subvisual

adjective

sub·​vi·​su·​al ˌsəb-ˈvi-zhə-wəl 

-zhəl;

-ˈvizh-wəl

variants or sub-visual

: not visible without the aid of special instruments : subvisible

… once you have seen the subvisual world through the microscope, you stop inventing demons and magic as the agents of change.

—Dava Sobel

Auroras have a wide range of brightness, usually rated from 0 to 4 on a logarithmic scale … in which each number is 10 times brighter than the previous one. Zero means subvisual, detected only with instruments.

—Robert H Eather

Word History

First Known Use

1873, in the meaning defined above