Abstract: Halogen lamps, pure water filtered heat rays and LED are the main conventional light sources for the optical microscope. Halogen lamp light source contains a lot of infrared rays from 760 to 1400 nm. The pure water filter incompletely filters out infrared rays, which results in scattering of some transmission light. For the LED light source, around the 500 nm wavelength, the light intensity is weak and the waveform is incomplete, which can cause samples to burn or can affect the final imaging quality. Therefore, conventional light sources are not suitable cold light sources for non-destructive and high-quality imaging microscopic observation and testing. Based on the comparison of imaging modes and the light source types, the advantages and disadvantages of different light sources are discussed. A new idea to obtain a cold light source through prisms and convex mirror groups is proposed. The idea is firstly to open the spectrum of the halogen lamp light source in order of frequency through the prism, then choose the visible spectrum, finally adjust the light direction through convex mirror groups and then compound the cold light without heat rays through the prism. Theory and practical application results by studying fluorescence in thin sections of sandstone showed that the cold light obtained by this method not only completely filters out heat rays, but also retains the whole visible spectrum. This method provides a feasible foundation for the projection imaging of a high-power cold light source microscope. The whole device includes two prisms and convex mirrors, and one halogen lamp and is especially suited for non-destructive imaging.