LED light source device

Abstract

To provide a stable LED light source device that reduces the temperature rise caused by lighting an LED and prevents the LED's light emission wavelength and light intensity from changing over time after lighting.SOLUTION: By using an LED light source device equipped with an input device and a display device for accurately adjusting the duty ratio, the duty ratio of the pulsed lighting of the LED light source is adjusted to a predetermined value of 0.01% or more and less than 100%, preferably 0.01% or more and 10% or less, thereby reducing changes in the light emission wavelength and light emission intensity with the lighting time when the LED light source device is turned on.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention solves the problem that the emission peak wavelength of an LED light source becomes longer and the emission intensity decreases due to the temperature rise of the LED accompanying energization for lighting, and provides a stable LED light source device with no temporal change in the emission peak wavelength and emission intensity for high-precision optical measurement.

Background Art

[0002] A small, power-saving, high-output LED light source capable of corresponding to various emission wavelengths is important as a light source for fluorescence characteristic evaluation of an optical crystal, or a fluorescence thermometer, or quality evaluation using light scattering or fluorescence, or a light source for still image or moving image shooting for quality inspection. As lighting methods for the LED light source used in these measurements, there are a method of continuously lighting using a DC constant current power supply, a method of pulse lighting the LED using a pulse power supply, and PWM (Pulse Width Modulation) dimming in which the ratio (Duty ratio) of the lighting time of the pulse lighting LED light source to the time of one pulse period is changed for dimming. The Duty ratio of the pulse lighting LED light source is a value representing the ratio occupied by the lighting time in one period of the pulse, and can be calculated as Duty ratio = 100x(lighting time in one pulse period) / (time of one pulse period)=100x(lighting time in one pulse period) / (lighting time in one pulse period + extinguishing time in one pulse period).

[0003] An LED light source continuously lit using a DC constant current power supply is used for measurements such as fluorescence, light scattering, light absorption, or refractive index. However, the LED generates heat due to energization for lighting of the LED light source, and the temperature of the LED gradually rises. Due to the temperature rise of the LED, the emission peak wavelength of the LED light source gradually becomes longer and the emission intensity of the LED light source gradually decreases. The instability of the LED light source accompanying energization for lighting has been a major problem when using the LED light source as a light source for precise measurement. In order to reduce the lengthening of the emission peak wavelength and the decrease in emission intensity due to the temperature rise of the LED, aging of 10 minutes to 30 minutes or more was required after lighting the LED light source.

[0004] LED light source devices that pulse-light LEDs using a pulse power supply have been used for measuring transient phenomena such as measuring temperature with a fluorescence thermometer that measures temperature with fluorescence lifetime and measuring the time-resolved spectrum of fluorescence. Pulse-lighting LEDs that repeat lighting and extinguishing at a constant period are advantageous for reducing temperature rise because the LED can be cooled during extinguishing. However, even in the case of a pulse-lighting LED light source, the LED generates heat during lighting, so the temperature rise of the LED cannot be completely prevented. For this reason, in order to reduce the lengthening of the emission peak wavelength and the decrease in emission intensity of the LED light source, aging to stabilize the temperature of the LED by energizing and lighting it for a long time before using the LED light source was essential.

[0005] A PWM dimming type LED light source device that dims by changing the duty ratio of a pulse-lighting LED light source has been widely used as a brightness adjustment technology for lighting fixtures using white LEDs. White LEDs emit pseudo-white light by combining blue LEDs and yellow-emitting phosphors (Ce-doped YAG phosphors). In white LED lighting, blue light emitted from the blue LED is used to generate yellow light from the yellow-emitting phosphor and mixed with the blue light of the blue LED to create pseudo-white light. When the current is adjusted to adjust the emission intensity of the white LED, the balance between the intensity of the blue light emitted by the blue LED and the yellow fluorescence emitted by the yellow phosphor changes, and the color of the white LED changes to "bulb color" or "warm white" or "day white" or "daylight color" in the order of decreasing ratio of blue light. For this reason, a PWM dimming type LED light source that dims by changing the duty ratio of a pulse power supply that can be dimmed without changing the current value flowing through the white LED has been used as a white light lighting fixture.

[0006] The PWM dimming technology for adjusting the brightness of LED light sources is described in Patent Document 1, Patent Document 2, and Patent Document 3. The temperature rise and output decrease phenomena due to the lighting of LEDs are described in Patent Document 2, but no positive preventive measures have been taken against the temperature rise of LED light sources. Also, the technology for stabilizing the emission color of LEDs using PWM dimming technology is described in Patent Document 4, Patent Document 5, Patent Document 6, and Patent Document 7. Thus, the conventional PWM dimming technology described in patent documents has been used for the purpose of adjusting the brightness of LED lighting fixtures and stabilizing the emission color associated with dimming. In conventional PWM dimming type LED light sources, it was impossible to prevent the decrease in emission intensity and the shift of the emission peak wavelength to longer wavelengths due to the temperature rise accompanying the lighting of LEDs. Therefore, when using a PWM dimming LED light source for dimming of white lighting fixtures as a stable light source for precise measurement, the temperature rise of LEDs due to long-time lighting or large current input and the accompanying shift of the peak wavelength to longer wavelengths and the decrease in emission intensity have been a major obstacle.

[0007] In conventional LED light sources, it was impossible to prevent the shift of the emission peak wavelength to longer wavelengths and the decrease in emission intensity due to the temperature rise of LEDs during lighting. In order to reduce the shift of the emission peak wavelength to longer wavelengths and the decrease in emission intensity due to the temperature rise of LEDs, methods such as temperature control of LEDs, feedback control of emission intensity, and long-time aging have been devised, either alone or in combination of multiple methods, but they have not been sufficiently effective countermeasures. Furthermore, these technologies for improving the stability of LED light sources have greatly impaired the advantages of LED light sources such as being small, simple, and low-cost due to drawbacks such as an increase in device cost, an increase in the size of the device, and an increase in power consumption. For this reason, as a light source device for precise optical measurement, a halogen lamp, a Xe lamp, a deuterium lamp, a laser, etc. that have a proven track record of being able to be used as a stable light source by performing aging have been used as before.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

[0009] [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-171480, December 21, 2005

[0010] [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-192421, February 2, 2007

[0011] [Patent Document 4] Japanese Patent Application Laid-Open No. 2022-76540, May 20, 2022

[0012] [Patent Document 5] Japanese Patent Application Laid-Open No. 2022-114904, August 8, 2022

[0013] [Patent Document 6] Japanese Patent Application Laid-Open No. 2023-54927, April 17, 2023

[0014] [Patent Document 7] Japanese Patent Application Laid-Open No. 2023-101954, July 24, 2023 [Summary of the Invention] [Problems to be Solved by the Invention]

[0015] In an LED light source that is lit using a conventional DC constant current power supply, the LED generates heat due to energization for lighting, causing the temperature of the LED to rise. The increase in the temperature of the LED causes the emission wavelength of the LED light source to shift to a longer wavelength and the emission intensity to decrease. When the input current of the LED is small, the temporal changes in the emission wavelength and emission intensity due to lighting are slight. However, when the input current is large, the temporal changes in the emission wavelength and emission intensity become large, posing a significant obstacle to precise measurement. Temperature control of the LED, feedback control of the emission intensity, and long-term aging, which were devised to solve these problems, impaired the advantages of the LED.

[0016] In an LED light source that is lit using a conventional pulse light source, the lighting and extinguishing of the LED light source are repeated within one cycle of the pulse. When the LED light source is lit using a pulse power supply, compared to when it is lit using a DC constant current power supply, the lighting time of the LED light source is shortened and there is an extinguishing time for cooling, which is advantageous for preventing temperature rise due to the heat generation of the LED. However, when the input current of the LED is large, it is not possible to completely prevent the temperature rise due to the heat generation of the LED, so the temperature of the LED gradually rises, and it has not been possible to solve the problems of the increase in the emission wavelength and the decrease in the emission intensity.

[0017] In conventional LED lighting fixtures, PWM dimming that adjusts the brightness of the LED lighting fixture by adjusting the ratio of the lighting time and extinguishing time of the pulse-driven LED light source has been used. By PWM dimming, the power consumption is kept low, and the brightness of the LED light source is adjusted by changing the ratio (duty ratio) of the lighting time and extinguishing time. However, in conventional PWM dimming, it has not been possible to prevent the increase in the peak wavelength and the decrease in the emission intensity due to the temperature rise during the lighting of the LED. In this invention, for the stabilization of the LED light source, which was impossible with conventional technologies, stabilization of the LED light source has been achieved by optimally adjusting the duty ratio of the pulse-driven LED light source. This invention solves the instability of the emission intensity and emission peak wavelength of the LED caused by the temperature rise of the LED during lighting by optimizing the duty ratio using pulse lighting without impairing the advantages of the LED light source.

Means for Solving the Problems

[0018] The time variations of the emission peak wavelength and the emission intensity of LEDs with various emission wavelengths when lit using a DC constant current power supply were measured in detail by changing the magnitude of the input current of the LEDs. As a result, when the LED light source was lit with a low input current of 10 mA or less, no time variations of the emission peak wavelength and the emission intensity were observed. When the LED was lit with a large current of 20 mA or more, time variations of the emission peak wavelength and the emission intensity were observed. The time variations of the emission peak wavelength and the emission intensity became more intense as the input current of the LED increased. It was found that these time variations of the emission peak wavelength and the emission intensity continued for 10 to 30 minutes after the LED light source was lit and then gradually stabilized. Therefore, in order to perform high-precision measurements with an LED light source device, it was necessary to perform aging for a long time of 10 to 30 minutes or more after the LED light source was lit in order to stabilize the emission intensity of the LED light source.

[0019] When the emission peak wavelength and the change in the emission intensity of the LED due to the temperature of the LED were measured by changing the temperature of the LED, the peak wavelength of the LED was shifted to a longer wavelength and the emission intensity decreased due to a temperature rise from 22°C to 80°C. From this result, it was found that time variations of the emission peak wavelength and the emission intensity occurred due to a temperature rise of the LED from 22°C to 80°C accompanying energization. Therefore, it was found that in order to prevent time variations of the emission peak wavelength and the emission intensity, it was necessary to stabilize the temperature of the LED during lighting by some method.

[0020] The time variation of the emission intensity of LEDs with various emission wavelengths due to the difference in the duty ratio of the power pulse when lit using a pulse power supply was measured in detail under the conditions of changing the lighting frequency and the input current of the LED. As a result, when the duty ratio of the pulse power supply was made smaller than a predetermined value, the change in the emission intensity of the LED light source could be reduced, and a stable light source could be realized. In the pulse lighting of the LED light source, the LED is heated and its temperature rises during lighting and is naturally cooled during extinguishing. Therefore, by optimizing the duty ratio with respect to the conditions of the pulse lighting frequency and the input current of the LED, the LED heated during lighting could be sufficiently cooled during extinguishing. As a result, it became possible to keep the LED at a stable temperature immediately after lighting, and it is considered that the LED light source could be stabilized. From this, it was found that by using a pulse-driven LED light source and making the duty ratio of the pulse power supply smaller than a predetermined value determined in advance, a stable light source with no time variation in the emission intensity during the lighting of the LED light source without long-term aging could be realized.

[0021] By pulse-driving the LED light source and optimizing the ratio of the lighting time to the time of one cycle (duty ratio), the decrease in the light source intensity due to the heat generation of the LED could be improved. In many cases, the time variation of the light intensity of the light source could be reduced under the lighting condition where the duty ratio was 10% or less. The increase in the emission peak wavelength and the decrease in the emission intensity accompanying the lighting of the LED light source become serious problems when a strong light source intensity is required. This LED light source device of the present invention is considered to be particularly important in cases where a stable light source such as fluorescence spectrum measurement requiring a strong light source is needed. Since a stable LED light source device can be realized with a simple lighting power supply applying a PWM dimming circuit, it can be applied to the improvement of performance of small-sized inspectors using light and the like.

Advantages of the Invention

[0022] The decrease in luminous intensity and the red shift of the emission peak wavelength associated with the heat generation of an LED due to energization have been inevitable problems for LED light source devices. Conventionally, methods such as temperature control of the LED, feedback control of the luminous intensity, and long-term aging have been devised and used alone or in combination to stabilize the LED light source. These methods have drawbacks such as the need for a temperature control device for the element, a detector and feedback circuit for the luminous intensity, and long-term aging before measurement, which compromise the advantages of being small, simple, and low-cost for LED light sources. With the method of the present invention, it is possible to provide an LED light source that does not require a special device for stabilizing the LED light source or long-term aging before measurement and enables highly accurate measurement immediately after lighting.

[0023] When an LED light source is lit using a pulse power supply, since lighting and extinguishing are repeated at the period of the pulse power supply, the energization time during lighting becomes short and the LED can be cooled during extinguishing. Therefore, when an LED light source is lit using a pulse power supply, it is possible to input a larger current compared to the case where the LED light source is lit using a DC constant current power supply. Furthermore, by adjusting the duty ratio to a predetermined value when lighting the LED light source using a pulse power supply, it becomes possible to perform cooling for a sufficient time with respect to the heating during the lighting time. It was possible to reduce the temperature rise of the LED due to energization and realize a stable LED light source with no temporal change in the emission peak wavelength and luminous intensity. Furthermore, since it became possible to sufficiently cool the LED during lighting, it became possible to use it with an input current larger than the rated input current of the LED. Therefore, it can be used as a powerful and stable light source in the measurement technology of trace fluorescent substances that require an LED light source with a powerful luminous intensity to excite weak fluorescence.

[0024] When the LED light source is lit with a small duty ratio using a pulse power supply, the visual light emission intensity becomes significantly weaker compared to when the LED light source is lit with a large duty ratio at the same frequency and the same input current. Also, the measured value of the true RMS of the light emission intensity becomes smaller. However, the measured value of the amplitude (Vp-p) of the light output when using a pulsed LED light source that lights the LED with a small duty ratio is the same as that when using a pulsed LED light source with a large duty ratio. Although the true RMS varies depending on the duty ratio of the LED light source, since the measured value of the amplitude (Vp-p) of the light output is not affected by the duty ratio of the light source, measuring the amplitude (Vp-p) of the light output is advantageous for measurements using the LED light source device of this invention, which is characterized by adjusting the duty ratio. To correct for the influence of the duty ratio on the true RMS, the relational expression between the true RMS and the peak value (Vp-p) can be used, or the calibration curve of the true RMS and the peak value (Vp-p) created in advance can be used.

[0025] In actual light measurement using the LED light source device of this invention, more stable measurement becomes possible by making the pulse lighting frequency of the LED light source device higher than the data sampling frequency of the measurement device. Also, stable measurement becomes possible by synchronizing the data sampling frequency of the measurement device with the pulse lighting frequency of the LED light source device.

Brief Description of the Drawings

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Mode for Carrying Out the Invention

[0027] The LED light source device of the present invention is shown in Fig. 1. The LED light source device in Fig. 1 is composed of a constant current pulse power supply 1, a PWM signal generator 2, a protection resistor 3 for current limiting, and an LED 4. As the LED 4, in addition to near-infrared (wavelengths 840 and 950 nm), red (wavelength 620 nm), yellow (wavelength 600 nm), green (wavelength 540 nm), blue (wavelength 480 nm), purple (wavelengths 405 and 415 nm), ultraviolet (wavelengths 365, 375, and 385 nm), UVC (wavelengths 265 and 275 nm), etc., LEDs with various emission wavelengths can all be used. The constant current pulse power supply 1 and the PWM signal generator 2 can use all kinds of pulse power supplies and PWM signal generators in addition to WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier or AFG-2125 manufactured by NF Circuit Design Block or Instek. Since the emission intensity of the LED light source is determined by the magnitude of the input current, it is best to use a constant current pulse power supply as the pulse power supply 1, but it is also possible to make the input current of the LED constant by using a combination of a constant voltage pulse power supply and the protection resistor 3 for current limiting shown in Figs. 1 and 2. In the LED light source device of the present invention, in order to limit the input current of the LED 4 or to prevent damage to the LED 4, a protection resistor 3 for current limiting with a resistance value (R) calculated using the formula R = (V - Vf) / I from the forward voltage (Vf), input current (I), and applied voltage (V) of the LED 4 is installed in series with the LED 4 in the circuit as needed.

[0028] Figure 2 shows an LED light source device in which a photodetector 5, a digital multimeter 6, an oscilloscope 7, and a measurement and control computer 8 are added to the LED light source device of FIG. 1, and are connected to the measurement and control computer 8 using a communication control cable 9 such as a USB cable together with the constant current pulse power supply 1 and the PWM signal generator 2. In addition to the USB cable, connection by a communication control cable such as RS232C, GP-IB, or LAN, or wireless connection by wireless LAN, WiFi, or Bluetooth is also possible. By connecting the digital multimeter 6, the oscilloscope 7, and the measurement and control computer 8 using the LED light source device of FIG. 2, high-precision optical measurements such as fluorescence spectrum measurement, light scattering spectrum measurement, and light absorption spectrum measurement using the LED light source device of the present invention become possible. Furthermore, by connecting the constant current pulse power supply 1, the PWM signal generator 2, and the measurement and control computer 8 using a communication control cable 9 such as a USB cable, it becomes possible to adjust manually or using the measurement and control computer 8 to an optimal duty ratio for stabilizing the light emission intensity of the LED light source device. For adjusting the duty ratio, a connection by a communication control cable such as RS232C, GP-IB, or LAN or a wireless connection by wireless LAN, WiFi, or Bluetooth may be used instead of the USB cable.

[0029] As a lighting method for an LED light source device, there are a method of constantly lighting with a DC constant current power supply, a method of pulse lighting with a pulse power supply, or a method of pulse lighting by adjusting the duty ratio of the pulse power supply. By using a DC constant current power supply (such as PMX18-2A manufactured by Kikusui) instead of the pulse power supply 1 for driving the LED and the pulse signal generator 2 for adjusting the duty ratio in FIGS. 1 and 2, it becomes an LED light source device of the conventional DC constant lighting method. FIG. 3 shows the time change 10 of the input current of the LED, the time change 11 of the temperature of the LED, the time change 12 of the light emission intensity of the LED, and the time change 13 of the light emission peak wavelength of the LED when the LED is lit by the method of constantly lighting with a DC constant current power supply. As shown in FIG. 3, in the LED lit by the DC constant current power supply, the temperature 11 of the LED rises with the lighting time, the light emission intensity 12 of the LED decreases, and at the same time the light emission peak wavelength 13 of the LED becomes longer. Each change is due to the temperature change 11 of the LED caused by lighting, and the change continued for a long time of 10 minutes to 30 minutes or more after lighting.

[0030] The state of the time change of the input current of the LED, the time change of the temperature of the LED, the time change of the light emission intensity of the LED, and the time change of the light emission peak wavelength of the LED when the LED is pulse lit using the LED light source device of FIG. 2 are shown in FIGS. 4 and 5. FIG. 4 shows an example when the duty ratio of the pulse lighting is large. When the duty ratio of the pulse lighting is large, along with the time change 14 of the input current of the LED, the time change 15 of the temperature of the LED is large, the light emission intensity 16 of the LED decreases with time, and the light emission peak wavelength 17 of the LED becomes longer with time. When the duty ratio is large, the time for cooling the heat generated by the LED during lighting by turning off the light is not sufficient, and the temperature of the LED rises with time. For this reason, the light emission intensity 16 of the LED decreases with the lighting time, and the light emission peak wavelength 17 of the LED becomes longer.

[0031] Fig. 5 shows an example of an LED light source device when the duty ratio of pulse lighting is small. When the duty ratio of pulse lighting is small, the time change 19 of the temperature of the LED accompanying the time change 18 of the input current of the LED is small, the change in the light emission intensity 20 of the LED is small, and the change in the light emission peak wavelength 21 of the LED is also small. Thus, when the duty ratio is small, it becomes possible to sufficiently cool the heat generated by the LED during lighting by turning off the light, so that the temperature of the LED can be stabilized. Therefore, by appropriately adjusting the duty ratio, the time change 16 of the light emission intensity of the LED and the time change 17 of the light emission peak wavelength of the LED can be reduced, and a stable LED light source device can be realized.

[0032] Fig. 6 shows the time change 22 of the input current and the time change 23 of the temperature of the LED during one pulse of an LED light source device with a small duty ratio of pulse lighting. When the duty ratio of pulse lighting is small, the temperature of the LED rises as the LED lights up due to energization. However, since the duty ratio is small, the off time is long compared to the on time, so the LED can be sufficiently cooled. Since it becomes possible to sufficiently cool the heat generated by the LED during lighting by turning off the light, it becomes possible to suppress the rise in the LED temperature. By appropriately adjusting the duty ratio, the temperature of the LED can be stabilized, so the time change in the light emission intensity and the time change in the light emission peak wavelength of the LED can be reduced.

[0033] Fig. 7 shows the time variation of the emission intensity of an LED light source device with a high pulse lighting frequency. When the duty ratio is small (24), the value of the true root mean square (true RMS) 25 of the emission intensity of the LED light source device and the value of the pulse height (Vp-p) 26 become constant after the LED is lit. When the duty ratio is large (27), the value of the true root mean square (true RMS) 28 of the emission intensity of the LED light source device and the value of the pulse height (Vp-p) 29 decrease significantly after the LED is lit. When the duty ratio is about 50% (30), the value of the true root mean square (true RMS) 31 of the emission intensity of the LED light source device and the value of the pulse height (Vp-p) 32 decrease after the LED is lit. It was found that the value of the true root mean square (true RMS) of the emission intensity of the LED light source device and the value of the pulse height (Vp-p) change more significantly as the duty ratio increases. Therefore, it was found that in order to realize an LED light source device with stable emission intensity, it is necessary to adjust the duty ratio to the lowest value. In optical measurements using a pulse light source such as the LED light source device shown in Fig. 2, in addition to the method of measuring the light intensity using the true root mean square (true RMS) employed by many AC measuring devices, it is possible to measure using the value of the peak intensity (Vp-p) that always becomes a constant value even when the duty ratio changes. Here, the duty ratio is from 0.01% or more to 10% or less, and the lower limit is set to 0.01% due to the specification constraints of the PWM signal generator 2 used in the experiment, which is the minimum value that can be set. In this range, it has been confirmed that the heat generated when the LED is lit can be sufficiently cooled during the off state. Even in the case of a duty ratio less than 0.01%, since the time when current flows through the LED is shorter than when the duty ratio is 0.01%, the amount of heat generated is also less, and it is certain that the heat generated when the LED is lit can be sufficiently cooled during the off state, and the emission intensity of the LED can be kept constant. On the other hand, if the duty ratio is made too small, the flowing current decreases, and it becomes difficult to achieve the predetermined emission of the LED. Therefore, this duty ratio needs to be set to a value that generates a current enabling this predetermined emission or a value larger than that.

[0034] In the actual light measurement using the LED light source device of the present invention, the measurement can be stabilized by adjusting the pulse lighting frequency of the LED light source device to be faster than the data sampling frequency of the measurement device, the shutter speed when taking a still image, or the frame rate when shooting a video. Also, stable measurement is possible by synchronizing the data sampling frequency of the measurement device with the pulse lighting frequency of the LED light source device.

[0035] The LED light source device of the present invention is composed of an LED and a pulse power source with an adjustable duty ratio. The pulse power source with an adjustable duty ratio has substantially the same configuration as an LED lighting circuit capable of PWM dimming, but in order to stabilize the temperature of the LED, it is a feature of the LED light source device of the present invention to adjust the duty ratio to a predetermined optimal value of 0.01% or more and less than 100%, preferably 0.01% or more and 10% or less. Therefore, the LED light source device of the present invention is equipped with a data input device that can be accurately adjusted to a duty ratio of 0.01% or more and less than 100%, preferably 0.01% or more and 10% or less, and a display device that can display the adjusted duty ratio. Furthermore, by adjusting them manually or using a computer 8 for measurement and control, a stable LED light source device for high-precision measurement becomes possible. By measuring in advance the duty ratio of the pulse power source of various LED light sources and the time change of the light emission intensity of the LED light source with respect to the frequency of various power pulses and the input voltage (current), and based on this result, a stable LED light source device can be realized by adjusting the duty ratio so that the time change of the light emission intensity of the LED light source can be reduced. In the LED light source device of the present invention, by pulse lighting the LED at the optimal duty ratio, the heat generated when the LED is lit can be sufficiently cooled during the off state, so that the light emission intensity of the LED can be kept constant.

Example

[0036] Using the LED light source device of FIG. 2, the time change of the emission intensity of the LED was measured by changing the duty ratio of the pulse power supply. As the LEDs, near-infrared (wavelengths 840 and 950 nm), red (wavelength 620 nm), yellow (wavelength 600 nm), green (wavelength 540 nm), blue (wavelength 480 nm), purple (wavelength 405 nm), ultraviolet (UVA (wavelength 365 nm), UVC (wavelengths 265 and 275 nm)) LEDs were used. As the pulse power supply and pulse generator, WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier or AFG-2125 manufactured by NF Circuit Design Block or Instek was used. To prevent damage to the LED, a resistor of 100 Ω to 600 Ω was calculated from the Vf value and input current value of the LED and installed in series with the LED as a protective resistor. For measuring the time change of the emission intensity, a Si photodiode (PDA36-EC manufactured by Solarbo or S6775 or S12698-04 manufactured by Hamamatsu Photonics), a digital multimeter (PC-7000 manufactured by Sunwa), a measurement and control computer 8 (manufactured by Dospara), and a USB oscilloscope (2204 or 2205A or 4224A manufactured by Picoscope) were used. These devices and the measurement and control computer 8 were connected by a communication control cable 9 such as a USB cable. Instead of the USB cable, connection by a communication control cable such as RS232C or GP-IB or LAN or wireless connection by wireless LAN or WiFi or Bluetooth may be used.

[0037] Using LEDs of near-infrared (wavelengths 840 and 950 nm), red (wavelength 620 nm or 405 nm), or ultraviolet (UVA (wavelength 365 nm) or UVC (wavelengths 265 and 275 nm)), the time variation of the emission intensity was measured under the conditions of direct current and pulsed current with the highest possible power supply frequency of 10 Hz, 100 Hz, 1 kHz, 10 kHz, 100 kHz, or 1 MHz, a duty ratio of 0.01% or more and less than 100%, and an applied voltage of 3.0 V to 10 V. For all the LEDs used in the measurement, a time variation of the emission intensity was observed when the input current was large and when the duty ratio was large. It was found that the magnitude of the time variation of the emission intensity increased as the input current of the LED increased.

[0038] Fig. 8 shows the results of measuring the time variation of the emission intensity of a red LED using the LED light source device of Fig. 2. The time variation 33 of the value of the true root mean square (true RMS) of the emission intensity of the red LED, the emission intensity 34 of the red LED when the duty ratio was 90% decreased rapidly after the LED was turned on, while the emission intensity 35 of the red LED when the duty ratio was 10% was constant after the LED was turned on. Similarly, the time variation 36 of the value of the pulse height (Vp-p) of the emission intensity of the red LED, the emission intensity 37 of the red LED when the duty ratio was 90% decreased rapidly after the LED was turned on. The emission intensities 38 of the red LED when the duty ratio was 50% and 39 of the red LED when the duty ratio was 20% also decreased after the LED was turned on, but the decrease in the LED intensity became smaller as the duty ratio decreased. The emission intensity 40 of the red LED when the duty ratio was 10% was constant after the LED was turned on. In order to reduce the time variation of the emission intensity when the input current of the LED is large, as shown in Fig. 9, it was found that it is necessary to pulse-light under the conditions of the duty ratio and the LED input current region 41 where the time variation of the emission intensity of the LED light source device with a duty ratio of 10% or less can be reduced. Using this result, it was possible to adjust the duty ratio to reduce the time variation of the emission intensity for various lighting conditions.

Example

[0039] The fluorescence spectrum was measured using the LED light source device of FIG. 2. As the LED, red (wavelength 620 nm) or yellow (wavelength 600 nm) or green (wavelength 540 nm) or blue (wavelength 480 nm) or purple (wavelength 405 nm) or ultraviolet rays (UVA (wavelength 365 nm) or UVC (wavelengths 265 and 275 nm)) were used. A pulse power supply and a pulse generator (WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier or AFG-2125 manufactured by Instek) were used. The time change of the emission intensity was measured under the conditions that the maximum power frequency that could be generated was 10 Hz or 100 Hz or 1 kHz or 10 kHz or 100 kHz or 1 MHz, the duty ratio was 0.01% or more and less than 100%, and the applied voltage was 3.0 V to 10 V. To prevent damage to the LED, a resistor of 100 Ω to 600 Ω was calculated from the Vf value and the input current value of the LED as a protective resistor and installed in series with the LED. An optical fiber spectrometer (Ocean Optics, USB2000) was used for the measurement of the fluorescence spectrum. For the measurement of the fluorescence intensity, a Si photodiode (PDA36-EC manufactured by Solarbo or S6775 or S12698-04 manufactured by Hamamatsu Photonics), a digital multimeter (PC-7000 manufactured by Sunwa), and a USB oscilloscope (2204 or 2205A or 4224A manufactured by Picoscope) were used, and each was connected to a measurement and control computer 8 (manufactured by Dospara) with a communication control cable 9 such as a USB cable. For the connection, a connection using a communication control cable such as RS232C or GP-IB or LAN instead of the USB cable or a wireless connection using wireless LAN or WiFi or Bluetooth may be used.

[0040] Ruby (Al2O3 crystal doped with 0.4 mol% Cr) was used as a sample, and the fluorescence spectrum and fluorescence intensity were measured under the conditions that the frequency of the pulse power supply was 300 Hz, Vp-p = 7 V, and the offset was 3.5 V. Fluorescence of the R line of ruby could be observed at a wavelength of 694 nm. By adjusting the duty ratio of the pulse LED light source to 10% or less as in the stable region 41 of Fig. 9, stable fluorescence spectrum measurement and fluorescence intensity measurement were possible without aging of the LED light source before measurement. A stable fluorescence spectrum was possible under the conditions that the frequency of the pulse power supply was 300 Hz or more and the integration time was 3 ms or more. Stable fluorescence spectrum measurement became possible with the combination of the integration time of the photodetector and the pulse frequency of the pulse LED light source. Based on the stable region shown in the region 41 of the duty ratio and the LED input current where the time change of the emission intensity of the LED light source device shown in Fig. 2 can be reduced in the LED light source device shown in Fig. 9, by adjusting the duty ratio, light absorption spectrum measurement and light scattering spectrum measurement are also possible.

Example

[0041] The measurement of the fluorescence temperature sensor was performed using the LED light source device of FIG. 2. As the LED, red (wavelength 620 nm) or green (wavelength 540 nm) or blue (wavelength 480 nm) or purple (wavelengths 405 nm and 415 nm) or ultraviolet (wavelength 365 nm) was used. A pulse power supply 4 and a pulse generator (WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier manufactured by NF Circuit Design Block, Inc., or AFG-2125 manufactured by Instek) were used. The time change of the emission intensity was measured under the conditions that the power supply frequency was 10 Hz or 100 Hz or 1 kHz or 10 kHz or 100 kHz or 1 MHz, the duty ratio was 0.01% or more and less than 100%, and the applied voltage was 3.0 V to 10 V. To prevent damage to the LED, a resistor of 100 Ω to 600 Ω was calculated from the Vf value and the input current value of the LED and installed in series with the LED as a protective resistor. For the measurement of the fluorescence thermometer, an optical fiber spectrometer (Ocean Optics, USB2000) and a Si photodiode (PDA36-EC manufactured by Solarbo, or S6775 or S12698-04 manufactured by Hamamatsu Photonics), a digital multimeter (PC-7000 manufactured by Sunwa), a measurement and control computer 8 (manufactured by Dospara) and a USB oscilloscope (2204 or 2205A or 4224A manufactured by Picoscope) were used. For the connection of these devices, instead of a USB cable, a connection using a communication control cable such as RS232C or GP-IB or LAN or a wireless connection using wireless LAN or WiFi or Bluetooth may be used.

[0042] Using a fluorescence temperature sensor with a ruby (Al2O3 crystal doped with 0.4 mol% Cr) attached to the tip of an optical fiber as a temperature sensor, the fluorescence intensity from the fluorescence temperature sensor was measured under the conditions of a pulse power supply frequency of 300 Hz, Vp-p = 7 V, and an offset of 3.5 V. In the measurement using an optical fiber spectrometer, fluorescence of the R line of ruby at a wavelength of 694 nm could be observed from the ruby temperature sensor. By adjusting the duty ratio of the pulsed LED light source to 10% or less as in the stable region shown in region 41 of the duty ratio and LED input current where the time change of the emission intensity of the LED light source device in Fig. 9 could be reduced, stable measurement was possible without aging of the LED light source before measurement.

Example

[0043] The measurement of the backscattering of milk and the measurement of fluorescence intensity were performed using the LED light source device of FIG. 2. LEDs with near-infrared (wavelengths 840 and 950 nm), or red (wavelength 620 nm), or yellow (wavelength 600 nm), or green (wavelength 540 nm), or blue (wavelength 480 nm), or purple (wavelengths 405 nm and 415 nm), or ultraviolet (wavelength 365 nm) were used. A pulse power supply and a pulse generator (WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier manufactured by NF Circuit Design Block, Inc., or AFG-2125 manufactured by Instek) were used. To prevent damage to the LEDs, a resistor with a resistance of 100 Ω to 600 Ω was calculated from the Vf value and the input current value of the LEDs and installed in series with the LEDs as a protective resistor. The time change in the emission intensity was measured under the conditions that the maximum possible power supply frequency was 10 Hz or 100 Hz or 1 kHz or 10 kHz or 100 kHz or 1 MHz, the duty ratio was 0.01% or more and less than 100%, and the applied voltage was 3.0 V to 10 V. For the measurement of the fluorescence thermometer, an optical fiber spectrometer (Ocean Optics, USB2000), a Si photodiode (PDA36-EC manufactured by Solarbo), a digital multimeter (PC-7000 manufactured by Sunwa), a computer 8 for measurement and control (manufactured by Dospara), and a USB oscilloscope (2204 or 2205A or 4224A manufactured by Picoscope) were used. For connection, instead of a communication control cable 9 such as a USB cable, a connection using a communication control cable such as RS232C or GP-IB or LAN, or a wireless connection using wireless LAN or WiFi or Bluetooth may be used.

[0044] When measuring the backscattering of whole milk using an optical fiber, the backscattering intensities caused by fat particles and protein particles could be measured. By optimizing the duty ratio of the pulse power supply of the LED light source device used as the backscattering light source under the conditions that the frequency of the pulse power supply was 10 Hz, Vp-p = 7 V, and the offset was 3.5 V, like the duty ratio where the time change of the light emission intensity of the LED light source device in Fig. 9 could be reduced and the stable region shown in region 41 of the LED input current, the time change of the scattering intensity could be prevented, and it became possible to start the backscattering measurement without aging. In the measurement of the fluorescence intensity of milk, vitamin B2, which is an important nutritional component contained in milk, could be evaluated by fluorescence measurement using purple LEDs (wavelengths 405 nm and 415 nm) as the excitation light source. By optimizing the duty ratio of the pulse power supply of the LED light source device used as the fluorescence excitation light source to the stable region 41 in Fig. 9, the time change of the fluorescence intensity could be prevented, and it became possible to start the fluorescence measurement without aging. In the fluorescence measurement of trace components, a particularly powerful excitation light source is required, and the time changes of the emission peak wavelength and the emission intensity associated with the heat generation of the LED used as the light source were important issues. Therefore, in fluorescence measurement using an LED light source, aging for a long time of 30 minutes or more was indispensable for highly accurate and stable measurement. By optimizing the duty ratio of the pulse power supply with the LED light source device of this invention, the stabilization of the LED light source device was realized, and highly accurate fluorescence measurement became possible without aging.

Example

[0045] The LED light source device shown in Fig. 2 was used as an excitation light source for photographing still images and videos of fluorescence images, and as a light source for photographing videos and still images of normal images. LEDs with near-infrared (wavelengths 840 and 950 nm), red (wavelength 620 nm), yellow (wavelength 600 nm), green (wavelength 540 nm), blue (wavelength 480 nm), purple (wavelength 405 nm), ultraviolet (wavelength 365 nm), or UVC (wavelengths 265 and 275 nm) were used. A pulse power supply and a pulse generator (WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier manufactured by NF Circuit Design Co., Ltd., or AFG-2125 manufactured by Instek) were used. To prevent damage to the LEDs, a resistor with a resistance of 100 Ω to 600 Ω was calculated from the Vf value and the input current value of the LEDs and installed in series with the LEDs as a protective resistor. The time change in the emission intensity was measured under the conditions that the maximum possible power supply frequency was 10 Hz or 100 Hz or 1 kHz or 10 kHz or 100 kHz or 1 MHz, the duty ratio was 0.01% or more and less than 100%, and the applied voltage was 3.0 V to 10 V. A digital single-lens reflex camera (Canon, EOS X10) was used for photographing still images of fluorescence images, and a (L-836USB camera manufactured by Hoshan) was used for photographing videos and still images of fluorescence images. A measurement and control computer 8 (manufactured by Dospara) was used for image recording and image analysis. For connecting these devices, instead of a communication control cable 9 such as a USB cable, a connection using a communication control cable such as RS232C or GP-IB or LAN, or a wireless connection using wireless LAN or WiFi or Bluetooth may be used.

[0046] Ruby (Al2O3 crystal doped with 0.4 mol% Cr) was used as a sample for fluorescence imaging. In the measurement using an optical fiber spectrometer, fluorescence of the R line of ruby at a wavelength of 694 nm could be observed from the ruby temperature sensor. Still images and moving images of the red fluorescence emitted by ruby were taken under the conditions of a pulse power frequency of 50 Hz, Vp-p = 7 V, and an offset of 3.5 V. By adjusting the duty ratio of the pulsed LED light source to 10% or less as shown in the stable region in region 41 of the duty ratio of the light emission intensity and the LED input current in the LED light source device of FIG. 9, it was possible to take stable fluorescence images without aging the LED light source before measurement. Since it became possible to take stable fluorescence images, advanced analysis based on the luminance distribution of the fluorescence images became possible. By setting the pulse frequency of the LED light source device to be higher than the shutter or frame rate of the camera, stable fluorescence images and normal images could be taken. In the case of the Hoshan L-836USB camera with a frame rate of 30 fps (frames / second), it was possible to take and analyze stable fluorescence images and normal images under the conditions that the duty ratio of the pulsed power supply of the LED light source device was 10% and the frequency was 50 Hz or more.

Example

[0047] FIG. 10 shows an LED light source device provided with a data input device for accurately adjusting the duty ratio and a display for displaying the adjusted duty ratio. An LED light source device provided with a dial knob for duty ratio adjustment and a liquid crystal display panel 42 for display, an LED light source device provided with a dial knob for duty ratio adjustment and a scale plate 43 for display, an LED light source device provided with a dial knob for duty ratio adjustment and a bar graph 44 for display, and an LED light source device provided with a dial knob for duty ratio adjustment and an analog meter 45 for display can be used. By using a pulse power supply with a duty ratio display and adjuster such as WaveFactory 1945 or 1943A or DF-1905 or LI5460 lock-in amplifier manufactured by NF Circuit Design Block, Inc., or AFG-2125 manufactured by Instek, while monitoring the duty ratio value displayed on the display, the input device for the duty ratio is operated to adjust the duty ratio to a value that can reduce the time variation of the emission intensity of the LED light source device in FIG. 9 to a predetermined duty ratio indicated in the region 41 of the LED input current. Furthermore, by incorporating a duty ratio display and adjuster as an integrated device with the power supply of the light source device and the PWM signal generation circuit, a small and easy-to-use LED light source device can be provided.

[0048] Based on the data acquired in advance, by always adjusting to the optimal duty ratio using a measurement and control computer, an LED light source device for stable and highly accurate optical measurement becomes possible. Furthermore, as shown in FIG. 2, by connecting the pulse power supply 1 for driving the LED, the pulse signal generator 2 for adjusting the duty ratio, the photodetector 5, the digital multimeter 6, and the oscilloscope 7 to the measurement and control computer 8 using a communication control cable 9 such as a USB cable, it becomes possible to always adjust to the optimal duty ratio while monitoring the output stability of the LED light source device. For the connection of these devices, instead of the communication control cable 9 such as a USB cable, a connection using a communication control cable such as RS232C or GP-IB or LAN or a wireless connection using wireless LAN or WiFi or Bluetooth may be used.

[0049] The light from the LED light source device is pulsed. In order to measure the intensity of such a pulse signal, a method of measuring the true root mean square (true RMS) is widely used. As shown in FIG. 8, the value of the true root mean square (true RMS) changes with the duty ratio. Therefore, when measuring while changing the duty ratio of the LED light source, a calibration curve between the true root mean square (true RMS) measured in advance and the duty ratio can be used, or the relationship between the value of the true root mean square (true RMS) and the duty ratio can be used to correct the influence of the duty ratio on the true root mean square (true RMS). Further, as shown in FIG. 8, by measuring the intensity of the pulse signal of the light from the LED light source device using the peak intensity (Vp-p), it is possible to measure the emission intensity with high precision and stability without the influence of the duty ratio. Also, stable measurement can be achieved by making the pulse lighting frequency of the LED light source device higher than the data sampling frequency of the measurement device, or by synchronizing the data sampling frequency of the measurement device with the pulse lighting frequency of the LED light source device.

Industrial Applicability

[0050] By adjusting the duty ratio of the pulse power supply for LED lighting of the LED light source device of the present invention to a value equal to or less than a predetermined value between 0.01% or more and less than 100%, preferably 0.01% or more and 10% or less, it becomes possible to effectively cool the LED heated and temperature - raised during lighting when it is turned off. For this reason, it is possible to reduce the temporal changes in the emission wavelength and emission intensity that could not be prevented in conventional LED light sources, and high - precision measurement using a stable LED light source becomes possible. The LED light source of the present invention can be used as a stable light source for fluorescence spectra, light absorption spectra, light scattering spectra, refractive index, sugar concentration, fluorescence thermometers, illuminance, turbidity, color sensors, photographing of still images and moving images, high - quality image photographing for measurement, etc. The LED light source of the present invention does not require measures such as aging for stabilization, and can be used as a stable light source immediately after lighting, so it can be applied as a high - performance light source in various industrial fields.

Explanation of Signs

[0051] 1 Pulse power supply for LED driving 2 Pulse signal generator for duty ratio adjustment 3 Protective resistor for current limiting 4 LED 5 Photodetector 6 Digital multimeter 7 Oscilloscope 8 Computer for measurement and control 9 Connection via a communication control cable such as USB 10 Time variation of the input current of the LED when the LED is continuously lit with a DC power supply 11 Time variation of the temperature of the LED when the LED is continuously lit with a DC power supply 12 Time variation of the luminous intensity of the LED when the LED is continuously lit with a DC power supply 13 Time variation of the emission peak wavelength of the LED when the LED is continuously lit with a DC power supply 14 Time variation of the input current of the LED when the LED is pulse-lit with a pulse power supply having a large duty ratio 15 Time variation of the temperature of the LED when the LED is pulse-lit with a pulse power supply having a large duty ratio 16 Time variation of the luminous intensity of the LED when the LED is pulse-lit with a pulse power supply having a large duty ratio 17 Time variation of the emission peak wavelength of the LED when the LED is pulse-lit with a pulse power supply having a large duty ratio 18 Time variation of the input current of the LED when the LED is pulse-lit with a pulse power supply having a small duty ratio 19 Time variation of the temperature of the LED when the LED is pulse-lit with a pulse power supply having a small duty ratio 20 Time variation of the luminous intensity of the LED when the LED is pulse-lit with a pulse power supply having a small duty ratio 21 Time variation of the emission peak wavelength of the LED when the LED is pulse-lit with a pulse power supply having a small duty ratio 22 Time variation of the input current of the LED accompanying lighting and extinguishing within one cycle of the LED lit with a pulse power supply Temperature change over time of an LED during one cycle of an LED lit by a 23-pulse power supply, along with its on and off states 24 Temporal change in the emission intensity from an LED in a pulse-driven LED light source with a small actual duty ratio 25 Temporal change in the emission intensity from an LED measured at the true root mean square (true RMS) in a pulse-driven LED light source with a small actual duty ratio 26 Temporal change in the emission intensity from an LED measured by the pulse amplitude (Vp-p) in a pulse-driven LED light source with a small actual duty ratio 27 Temporal change in the emission intensity from an LED in a pulse-driven LED light source with a large actual duty ratio 28 Temporal change in the emission intensity from an LED measured at the true root mean square (true RMS) in a pulse-driven LED light source with a large actual duty ratio 29 Temporal change in the emission intensity from an LED measured by the pulse amplitude (Vp-p) in a pulse-driven LED light source with a large actual duty ratio 30 Temporal change in the emission intensity from an LED in a pulse-driven LED light source with an actual duty ratio of about 50% 31 Temporal change in the emission intensity from an LED measured at the true root mean square (true RMS) in a pulse-driven LED light source with an actual duty ratio of about 50% 32 Temporal change in the emission intensity from an LED measured by the pulse amplitude (Vp-p) in a pulse-driven LED light source with an actual duty ratio of about 50% 33 Variation of the decay of the emission intensity (pulse amplitude (Vp-p)) of a red LED with respect to the duty ratio of the source pulse 34 Variation of the emission intensity (pulse amplitude (Vp-p)) of a red LED with a duty ratio of 80% with respect to the lighting time 35 Variation of the emission intensity (pulse amplitude (Vp-p)) of a red LED with a duty ratio of 10% with respect to the lighting time 36 Variation of the decay of the emission intensity (true root mean square, true RMS) of a red LED with respect to the duty ratio of the source pulse 37 Variation of the emission intensity (true root mean square, true RMS) of a red LED with a duty ratio of 80% with respect to the lighting time 38 Change in emission intensity (true RMS) of red LED with a duty ratio of 50% over lighting time 39 Change in emission intensity (true RMS) of red LED with a duty ratio of 20% over lighting time 40 Change in emission intensity (true RMS) of red LED with a duty ratio of 10% over lighting time 41 Region of duty ratio and LED input current where the time change in emission intensity of the LED light source device can be reduced 42 Dial knob for duty ratio adjustment and liquid crystal display panel for display 43 Dial knob for duty ratio adjustment and scale plate for display 44 Dial knob for duty ratio adjustment and bar graph for display 45 Dial knob for duty ratio adjustment and analog meter for display

Claims

1. In an LED light source device that pulse-lights an LED using a pulse power source that periodically repeats lighting and extinguishing, the duty ratio of the pulse power source defined by Duty ratio = 100 x (lighting time) / (time of one cycle) = 100 x (lighting time) / (lighting time + extinguishing time) is adjusted to a predetermined value of 0.01% or more and less than 100%, preferably 0.01% or more and 10% or less, thereby reducing the time change of the emission peak wavelength and emission intensity of the LED light source to 1.0% / min or less, preferably 0.1% / min or less. An LED light source device characterized by this.

2. The LED light source device according to claim 1, wherein the LED light source is pulse-lit at a predetermined duty ratio of 0.01% or more and less than 100%, preferably 0.01% or more and 10.0% or less, so that the temperature rise of the LED due to energization during lighting can be sufficiently cooled during extinguishing.

3. In an LED light source device characterized by pulse-lighting an LED at a predetermined duty ratio of 0.01% or more and less than 100%, preferably 0.01% or more and 10.0% or less, the plurality of LEDs are lit simultaneously or the lighting start times of the plurality of LEDs are delayed and lit. The LED light source device according to claims 1 to 2.

4. In an LED light source device characterized by pulse-lighting a plurality of LEDs simultaneously or with a delayed lighting start time at a predetermined duty ratio of 0.01% or more and less than 100%, preferably 0.01% or more and 10.0% or less, the plurality of LEDs include red-emitting LEDs, green-emitting LEDs, and blue-emitting LEDs. The LED light source device according to claims 1 to 3.

5. In an LED light source device characterized by pulse-lighting an LED at a predetermined duty ratio of 0.01% or more and less than 100%, preferably 0.01% or more and 10.0% or less, the LED used is an LED that emits white light of any one of bulb color, warm white, daylight white, or daylight color. The LED light source device according to claims 1 to 4.

6. The LED light source device according to claims 1 to 5, characterized by being used as a light source for measuring a fluorescence spectrum or fluorescence intensity, or a light scattering spectrum or light scattering intensity, or a light absorption spectrum or light absorption intensity.

7. The LED light source device according to claims 1 to 6, characterized in that it is used as a light source for a fluorescence thermometer, a refractometer, a saccharimeter, an illuminometer, a color sensor, or a turbidimeter.

8. The LED light source device according to claims 1 to 7, characterized in that it is used as a light source for photographing a two-dimensional distribution of fluorescence, light scattering, light absorption, or light reflection in a still image, a moving image, or both.

9. The LED light source device according to claims 1 to 8, characterized in that it is used as a light source for photographing a still image, a moving image, or both of an object to be photographed.

10. In an LED light source device characterized by pulse lighting an LED at a predetermined duty ratio, a data input device for accurately adjusting the duty ratio to a value of 0.01% or more and less than 100%, preferably 0.01% or more and 10.0% or less, and a display device for displaying the adjusted duty ratio value. The LED light source device according to claims 1 to 9, characterized by comprising both.

11. In an LED light source device characterized by pulse lighting an LED at a duty ratio equal to or less than a predetermined value, the data input device for accurately adjusting the duty ratio to a value of 0.01% or more and less than 100%, preferably 0.01% or more and 10.0% or less, is any one of a dial, a touch panel, or a numeric keypad, and the display device for displaying the adjusted duty ratio value is any one of a scale plate, a liquid crystal display panel, an EL panel, an LED display, a bar graph, or an analog meter, or a combination of a plurality of display devices and the data input device. The LED light source device according to claims 1 to 10, characterized by being such.

12. Monitoring the time change of the emission intensity of an LED light source measured using a photodetector using a computer, and based on the relationship between the predetermined time change of the emission intensity and the duty ratio of the pulse lighting of the LED light source, the time change of the emission intensity of the LED light source is 1.0% / min or less, preferably 0.1% / min or less. The LED light source device according to claims 1 to 11, characterized by adjusting the duty ratio of the pulse light source device using a computer so as to be.

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