Koehler illumination is free from glare when viewing specimens. While they can be viewed brightly there is an even light distribution in the entire field of view. Ever since its development, scientists prefer to use microscopes that view things in this way. These are special microscopes which utilize this type of illumination.
Koehler illumination does not require a glass for diffusing light placed over the microscope's light bulb, which was necessary in the past. This glass had the effect of reducing the light spectrum. With Koehler microscopes you always are able to get uniform specimen illumination fully using the light.
Another benefit of the method is that specimens experience a reduction in heat. When specimens are made hot, the water around the specimen evaporates faster. When this occurs, dissolved oxygen is also reduced. This can be a problem when viewing living organisms.
Another benefit of Koehler illumination is that light reflections are greatly reduced when photographing specimens. Excess light can cause unwanted visual effects. When using Koehler illumination the final result is a sharper contrast in photographic images that gives them clarity.