An instrument for measuring gravitational acceleration from within a borehole, the instrument including: a light source having a semiconductor that comprises a bandgap greater than about two electron volts (eV); and a gravimeter for receiving light from the light source and providing output light with a characteristic related to the gravitational acceleration, the gravimeter implemented at least one of a nano electro-mechanical system (NEMS) and a micro electro-mechanical system (MEMS); wherein the light source and the gravimeter are disposed in a housing adapted for insertion into the borehole.