Infrared Rangefinders: "Infrared" Is a Range, Not a Specification
Half the catalogue pages in this industry say "infrared rangefinder" as if it were one product. It covers everything from 850 nm to 1550 nm, and the differences between those bands matter more than the label.
The four bands you'll actually meet
850–905 nm is silicon territory. Cheap detectors, mature optics, short range and low eye-safety limits. Most industrial and consumer distance sensors live here.
1064 nm is Nd:YAG. InGaAs detectors, good atmospheric transmission, and a retina hazard that constrains how much energy you can use.
1535 nm is Er:Yb glass. InGaAs again, but the light is absorbed in the cornea before it reaches the retina, so the permissible energy is much higher. That's why long-range, person-adjacent systems use it.
1550 nm and beyond behaves like 1535 for safety, with more water absorption. Useful for some short-path work, less so for long range in humid air.
The detector decides the rest
Silicon stops responding past about 1100 nm, so you can't put a cheap Si detector behind a 1535 nm source. InGaAs costs more, has more dark current, and sets the noise floor of the receiver. When someone quotes you a very cheap 1535 nm module, ask what detector is in it.
Optics change with the band
Window materials, anti-reflection coatings and interference filters are all wavelength-specific. A filter centred at 905 nm does nothing for a 1535 nm receiver, and its passband shifts with temperature and angle of incidence.
The AR coating matters too: a lens coated for the visible will lose several percent per surface in the short-wave infrared, and that loss shows up directly in the range budget.
What to ask a supplier
Exact wavelength and tolerance, detector material, filter bandwidth, and the eye-safety class of the finished product — not of the source. Those four answers tell you more than any "infrared rangefinder" headline.
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