Both Continuous Wave (CW) and Pulse Wave (PW) are used in Low-level Light Therapy (LLLT) treatment of skin diseases, wound healing, and hair transplantation. At present, LLLT is being used in Alzheimer’s disease treatment. It was found that LLLT can prevent nerve cell death in an in-vitro test. However, LLLT for Alzheimer’s disease requires high energy of light so that the light can pass through the skull and be sufficient to treat Alzheimer’s disease. This study focuses on designing uniform light illumination on the skull, both CW and PW, at a wavelength of 810 nm using the local search algorithm without harming the skin to make the light pass through the skull.Moreover, this study measured the energy density of light when the light through the skull from the simulation. The results found that PW irradiation was able to produce more energy density than CW irradiation, and the energy density that passes the skull is enough to treat Alzheimer’s disease without harming the skin. Also, the PW treatment duration was shorter than CW, where the coefficient of variation of energy density on the skull surface of PW and CW were 0.037 and 0.036, respectively.

1. A. Association, “2018 alzheimer’s disease facts and figures,” Alzheimer’s & Dementia, vol. 14, no. 3, pp. 367–429, 2018. doi: https://doi.org/10.1016/j.jalz.2018.02.001
2. K. L. Puig and C. K. Combs, “Expression and function of APP and its metabolites outside the central nervous system,” Experimental Gerontology, vol. 48, no. 7, pp. 608–611, 2013. doi: https://doi.org/10.1016/j.exger.2012.07.009
3. Alzheimer’s society. Effects of Alzheimer’s disease drugs. [Online]. Available: https://bit.ly/3AP8Pne
4. E. Mester, B. Szende, and P. Gärtner, “The effect of laser beams on the growth of hair in mice,” Radiobiologia, Radiotherapia, vol. 9, no. 5, pp. 621–626, 1968.
5. N. N. Houreld, “Shedding light on a new treatment for diabetic wound healing: A review on phototherapy,” The Scientific World Journal, vol. 2014, pp. 1–13, 2014. doi: https://doi.org/10.1155/2014/398412
6. M. H. Berman, J. P. Halper, T. W. Nichols, H. Jarrett, A. Lundy, and J. H. Huang, “Photobiomodulation with near infrared light helmet in a pilot, placebo controlled clinical trial in dementia patients testing memory and cognition,” Journal of Neurology and Neuroscience, vol. 8, no. 1, pp. 1–8, 2017. doi: https://doi.org/10.21767/2171-6625.1000176
7. S. K. Sharma, G. B. Kharkwal, M. Sajo, Y.-Y. Huang, L. De Taboada, T. McCarthy, and M. R. Hamblin, “Dose response effects of 810 nm laser
   light on mouse primary cortical neurons,” Lasers in Surgery and Medicine, vol. 43, no. 8, pp. 851–859, 2011. doi: https://doi.org/10.1002/lsm.21100
8. NeuroVault. (2016) ICBM 2009c Nonlinear Asymmetric (PD). [Online]. Available: https://neurovault.org/images/29408/
9. Q. Wu, W. Xuan, T. Ando, T. Xu, L. Huang, Y.-Y. Huang, T. Dai, S. Dhital, S. K. Sharma, M. J. Whalen et al., “Low-level laser therapy for closed-head traumatic brain injury in mice: Effect of different wavelengths,” Lasers in Surgery and Medicine, vol. 44, no. 3, pp. 218–226, 2012. doi: https://doi.org/10.1002/lsm.22003
10. P. Avci, A. Gupta, M. Sadasivam, D. Vecchio, Z. Pam, N. Pam, and M. R. Hamblin, “Low-level Laser (light) Therapy (LLLT) in skin: Stimulating, healing, restoring,” Seminars in Cutaneous Medicine and Surgery, vol. 32, no. 1, pp. 41–52, 2013.
11. M. A. L. Bell, A. K. Ostrowski, K. Li, P. Kaanzides, and E. Boctor, “Quantifying bone thickness, light transmission, and contrast interrelationships in transcranial photoacoustic imaging,” in Photons Plus Ultrasound: Imaging and Sensing 2015, vol. 9323. International Society for Optics and Photonics, 2015. doi: https://doi.org/10.1117/12.2078613 pp.930–932.
12. T. Correia, A. Gibson, and J. Hebden, “Identification of the optimal wavelengths in optical topography using photon density measurement functions,” in Biomedical Applications of Light Scattering III. International Society for Optics and Photonics, San Jose, CA, 2009. doi: https://doi.org/10.1117/12.809295
13. T. Ando, W. Xuan, T. Xu, T. Dai, S. K. Sharma, G. B. Kharkwal, Y.-Y. Huang, Q. Wu, M. J. Whalen, S. Sato et al., “Comparison of therapeutic effects between pulsed and continuous wave 810-nm wavelength laser irradiation for traumatic brain injury in mice,” PloS one, vol. 6, no. 10, pp. 1–9, 2011. doi: https://doi.org/10.1371/journal.pone.0026212
14. M. R. Hamblin, “Photobiomodulation for traumatic brain injury and stroke,” Journal of Neuroscience Research, vol. 96, no. 4, pp. 731–743, 2018.
15. Y.-Y. Huang, A. Gupta, D. Vecchio, V. J. B. d. Arce, S.-F. Huang, W. Xuan, and M. R. Hamblin, “Transcranial low level laser (light) therapy for traumatic brain injury,” Journal of Biophotonics, vol. 5, no. 11-12, pp. 827–837, 2012. doi: https://doi.org/10.1002/jbio.201200077
16. E. M. Lillie, J. E. Urban, S. K. Lynch, A. A. Weaver, and J. D. Stitzel, “Evaluation of skull cortical thickness changes with age and sex from computed tomography scans,” Journal of Bone and Mineral Research, vol. 31, no. 2, pp. 299–307, 2016. doi: https://doi.org/10.1002/jbmr.2613
17. H. Mahinda and O. P. Murty, “Variability in thickness of human skull bones and sternum-an autopsy experience,” Journal of Forensic Medicine and Toxicology, vol. 26, no. 2, pp. 26–31, 2009.
18. H. Newey. (2018) The anatomy of the human skull. [Online]. Available: https://bit.ly/3IYbVbq
19. T. N. Demidova-Rice, E. V. Salomatina, A. N. Yaroslavsky, I. M. Herman, and M. R. Hamblin, “Low-level light stimulates excisional wound healing in mice,” Lasers in Surgery and Medicine: The Official Journal of the American Society for Laser Medicine and Surgery, vol. 39, no. 9, pp. 706–715, 2007. doi: https://doi.org/10.1002/lsm.20549
20. G. K. Keshri, A. Gupta, A. Yadav, S. K. Sharma, and S. B. Singh, “Photobiomodulation with pulsed and continuous wave near-infrared laser (810 nm, Al-Ga-As) augments dermal wound healing in immunosuppressed rats,” PloS One, vol. 11, no. 11, pp. 1–21, 2016. doi: https://doi.org/10.1371/journal.pone.0166705
21. I. Moreno, M. Avendaño-Alejo, and R. I. Tzonchev, “Designing light-emitting diode arrays for uniform near-field irradiance,” Applied Optics, vol. 45, no. 10, pp. 2265–2272, 2006. doi: https://doi.org/10.1364/AO.45.002265
22. H. Yang, J. W. Bergmans, T. C. Schenk, J.-P. M.Linnartz, and R. Rietman, “Uniform illumination rendering using an array of LEDs: A signal processing perspective,” IEEE Transactions on Signal Processing, vol. 57, no. 3, pp. 1044–1057, 2008. doi: https://doi.org/10.1109/TSP.2008.2009269
23. J. T. Hashmi, Y.-Y. Huang, S. K. Sharma, D. B. Kurup, L. De Taboada, J. D. Carroll, and M. R. Hamblin, “Effect of pulsing in low-level light therapy,” Lasers in Surgery and Medicine, vol. 42, no. 6, pp. 450–466, 2010. doi: https://doi.org/10.1002/lsm.20950

N. Thanuthep, A. Khantachawana, and K. Ngamkham, “Investigation of effect of low-level light therapy by continuous wave and pulse wave through dry skull by using mathematical modeling,” International Journal of Applied and Physical Sciences, vol. 7, pp. 10-17. 2021. Doi: https://dx.doi.org/10.20469/ijaps.7.50002