What is an IR-cut filter?

"An IR-cut filter is a color filter blocking the infrared light. There are several good reasons for using an IR-cut filter. All JAI color camera include an IR-cut filter in order to achieve proper white balance and realistic colors. Monochrome cameras are sometimes equipped with an IR-cut filter, to block out unwanted energy from light sources inclucing longer wavelengths (typically above 600 nm). Such light sources may be halogen tungsten lamps or even the sun. Reducing the IR contents in monochrome cameras helps improve the MTF (Modulation Transfer Function) which results in sharper images, allowing cameras to visualize finer detail."