The problem of detecting lightning flashes from space is becoming more and more important as the remote sensing of Earth, climatology and atmospheric physics develop. Orbital lightning detectors are designed both in Russia and abroad. The paper considers the problem of mathematical and physical simulation of a high-speed camera designed to observe lightning flashes from onboard spacecraft in low Earth orbit. Our previous works substantiated the exterior design of the lightning detector, computed its properties and described the algorithms behind the software. In order to validate the design results, we need to prototype the instrument. We describe the main problems of detecting lightning flashes as observed from space. We show a computer simulation method producing snapshots that takes into account the interference generated by the background and the photodetector. We studied the problems of recreating the target environment during prototyping of the lightning detector, accounting for the properties of the phenomenon observed, that is, the flash spot dimensions and the ratio of the background brightness to that of the lightning. We describe the principle of comparing these two types of snapshots (taken by the prototype and synthesised by the software) and compared the results of processing the images obtained. The results matched, which allowed us to validate the snapshot processing algorithm and confirmed that the lightning detector simulation method developed is correct