When I used the twins in my nose I got a dull ache behind my eyes as well but I put this down to my tumor. I simply removed one of the twins, wrapped it in 3 layers of black tape, left it out and re-started the pre-set. Halved the input power (Amplitude in the Settings tab).
To understand more about the threshold voltage, please click here:
This is the simplest link I can find to give some understanding of the threshold voltage of laser LEDs. If this voltage is not reached there is no laser wave created.
From the time voltage is applied to the LED, it takes time to reach the threshold voltage. This may be minute but it is there and at higher frequencies. This can be a significant percentage of the cycle.
This is why we have to be aware of the voltage applied to the LED and the frequency that we apply if we want to successfully use the cold laser for anything.
For more details, please check the link from: