JP2013025966A - Light-emitting diode lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-emitting diode lighting device capable of lessening a calorific value on the assumption that it is used for indoor cultivation facilities for vegetables, plants and the like, and having longer lifetime.SOLUTION: In the light-emitting diode lighting device where a plurality of resin-sealed type light-emitting diodes are mounted on a printed circuit board and the printed circuit board is stored in a case made of transparent resin, a value of average current made to flow in the light-emitting diodes is to be 55 to 85% of its rated value, and the value of average current is preferably limited to about 70% of the rated value. Further, establishment density of the light-emitting diodes mounted by neighboring each other on the printed circuit board is to be 1.0 to 1.5 pieces per one square centimeter, and it is preferably limited to about 1.2 pieces per one square centimeter.

Description

  The present invention relates to an illuminating device in which a large number of light emitting diodes are laid on a printed circuit board, and more particularly to a light emitting diode illuminating device used for cultivation of plants and the like indoors.

  With the rapid development of semiconductor technology in recent years, the characteristics and efficiency of light-emitting diodes have been remarkably improved, and the price of light-emitting diodes has been rapidly reduced along with significant progress in manufacturing technology and increase in production scale. Also, according to the recent increase in social interest regarding energy saving and power saving, lighting devices using light emitting diodes are being replaced by conventional incandescent lamps and fluorescent lamps and are becoming widely used in society.

  In addition, lighting devices using light emitting diodes are widely used in various fields in addition to lighting in ordinary homes and offices. In particular, the use in cultivation facilities that grow plants and vegetables in large quantities indoors using artificial lighting called “plant factories” has recently attracted attention. This is because the emission wavelength characteristic peculiar to a light emitting diode and its low power consumption are suitable for use in cultivation facilities such as plants indoors.

  Generally, the light-emitting-diode illuminating device used in an indoor cultivation facility has a shape as shown in Patent Document 1. That is, a light-emitting unit in which a large number of light-emitting diodes are laid on a vertically long printed board is manufactured, and this is housed in a cylindrical case made of transparent resin or glass to form an illuminating device using the light-emitting diodes.

  By the way, the energy conversion efficiency from electricity to light in the light emitting diode is still about 4 to 10% although it is improved as compared with the conventional incandescent lamp. Therefore, in a lighting device using a light emitting diode, if the illuminance is increased, the amount of heat generated by the lighting device itself increases accordingly. However, semiconductor materials such as gallium arsenide and gallium nitride used for light-emitting diodes are vulnerable to heat, and it is said that deterioration of the device starts at 80 degrees Celsius or higher. If it continues, it is said that the lifetime as a light emitting diode will be shortened extremely.

  Therefore, in order to solve such a problem in a lighting device using a light emitting diode, for example, a metal heat sink is provided in the lighting device to promote heat dissipation from the device, or a current driving circuit of the light emitting diode is used. In order to reduce the amount of heat generation, a current limiting circuit as shown in Patent Document 2 or Patent Document 3 is provided to suppress the current flowing through the light emitting diode.

JP 2002-141555 A JP 2004-214519 A JP 2010-103217 A

  However, the method of adding a heat sink to the lighting device causes a significant increase in device weight and an increase in device cost. In addition, the addition of the current limiting circuit as shown in the above-mentioned prior patent document makes the control circuit of the lighting device complicated, resulting in an increase in device cost and an increase in failure factors due to an increase in electronic components used. There is a fear. In particular, in the lighting device used in the indoor cultivation facility described above, since a large number of light emitting diodes are used for one lighting device, such a defect is regarded as a fatal defect in the widespread use of the lighting device. It was.

  The present invention is intended to solve such conventional problems and inconveniences, and more specifically, the calorific value assuming use in indoor cultivation facilities such as vegetables and plants. An object of the present invention is to provide a light-emitting diode illuminating device having a small life and a long device life.

The light-emitting diode illuminating device according to the first aspect of the present invention achieves the above-described object,
A light-emitting diode illuminating device in which a large number of resin-sealed light emitting diodes are laid on a printed circuit board, and the printed circuit board is housed in a case such as a transparent resin,
The value of the average current flowing through the light emitting diode is set to 55% to 85% of the rated value, more preferably limited to around 70% of the rated value.

Moreover, the light-emitting diode illuminating device according to the second aspect of the present invention is the first aspect,
The installation density of the light emitting diodes laid adjacently on the printed circuit board is set to 1.0 to 1.5 per square centimeter, and more preferably limited to about 1.2 per square centimeter. And

The light-emitting diode illuminating device according to the third aspect of the present invention is the first or second aspect,
A value obtained by multiplying the reduction ratio α of the current flowing through the light emitting diode by a coefficient of 0.8 to 1.0 with respect to the numerical value of 1 / α is defined as an increase rate β of the installation density of the light emitting diodes on the printed circuit board. The number of light emitting diodes on the printed circuit board is increased in accordance with the rate β, and the illumination device as a whole is characterized by maintaining almost the same illuminance as before the current reduction.

Moreover, the light-emitting diode illuminating device according to the fourth aspect of the present invention, in at least one of the first to third aspects,
It further includes a predetermined current control means, and is characterized in that a current value flowing through the light emitting diode can be freely adjusted within a predetermined range.

Moreover, the light-emitting diode illuminating device according to the fifth aspect of the present invention, in at least one of the first to fourth aspects,
In indoor cultivation of plants, the plant can be installed at a distance of about 10 centimeters from the cultivated plant.

  According to the light emitting diode illuminating device of the present invention, the illuminance of the entire illuminating device is maintained by increasing the number of light emitting diodes mounted on the illuminating device based on predetermined setting conditions while reducing the driving current of the light emitting diode. can do. As a result, the amount of heat generated from the lighting device can be reduced, the life of the light-emitting diode used in the lighting device can be extended, and the economics of the light-emitting diode lighting device used in indoor cultivation facilities can be further increased.

  Embodiments, which are the best modes for carrying out the present invention, will be described below with reference to the drawings attached to the specification of the present application.

  First, FIG. 1 shows the structure of a light-emitting diode illuminating device 10 of the present invention (hereinafter simply referred to as “illuminating device 10”). Incidentally, FIG. (1-a) is a plan view of the apparatus, FIG. (1-b) is a front view of the apparatus, and FIG. (1-c) is A in (1-a) (1-b). A schematic sectional view taken along line -A 'is shown respectively. Note that various wiring materials, electronic components, various electronic circuits, and the like included in the apparatus are not directly related to the gist of the present invention, and are not described.

  As is clear from FIG. 1, the illumination device 10 mainly includes a printed circuit board 11, a light emitting diode 12, and a transparent case 13. The printed circuit board 11 is a printed circuit board that is widely used in general electronic circuits. For example, any printed circuit board material such as paper epoxy, glass epoxy, or bakelite can be used.

  In order to electronically connect a large number of light emitting diodes 12 mounted on the printed circuit board 11 to the printed circuit board 11, a printed pattern made of copper foil is provided on the front or back surface of the circuit board by a technique such as photoetching (see FIG. Not shown). For connection between the light emitting diodes 12 mounted on the printed circuit board 11, various connection circuits can be configured. For example, a connection circuit as shown in FIG. 2 can be used. .

  In the circuit shown in the figure, about 10 to 15 light emitting diodes 12 are connected in series, and a current limiting resistor 14 is connected to this to generate one series branch. A printed circuit board is formed by connecting in parallel. Note that the current limiting resistor 14 can be omitted by appropriately selecting the characteristics, circuit method, and the like of the power supply circuit 15.

  In the circuit shown in FIG. 2, since all the light emitting diodes 12 are connected in series in one series branch, all the current values flowing through the diodes have the same value. Moreover, since all the serial branches are connected in parallel, the voltage values applied to the respective serial branches are all the same value. Note that the connection circuit shown in the figure is merely an example of the present invention, and needless to say, the implementation of the present invention is not limited to the connection circuit according to the present invention.

  The light emitting diode 12 can be of any type and type as long as it is a resin-sealed light emitting diode molded into a so-called bullet shape. In addition, about the luminescent color, it is possible to select the luminescent color from various semiconductor materials according to conditions, such as the attribute of the plant or vegetable used as a cultivation object in an indoor cultivation facility, or a cultivation method. is there.

  For example, if the red emission color is emphasized, it is preferable to use a light emitting diode made of a semiconductor material of aluminum / gallium arsenide or gallium arsenide phosphorus, and if the blue / green emission color is emphasized. It is preferable to use a light emitting diode made of a semiconductor material of zinc selenide or silicon carbide. Further, various light emitting diodes having different light emission colors may be used in combination in accordance with the application and purpose.

  In view of reducing the thermal stress applied to the light-emitting diode and extending its life, which is the object of the present invention, the light-emitting element itself is larger than a high-brightness / chip-type light-emitting diode with a small heat capacity. It is preferable to use a bullet-shaped resin-sealed light emitting diode having a large heat capacity.

  In addition, since the current trend of light-emitting diodes in the market has shifted to the high-brightness chip type, the bullet-type resin-encapsulated type has become an old model in the market and its price is also decreasing. Therefore, by using a bullet-shaped resin-encapsulated light emitting diode, an effect of suppressing the product cost of the entire lighting device can be expected.

  On the other hand, the transparent case 13 is a case for housing the printed circuit board 11 on which a large number of light emitting diodes 12 are mounted, and is a part that becomes a housing of the lighting device 10. As a material of the transparent case 13, for example, polymer materials such as acrylic, polycarbonate, or plastic, and various materials such as glass can be used. Also, the shape is not limited to the cylindrical case shown in FIG. 1, and it is needless to say that various shapes and shapes can be taken according to the actual usage.

  The transparent case 13 is basically required to be transparent in order to radiate the light of the light emitting diode placed inside it to the outside of the case. However, in order to scatter the radiated light, for example, the surface may be translucent, or a discontinuous surface such as a step or unevenness may be provided on the surface.

  The power supply circuit 15 shown in FIG. 2 may be stored inside the transparent case 13 or may be configured to be installed outside the case. Incidentally, from the viewpoint of reducing the thermal stress applied to the light emitting diode mounted on the printed board, it can be said that it is preferable to provide the power supply circuit that generates heat and various electronic control circuits outside the transparent case 13.

  Next, functions and operations of the lighting device 10 according to the present invention will be described. First, various data obtained by the experiment of the lighting device 10 this time are shown in the chart of FIG. The experimental data shown in FIG. 3 describes and measures various parameters described in the left column of the chart for the three experimental cases of case 1 to case 3.

  Incidentally, in both cases 1 to 3, the mounting form of the light emitting diodes is such that 12 light emitting diodes are connected in series to form one series branch. In case 1 case, 30 rows and in case 2 case 36 In the case of row, case 3, 43 serial branches are provided on each printed circuit board. Therefore, in each case, 360, 432, and 516 light emitting diodes are mounted, respectively.

On the other hand, the printed circuit board 11 used in this experiment has a long rectangular shape with a length of 102.6 cm and a width of 4.4 cm, and the portion where the light emitting diode 12 is mounted is 99.1 cm × 3. The size is 6 cm. Therefore, the substantial area of the light emitting diode mounting portion is 357.6 cm 2, and the mounting density of the light emitting diodes in each case is as follows.
Case 1 1.007 pieces / cm2
Case 2 1.208 / cm2
Case 3 1.443 / cm2

In this experiment, a DC constant current power source was used as the power source of the illumination device 10, and the supply current to the printed circuit board 11 was set to the same 500 mA in each case. Therefore, in each case, the average current flowing through one line of serial branches, that is, the average current flowing through one light emitting diode has the following values.
Case 1 500mA / 30 rows ≒ 16.7mA
Case 2 500mA / 36 rows ≒ 13.9mA
Case 3 500mA ÷ 43 rows ≒ 11.6mA

  The rated current of the light emitting diode used in this experiment is about 20 mA. Therefore, in each of the above cases, a drive current of approximately 84%, 70%, and 58% of the rated current flows through each light emitting diode.

  Incidentally, it is known that the amount of heat generated from the light emitting diode is proportional to the output (power consumption), and the power consumption is proportional to the square of the current flowing through the light emitting diode. Therefore, the relationship between the heat generation amount of the light emitting diode and the drive current flowing through the light emitting diode generally has a form in which the heat generation amount rapidly increases as the current increases as shown in FIG.

  For example, when the current flowing through the light emitting diode is reduced to about 60 to 70% Io with respect to the rated current Is, the heat generation amount Qo of the light emitting diode is less than half of the heat generation amount Qs when the rated current Is is passed. Reduced to That is, by reducing the current flowing through the light emitting diode, the thermal stress applied to the light emitting diode can be reduced, in other words, the lifetime can be extended.

  On the other hand, it has been confirmed that the relationship between the current flowing through the light emitting diode and its illuminance (luminance) changes almost linearly within the rated current range. Therefore, when the current flowing through the light emitting diode is reduced, the luminance at the time of light emission is naturally lowered.

  The present invention compensates for such a decrease in luminance by increasing the number of light emitting diodes, and this can be compared to a simple metaphor as follows. That is, when one light-emitting diode is replaced with two adjacent light-emitting diodes and half of the current is passed through each light-emitting diode, the same overall brightness is obtained, and the heat generation of each light-emitting diode is achieved. The amount is suppressed to 1/4 or less of that at one time, and the lifetime is increased.

  The gist of the present invention is that even when the current flowing through the light-emitting diode is reduced, the number of light-emitting diodes is increased to maintain substantially the same illuminance, and between the current reduction rate and the light-emitting diode increase rate. This is the point at which a practical correlation was obtained experimentally.

For this purpose, in this experiment, the current reduction rate α and the mounting density increase rate β of the light emitting diodes in other cases 2 to 3 are obtained with the case 1 as a reference. In the present invention, the illuminance coefficient k is defined as follows as a parameter relating the current reduction rate α and the mounting density increase rate β.
k = α × β …… (1)

If the above equation (1) is modified
β = (1 / α) x k (2)
Therefore, by using the illuminance coefficient k obtained experimentally or empirically using the above equation (2), the increase rate β of the mounting density of the light emitting diodes can be obtained from the target current reduction rate α. Can also be predicted.

The numerical values of α, β, and k in this experiment are as shown in the chart of FIG. 3. If this is described again, the following values are obtained.
In case 2 α = 0.732 β = 1.200 k = 0.998
In case 3 α = 0.695 β = 1.433 k = 0.996

  In this experiment, using the fact that the brightness of the light emitting diode changes almost in proportion to the current within the rated current range, the current decrease rate α and the mounting density increase rate β cancel each other. In other words, β was calculated in advance so that k≈1, and the number of light emitting diodes mounted in cases 2 and 3 was determined based on β.

  Next, the illuminance measurement result of each case in this experiment will be described. Incidentally, the illuminance measurement method is performed according to the method of “JIS C7612”, and the illuminance measurement device is performed using an illuminance measuring device according to “JIS C1609”. The results of the illuminance measurement in each case are as shown in the chart of FIG. 3. In cases 2 and 3, the current flowing through the light-emitting diode was reduced compared to case 1 in comparison with case 1, but less than in case 1. The illuminance was increased by 10% and by about 20%.

  In view of such experimental data, it was actually found that even if the value of the illuminance coefficient k is set to a value lower than the above numerical value (k≈1), as a result, substantially the same illuminance can be obtained. . That is, it has been proved that substantially the same illuminance can be actually obtained even when the increase rate β of the mounting density of the light emitting diodes is suppressed lower than the current reduction rate α.

  Based on the experimental results, it was assumed that almost the same illuminance was obtained in each case, and the illuminance coefficient correction value k ′ was calculated. Based on the value, a correction value β ′ for the increase rate of the mounting density was calculated using the above equation (2). The values of k ′ and β ′ obtained in this way are as shown in Chart 3, and the assumed number of light-emitting diodes mounted in cases 2 and 3 estimated from β ′ is shown in the chart.

  Further, the input power in this experiment, that is, the input power on the primary side of the power supply device 15 is 21.7 W in each case, and the luminous efficiency (lux / W) in each case is the value shown in the chart of FIG. It becomes. In general, in view of the luminous efficiency of the existing “32W + 30W” type fluorescent lamp is around 23 (lux / W), the experimental data can be said to be a very good result.

  In the present invention, it goes without saying that the current supplied to the light emitting diode can be freely adjusted by incorporating a predetermined current control means (not shown) in the lighting device 10. It is also possible to maintain a current supplied to the light emitting diode at an appropriate value by providing a predetermined temperature sensor and an illuminance sensor (not shown) in combination and performing current feedback control.

  By the way, since plants produce their nutrients by photosynthesis, in indoor cultivation of plants, it is preferable to place a light source as close to the plant as possible and apply a sufficient amount of light to the leaves and stems of the plant. In general, the light emitted from the light source is attenuated in inverse proportion to the square of the distance from the light source. However, since the amount of heat generated in the conventional lighting device is large, if the lighting device is placed in the vicinity of the cultivated plant, there is a possibility that the leaves and stems of the plant may be damaged by the heat generated from the device.

  However, according to the illuminating device according to the present invention, the light emitting diode is driven with a current smaller than the normal rated current, so that the amount of heat generated from the illuminating device can be kept extremely low. For this reason, in an indoor cultivation facility such as a plant, even if a lighting device is installed in the vicinity of a plant leaf or stem (for example, a distance of about 10 cm), the cultivated plant may be damaged by heat generated from the lighting device A small amount of light can be given to the plant.

  In the present invention, since the drive current flowing through the light emitting diode is small, it is possible to reduce current noise that increases in proportion to the drive current. Furthermore, thermal runaway breakdown due to a decrease in the forward voltage of the light emitting diode, which tends to occur due to an increase in drive current (the forward voltage decreases due to heat generation at the PN junction surface of the diode accompanying the increase in current, thereby further increasing the current. The risk of device destruction caused by a vicious circle can also be reduced.

  As described above, according to the present invention, while maintaining almost the same illuminance as that of the conventional lighting device, the amount of heat generation is remarkably small, and the lifetime of the light-emitting diode is greatly increased. A light-emitting diode illuminating device can be realized at a low price.

  The embodiments of the present invention are not limited to the examples described above. For example, the shape and arrangement of each part constituting each of the examples, or the material thereof is the gist of the present invention. It goes without saying that changes can be made as appropriate according to actual embodiments without departing.

The configuration of the present invention described above can be used in the field of lighting devices using light emitting diodes used in indoor cultivation facilities such as plants and vegetables.

It is a figure which shows the outline | summary of the light emitting diode illuminating device by this invention. It is a figure which shows an example of the circuit structure of the light emitting diode illuminating device by this invention. It is a graph which shows the experimental data regarding the light emitting diode illuminating device of this invention. It is a figure showing the relationship between the electric current in a light emitting diode, and the emitted-heat amount.

DESCRIPTION OF SYMBOLS 10 ... Light emitting diode illuminating device 11 ... Printed circuit board 12 ... Light emitting diode 13 ... Transparent case 14 ... Current limiting resistor 15 ... Power supply circuit

Claims (5)

A light-emitting diode illuminating device in which a large number of resin-sealed light emitting diodes are laid on a printed circuit board, and the printed circuit board is housed in a case such as a transparent resin,
The light-emitting diode illuminating device characterized in that the value of the average current flowing through the light-emitting diode is set to 55% to 85% of the rated value, more preferably around 70% of the rated value.   The installation density of the light emitting diodes laid adjacently on the printed circuit board is set to 1.0 to 1.5 per square centimeter, and more preferably limited to about 1.2 per square centimeter. The light-emitting diode illuminating device according to claim 1.   A value obtained by multiplying the reduction ratio α of the current flowing through the light emitting diode by a coefficient of 0.8 to 1.0 with respect to the numerical value of 1 / α is defined as an increase rate β of the installation density of the light emitting diodes on the printed circuit board. 3. The light-emitting diode illuminating device according to claim 1, wherein the number of light-emitting diodes laid on the printed circuit board is increased in accordance with the rate β, and the illuminating device as a whole maintains substantially the same illuminance as before the current reduction. .   4. The light emitting diode illumination according to claim 1, further comprising a predetermined current control unit, wherein a value of a current flowing through the light emitting diode can be freely adjusted within a predetermined range. 5. apparatus. 5. The light-emitting diode illuminating device according to claim 1, wherein the light-emitting diode illuminating device can be installed at a distance of about 10 centimeters from a cultivated plant in indoor cultivation of the plant.

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