## 4 Discussion
Additionally, the hands-free devices, including caps [29] and helmets [30; 32; 37], which have proven clinical effectiveness, usually used a high number of diodes ranging from 40 to 304 diodes with user-friendly capabilities. Patients could manage their daily activities during treatment sessions. Among 32 home-use LLLT devices, the majority (87.5%) of them were composed of only one LD, with essential lasers for therapeutic benefits. Following the collimated, coherent, highly monochromatic beam properties, the possibility of high-power densities was then considered preferable [38]. Interestingly, this systematic review revealed a significant difference between light and laser sources. However, the non-coherent light sources, such as LEDs and broad-band lamps, have recently become common with the advantages of LED, including no laser safety considerations, the ease of home use, the ability to irradiate a large area of tissue at once, the possibility of a wearable device, and the much lower cost per mW. A range of light energy sources, from LEDs to lasers, have been used with specific advantages and limitations [39]. Currently, there is evidence to show the non-dependence of photo-biomodulation on lasers or coherence. However, the monochromatic LED devices could also yield physiological effects [38]. The study of LLLT devices for MPHL and FPHL treatments consisted of 224 red LDs (660 nm, 5 mW) for the treatment group, while the sham devices were composed of 224 LED (650 + 20 nm) for the control group. Each LD had optical power at the irradiance of 3.5 mW/cm\({}^{2}\), whereas LEDs had the power of 0.5 mW/diode (ten times lower than LD). The results of the study yielded an increase in HD and in hair diameter in both groups. The treatment group was significantly superior to the sham devices. The mean change from baseline to week 24 for HD was 10.21 \(\pm\) 3.25 hairs/cm\({}^{2}\) in the treatment group, versus 3.95 \(\pm\) 1.32 hairs/cm\({}^{2}\) in the sham group. The mean change for the hair diameter was 6.11 \(\pm\) 2.15 um in the laser group versus 3.76 \(\pm\) 1.24 um in the sham group. Therefore, the LEDs seemed to influence photo-biomodulation, as well as the LDs. Due to the very low power of LEDs used in this study (0.5 mW/diode), when compared to the appropriate dose of 2-4 J/cm\({}^{2}\), the results of LEDs in this study could not be concluded [28]. Nevertheless, some head-to-head studies that compared both light sources showed no difference in their effects [37]. Hence, more high-quality head-to-head comparison studies are recommended to verify the significant differences between dose responses and the physiological effects of LEDs and laser PBMs [37; 39]. When considering the wavelength, all devices used the light/laser sources with 620-678 nm due to the absorption peak at 660 nm [40], with CCO as the chromophore for LLLT. According to the Arndt-Schulz Law, as reported in the article of [PERSON] et al. [41], it is widely accepted that if the irradiance or the duration is too short, there is no response. Similarly, if the irradiance or duration is too high, then the response may be instead inhibited. According to [PERSON] et al. [41], the irradiance of 2-4 J/cm\({}^{2}\) was suspected to be appropriate. When this theory was applied to the LLLT devices, it usually provided patients with therapeutic irradiance. From the published articles that support the effectiveness of the devices, it is obvious that the included participants had only mild to moderate MPHL and/or FPHL. However, no study has been conducted for severe cases of HL. In a study that compared the effectiveness of standard treatments, including oral finasteride and topical mixoxidil with LLLT, 1 mg of Finasteride(r) in MPHL for 12 months significantly increased the total hair counts by 7.3% and 8.99% at 6 and 12 months, respectively (\(p\) < 0.001) [42], whereas 2% and 5% topical Minoxidil(r) demonstrated a significant increase in non-vellus hair counts of 8.84% (\(p\) = 0.013) and 12.3% (\(p\) < 0.001) at 48 weeks, respectively [43].