It's basically self experimentation, and cross-checked with literature to make sure I don't overdose. Overdose is not that bad (it surely happened to me), slight light-headedness and confusion for a few hours, in my case. Not stay-at-home bad, only a bit annoying. I quickly learned not to overdose, and haven't for over a year. Prof Hamblin from Harvard gave an interesting video interview with the guy from selfhacked (should be on youtube) where he mentions that he uses near infrared on his forehead to increase cognitive function, for a certain timespan (don't remember how often he does it). Since he's probably the most versed person (with a scientific background) on that topic, I thought it would be valid.