Keywords

1 Introduction

The development of light-based technologies has facilitated the use of various types of phototherapy devices in the medical field. Representative phototherapy devices are laser surgical instruments and medical laser irradiators. The former are used for the removal, ablation, and destruction of areas in need of treatment using the light of a strong laser; the latter irradiate the skin, induce skin regeneration, and relieve pain [1]. These medical devices are used under the guidance of healthcare providers in medical institutions and can be hazardous because they use strong light. According to the Korean Ministry of Food and Drug Safety, medical devices are divided into four classes according to the hazard level [2]. Devices such as lasers are currently represented by Class 3, which is the grade with high risk. However, various types of personal phototherapy devices have recently emerged and are used without any instructions from healthcare providers. Among them, representative personal phototherapy devices include phototherapy devices using LED. LED phototherapy devices use a low-level phototherapeutic method known as Low-Level Laser Therapy (LLLT). LLLT is used for relief of pain or inflammation, scar healing, and skin resurfacing using low output power [3]. LED phototherapy devices with LLLT are used for skin improvement and cosmetic purposes. They vary in shape depending on the site at which to be used, and are of various types. Certain devices use only LEDs, while others are used in combination with laser—their boundary with medical laser irradiators is vague. Based on the report on personal phototherapy devices by the Korea Consumer Agency, there were 172 adverse events of LED masks, which were home phototherapy devices, from 2018 to August 2020. They comprise 134 cases of skin and subcutaneous tissue injuries, 6 of burns, 1 of heat sensation and dyspnoea, and 1 of bruise [4]. As various phototherapy devices continue to be developed, assuring adequate safety is paramount.

This study contributed to the industrial development of LED phototherapy devices and new phototherapy devices. We derived a performance test method to secure safety related to the performance of phototherapy devices using LEDs, from a Korean perspective.

2 Materials and Method

2.1 Determination of Performance Test Items Related to LED Phototherapy Devices

It's determine to derive the performance test method to preserve the stability of LED optical medical devices and to obtain suitable test materials for these devices by investigating performance issues and conducting related performance tests. As a research method, we proceed by reviewing previous research and standards related to optical medical devices such as International Organization for Standardization (ISO) and Inter-national Electrotechnical Commission (IEC). For the literature review, a literature search medium was used, and the search was conducted with “LLLT,” “PBM,” and “LED” as search keywords. Based on the reviewed literature, performance test items and methods were derived by examining key performance issues related to optical medical device therapy and LED optical medical device standards.

2.2 Performance Test Method for the Phototherapy Device Sample

We examined the safety of the LED phototherapy devices by applying the performance test items derived from this study to the LED medical device developed by T company, shown in Fig. 1. The company’s LED phototherapy device samples were developed for the treatment of hair loss and scalp improvement and was shaped like a helmet. The LED phototherapy device comprises 54 lasers and 126 tri-color LEDs. Its performance items are 10 mW for the output power of the laser, 3 mW for the intended output power, and 650 nm for wavelength. Each LED has an output power of 3 mW, with wavelengths of red 625 nm, blue 455 nm, and infrared (IR) 845 nm. The key performance test items and methods of optical medical devices are obtained and used in the model to protect the validity of the test.

Fig. 1.
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LED phototherapy device sample.

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3 Results

3.1 LED Optical Medical Device Literature Investigation

As a result of the literature review, three volumes were reviewed for LLLT, two volumes for LED, two volumes for PBM optical medical device-related literature, and five volumes for related standards. In addition, two books related to Korean medical devices and photo-therapy were mentioned. By reviewing the research literature, main performance items according to the treatment of LED light medical devices, standards related to LED light medical devices, and performance test items and methods were obtained.

3.1.1 Key Performance Points for Treatment Using LED Optical Medical Devices

Phototherapy is a medical technique that has been used for thousands of years to treat various diseases. An example is sun therapy by Hippocrates, the father of Western medicine [5]. In modern times, various treatments using light have evolved. A common treatment that uses LEDs is photobiomodulation (PBM). This was previously called Low-Level Laser Therapy (LLLT) and was later changed to Low-Level Light Therapy by Kendrick C. Smith due to the advent of the next generation LED with higher photon intensity. Photobiologist [6]. After the change, the name was again changed to PBM due to uncertainty about the exact meaning of low power [7]. PBM was proposed by Andre Meister (1903–1984), a medical expert who researched and published the biological effects of low-power lasers in 1967 [8]. According to the literature, PBM is a treatment that uses a low-power laser or LED in the 1m to 50mW range to induce tissue regeneration and relieve inflammation. Red or near-infrared light with a wavelength of 600 nm to 1000 nm is used, and, unlike other laser treatments that destroy tissue, PBM is known for its photochemical effect similar to plant photosynthesis [9]. The mechanism of PBM is not yet clearly elucidated; however, when tissue is irradiated with low-output IR light, it is absorbed by a chromophore that penetrates the skin surface and absorbs light in a specific wavelength band. In the body, at this time [10], the absorbed light energy is converted into chemical energy and increases the synthesis of Adenosine Triphosphate (ATP), which is the energy source of the cells in the cell tissue, resulting in cell regeneration and rehabilitation, pain and inflammation relief, which is known [11, 12]. According to the literature related to LED-LLLT, the main performance issues for LED light sources used in PPM include wavelength, power density, and luminance. In terms of wavelength, the first law of light biology, the Grothes-Draper law, states that when the light of the appropriate wavelength is applied to the chromophore, the chromophore has no absorption nor reaction. Power density refers to the output used per unit area, and the unit is W∕Cm^2. When the power density is insufficient, light absorption does not occur in the tissue, and when the power density is high, it is converted to excessive heat for the tissue, which could be harmful. Fluence (energy density) or “dose” refers to the amount of energy applied per unit area. The energy density is multiplied by the radiation time, and the unit is J∕Cm^2. If the power density is too low, the irradiation time must be extended to achieve the best power density, which is why the desired results cannot be obtained [6, 10].

3.1.2 Items for Standards Related to LED Phototherapy Devices

To derive LED phototherapy device test items, the relevant standards were investigated by referring to the international standards, ISO and IEC, as well as Korean standards. Currently, there are two main categories of common standards for medical devices in South Korea. The classification consists of standards applied comprehensively and standards applied separately by medical device items. Additionally, it comprises medical devices that use electricity as a whole and those that do not use electricity [13]. Comprehensive standards are common standards for electromechanical safety, electro-magnetic waves and safety, and biological safety. The common standards for electromechanical safety are those applicable to the basic safety and essential performance of medical electrical appliances and medical electrical systems [13]. In the common standards on electromechanical safety, standards related to phototherapy devices were IEC 60601-1, IEC 60601-2-22, IEC 60825-1, IEC 60825-8, and IEC 62471-2. IEC 60601-1 is a set of standards that ensure the safety of medical electrical equipment, cover basic safety and essential performance requirements of medical electrical equipment, and prevent electrical, mechanical, or functional errors that present unacceptable hazards to patients and operators [14]. IEC 60601-2-22 is an individual standard of IEC 60601–1 standard applied to basic safety and essential performance of surgical, therapeutic, diagnostic, cosmetic, and animal laser instruments for use in humans or animals. IEC 60601-2-22 is a standard applicable to phototherapy devices corresponding to classes 3B to 4 and applied to the safety of laser output power. For example, on the 201.12.1.101 laser output power display, the actual laser output power measured in the operating area should not exceed ±20% of the set value [15]. IEC 60825-1 is a standard applied to the safety of laser products that emit light with a wavelength range of 180 nm to 1 mm. Per this standard, classes are di-vided into 1, 1M, 1C, 2, 2M, 3R, 3B, and 4, as described in Table 1 [16].

Table 1. Laser classes according to IEC 60825–1 [16].
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These ratings are classified as per the accessible emission limit (AEL) according to the Maximum Permissible Exposure (MPE) in Annex A of IEC 60825-1, as shown in Table 2. The MPE provided in IEC 60825-1 presents additional information that can assist the manufacturer in assessing safety items for the intended use of the user. The MPE contained in the standard has been adopted from exposure limits published by the International Commission on Non-Ionized Radiation Protection, and MPE values have been used as the basis for safe design of products and for providing information to users. [16] IEC 60825-8 provides guidance to employers, competent authorities, laser safety managers, and others, on the safe use of laser and laser equipment classified as 3B and 4. An investigation identified potential side effects according to wavelengths in Appendix A of IEC 60825-1, which are shown in Table 2 [17].

3.1.3 LED Phototherapy Device Performance Test Items and Method Derivation

The main performance requirements and specifications related to performance test-ing for optical medical devices were grasped through the literature. It has been con-firmed that wavelength, power density, and fluorescence are key performance parameters for LED optical medical devices. If a wavelength that does not match the chromophore of the target to be treated is used, suitable results cannot be obtained; in the case of fluorescence that does not match, the desired result cannot be obtained, and thermal damage can be expected. Therefore here, the key performance test items obtained were wavelength, power, and power density, as shown in Table 3. For assessing wavelength, we used the wave-length accuracy test method according to IEC 62471-1 Annex B; the accurate calculation formula was used to obtain the measured value and the actual value as a percent-age, and the quality of the test ± □% within the error range was determined. Power density is the output per unit area, and an accuracy test for output and a test for illumination was obtained. Output Accuracy Test IEC 62471-1 Annex C. As a test method, the measured and the actual values are calculated as a percentage using a power meter. The quality of the test should be ± □% with an error margin of ± □%. The test for illumination is IEC 62471–1. 5, wherein we follow the measurements of the lamp and the lamp device and measure it using an illuminance meter. The test standard is IEC 62471-1. 4. 4. The test method that follows the hazard exposure limits is IEC 62471-1.5. The test method was obtained ac-cording to the measurement of lamps and lighting fixtures, and IEC 62471-1 4. Exposure limit standards were followed. Energy density, one of the key performance factors, is the product of energy density and irradiation time, and the test item of energy density was obtained. However, irradiation time was excluded because it was difficult to be obtained. The test item will vary depending on the LED optical medical device.

Table 2. Laser classes according to IEC 60825-1 [16].
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Table 3. Measured values by mode in the samples of T company’s device and the accuracy of wavelength.
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3.2 LED Optical Medical Device Literature Investigation

Among the test items obtained from Sect. 3.1.3, the wavelength accuracy test was applied to LEDs built into the Company T model, and the same test was performed on the laser built into the model. To measure the wavelength, as shown in Fig. 2 below, we want to measure the main performance factors of the two models of the T company, the laser wavelength, and the LED wavelength, using the spectrometer of the T company. The two models have the same performance and we wanted to compare them by measuring the wavelengths in each mode.

Fig. 2.
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Wavelength performance test devices (Left: a spectrometer; Right: the sensor of the spectrometer)

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As for the measurement method, the light source to be measured was aligned with the spectrometer's wavelength meter sensor, as shown in Fig. 3. The wavelength meas-ured was then checked by the monitoring function in the software on the computer con-nected to the spectrometer.

Fig. 3.
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Wavelength measurement for the light source.

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3.3 Performance Test Results of LED Phototherapy Devices

The two samples of T company were numbered 1 and 2, and the laser and LED were measured for each mode of the samples. The set values for each mode of samples were the same for the laser and IR LED, and the set values for the laser and the IR LED were 650 nm and 845 nm, respectively. The set values for the red LED in H (Hair) mode and the blue LED in S (Scalp) mode were 625 nm and 455 nm, respectively. The measured values for the two samples are shown in Fig. 4.

Fig. 4.
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Results of laser wavelength measurements by mode of T company’s samples.

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The laser wavelengths per the mode of T company’s samples measured with the spectrometer are shown in Fig. 5. The graph shows a maximum peak value of 654 nm. When the measured wavelength band was visually checked, the graphs overlapped be-cause the measured laser wavelength bands were similar to the set value of 650 nm. However, as it was difficult to accurately differentiate the superimposed graph with the naked eye, the graph was adjusted to distinguish the laser wavelength band measured, as shown in Fig. 6. Using the adjusted graph, the measured wavelength for each mode of the two samples and the accuracy of the laser wavelengths were checked.

Fig. 5.
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Enhanced graph of laser wavelengths measured in modes of T company’s samples.

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Fig. 6.
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LED wavelength graph measured in sample modes of T company’s device.

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Laser measurements of T company’s samples revealed 654 nm in H mode, 654 nm in S mode (Sample-1), 652 nm in H mode, and 653 nm in S mode (Sample-2). They differed by 2 to 4 nm from the set value of 650 nm in the laser. As each of the measured lasers was the same for each of the samples, Sample 1 indicated the same value. However, Sample 2, though it was the same object, demonstrated a difference of 1 nm depending on the mode. When each measured value was applied to the wavelength accuracy equation, Sample 1 showed an error range of ±0.615% because the values per mode were the same. As for Sample 2, the error range was ±0.31% in H mode and ±0.461% in S mode. The laser wave-lengths of the two samples were within the error range of ±5%, which was the test standard set by the manufacturer. For both samples, LED measurements with the spectrometer revealed the maximum peak values of 627 nm, 454 nm, and 838 nm, which were visible to the eye. When the graph was checked, both samples were found to be similarly matched and overlapped with the laser graph measured earlier. However, a difference of 1 to 3 nm was observed compared to the LED set values of 625 nm for red, 455 nm for blue, and 845 nm for IR. The graphs were adjusted, as shown in Figs. 7, 8, and 9 for precise determination. The respective graphs confirmed LED wavelengths by each mode and the accuracy of wave-lengths for the two samples.

Fig. 7.
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Graph of laser wavelengths.

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The IR LED measured value was 838 nm in both H and S modes for Sample 1. In Sample 2, the values for H and S modes were 840 nm and 839 nm, respectively. For each wavelength, there were differences of 7 nm in Sample 1 and 5 to 6 nm in Sample 2 from the set value of 845 nm. The wavelength accuracy of Sample 1 was within ±0.828% because all measured values were the same. The wavelength accuracy of Sample 2 was ±0.591% in H mode and ±0.71% in S mode. Both samples were within the test standard of ±5%. In the case of IR LED and laser, the same object was applied for each mode. The measured values according to the mode were distinctly different from the set value.

Fig. 8.
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Red LED wavelength graph measured in the samples of T company’s device.

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The red LED of T company's samples was used only in H mode. The measured values in Samples 1 and 2 were 627 nm with a difference of 2 nm from the set value of 625 nm. The accuracy of the red wavelength was ±0.32% for both samples, thus indicating that both samples had an error range within ±5%. Unlike the laser and IR LED measured earlier, the red LEDs had the same values for Samples 1 and 2, and the difference from the set value was small.

Fig. 9.
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Blue LED wavelength graph measured in the samples of T company’s device.

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The blue LED of T company’s samples is used only in S mode. The measured values were 455 nm in Sample 1 and 454 nm in Sample 2. In Sample 1, the measured value was the same as the set value of 455 nm, whereas Sample 2 had a difference of 1 nm. Regarding the accuracy of wavelength, Sample 1 had an error range of ±0% because the measured value was equal to the set value, whereas Sample 2 had ±0.219% in the error range. Thus, the values were within the test standard of ±5% in the error range. In this study, we tested the wavelength performance of both the laser and the LED used in the samples of the T company, from which we found that all measured values were within the reference values. The measured value of the blue LED was the closest to the set value than the data measured earlier, which was found stable, as shown in Fig. 9. The values of the wave-lengths measured in this study and their accuracy are shown in Table 4. In conclusion, all measured values were within ±5%, the test standard. However, the laser and IR LED, which are used regardless of mode, had larger differences between the measured values and the set values among the measurements.

4 Conclusions

This study investigated items related to the performance of LED phototherapy devices to ensure their safety. Although LLLT using LED phototherapy devices, which have been recently examined, have no reported principle, it was possible to identify wavelength as the main performance item, which is the same for other phototherapy devices. The standard of phototherapy devices equipped with both LED and lasers such as T company’s phototherapy device needs to be explored in combination with LED and laser standards. The investigation of standards was able to identify the classes of medical laser de-vices in IEC 60825-1 and their hazard depending on wavelength in IEC 60825-8, the appendix of IEC 60825-1. However, certain laser standards were found to be applied to 3B or higher classes of a laser. As the samples of T company’s device used in this study were used in combination with LED and low-level laser, it was difficult to investigate the standards because of the differentiation between LED and laser. For LED phototherapy devices, IEC 62471-1, which is the same standard as lamp-based medical devices, was applied. Referring to IEC 62471-1 and the relevant literature and guidelines, this study de-rived the performance test method and test items for wavelength, the main performance item, and applied them to samples of the T company’s device. The derived performance evaluation item was the accuracy test of the wavelength according to IEC 62471-1. The test was to determine whether the LED and laser wavelengths were stable. The test standard was within ±5% in the error range corresponding to the test standard of T company. The test method checked whether the measured wavelength shown through the spectrometer was within the error range through the percentage. According to the measurement results, the light sources of the samples complied with the test standard set by the manufacturer. The measured wavelength for samples differed from the set value by 1 to 2 nm in red and blue LEDs, and the accuracy error range of the wavelength was close to 0%. However, laser and IR LEDs, unlike red and blue LEDs, had a difference as large as 2 to 7 nm between the set value and the measured value, though they are used regardless of the mode. More-over, the error range was also shown to be close to 1%, unlike those of the red and blue LEDs. To make it closer to the set value, it is necessary to study the wave-length of photo-therapy devices whose accuracy is important for safety. We believe that a study on the wavelength of the phototherapy device similar to the set value would con-tribute to the safety of LED phototherapy devices and the industrial advancement of phototherapy de-vices similar to LED phototherapy devices.