Full spectrum conversion is a type of infrared conversion you can get for your digital camera.

Much like an infrared conversion, this modification removes the  internal IR cut filter over your camera’s sensor. During a full spectrum  conversion, this filter is replaced with a piece of clear glass, making  the camera sensitive to UV, visible, and infrared—the full spectrum of light.

This increased sensitivity allows your camera to absorb more light, making it a very useful tool for astrophotography and low-light applications.

You  get the most flexibility when you have a full spectrum conversion.  Since the camera sensor is sensitive to all spectra of light, you are  able to shoot in all spectra of light. 

The main benefit here is that you can use external filters (i.e., lens filters, drop-in filters, or clip-in filters) to narrow the spectrum to a particular range. Putting an IR filter on the lens will still allow for handheld infrared photography, just like a converted camera.

With just one camera, you can shoot in IR with any of our infrared filters, ultraviolet with a UV bandpass filter (provided you use a good UV lens), or normal color photography using a UV/IR cut hot mirror filter. 

This  is the most versatile conversion you can get, giving you 10+ options in  only one camera. Additionally, full spectrum is the only conversion  option compatible with the IR Chrome and Blue IR filters, as well as with UV and normal photography.

From : https://kolarivision.com/full_spectrum_conversion/