this post was submitted on 05 Jun 2024
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Touché
Now that I've read my own comment, I see that it came off harsher then I intended it to. Interpret it literally and not like a sarcastic statement.
Btw, just occurred to me that these would probably not work in a car at all, because regular glass is usually opaque to IR.
I'm almost 100% positive that this is not correct, because I've been driven around by someone wearing PVS-14 NODs with no headlights, on dirt roads, in a commercial van. (Edit - most red dot sights also work very well with NODs, and those have one or two layers of glass, depending on which type of system it is. The sights that don't work well usually can't dim the dot enough to avoid massive bloom.) Glass is mostly opaque to thermal though, and a lot of glass significantly reduces UV.
I can't say I have any experience with PVS-14 or any Night Optical Devices, but from what I see online, it amplifies certain visible spectrum as well as near-IR. It doesn't seem to rely on IR much. And red dot sights aren't even IR are they? At least not entirely, cause you can see them with the naked eye.
Regarding glass being opaque to IR, apparently, it depends on the type of glass. I just remembered it from a Vsauce video (IIRC) where it was demonstrated to be opaque. But since term IR is vague and doesn't have super defined borders, and there are different types of glass, yeah, it's not a certain statement.
Okay, so you're talking about the IR that most people would refer to as thermal, rather than the IR that's technically NIR, and is used in most image intensification. My mistake; as you say, these things get slippery because most of the time people aren't talking about specific wavelengths and frequencies.
Yes, IR-as-in-thermal is going to be stopped by most glass. IR-as-in-NIR-for-NODs is not. The IR lasers and weapon lights that show up very well with NODs are definitely not visible to the naked human eye, so they're outside of the visible light spectrum, and get generally labeled as IR, even if they're outside of the spectrum of IR that's used by most thermal optics. (It would be interesting to see if a Steiner DBAL could illuminate an area that had low IR for a FLIR camera.) And yes, for that, a red dot sight will work, because it will be set to very, very dim; too dim to be seen by the naked eye.
I'm sorry if I made the false impression that I know what I'm talking about. I'm just discussing and learning as I go. But I went back to the article and looked for the specific figures, and you were right, they are amplifying 1550-nm wavelength, which is NIR. And average glass is usually opaque to wavelength at around 2500nm, so it shouldn't get blocked. At least not much.