What is hdr-m-2.54?

The high dynamic range illumination is 2.54. HDR is a commonly used technology in photography, which is the abbreviation of English High-DynamicRange, meaning high dynamic range. HDR technology can overcome the shortcomings of limited dynamic range of most camera sensors, and control the tone of the picture within the range that can be recognized by human beings. M is the sign of photometry mode in photography technology, and the value displayed behind the sign is the measured illuminance, for example, m2.54 stands for illuminance 2.54.