Hello. Is infrared floodlight useful for passive fire control systems and does it affect their efficiency? Can you explain this to me with pictures?
Hi. Short answer is - it depends. Consider the historical context of the 1970s - combined with 1st gen NV with practical visibility of a few hundred meters, it was the only possibility of night combat, aside from using a visual spectrum floodlight. Naturally, this is not one-way: if you're emitting your IR floodlight, anyone can see you shining like a Christmas tree to anyone else with a NV device. Even while being quite dangerous, it was a fully workable solution for the expected lifetime of a tank crew in the 1970s, at European combat ranges of <1500 m.
Soon after, 1980s came, and with them came the thermals. First editions were bulky and required cooling with cryogas of some sort, but soon that was bypassed with a Stirling device. Thermals do not require a floodlight. The West invested heavily into the technology, and proliferation of thermals on Western tanks came rapidly, allowing for dramatic results in the Gulf War.
In Soviet use, a huge reluctance existed towards implementing (early) thermals, as they'd have required a separate logistic chains for cryogas. Combine that with an industrial/technological output that could not even supply enough fire control systems (which is a dramatic game changer of an improvement in tanks), and a technological gap became very apparent in the late 80s. Even today, IR spotlights are a common sight on Russian tanks. Not only that, Russia was even toying around of using a heavily focused IR spotlight made out of IR laser output, which is also an absurd way to go around night combat. Only in the last decade did Russia see a proliferation of thermals in its army.
In Yugoslav use, 2nd gen NV tubes were adopted very early on in our domestic tank production, obviating the need for an infrared floodlight. Combined with a highly capable, state of the art FCS, that made the M-84 tank the finest T-72oid in the world. Introduction of thermals in Yugoslav tanks was planned for the early 90s, which was sadly interrupted by the civil war and breakup.