Principle of operation of cold mirrors
Dielectric Interference Coating: through the precise stacking of multiple layers of TiO₂/SiO₂ and other thin films, the following can be realized: high reflectance of visible light (R>95%@400-700nm), highly efficient transmittance of infrared light (T>80%@700-2500nm).
Heat Dissipation: the infrared energy penetrates through the mirrors directly, which avoids the accumulation of heat from the light source (e.g., halogen lamps, LEDs).

What are the applications of cold mirrors?
Projection Systems: reducing thermal stress on LCD/DLP projectors to extend chip life.
Microscope Lighting: reducing thermal damage to samples and improving observation clarity.
Stage Lighting: reducing equipment temperature while maintaining high brightness output. 
Medical Equipment: heat management for surgical shadowless lamps.