[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5705357/#B12] Cell proliferation -660 nm at 10 J/cm2 was the most potent in promoting hDPC proliferation. Wnt/β-catenin signaling: -Both 660 nm and 830 nm significantly enhanced β-catenin mRNA expression. -All four wavelengths significantly increased Axin2 expression -Wnt3a expression was increased by 660 nm and 830 nm of 10 J/cm2 and Wnt5a expression was increased by 415nm of 1 J/cm2 and 660nm of 5 J/cm2 compared to control -Wnt10b mRNA expression was markedly enhanced as much as 10- to 15-fold by 525 nm at 10 J/cm2, 660 nm at 5 and 10 J/cm2 and 830 nm at all doses Protein expression of β-catenin and cyclin D1 -660 nm at 5 J/cm2 induced the maximum peak expression of β- and 525 nm at 5 J/cm2 also increased β-catenin protein expression -415 nm at 5 J/cm2, 525 nm at 10 J/cm2, 660 nm and 830 nm at all doses increased cyclin D1 protein expression ERK signaling pathway -MEK phosphorylation was profoundly increased as much as 5- to 6-fold by 660 nm and 830 nm at 5 J/cm2 -ERK phosphorylation was highly increased as much as 5- to 8-fold by 415 nm at 10/cm2, 525 nm at 10/cm2, 660 nm at 5 and 10 J/cm2, and 830 nm at 5 and 10 J/cm2 Hair length -HFs irradiated with 415 nm of 1 J/cm2 grew 9 % longer than control and those with 660 nm of 1 J/cm2 and 10 J/cm2 grew 20% longer than control -HFs irradiated with 830 nm of 5 J/cm2 grew 17% longer than control -525 nm irradiation produced no significant effect on hair shaft elongation compared to control MY COMMENTS: It is interesting to note the effects of light wavelengths on the properties of hair dermal papilla cells. Based on the results provided, we can see that various frequencies have various effects, and that the total amount of light energy delivered can greatly affect the results. From some of the tables we can see that using the wrong dose (whether that is a too low, or too high dose) can not only cancel out any benefits, it can even make some of the parameters worse than the control. In short, using these lights in the wrong manner may at best give you no obvious benefit, and at worst make your hair loss worse. Thus, it is not only important to consider the proper wavelengths, but also the optimal dosage. It's important to consider that this study was done on cells sitting in a dish, outside of the human body and directly exposed to light. They did not have the problem of the light having to penetrate into the skin to reach the hair follicle, as it would in a living human being trying to treat hair loss. Different wavelengths of light reach different depths of the skin, and based on various sources, it is unlikely that short wavelengths of < 600 nm can adequately reach to the hair follicle, so I think in practical application, we can mostly ignore the results of the 415 and 525 nm light sources. Based on the overall results it seems that 660 nm & 830 nm would be the most optimal light wavelengths to use, and the overall most beneficial dose is likely to lie in the range of 5 - 10 J/cm^2. To calculate the proper distance and time to obtain this dosage in the real world is also made difficult by the fact that you again have the skin barrier to deal with. That is, you need to take into account how much of the light energy is lost diffusing into the skin by the time it reaches the hair follicle. Ignoring this problem for now, we can assume a basic calculation of a real world practical example: DEVICE: INFRARED MINI 830 OUTPUT: 200 mW/cm² @10cm Given the formula we can calculate how long we would need to shine the light over our head to achieve the required dose: So, to achieve the 10 J / cm^2 from the study with this device, we would need to shine this light over our head for a duration of 50 seconds. As I said, this assumes that 100% of the light energy reaches the hair follicle, which is quite unlikely, so in practice depending on the light transmission this number can vary significantly. The other consideration is that the total energy can be delivered equally but at different power density over time. For example, the 10 J can be delivered over a time period of 50 seconds @200 mW, or from a greater distance at 50 mW at a length of 200 seconds, for example (as the power output lessens via increasing distance with the inverse square law, the duration needs to increase to achieve the same amount of energy) Dosing longer from a greater distance, may be more optimal than using a high power density up close for a short time ( or it may be the opposite, there is not much data on this ). Altogether, I think light therapy can be a decent addition to a regimen, but the application is made complicated by various things such as: differing wavelengths have different biological effects, finding the optimal power output, real world consideration factors, etc.