Examples from the Web for substage
Adjust the substage mirror so that the light is reflected upward.
Rick spread a small amount on a slide, switched on the substage light, and put the slide on the stage.
If it no longer occupies the centre of the field, alter the angle of the substage mirror until it does.
Remove the substage condenser and replace it by the dark ground condenser.
Rick set up his microscope on the kitchen table and plugged in the substage illumination.