An important aspect is the chromatic fidelity that the light source allows to obtain.
The human eye is used to observing everything around us thanks to sunlight.
The colour of light is expressed in Kelvin (K) and is called "Colour Temperature".
A halogen bulb produces a colour temperature of around 3200°K (tending to yellow).
A white LED produces a colour temperature very similar to the daylight one (5500°K).
A "daylight blue" filter absorbs some of the yellow light from the microscope bulb, provided that the microscope is equipped with an halogen bulb, resulting in colouration much closer to natural daylight which is beneficial comfortable viewing.
Use of a daylight blue filter is not needed with modern microscopes as they are equipped with LED illumination.

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