850nm vs 940nm IR: which wavelength for which job?

Every Nightfox IR torch and floodlight comes in a choice of wavelength, and customers ask us which one to pick almost every day. The short answer: 850nm gives you better range and picture quality, 940nm gives you better stealth. The right choice depends on what you're actually doing with it.

What's the actual difference?

Both wavelengths are infrared, so neither is visible to the naked eye as light. But 850nm sits close enough to the visible spectrum that a running LED gives off a faint red glow at the source, especially on higher-power units. 940nm sits further out, so that glow all but disappears. The trade-off is that digital night vision sensors are more sensitive to 850nm, so you get a brighter, sharper image and a longer usable range at that wavelength. Pick 940nm and you sacrifice some range and clarity in exchange for near-invisibility.

Wildlife watching and ecology surveys

For most fieldwork, 850nm is the better default. We haven't had reports of wildlife being disturbed by the glow, and the extra range and clarity matter more than covertness for the majority of surveys. If your methodology specifically calls for minimal light disturbance, for example around wary or heavily-pressured animals, 940nm is the more conservative choice. Both the XB5 and XB5 Pro come in either wavelength, so you're not locked in; the Pro adds a built-in rechargeable battery and USB charging on top.

Airsoft and stealth use

Here the calculation flips. Giving away your position to another IR user is the main risk, so most airsoft players run 940nm. Some still prefer 850nm for the range advantage and accept the trade-off. Worth remembering: if you're relying on a teammate's or a fixed IR source nearby rather than carrying your own, wavelength choice matters a lot less.

Static setups: the Arc floodlight

Not every job calls for a handheld torch. The Arc is a fixed, wide-angle IR floodlight built for static positions, lighting a bat roost or building entrance for the length of an overnight survey. It's 850nm only, so if covertness is the priority for a fixed setup, a torch is the better fit; the Arc is built for range and coverage, not stealth.

Practical summary

• Best range and image quality: 850nm
• Best stealth: 940nm
• Fixed, wide-area static lighting: Arc (850nm only)