It's worth noting that the goggles won't shield you from the mental trauma of what they highlight. You look through the lens, you gotta deal with what you see. If you go snooping through an Illithid's lair with a pair of these, and you want to see if you can use the lenses to identify some mystery slime, you might not want to know what the slime is. Because once you know, you can't un-know.
And trust me, your DM won't pull any punches here.
The mechanics here are pretty loosey-goosey, but that's deliberate. The goggles are essentially batman-style Detective Vision, limited by the fact that you can't have a lens for every potentially plot-relevant fluid. It's a McGuffin-y piece of loot that plays best when you limit it to just a few highly specific lenses. Just enough to let your players feel like they have a leg up on the next CSI-inspired quest you throw at them, while also giving you wiggle room to *Yes, and...* or *No, but...* them in the right direction.
And remember, just because a player has a lens that shows blood splatters with a fluorescent outline, doesn't mean there's a neat and tidy trail that leads straight past your planned plot arc.