What is the main function of an IR cut filter?
Core Function
Blocks infrared light: natural and artificial light sources often contain visible and infrared light. However, image sensors (e.g. CMOS/CCD) are sensitive to infrared light, which, if not filtered out, can lead to color distortion (e.g. red color bias, loss of contrast).
Enhanced Color Reproduction: by precisely filtering infrared wavelengths, it ensures that the sensor receives only visible light, making the imaged colors closer to what the human eye sees.

How do IR cut filters work?
Spectral selectivity: filters are designed with special coatings or materials to maintain high transmittance (>90%) in the visible wavelength band (400-700nm), while transmittance drops sharply (<5%) in the infrared wavelength band (e.g. 700-1200nm).
Reflect or absorb infrared light: some filters reflect infrared light by means of multilayer interference coatings, while others achieve this by means of absorptive materials (e.g. blue glass).

How to distinguish between real and fake IR cut filters?
Tested with IR remote control: the genuine filter will block the IR signal of the remote control (cell phone camera can't see the remote control glowing).