LIGHTING ASSEMBLY

Abstract

A lighting fixture for facilitating plant growth and a light emitting component. The fixture includes a single light emission source LED device which provides at least two emission peaks in the wavelength range of 300-800 nm and at least one of the emission peaks has Full Width of Half Maximum (FWHM) at least 50 nm or higher. The emission peaks of the LED match well with a plant photosynthesis response spectrum and is therefore particularly suitable for high efficiency artificial lighting.

Claims

1. A horticultural lighting fixture comprising: at least one light emitting diode (LED) exhibiting main spectral characteristics in the photosynthetically active radiation (PAR) (400-700 nm) area, and at least one side spectral characteristics selected from first side spectral characteristics in the 700-800 nm area and second side spectral characteristics in the 300-400 nm area.

2. The horticultural lighting fixture according to claim 1, wherein intensities of emissions of the main spectral characteristics and the at least one side spectral characteristics are independently adjustable.

3. The horticultural lighting fixture according to claim 2, wherein the at least one LED comprises at least one first LED and at least one second LED, the at least one first LED being configured to emit the main spectral characteristics, the at least one second LED being configured to emit the at least one side spectral characteristics.

4. The horticultural lighting fixture according to claim 3, further comprising at least one electronic control system to switch the at least one first LED and the at least one second LED independently on and off or alternatively dim independently by 0-100% power.

5. The horticultural lighting fixture according to claim 3, wherein the main spectral characteristics comprise at least one peak coinciding with an absorption peak of photoreceptors of a plant.

6. The horticultural lighting fixture according to claim 5, wherein the main spectral characteristics comprise at least two peaks matching carotenoid and chlorophyll absorption peaks.

7. The horticultural lighting fixture according to claim 6, wherein the main spectral characteristics comprise first main spectral characteristics including a peak in the wavelength range from 600 to 700 nm and arranged to exhibit a full width of half maximum of at least 50 nm or more, and second main spectral characteristics with a maximum of 50 nm full width of half maximum and arranged to exhibit a peak wavelength in the range from 440 to 500 nm.

8. The horticultural lighting fixture according to claim 7, wherein at least a part or the whole of the emission at wavelengths of 500-600 nm is minimized and/or omitted and/or reduced below the intensity in the 400-500 nm band and below the intensity in the 600-700 nm band.

9. The horticultural lighting fixture according to claim 6, wherein the side spectral characteristics comprise a peak in the far-red wavelength region.

10. The horticultural lighting fixture according to claim 3, wherein all or part of the emission at a frequency of 600-800 nm is generated using a whole or partial wavelength up-conversion of LED chip radiation power.

11. The horticultural lighting fixture according to claim 10, wherein the wavelength up-conversion is generated with at least two up-conversion materials, and the main spectral characteristics and the at least one side spectral characteristics are generated with different sets of up-conversion materials.

12. The horticultural lighting fixture according to claim 11, wherein the main spectral characteristics comprise at least two peaks coinciding with an absorption peak of photoreceptors of a plant, the main spectral characteristics including a peak in the blue wavelength region and a peak in the red wavelength region, the peak in the blue wavelength region being generated with a primary emission of the at least one LED.

13. The horticultural lighting fixture according to claim 12, wherein the side spectral characteristics comprise a peak in the far-red wavelength region.

14. The horticultural lighting fixture according to claim 1, wherein all or part of the emission at a frequency of 600-800 nm is generated using a whole or partial wavelength up-conversion of LED chip radiation power, the wavelength up-conversion being generated with at least two up-conversion materials.

15. The horticultural lighting fixture according to claim 14, wherein the main spectral characteristics comprise at least two peaks coinciding with absorption peaks of photoreceptors of a plant, the main spectral characteristics including a peak in the blue wavelength region and a peak in the red wavelength region, the peak in the blue wavelength region being generated with a primary emission of the at least one LED.

16. The horticultural lighting fixture according to claim 15, wherein the side spectral characteristics comprise a peak in the far-red wavelength region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0081] FIG. 1 shows relative absorption spectra of the most common photosynthetic and photomorphogenetic photoreceptors in green plants;

[0082] FIG. 2 shows the emission peaks of a first single light emission source LED device according to the invention;

[0083] FIG. 3 shows the emission peaks of a second single light emission source LED device according to the invention;

[0084] FIG. 4 shows the emission peaks of a third single light emission source LED device according to the invention;

[0085] FIG. 5 shows the emission peaks of a fourth single light emission source LED device according to the invention; and

[0086] FIGS. 6a to 6c show in a schematical fashion the various process steps of a method of producing a modified LED device according to a preferred embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0087] As already discussed above, the present invention relates in general to a single light emission source LED device that has optimal properties to be used as greenhouse cultivation light source. Specifically this approach to construct the light sources has optimal properties and flexibility for matching the photosynthesis frequencies in plant cultivation. By using this approach, the light sources can be designed to reach superior PPF and PPF per watt efficiency and performance and very low power consumption and very long operation lifetime when compared to the existing technologies.

[0088] In particular the single light emission source LED device provides at least two emission peaks in the wavelength range of 300-800 nm and at least one of the emission peaks has Full Width of Half Maximum (FWHM) at least 50 nm or higher. The emission peaks and relative intensities are selected to match the photosynthesis frequencies for the plant. Also the required PPF quantity for the light source is optimized to meet the plant requirement.

[0089] The emission at a frequency of 300-500 nm is generated by the semiconductor LED chip and the emission at frequency of 400-800 nm is generated using a complete or partial wavelength up-conversion of the LED chip radiation power. The partial wavelength up-conversion can be selected to be in range of 5-95%, preferably 35-65%, of the semiconductor LED chip radiation. The wavelength up-conversion to produce the 400-800 nm radiation is achieved by using one or more up-conversion materials in proximity with the LED emission source. The wavelength up-conversion is realized by using either organic, inorganic or combination of both types of materials. These materials can be particular (nano- or other size particles), molecular or polymeric materials. Furthermore the materials can have structural arrangement that results in wavelength up-conversion of the emission source.

[0090] According to one particular embodiment, a lighting fixture for facilitating plant growth comprises a UV LED, optionally with external luminescent emission characteristics. The LED exhibits typically

[0091] a) first phosphorescent spectral characteristics with a peak wavelength in the range of 350 to 550 nm;

[0092] b) second optional phosphorescent spectral characteristics with a peak wavelength in the range of 600 to 800 nm; and

[0093] c) third optional phosphorescent spectral characteristics with a peak wavelength freely adjustable between 350 and 800 nm.

[0094] In this application adjustable peak wavelength as in the above is construed as a peak wavelength that can be adjusted during assembly of the lighting fixture at the factory, and/or also adjustable as in an adjustable dial in the lighting fixture for on site peak wavelength adjustment. In addition adjusting the peak wavelengths of the LED during manufacturing process of the LED is also in accordance with the invention, and adjustable should be construed to also include adjustments made during the manufacturing process of the LED. All aforementioned embodiments of an adjustable peak wavelength, or any other adjustable light source or LED variable are within the scope of this patent application.

[0095] Preferably the phosphorescent emission intensities of first, optional second and optional third spectral characteristics are adjustable in any ratio.

[0096] FIGS. 2 to 5 illustrate a few examples of the emission peaks of the single light emission source LED devices.

[0097] In FIG. 2, the semiconductor LED chip emission frequency peaks at a wavelength of 457 nm with emission peaks Full Width of Half Maximum (FWHM) of 25 nm. In this case the wavelength up-conversion is done by using two up-conversion materials. These two wavelength up-conversion materials have individual emission peaks at 660 nm and 604 nm FIG. 2 shows the combined emission peak from these two wavelength up-conversion materials peaking at 651 nm wavelength with emission peaks FWHM of 101 nm. In this case about 40% (calculated from the peak intensities) of the semiconductor LED chip emission, is up-converted to 651 nm emission by two individual up-conversion materials.

[0098] In FIG. 3, the semiconductor LED chip emission frequency peaks at a wavelength of 470 nm with emission peaks Full Width of Half Maximum (FWHM) of 30 nm. In this case the wavelength up-conversion is done by using two up-conversion materials. These two wavelength up-conversion materials have individual emission peaks at 660 nm and 604 nm FIG. 2 shows the combined emission peak from these two wavelength up-conversion materials peaking at 660 nm wavelength with emission peaks FWHM of 105 nm. In this case about 60% (calculated from the peak intensities) of the semiconductor LED chip emission, is up-converted to 660 nm emission by two individual up-conversion materials.

[0099] In FIG. 4, the semiconductor LED chip emission frequency peaks at a wavelength of 452 nm with emission peaks Full Width of Half Maximum (FWHM) of 25 nm (not shown in the figure). In this case the wavelength up-conversion is done by using one up-conversion material. FIG. 3 shows the emission peak from this up-conversion material peaking at 658 nm wavelength with emission peaks FWHM of 80 nm. In this case about 100% (calculated from the peak intensities) of the semiconductor LED chip emission, is up-converted to 658 nm emission by the up-conversion material. This can be noticed from the FIG. 4, as there are no 452 nm emission exiting the LED device.

[0100] In FIG. 5, the semiconductor LED chip emission frequency peaks at a wavelength of 452 nm wavelength with emission peaks Full Width of Half Maximum (FWHM) of 25 nm. In this case the wavelength up-conversion is done by using one up-conversion material. FIG. 5 shows the emission peak from this up-conversion material peaking at 602 nm wavelength with emission peaks FWHM of 78 nm. In this case about 95% (calculated from the peak intensities) of the semiconductor LED chip emission, is up-converted to 602 nm emission by the wavelength up-conversion material.

[0101] For the above mentioned spectrum the device can be constructed as explained in details below. The semiconductor LED chip emission frequency should be selected the way that it is suitable for exciting the used phosphor molecules in the device. The emission from the LED chip can be between 400 nm and 470 nm.

[0102] The used phosphor molecule or molecules should be selected the way that a desired emission spectra from the LED is achieved.

[0103] In the following we will describe a procedure for using two phosphor materials (wavelength up-conversion materials) in the LED device to achieve the desired spectra (cf. FIGS. 6a to 6c).

[0104] Phosphor A and Phosphor B are mixed in a pre-determined ratio to achieve desired phosphor emission spectra from the LED device (cf. FIG. 6a). The ratio of the phosphors can be for example 99:1 (A:B) to 1:99. This mixture of phosphors A+B is mixed into a material C (for example a polymer) at a pre-determined concentration to form an encapsulant. The concentration of the phosphors in material C can be for example 99:1 (phosphor mixture:material C) to 1:99. This mixture of material C+phosphors (A and B) is then deposited in direct proximity of the LED chip (FIGS. 6b and 6c). By proximity we mean it can be deposited directly on the surface of the LED chip or spaced out with other optical material. The concentration of the phosphor mixture in material C determines the wavelength up-conversion amount of the semiconductor LED chip emission frequency, meaning how much of the original LED chip emission frequency is seen in the final LED device emission and how much is converted into the phosphor emission in the LED device.

[0105] The thickness of the encapsulant (into which the phosphor is mixed) typically varies from 0.1 um to 20 mm, in particular 1 um to 10 mm, preferably 5 um to 10 mm, for example about 10 um to 5 mm, depending on the concentration of the phosphor.

[0106] Typically the concentration of the phosphor (calculated from the total weight of the encapsulant) is about 0.1 to 20%, preferably about 1 to 10%.

[0107] The wavelength up-conversion can be 100%, meaning that there is only phosphor emission seen from the LED device or it can be less than 100%, meaning that some of the LED chip emission is transmitted out from the LED device.

[0108] To summarize, by tuning the phosphor ratio A:B it is possible to tune the desired phosphor emission spectra from the LED device and by tuning the phosphor concentration in material C it is possible to tune the desired LED chip emission quantity/amount for the LED device.

[0109] The amount (physical thickness) of material C (with certain phosphor concentration) on top of the LED chip also affects the amount of LED chip emission transmitting from the LED device. The thicker the material C layer on top of the LED chip, the lower the transmission.

[0110] Material C can be for example a solvent, inorganic or organic polymer, silicon polymer, siloxane polymer or other polymer where the phosphor can be mixed into. Material C can have one or more components that have to be mixed prior to usage together with the phosphor. Material C can be a thermally or UV curable material.

[0111] The mixture of the phosphor(s) and the solvent material C (solid or liquid) can be translucent or transparent, preferably transparent, to allow for passage of the light emitted from the LED.

[0112] In one embodiment that is especially preferable the far red radiation (700-800 nm) is produced by for example europium-cerium co-doped Ba_x Sr_y ZnS_3 phosphors and/or cerium doped lanthanide oxide sulfides. These phosphor and sulfide types have emission peak maxima between 650-700 nm wavelength region and exhibit also broad (50-200 nm) full width of half maximum and therefore also produce light emission at higher wavelength, i.e., above 700 nm wavelength range.

[0113] In addition to or as an alternative to using phosphors or other similar materials it is also possible to realize the wavelength up-conversion by means of at least one semiconductor quantum dot or the like, which is placed near the LED.

Example

[0114] A LED lighting fixture was constructed for comparison testing purposes based on the single LED device having identical output spectrum of the FIG. 3. The lighting fixture consisted of 60 individual LED units having a power consumption of 69 W which includes the power consumption of the AC/DC constant current driver.

[0115] The comparison devices were commercial HPS (High Pressure Sodium) lamp greenhouse lighting fixture with total power consumption of 420 W and commercial LED greenhouse LED fixture. The commercial LED fixture was based on individual blue and red LED devices having total power consumption of 24 W.

[0116] The LED lighting fixture according to the present invention was tested against the above-mentioned commercial LED devices using following PPF measurement procedure and arrangement.

[0117] PAR irradiance (irradiance value between 400 nm and 700 nm) and PPF-values were calculated by measuring the light fixture spectra from 300 nm to 800 nm and absolute irradiance value at band from 385 nm to 715 nm. The spectrum of each lamp were measured with ILT700A spectroradiometer at one distance. The absolute irradiance-values were measured with precision pyranometer at certain distances and were later used to calculate the absolute spectra to these distances. These absolute spectra were used to calculate PAR- and PPF calculations. PAR-irradiance (W/m.sup.2) was calculated by integrating the absolute spectrum from 400 nm to 700 nm PPF-values were calculated by first translating the irradiance value of each channel of the spectrum from W/m.sup.2 to microeinsteins and then integrating this spectrum over the desired wavelength band.

[0118] The comparison result of these two commercial greenhouse lamp fixtures and the LED fixture according to the innovation are presented in the table below. The results are also normalized against the commercial HPS lighting fixture.

TABLE-US-00001 Type HPS Ref. Grow LED LED of Invention Power (W) 420 24 69 Total PPF 164 26 88 PPF/Watt 0.39 1.08 1.28 PPF efficiency 1 2.77 3.27 normalized to Ref. HPS PPF efficiency 100% 277% 327% normalized to Ref. HPS (%)

[0119] As will appear from the test results shown, an LED lighting fixture according to the present invention provides 3.27 times higher PPF efficiency compared to HPS and 1.18 times better PPF efficiency compared to commercial LED greenhouse fixture based on individual blue and red LED devices. Naturally all of the LEDs or lighting fixtures are arranged to be used especially in greenhouses for plant cultivation as greenhouse lights in many embodiments of the invention.

[0120] The above examples have described embodiments in which there is one Light Emitting Diode (LED) having the indicated spectral characteristics. Naturally, the present lighting fixtures may comprise a plurality of LEDs, at least some (say 10% or more) or preferably a majority (more than 50%) of which have the indicated properties and characteristics. It is therefore possible to have fixtures comprising combinations of conventional LEDs and LEDs of the present kind. There are no particular upper limits to the number of LEDs. Thus, lighting fixtures of the present kind can have roughly 1 up to 10,000 LEDs, typically 1 to 1000 LEDs, in particular 1 to 100 LEDs.

[0121] It is in accordance with the invention to include LEDs with different peak emissions in one luminaire and to control these in order to provide a desirable spectral emission to achieve a determined growth result or physiological response. In this way, the lighting system would allow a versatile control of lighting intensity and spectrum. Ultimately, the control of other abiotic parameters such as CO.sub.2 concentration, temperature, daylight availability and humidity could be integrated within the same control system together with lighting, optimizing the crop productivity and the overall management of the greenhouse.

REFERENCES

[0122] EP 2056364 A1, Satou et al. [0123] US 2009/0231832, Zukauskas et al.