Types of microscope light sources
Resolution increases with the quality of the light that passes through your specimen.
That is why old or cheap microscopes that use a rotating mirror to catch ambient light lead to unsatisfactory images especially at higher magnifications.
You will need a built-in, dimmable electric light source, as shown on point A of the above diagram.
Resolution is improved when shorter wavelengths of light are used to illuminate your specimen because shorter wavelengths are more intense. Different type of light have different wave lengths.
A hot light, like a tungsten globe is likely to dry out the specimen. Tungsten globes are cheap but are often hard to replace in older microscope models because they were not standardised when they became popular for built in microscope lighting.
Fluorescent and LED globes are cool, cheap to run and long-lasting.