Answer;
Adjustment knobs are used to focus light in a light microscope.
Step-by-step explanation;
-A light microscope is an instrument that uses visible light and magnifying lenses to examine small objects not visible to the naked eye, or in finer detail than the naked eye allows.
-Illuminator is the light source for a microscope, typically located in the base of the microscope. Most light microscopes use low voltage, halogen bulbs with continuous variable lighting control located within the base. Condenser is used to collect and focus the light from the illuminator on to the specimen.