JP2002027831A - Led light source for raising plant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a light source for raising plants, having high efficiency and high reliability by covering both absorption peaks of chlorophyll with one LED. SOLUTION: Firstly, a first luminous layer forming light rays at 400-480 nm wavelength and a second luminous layer for forming light rays at 650-700 nm wavelength in one LED. Secondly, a leak at a short wavelength side (400-480 nm) is formed by a LED main body and a peak at a long-wavelength side (650-700 nm) is formed by a substrate placing the LED. A fluorescent substance for absorbing light rays (400-480 nm) formed by the LED main body and forming light rays at 650-700 nm is used as the substrate. For example, such a fluorescent substrate can be obtained by adding chromium or titanium to sapphire which has been conventionally used as a substrate for a semiconductor light emitting diode. Thirdly, similarly a peak at a short wavelength side is formed by the LED main body and a peak at a long-wavelength side is produced by a fluorescent substance covering the LED main body. Sapphire to which chromium or titanium added is similarly used as the fluorescent substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a highly efficient and highly reliable light source for growing plants, which can be used in cultivation farms and so-called plant factories.

[0002]

2. Description of the Related Art As the food problem is becoming more serious, the development of an artificial cultivation technique for stably growing plants without being affected by the environment has become an important issue worldwide. One of the important artificial cultivation techniques is an artificial light source for growing plants. In order to stably grow plants without being affected by the weather, artificial light sources that are supplementarily used for natural light (sunlight) or completely substitute for natural light are particularly important in technologies such as plant factories. Occupy. According to the artificial light source, by appropriately controlling the irradiation timing, time, intensity, and the like according to the type of the plant, the plant can be stably and efficiently grown, and the harvest can be obtained.

[0003]

FIG. 1 is a graph showing the light absorption characteristics of chlorophyll (chlorophyll). Chlorophyll a and b (chlorophylls a and b are present in the chloroplasts of C ₃ plants in higher plants at a ratio of approximately 3 to 1) are both 400.
It can be seen that there are light absorption peaks in the violet / blue region of 480480 nm and the red region near 650-700 nm. Kenmasa Okamoto of the Faculty of Engineering, Kagawa University found that these light absorption peaks almost coincided with the emission peaks of GaAlAs-based ultra-bright red light-emitting diodes (LEDs) and the newly developed ultra-bright blue LEDs. We have succeeded in cultivating plants by arranging these LEDs on a substrate and prototyping a cultivation device ("New applications of high-brightness LEDs in the biomedical field" Kenmasa Okamoto, Japanese Academy of Sciences) (Proceedings of the 168th workshop of the 125th Committee of the Japan Society for the Promotion of Photovoltaic Conversion, May 25, 2000).

[0004] Okamoto's prototype device is a chlorophyll 2
Red LED and Blue L corresponding to two absorption peaks
Although the present invention uses a separate LED called ED, the present invention covers both absorption peaks (blue range and red range) of chlorophyll with one LED, and is a highly efficient and reliable light source for growing plants. Is provided.

[0005]

Means and Effects for Solving the Problems As described above,
Although the present invention basically supplies light of both absorption peaks required by chlorophyll with one LED at the same time,
The specific means are divided into three types.

The first means is to supply the light having both absorption peaks through two (or more) light emitting layers provided in one LED. That is,
The first to generate light with a wavelength of 400 to 480 nm in one LED
A light-emitting layer and a second light-emitting layer that generates light of 650 to 700 nm are formed.

The second means is to generate a peak on the short wavelength side (400 to 480 nm) by the LED main body and to generate a peak on the long wavelength side (650 to 700 nm).
The peak of m) is generated on the substrate on which the LED is mounted. For this substrate, a phosphor that absorbs light (400 to 480 nm) generated by the LED body and generates light of 650 to 700 nm is used. In addition, "placement" here
In addition to the case where each layer of the LED is sequentially laminated on the substrate,
This includes the case where an LED formed separately is placed on a substrate.

For example, such a fluorescent substrate can be obtained by adding chromium or titanium to sapphire conventionally used as a substrate of a semiconductor light emitting diode.

[0009] The third means is likewise on the short wavelength side (400 to 480).
(nm) peak is generated by the LED body, and the longer wavelength side (650
〜700 nm) is generated by the phosphor covering it. As the phosphor, sapphire to which chromium or titanium is added can be used.

[0010] In any of the above three embodiments, both the blue and red peaks required for plant growth are assigned to one LED.
Can be supplied all at once. By using one LED as described above, the space efficiency and reliability of the light source are improved, and the light source is particularly suitable for use in a plant factory or the like in which unattended long-term automatic operation is performed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION A plant which is an embodiment of the first means
FIG. 2 shows an example of the growth light source 10. This example is based on InGaN
A semiconductor light emitting diode is used, and one LE
In in D_xGa _1-xTwo N-emitting layers 11 and 12 provided
It is. These two light emitting layers 11 and 12 are n-GaN negative electrode layers
Between the active layer 12 and the p-GaN layer.
Reduces the overflow of electrons from the n-GaN layer.
P-Al_zGa_1-zN layer (z is usually about 0.2) is sapphire
(Al_TwoO_Three) Between the substrate and the n-GaN negative electrode layer
A GaN buffer layer is provided.

The first light emitting layer 11 has an emission peak of 400
Adjust the In: Ga mixed crystal ratio x to be within 480 nm (0.1 to
0.3). Desirably, the emission peak is adjusted so as to match the chlorophyll (a or b) of the plant to be grown, and the emission peak of the chlorophyll a or b in FIG. In the second light emitting layer 12, the In: Ga mixed crystal ratio x is adjusted (about 0.4 to 0.8) so that the light emission peak is within 650 to 700 nm. Similarly, it is desirable to adjust according to the absorption peak of chlorophyll a or b.

In the case of InGaN-based semiconductors, the long wavelength side (650 to
(700 nm) emission still has some difficulties. Therefore, another group V atom such as P (phosphorus), As (arsenic), Sb (antimony), or Bi (bismuth) is used as an isoelectronic trap forming element to be replaced with the N atom in In _x Ga _1-x N. The doped layer may be used as the second light emitting layer 12. That is, as the light emitting layer 12 on the long wavelength side, the general formula In _x Ga _1-x N _1-y X _y
(0 <x <1; X = P, As, Sb, Bi; 0 <y <0.01, preferably 0 <y
<0.005) is used. The reason is described in detail in Japanese Patent Application No. 2000-231572.

However, since techniques for adjusting the emission wavelength of semiconductor light emitting diodes of various compositions have recently been developed, various types of semiconductor light emitting diodes other than the above InGaN-based semiconductors can be used.

FIG. 3 shows the structure of a light source according to a first embodiment of the second means of the present invention. In this embodiment, the light source 20 includes a substrate 21 and an LED 22 mounted thereon.

As the substrate 21, sapphire (Al ₂ O ₃ : Ti) to which titanium is added is used. Such a substrate can be easily obtained by mixing sapphire (Al ₂ O ₃ ) with titanium oxide (Ti ₂ O ₃ ) and performing melting and crystallization. Titanium-doped sapphire is a red transparent crystal, and due to its Ti ³⁺ ions, as shown in FIG. 4, becomes a phosphor having an absorption peak near 500 nm and a broad emission peak in the red to infrared region from 700 to 850 nm. ing. On the back surface of the substrate 21, a metal film 23 for light reflection is deposited.

The LED 22 mounted on the substrate 21
Has a structure in which an n-GaN negative electrode layer and a p-GaN positive electrode layer are stacked with an In _x Ga _1-x N active layer (light emitting layer) 24 interposed therebetween. Between the active layer 24 and the p-GaN layer in order to suppress the overflow of electrons from the n-GaN _{layer, p-Al z Ga 1-} z N layer (z is usually about 0.2)
Is provided. A GaN buffer layer for crystal matching is provided between the substrate 21 and the n-GaN negative electrode layer.

In _x Ga _{1 -x} N active layer (light emitting layer) of LED 22
In No. 24, the mixed crystal ratio x is set so as to emit blue light having a peak near 480 nm (specifically, about 20%).

As schematically shown in FIG. 5, a part of the light generated in the active layer 24 of the LED 22 is emitted from the upper part, but a part proceeds downward and enters the substrate 21. A part of the light passes through the substrate 21 (including the case where the light passes through after being reflected on the back surface of the substrate 21), and the rest of the light passes through the substrate 21.
To excite the substrate 21. The excited substrate 21 emits part of its energy as fluorescence. Therefore, the wavelength of this fluorescence is equal to the absorbed light (ie, LE
D22). In addition, it generally has a spread in the wavelength direction.

As described above, titanium-added sapphire is shown in FIG.
And absorbs blue light of 480 nm generated by the LED 22 with high efficiency. Therefore, the light generated by the LED 22 excites the titanium-added sapphire substrate 21, and the substrate 21 generates red-to-infrared light that rises rapidly from around 650 nm. Therefore, from the light source 20 of the present embodiment, the LED 22
A mixed light of blue light near 480 nm and light in a red region including 650 to 700 nm, which is directly emitted from the light source, is generated. These are lights necessary for growing plants, as shown in FIG. 1, and the light source of the present embodiment can generate them very efficiently.

The light thus generated from the LED and the fluorescence from the substrate excited and generated by the light are the short-wavelength absorption peak (400-480 nm) and the long-wavelength absorption peak (650-700 nm) of the chlorophyll, respectively. Has a wavelength close to

Next, a second embodiment of the second means will be described. This embodiment has the same structure (FIGS. 3 and 5) as the first embodiment except that chromium-added sapphire (ruby) is used for the substrate. Chrome-added sapphire
(Al ₂ O ₃ : Cr) has absorption peaks around 410 nm (purple) and around 550 nm (green) as shown in FIG. 6A, and 693 nm and 694 nm (green) as shown in FIG. It is a phosphor having a sharp emission peak in (red). Note that chromium-added sapphire is a red transparent crystal, similar to titanium-added sapphire, and emits fluorescence by its Cr ³⁺ ions.

As described above, by appropriately setting the InGa mixed crystal ratio x of the In _x Ga ₁ -xN active layer (light emitting layer) of the LED 22 to emit light near 410 nm, the LED 22 has a short chlorophyll a. Light having a wavelength close to the absorption peak on the wavelength side
1 emits fluorescence having a wavelength close to the long-wavelength absorption peak of chlorophyll. Similarly to the above, the light source 20 of the present embodiment can efficiently generate light necessary for growing plants.

In the first and second embodiments (FIGS. 3 and 5), it is necessary to provide an electrode and a lead wire on the light emitting side of the upper surface of the LED 22, so that the area of the electrode pads 26 and 27 is as small as possible. It is desirable to keep.

A third embodiment of the second means of the present invention will be described. In this embodiment, as shown in FIG. 7, the substrate 31 is on the light emitting side. The first and second substrates are provided on the substrate 31.
Any of the titanium-added sapphire and the chromium-added sapphire used in the embodiment can be used. LED
The back surface side of 32 is an electrode / reflection surface 36 by metal deposition or the like,
Set it to 37.

By adopting such a structure, the LED
Most of the light emitted from 32 enters the light emitting side substrate 31. By appropriately setting the concentration of titanium or chromium added to the substrate 31 and the thickness of the substrate 31,
Part of the light from the substrate 32 passes through the substrate 31 and part of the light from the substrate 3
1 and emit fluorescence as described above. Therefore, it is the same as the first and second embodiments that the light emitted from the present light source 30 is a mixed light thereof and that the emission color can be appropriately adjusted. The light source has a feature that light can be emitted with high efficiency because light is not blocked by an electrode pad or the like on the light emitting surface side (upper side in FIG. 7).

FIG. 8 shows an embodiment of the third means of the present invention. The light source 40 of this embodiment is one in which a substrate 41 is made of normal sapphire, and the upper surface of an LED 42 is covered with the titanium / chromium-added sapphire phosphor 43. The operation and the effect are described in the third embodiment of the second means (FIG. 7).
Is the same as

[Brief description of the drawings]

FIG. 1 is a graph showing light absorption characteristics of chlorophyll (chlorophyll).

FIG. 2 is a cross-sectional view showing an example of a plant growing light source which is an embodiment of the first means of the present invention.

FIG. 3 is a cross-sectional view showing a configuration of a plant growing light source according to a first embodiment of the second means of the present invention.

FIG. 4 is a graph showing absorption / emission characteristics of titanium-added sapphire (Al ₂ O ₃ : Ti).

FIG. 5 is a schematic diagram showing a light emitting state of the light source in FIG. 3;

FIG. 6 is a graph showing absorption (a) and emission (b) characteristics of chromium-doped sapphire (Al ₂ O ₃ : Cr).

FIG. 7 is a cross-sectional view showing a configuration of a plant growing light source according to a third embodiment of the second means of the present invention.

FIG. 8 is a sectional view showing a configuration of a light source for growing a plant, which is an embodiment of the third means of the present invention.

[Explanation of symbols]

10, 20, 30, 40 ... light source for plant growth 11, 21, 31, 41 ... substrate 12, 22, 32, 42 ... InGaN-based nitride semiconductor light emitting diode 23 ... reflection film 14, 24, 34 ... active layer 16, 17, 26, 27 ... electrode pad 36, 37 ... electrode and reflection surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01L 33/00 H01L 33/00 CLF term (Reference) 2B022 DA08 4H001 CA02 CA04 CC14 XA07 XA15 XA31 XA33 XA49 XA51 XA83 5F041 AA11 AA12 CA34 CA40 EE25 FF16

Claims (6)

[Claims] 1. A first light emitting layer that generates light having a wavelength of 400 to 480 nm and a second light emitting layer that generates light having a wavelength of 650 to 700 nm in one LED.
LED for growing plants characterized by forming a light emitting layer
light source. 2. The method according to claim 1, wherein the first light emitting layer is formed of In _x Ga ₁ -xN (0.1 <x <0.
3) wherein the second light-emitting layer is In _x Ga _1-x N _1-y X _y (0 <x <1; X = P,
2. The LED light source for growing plants according to claim 1, wherein As, Sb, Bi; 0 <y <0.01). 3. An LED including a light emitting layer that generates light having a wavelength of 400 to 480 nm is formed by absorbing light from the light emitting layer to emit light having a wavelength of 650 to 7 nm.
An LED light source for growing plants, which is mounted on a substrate that generates 00 nm fluorescence. 4. The LED light source for growing plants according to claim 3, wherein the light emitting layer is In _x Ga ₁ -xN (0.1 <x <0.3), and the substrate is sapphire to which chromium or titanium is added. 5. An LED including a light-emitting layer that generates light having a wavelength of 400 to 480 nm, the light having a wavelength of 650 to 7 that absorbs light from the light-emitting layer.
An LED light source for growing plants, which is covered with a phosphor that generates fluorescence of 00 nm. 6. The LED light source for growing plants according to claim 5, wherein the light emitting layer is In _x Ga ₁ -xN (0.1 <x <0.3), and the phosphor is sapphire to which chromium or titanium is added.