This reminds me of F. Alton Everest's notes in "The Master Handbook of Acoustics" that the threshold of hearing lies coincident with the SPL of Brownian motion

This reminds me of F. Alton Everest's notes in "The Master Handbook of Acoustics" that the threshold of hearing lies coincident with the SPL of Brownian motion of air particles on the ear drum... except this is with respect to light.