In the main figure for HEGduino, it says that the low power of the sensor circuit protects tissue. While it is intuitive that an extremely high power EM field in close proximity would cause damage, I was wondering what backing there is for this statement specifically in relation to the device. Doing some searching on the subject, I found some relevant research, but it's a bit difficult for me to parse so I figured I'd ask and see if there was an easy answer.
Part of my concern comes from the fact I've been getting headaches after/during long (1-3hr) sessions using the device purely for recording, without attempting to control blood flow. Pain usually starts nearing the end of the first hour and continues for about 30-45mins after discontinuing use. It is possible that the discomfort comes from having the device strapped there and the hardness of the sensors/emitters, and I'll do a trial tomorrow to test that, but I find it unlikely.
That's interesting then! Definitely something to narrow down the reason for. I'm using 950nm and 650nm LEDs. The ESP32 shouldn't be sending more than 40mA through them even though the resistors allow more than that. So there's your reference frame. Most pulse ox's have 20mA-100mA LEDs as far as I know, generally about 50mA. I've looked into red and IR-A (the segment of infrared we use) for damage concerns but found none for LEDs, esp at these amplitudes. No long term issues reported by the biofeedback people I know who've worked with this stuff for a couple decades. Only note I've gotten from someone I know was that ~840nm flickering at 40Hz *might* cause actual changes in brain state that are not apparent at other wavelengths, but we're at ~20Hz and ~950nm so a little off.