Long wavelength light, such as red light, can penetrate the skull and reach deep brain tissue.

“If you look at um if you if you look at a longwave light source and again this is published Bob Fosbury did this he put his hand on one come straight through his hand but the interesting thing is you can't see the bones it's passing through the bone so that led me to go into grabbing a few skulls and yeah it's it's really not affected that much by bone”