Yeah… tons of attenuation, but that was to be expected… and we set it all up to purposely be the worst of conditions. Got around 50uW from a 100W incandescent flood lamp suspended about 48 inches or so directly above my arm in an otherwise totally dark room. That was through blood pooling on top too.
Infrared light goes deepest through tissue so I started looking for IR panels. Most up-convert low energy photons which makes them inefficient… but there was talk of nanotech coming that would directly convert an IR photon into a free electron… never made it commercially though. So that leaves more visible light spectrum doing the heavy lifting, and I’m a little concerned it might be a racist technology - i.e. not working well at all for darker skinned people.