What is a colored glass filter?

Colored glass filters are made from glasses that have a specific color and only allow part of the light spectrum to pass through. They are often used as simple optical filters to block unwanted wavelengths. Unlike interference filters, color glass filters are only available with a larger bandwidth, i.e. they allow a relatively large range of wavelengths to pass through. Also the edge steepness is  low, i.e. they have a smooth transition between the transmitted and the blocked area. Colored glass filters are inexpensive, robust and easy to manufacture.

Colored glass filters absorb light, whereas interference filters reflect it. They filter independently of the angle of incidence of the light and have no polarizing effect. This can be an advantage for certain applications. They are therefore used, for example, for NIR filters in front of camera sensors.