of a wide angle/parabolic mirrors arranged to condense collected light into a narrow bodies transfer device such as a bundle of fibers. In this embodiment the larger diameter lower parabola 100 collects light rays 96 and reflects it onto a smaller diameter secondary parabola 102 which creates a collimated beam. This beam is directed through an aperture 104 located at the center of the larger parabola into the transfer tube (not shown). The dual parabola harvester design has optimal collection while aligned directly with the sun and efficiency falls sharply as the sun progresses across the sky throughout the day. Therefore such a system will need a mechanism to automatically move the dish to track the sun. Solar tracking technology is very mature and control mechanisms to enable its use are readily available. The additional complexity and cost of these elements can be mitigated by delivering light to a given threshold number of trees per base station. The smaller mirror 102 can advantageously by a "cold mirror" which has filter capabilities. As shown in the diagram some light (near infrared) passes through the mirror 102 and so is not concentrated and transmitted into the canopy.

[0052] In addition to providing additional light for photosynthesis, the invention also allows ready adjustment of light quality. Light collected and transmitted to the lower/inner part of a plant can be modified before delivery to within/underneath to the canopy, by altering its wavelength (using optical filtration), diffusivity (by appropriately chosen diffusers), intensity (by partial obturation, if and when appropriate) all of which have been found to positively modify crop yield or quality. Adjustment of the light quality can be achieved with filters (both band-pass and dichroic) and by adding light from a supplemental source such as LEDs.

[0053] Spectral optimization of light before re-delivery provides a number of advantages. Solar radiation provides heat energy as well as photosynthetic energy so that boosting the total solar irradiance to enhance photosynthesis can also result in thermal damage. It is possible to remove selected thermal components (NIR and IR) of the solar spectrum, thus avoiding over-heating the illuminated area beyond the naturally occurring microclimate. In addition, the delivered light can be wavelength-filtered to match the best known spectral signatures for productivity (Rajapakse and Shahak, 35; Shahak et al., 38, 39; Shahak, 37; Longstaff, 26), pest and disease regulation (Karpinski et al., 22; Ben-Yakir et al., 9; Antignus, 2), etc.

[0054] The second component of the invention is a transmitter/conveyer that attaches to the light harvester so as to convey or transmit the concentrated solar radiation. Although the drawings generally show a single light harvester per transmitter, there is no reason that a plurality of light harvesters cannot be operatively coupled to a single transmitter. Such a transmitter can be a purely reflective system constituting as an "inverse" periscope constructed from mirrors and/or prisms. Typically the transmitter is a rigid pipe with a reflective inner surface able to penetrate through the outer plant canopy or the cover of a glass or plastic greenhouse or net-house. Fig. 10 shows such device 98. The pipe is designed such that multiple sections 99 can easily be slotted together to customize the length depending on the application scenario. The transmitter will act as the support and main anchoring point for the system as a whole, attaching either to the plant directly or to infrastructure already present such as trellis systems. This component will have cross sectional symmetry to match that of the harvester unit to allow for most efficient light transfer.

[0055] For transmission purposes an open, internally reflective pipe is generally preferable. These can be made from plastics or aluminized cardboards that are readily recyclable and can even be selected to be biodegradable. The presently preferred plastic construction of the whole device will be entirely from UL 746C (f1 ) certified plastics able to withstand prolonged exposure to UV, water and high temperatures. One of the beneficial features of the present invention is that by stimulating photosynthesis, the invention actually reduces atmospheric greenhouse gases (carbon dioxide). Using recyclable materials can lead to an even smaller carbon footprint for the entire system.

[0056] Another embodiment of the transmitter subsystem is a dense bundle of flexible optical fibers in a flexible protective sheath that can be threaded through the outer plant canopy or the cover of a glass or plastic greenhouse or net-house. Optical fibers have previously been used to monitor penetration of light through plant canopy layers (Bauerle and Bowden, 7) but not to actively deliver light into plant canopies. For communication (i.e., data transmission) purposes optical fibers are generally formed from high purity glass so that signals can be transmitted for great distances without significant attenuation. For the present invention it is often more economical and ecological to use optical fibers made of plastic. Although plastic optical fibers (POF) show greater attenuation than glass fibers, plastic is readily recyclable and can even be selected to be biodegradable. The presently preferred plastic fibers are made from polyperfluorobutenylvinyl ether; these fibers have larger diameters than glass ones, high numerical apertures, and good properties such as high mechanical flexibility, low cost, low weight, etc. Importantly, progress has been made on the attenuation, which now can be easily brought down to less than 1 dB/meter which represents an insignificant loss considering that the fibers in the present invention will be typically no more than a couple of meters in length. One of the beneficial features of the present invention is that by stimulating photosynthesis, the invention actually reduces atmospheric greenhouse gases (carbon dioxide). Using recyclable plastic materials can lead to an even smaller carbon footprint for the system.

[0057] The third component of the system is a diffuser that is attached to the end of or positioned slightly below transmitter / conveyor opposite the light harvester. The job of the diffuser is essentially the reverse of the light harvester. Whereas the light harvester collects solar radiation from a relatively large area (the surface area of the harvester) and concentrates it into the smaller area of the transmitter (e.g., the hollow tube or fiber-optic bundle), the diffuser reverses this process and scatters the light around the inner canopy of the plant. The horticultural advantages of diffused light are well known (Sinclair et al. 40; Hemming et al., 18; Nissim-Levi et al., 28; Hemming, 17; Dueck et al., 13).

[0058] There are a number of designs for the diffuser to allow for customization of the system to various agricultural applications and plant geometries. For nonimaging systems the diffuser can consist of a combination of shaped diffusively reflecting surfaces. As shown in Figs. 1 1 a and 1 1 b a combination of a large concave mirror 90 and a smaller convex mirror 92 can spread the light rays 96 exiting the aperture 94 of a transfer tube 98. This spread beam is ideal for use in a tree inner canopy such as with a citrus tree. For plants in rows such as grape vines these surfaces can include shapes such as elongated hammock style reflectors of flexible reflective material such as aluminized Mylar are shown in Fig. 12. The flexible reflective Mylar (or similar material) 106 is supported by a wire frame 108. Straps (not shown) can be attached to the peripheral parts 1 10 of the wire frame to suspend the reflector/diffuser. Linear "troughs" made of rigid reflective materials as shown in Fig. 13. The trough has reflective surfaces - inner or outer depending on the mounting configuration. The unit can be suspended by wires to hang beneath plants or simply rested on the ground. Many other possible geometries will be apparent to those skilled in the art.

[0059] For imaging systems where light transfer is via a fiber optic system terminating the transmitter within a diffusing sphere such as an internally coated Mylar balloon or a translucent ball provides an effective diffuser. Depending on the shape of the plant the diffuser can be designed to diffuse light into a number of different three dimensional shapes. For example a conventional citrus tree having a rounded canopy would use a diffuser that projects a sphere or partial sphere of light. A single optical fiber transmitter can terminate in several diffusers arranged within the plant for the best coverage.

[0060] There are a number of additions or modifications to the three basic components. As already mentioned the light harvester can be equipped with various mechanical interfaces to allow it to be adjusted to follow the seasonal and/or diurnal changes in solar position. Modification of the spectrum of the transmitted light has also been mentioned above. For this purpose filter materials (either absorptive or interference/reflective) can be applied to the light harvester and/or diffuser. It is also possible to add filtering substances to the optical fibers themselves. For wavelengths (e.g., infrared) that are generally rejected, an optical device such as a prism, dichroic or grating can be used to reject these wavelengths so as not to heat any of the components. In some cases it could be beneficial to add supplementary light sources (e.g. LEDs) to the system to supply light in excess of that available from the sun and/or to augment certain wavelengths of light. This would be used where the economic benefits of the added light outweigh the energy costs. The additional light sources can be aimed into the Light Harvester, directly coupled to the Transmitter or disposed within the Diffuser.

[0061] The benefits for the users include increased plant productivity and fruit yield resulting from enhanced photosynthesis, and/or enhanced photo- morphogenetic activities such as flowering induction and bud initiation in the otherwise shaded, inactive parts of the canopy. Also, the supplementary irradiation provided by the invention can result in improved fruit quality: size, color, postharvest quality / storability / shelf life / nutritional value. Because the system makes the plant healthier, one sees improved pest and disease control— possibly achieved through spectral manipulation deterring pests and diseases, and/or enhancing plant resistance to biotic stresses (Karpinski et al., 22; Ben-Yakir et al., 10, 2014; Kong et al., 24). This results in reduced need for applications of agrochemicals such as pesticides, fungicides and plant growth regulators. Because the system is capable of providing PAR without thermal (near infrared (NIR) and infrared) radiation, there is less heating of the plant tissue resulting in a reduction of water use (improved water- use-efficiency). There can also be saving occasioned by lowered use of such traditional practices as pruning, training and use of light-scattering materials. The problem of determining optimum plant spacing is also reduced because the inventive system can be moved and rearranged to accommodate changes caused by plant growth. Finally, the amount and direction of a plant's growth can be controlled by the additional light supplied, and its spectrum, e.g. by reducing tree height for easier harvesting (without sacrificing per tree yield), or by achieving a certain shape— e.g., for decorative purposes (Warrington and Mitchell, 41 ; Mortensen and Moe, 27; Rajapakse et al., 34; Oren-Shamir et al., 29; Rajapakse and Shahak, 35; Aiga et al., 1 )-

[0062] The system is ideal for perennial crops although it can be used with almost any plant. It can advantageously be applied on individual trees in orchards. It can be used in small fruit "vineyards" (table grapes, wine grapes, kiwi fruit and berries) where horizontal light dispersion can be particularly valuable. It is also useful for protected cultivation of vegetables, ornamental crops, berries (blueberries, raspberries, blackberries, strawberries) and nurseries in greenhouses, net-houses, screen houses, plastic tunnels ("hoop" greenhouses), and "plant factories" (Kozai, 25). In these cases the invented devices will cross the construction roof. The number of units per house area can be readily adjusted according to the cultivated crop.

[0063] Use of prototype units provides some idea of how much light the system can readily harvest and deliver to a given location on the plant. PAR reading (μιηοΙ photons/m 2 /s) were made at mid-day in a citrus grove using a PAR meter (Apogee Instruments, Logan, UT) with the sensor face held sun-oriented (i.e., perpendicular to the sun's rays). Peak readings in a region without citrus trees were 2040-2060; peak readings between the rows of trees were 1920-1945; while peak readings within the inner canopy of the trees were only 8-15. The experimental light harvester was located at the outer canopy layer so it was partly shaded by adjacent trees. Nevertheless, the peak readings at the exit of the harvester were 1800-2500. Measurements within the canopy at a distance of approximately 150 cm from the exit of the light transmitter were 800-1000. (When the light harvester was placed in full, unobstructed sun light it delivered 8500-9500 photons/m 2 /s; the upper reading of the meter is 3000 so these figures were obtained by using a neutral density filter on the meter.)

[0064] Similarly, in a pistachio orchard, the reading between the rows was 1800- 1900, while the reading underneath the trees ranged from 40-350. This is because the canopy of a pistachio tree is less dense than that of a citrus tree. The shade regions receiving the output of the light harvester gave a reading of 2000-3000 as measured on the ground. In a table-grape vineyard the reading away from the vines was about 2000, while the reading beneath the trellis-grown vines was only 13-25. The exit from the light collector/transmitter gave a reading in excess of 3000. Using Mylar diffusers similar to those of Fig. 12 with the meter sensor located adjacent to the illuminated fruit clusters (with the sensor plane making an approximately 45 degree angle with the ground plane) gave a reading of 800-1045, which should be sufficient to significantly affect fruit maturation.

[0065] Of course, the devices can also be used in other forms for husbandry where light can have a beneficial effect even though photosynthesis may not be involved. Animal husbandry, particularly poultry cultivation, can be benefited by increased light. Aquiculture is also a natural use for the inventive devices.

References

1. Aiga et al.; US Patent No. 5,953,857 "Method for controlling plant growth" .

2. Antignus, Y. 2014 Management of Air-Borne Viruses by "Optical Barriers" in Protected Agriculture and Open-Field Crops. In Advances in Virus Research: (G. Loebenstein and N. Katis, editors), Vol. 90, pp. 1 -33, Burlington: Academic Press.

3. Baranov, V. K. 1965. Opt. Mekh. Prom. 6, 1-5.

4. Baranov, V. K. 1966. Geliotekhnika 2, 11-14 [English transl.: Parabolotoroidal mirrors as elements of solar energy concentrators. Appl. Sol. Energy 2, 9-12.].

5. Baranov, V. K. 1967. "Device for Restricting in One Plane the Angular Aperture of a

Pencil of Rays from a Light Source" (in Russian). Russian certificate of authorship 200530, published October 31 , 1967.

6. Baranov, V. K., and Melnikov, G. K. 1966. Study of the illumination characteristics of hollow focons. Sov. J. Opt. Technol. 33, 408-411.

7. Bauerle WL, Bowden JD 2004. A fiberoptic-based system for integrating

photosynthetically active radiation in plant canopies HortScience 39 (5): 1027-1029.

8. Baylor, D. A., and Fettiplace, R. (1975). Light and photon capture in turtle receptors. J.

Physiol. (London) 248, 433-464.

9. Ben-Yakir, D. Antignus, Y., Offir, Y. and Shahak, Y. 2012a. Optical Manipulations:

An advance Approach for Controlling Sucking Insect Pests. In: Advanced Technologies for Managing Insect Pests (I. Ishaaya, S.R. Palli, R. Horowitz, eds.) Springer Science+Business Media Dordrecht, pp. 249-267.

10. Ben-Yakir, D., Antignus, Y., Offir, Y. and Shahak, Y. 2012b. Colored shading nets impede insect invasion and decrease the incidences of insect transmitted viral diseases in vegetable crops. Entomol. Exp. etAppl. 144:249-257.

11. Ben-Yakir, D., Antignus, Y., Offir, Y. and Shahak, Y. 2014. Photoselective nets and

screens can reduce insect pests and diseases in agricultural crops. In: Proc. International CIPA Conference 2012 on Plasti culture for a Green Planet (A. Sadka, ed.). Acta Hort. (ISHS) 1015: 95-102.

Briggs W.R., Lin C.T. 2012 Photomorphogenesis- from One Photoreceptor to 14: 40 Years of Progress. Mol. Plant (2012) 5 (3): 531 -532.

Dueck, T., Janse, J., Li, T., Kempkes , F. and Eveleens, B. 2012. Influence of diffuse glass on the growth and production of tomato. Acta Hort. (ISHS) 956:75-82.

Glenn, D.M. (2009) Particle Film Mechanisms of Action That Reduce the Effect of Environmental Stress in 'Empire' Apple. J. Amer. Soc. Hort. Sci. 134(3): 314-321 Glenn, D.M., Sekutowski, D.G. and Puterka, GJ. (2000); U.S. Patent No. 6,1 10,867;

"Method for providing enhanced photosynthesis."

Harper, D. A., Hildebrand, R. H., Pernlic, R., and Piatt, S. R. (1976). Heat trap: An optimized far infrared field optics system. Appl. Opt. 15, 53-60.

Hemming, S. (2011) Use of Natural and Artificial Light in Horticulture - Interaction of Plant and Technology Proc. 6 th IS on Light in Horticulture Eds.: E. Goto and S. Hikosaka. Acta Hort. ISHS 907, 25-35.

Hemming, S.: Dueck, T.A.; Janse, J.; Noon, F.R. van 2008 The Effect of Diffuse Light on Crops. Proc. IS on GreenSys (Eds.:S. De Pascale et al. ) Acta Hort. 801 , ISHS.

Hinterberger, H., and Winston, R. (1966a). Efficient light coupler for threshold Cerenkov counters. Rev. Sci. lustrum. 37, 1094-1095.

Hinterberger, H., and Winston, R. (1966b). Gas Cerenkov counter with optimized light- collecting efficiency. Proc. Int. Conf. Instrum. High Energy Phys. 205-206.

Holter, M. L., Nudelman, S., Suits, G. H., Wolfe, W. L., and Zissis, G. J. (1962).

"Fundamentals of Infrared Technology." Macmillan, New York.

Karpinski, S., Gabrysy, H., Mateo, A., Karpinska, B. and Mullineaux, P.M. (2003) Light perception in plant disease defense signaling. Current Opinion in Plant Biology 6:390-396 Kasperbauer,MJ. (1994). "Light and plant development." In: Plant-environment

Interactions. Wilkinson R.E (Ed.) Marcel Dekker Inc. NY. pp. 83-123.

Kong, Y. Avraham, L., Perzelan, Y., Alkalai-Tuvia, S., Ratner, K., Shahak, Y. and Fallik, E. (2012). Pearl netting affects postharvest fruit quality in 'Vergasa' sweet pepper via light environment manipulation. Scientia. Hort., 150: 290-298.

Kozai, T. (2013) Plant factory in Japan - Current situation and perspectives. Chronica Horticulturae (ISHS) 53 (2): 8-10.

Longstaff; US Patent No. 5,022,181 "Method and apparatus for use in plant growth promotion and flower development".

Mortensen L.M. and Moe, R. (1992) Effects of selective screening of the daylight spectrum, and of twilight on plant growth in greenhouses. ActaHort. 305: 103-108.

Nissim-Levi, A., Farkash, L., Hamburger, D., Ovadia, R., Forrer, I., Kagan, S. and Oren-Shamir, M. (2008) Light-scattering shade net increases branching and flowering in ornamental pot plants. J. Hort. Sci. Biotech. 83, 9-14.

Oren-Shamir M., Gussakovsky E. E., Shpiegel E., Nissim-Levi A, Ratner K., Ovadia R., Giller Y. E. and Shahak Y. 2001 , Coloured shade nets can improve the yield and quality of green decorative branches of Pittosporum variegatum. J. Hort. Sci. Biotech. 76: 353-361. Ploke, M. (1967). Lichtfuhrungseinrichtungen mit starker Konzentrationswirkung. Optik 25, p 31.

Ploke, M. (1969) "Axially Symmetrical Light Guide Arrangement." German Patent Application #14722679.

Rabl, A., and Winston, R. (1976). Ideal concentrators for finite sources and restricted exit angles. Appl. Opt. 15, 2880-2883.

Rabe, E. (2004) Citrus tree spacing and tree shape: Concept, effect on early production profile and fruit quality aspects - An overview. Int. Soc. Citriculrure 1 :297-301.

Rajapakse N. C, Young, R.E., McMahon M. J. and Oi, R. (1999). Plant height control by photoselective filters: current status and future prospects. Hortechnology, 9: 618- 624.

Rajapakse, N.C. and Shahak, Y. (2007) Light quality manipulation by horticulture industry. In: Light and Plant Development (G. Whitelam and K. Halliday, eds.), pp 290- 312, Blackwell Publishing, UK. (A book chapter).

Senthilkumar S and Yasodha N, "Design and Development of a Three Dimensional Compound Parabolic Concentrator and Study of Optical and Thermal Performance.", 2012, Intl. J. Energy Sci. Vol. 2 no. 2 p64 - 68.

Shahak, Y. (2014) Photoselective netting: an overview of the concept, R&D and practical implementation in agriculture. In: Proc. International CIPA Conference 2012 on

Plasticulture for a Green Planet (A. Sadka, ed.). Acta Hort. (ISHS) 1015: 155-162.

Shahak, Y., Oren-Shamir, M., Gal, E., Bachar, A., Guthman, Y., Gemure, A. and Gussakovsky, E.E.; WO/2002/019800 (PCT/ILOl/00851) "New technology for improving the utilization of sunlight by plants."

Shahak, Y., Ratner, K., Giller, Y.E., Zur, N. Or, E., Gussakovsky, E.E., Stern, R., Sarig, P ., Raban , E., Harcavi, E ., Doron , I . and Gre enb lat-Avron, Y . (2008).

Improving solar energy utilization, productivity and fruit quality in orchards and vineyards by photoselective netting. In: Proc. 27 th IHC - Enhancing Econ. & Environ. Sustain, of Fruit Prod, in a Global Econ. (J.W. Palmer, Ed-in-Chief) Acta Hort. 772: 65- 72.

Sinclair, T.R., Shiraiwa, T. and Hammer, G.L. (1992) Variation in Crop Radiation-Use Efficiency with Increased Diffuse Radiation. Crop Sci. 32:1281-1284.

Warrington, IJ. and Mitchell, KJ. (1976) The influence of blue- and red-biased light spectra on the growth and development of plants. Agric. Meteorol. 16: 247-262.

Williamson, D. E. (1952). Cone channel condenser optics. J. Opt. Soc. Am. 42, 712-715. Winston, R. 1970. Light collection within the framework of geometrical optics. J. Opt. Soc. Am. 60, 245-247.

Winston, R. 1974. Principles of solar concentrators of a novel design. Sol. Energy 16, 89- 95.

Winston, R. (1976a). U.S. Patent No. 3,923,381 , "Radiant Energy Concentration." Winston, R. (1977b). U.S. Patent No. 4,003,638, "Radiant Energy Concentration." Winston, R. (1977b). U.S. Patent No. 4,002,499, "Cylindrical Concentrators for Solar Energy."

Winston, R., and Hinterberger, H. (1975). Principles of cylindrical concentrators for solar energy. Sol. Energy 17, 255-258.

Witte, W. (1965). Cone channel optics. Infrared Phys. 5, 179-185.