NIR-Bildgebung für die industrielle Bildverarbeitung: 850 nm vs. 940 nm, Bandpassfilter und IR-korrigierte Objektive
Near-infrared reveals contrast that visible light misses. This guide covers how to pick between 850nm and 940nm and what the complete filter-lens-illumination stack requires.
850nm LEDs produce a faint visible red glow; 940nm shows none under normal conditions. On many silicon sensors, quantum efficiency at 940nm runs near half of the 850nm value, sometimes lower, so check the specific sensor's QE curve before sizing illumination; the wavelength section below covers what that means for power and exposure.
A complete NIR system also needs a bandpass filter matched to the illumination wavelength and, if it must also image in visible light from the same focus position, an IR-corrected lens.
850nm vs 940nm: How to Choose the Right NIR Wavelength
Choose 850nm when a faint glow is acceptable and detection range or exposure time is the binding constraint. Choose 940nm when the illuminator must show no visible glow to people, or when the system runs in bright daylight where suppressing ambient NIR matters more than sensor quantum efficiency. Commonlands stocks matched bandpass filters for both wavelengths.
850 nm: höhere Quanteneffizienz des Sensors bei einem schwachen sichtbaren Leuchten
Silicon CMOS sensors have higher quantum efficiency at 850nm than at 940nm, so for the same drive power an 850nm source typically gives more usable signal, supporting shorter exposures or lower illumination power. The tradeoff is glow: the CIE photopic curve is tabulated to 780nm, so 850nm sits past the edge of human vision, but deep-red response fades gradually rather than stopping there, and an 850nm LED emits a short-wavelength tail into that fading region. At high drive currents this glow is detectable in dark environments.
940nm: no visible glow but lower silicon QE
940nm sits far enough outside the eye's response that it produces no perceptible glow under normal conditions. The cost is sensor response: silicon QE at 940nm is commonly around half or less of its 850nm value, varying by sensor. A 940nm system therefore needs more power, longer exposure, or both to reach the signal-to-noise ratio an 850nm system achieves at the same range. Before committing a high-throughput line, verify this margin against the actual sensor QE curve, LED radiant power at drive current and temperature, and filter transmission.
Aspekte in Bezug auf die Atmosphäre und den Außenbereich
Outdoors, ambient sunlight carries strong NIR that competes with active illumination. Atmospheric water vapor absorbs solar radiation in a band around roughly 930nm to 970nm, which suppresses ground-level solar irradiance at 940nm relative to 850nm. That is a large part of why 940nm suits outdoor systems such as driver monitoring and face recognition: the ambient background is lower, partly offsetting the QE penalty. 850nm sees the full solar NIR floor.
| Kriterium | 850 nm | 940 nm |
|---|---|---|
| Quantenausbeute des Sensors | Höher, mit einem stärkeren Signal pro Watt Beleuchtungsstärke | Niedriger, in der Regel etwa die Hälfte des 850-nm-Werts oder weniger; je nach Sensor überprüfen |
| Sichtbares Leuchten | In dunkler Umgebung ist ein schwaches rotes Leuchten zu erkennen | Unter normalen Bedingungen kein wahrnehmbares Leuchten |
| Erforderliche Beleuchtungsleistung | Niedriger bei einem bestimmten Signalpegel | Higher, to close the sensor quantum efficiency gap |
| Typischer Anwendungsfall | Industrielle Inspektion, Barcode-Erfassung, Verkehrsüberwachung, bei der ein leichtes Leuchten akzeptabel ist | Verdeckte oder für Menschen sichtbare Installationen, bei denen die Sichtbarkeit der Beleuchtung nicht akzeptabel ist |
| Anpassung eines Einband-Bandpassfilters | CBP850 | CBP940 |
| Angepasster Zweiband-Passfilter | CDB850 | CDB941 |
These filters are not interchangeable: a 940nm bandpass filter blocks 850nm illumination and produces a dark image if paired incorrectly. See bandpass filter machine vision for how center wavelength and passband width factor into the selection.
What NIR Imaging Means in Machine Vision
In silicon machine vision, NIR means roughly 700nm to 1000nm, just beyond visible red: the band where silicon still responds. Optical convention runs NIR out to about 2500nm, which needs InGaAs rather than silicon detectors. In machine vision the term almost always means active illumination at 850nm or 940nm paired with a camera set to detect that band, not ambient infrared or thermal imaging.
Switching to NIR moves four elements of the optical stack together:
- The IR-cut filter must be out of the optical path. It typically blocks wavelengths above roughly 650nm, a design-dependent boundary, and stops NIR from reaching the sensor.
- The lens must transmit the NIR wavelength, and its focus plane shifts between visible and NIR unless the lens is IR-corrected.
- A bandpass filter matched to the wavelength rejects ambient visible light and improves signal-to-noise ratio.
- The sensor needs meaningful quantum efficiency at the target wavelength. Silicon QE drops significantly above 850nm.
Removing the IR-cut filter and switching on an LED, with nothing else changed, is not enough. The image comes out dim, soft, or noise-limited. Most machine vision NIR is active: a dedicated illuminator with a matched bandpass filter controls wavelength and intensity independent of ambient light. Passive NIR relies on ambient NIR already in the scene, so it works outdoors in daylight but fails at night and under modern white LED or fluorescent fixtures.
See the Commonlands image sensor selection guide for how NIR response weighs against resolution, pixel size, and shutter type.
Why NIR Reveals Contrast That Visible Light Misses
NIR imaging is useful because reflectance, transmission, and absorption vary with wavelength, so many materials look different in NIR than under white light. That difference is the entire basis for NIR machine vision, not a general-purpose upgrade to image quality.
Tinten und Druckgrafiken
Carbon-based inks absorb visible light and stay dark. That absorption carries into the NIR band, so carbon-ink printing keeps its contrast against the substrate under 850nm or 940nm. Many dye-based inks that look opaque black to the eye are largely transparent in NIR, so a barcode printed in dye-based ink can effectively disappear in a 940nm image, revealing the substrate beneath.
That cuts both ways: disappearing ink helps when inspecting a feature under a label, but it defeats an OCR or print-verification system reading dye-based characters. Carbon-based ink does not have this problem. Verify ink composition on the actual production substrate before committing to a wavelength.
Surface glare and coatings
Specular reflections from glossy or metallic surfaces saturate visible pixels when ambient light is not controlled. Narrow-band NIR with a matching bandpass filter rejects the broadband visible glare, so the sensor mainly captures the NIR scattered from the surface. It does not remove specular reflection from the NIR source itself, but it removes the visible glare that dominates typical factory lighting.
Thin films and coatings that look uniform under white light can show different NIR reflectance by composition or thickness. Biological and food-grade materials often show NIR contrast tied to water content, which is why NIR appears in fill-level inspection, food sorting, and pharmaceutical packaging.
Was NIR nicht leistet
NIR is not universally better than visible. Color discrimination and legibility of visible ink are usually better served by visible light. NIR does not penetrate opaque materials the way X-ray does, and useful penetration depth varies by material and must be validated on real samples. A datasheet contrast difference does not guarantee the same result on production parts.
Where NIR Imaging Shows Up in Production Systems
NIR imaging shows up wherever visible-light contrast fails on a specific material pairing, which clusters around a few recurring problems.
Traffic and license-plate systems are among the most common deployments. Retroreflective plate coatings return a strong signal under 850nm synchronized with a short exposure, giving high-contrast plates regardless of ambient light or headlight glare. Because these run day and night, they are the most common use for the Commonlands CLA216-ICR-850BP switcher: color video by day, 850nm NIR at night, one camera. See lenses for traffic monitoring for lens selection.
Barcode reading uses NIR when the code is carbon-based ink on an NIR-reflective substrate, or when ambient lighting is uncontrolled. Robotics platforms near people sometimes pick 940nm so the illumination shows no visible glow to bystanders. Quality-inspection lines for packaging and seals use NIR to reveal defects invisible in the visible band, running single-bandpass under controlled illumination.
Filters, Lenses, and Switching Architectures for NIR Systems
Beyond sensor and illumination choice, an NIR system needs three hardware decisions: filter type, lens IR correction, and whether it must switch between visible and NIR modes at all.
Filterauswahl
The IR-cut filter is the most misunderstood element: it blocks NIR and must be out of the optical path, but removing it is necessary, not sufficient, because without a bandpass filter the sensor still sees ambient visible light. A single bandpass filter passes only the illumination band.
A dual-bandpass filter passes a visible and an NIR window at once for RGBIR (red, green, blue, infrared) sensors. The filter does no separating on its own, but the system still can: an RGBIR sensor separates the bands by pixel, and modulating the NIR illuminator and differencing frames separates them in time. An electronic switcher separates them optically, moving an IR-cut and a bandpass filter in and out.
Wann die IR-Korrektur eines Objektivs eine Rolle spielt
If a system runs only in NIR, focus at the NIR wavelength and IR correction is unnecessary. If it must stay sharp at both visible and NIR from one focus position (day/night cameras, RGBIR sensors, dual-mode inspection), an IR-corrected lens is required. A standard lens has chromatic focus shift between visible and NIR from dispersion in the glass. Removing the IR-cut filter does not close that gap, since the shift is in the lens design, not the filter.
Sensor selection
Not every sensor is a good NIR candidate. Many consumer and some machine vision sensors have an NIR-blocking layer in the pixel stack itself, independent of any external IR-cut filter, capping sensitivity at 850nm and 940nm. Pull the sensor's spectral QE curve and read the value at each wavelength rather than assuming a generic silicon response. RGBIR sensors often use a dual-bandpass filter to define the NIR passband, or leakage degrades daylight color.
Commonlands NIR Imaging Components
Commonlands stocks IR-corrected M12 lenses, 850nm and 940nm single-bandpass filters, and an electronic filter switcher for NIR systems. The six Commonlands parts below cover 850nm and 940nm builds, ordered for dual-mode systems that must stay sharp in visible and NIR from one focus position. An NIR-only build focuses once at the illumination wavelength, skips the IR-corrected lens, and starts at the bandpass filter.
| Rang | Komponente | Typ | Wichtigste technische Daten | Am besten geeignet für |
|---|---|---|---|---|
| 1 | CIL122 | IR-korrigiertes M12-Objektiv | 12mm EFL, F/2.0, 1/1.7in 8-12MP | Tag-/Nacht- und Dual-Mode-Systeme, die aus einer einzigen Fokusposition heraus sowohl im sichtbaren Licht als auch im NIR-Bereich scharf bleiben müssen |
| 2 | CBP850 | 850-nm-Einbandpassfilter | Lässt 850 nm durch, blockiert sichtbares Licht; 7,0 mm Durchmesser, 0,3 mm dick | Aktive Beleuchtung bei 850 nm, bei der ein schwaches LED-Leuchten akzeptabel ist und eine höhere Sensor-Quantum-Effizienz (QE) entscheidend ist |
| 3 | CBP940 | 940-nm-Einbandpassfilter | T>90 % bei 940 nm, blockiert den sichtbaren Bereich | Verdeckte oder für Menschen sichtbare 940-nm-Systeme, bei denen kein sichtbares Leuchten zulässig ist |
| 4 | CLA216-ICR-850BP | Elektronischer IR-Sperrfilter / 850-nm-Bandpass-Umschalter | IR-Sperrfilter und 850-nm-Bandpassfilter in einem beweglichen Halter, Höhe 7,6 mm | Ein-Kamera-Tag-/Nachtbetrieb mit vollständiger Unterdrückung in jedem Modus; in Kombination mit dem IR-korrigierten Objektiv |
| 5 | CDB850 | Zweiband-Passfilter (sichtbares Licht + 850 nm) | Lässt ein sichtbares Fenster und ein 850-nm-Fenster in einem festen Element durch | Schalterlose Tag-/Nacht-Umschaltung über RGBIR-Sensoren bei 850 nm, keine beweglichen Teile |
| 6 | CDB941 | Zweiband-Passfilter (sichtbares Licht + 940 nm) | Lässt ein sichtbares Fenster und ein 940-nm-Fenster in einem festen Element durch | Schalterlose Tag-/Nacht-Umschaltung über RGBIR-Sensoren bei 940 nm, kein sichtbares Leuchten |
The order follows build sequence, not price: in a dual-mode system chromatic focus shift originates in the lens glass and cannot be filtered out afterward, and a bandpass center-wavelength mismatch costs the most signal of any single choice. MidOpt (midopt.com) and Edmund Optics also sell bandpass and dual-bandpass lines outside the Commonlands filter range.
Use the field of view calculator for the lens field angle, then check that angle against the illuminator's measured beam distribution over the working plane. The calculator describes the lens. It says nothing about the illuminator's angular irradiance profile.
Häufig gestellte Fragen
Was ist der Unterschied zwischen 850 nm und 940 nm in der industriellen Bildverarbeitung?
850nm and 940nm are the two most common NIR illumination wavelengths. Silicon sensors have higher quantum efficiency at 850nm, so it gives a stronger signal for the same illuminator power, but the LEDs emit a faint visible red glow. 940nm shows no visible glow to people, though silicon sensors, color included, still respond unless an IR-cut stack blocks it. It usually needs more power or exposure to match 850nm, by a ratio set by the sensor's QE curve, LED radiant power, filter transmission, drive current, temperature, and target reflectance.
Was versteht man unter NIR-Bildgebung in der industriellen Bildverarbeitung?
NIR imaging uses near-infrared wavelengths, typically 850nm or 940nm, to illuminate and image a scene outside the visible band. A complete system needs a sensor with no IR-cut filter in the path, a bandpass filter matched to the wavelength, an NIR light source, and an IR-corrected lens if it must also image sharply in visible light from the same focus position.
Wann sollten Ingenieure die NIR-Bildgebung anstelle von sichtbarem Licht einsetzen?
Use NIR when visible light does not give enough contrast on the target: printed graphics where ink and substrate share similar visible reflectance, specular glare from glossy surfaces, coatings that look uniform under white light but vary in NIR, or unpredictable ambient lighting. NIR is not always better. Validate that the real materials produce the expected NIR contrast first.
Welche Filter werden für die NIR-Bildgebung verwendet?
Three filter types appear in NIR systems. A single bandpass filter at 850nm or 940nm passes only the illumination wavelength and blocks visible light. A dual-bandpass filter passes a visible window and an NIR window at once in one fixed element, used for switcherless day/night on RGBIR sensors. An electronic switcher moves an IR-cut filter and a bandpass filter in and out for true day/night separation.
Benötige ich für die NIR-Bildgebung ein IR-korrigiertes Objektiv?
If the system operates only in NIR, focus at the NIR wavelength and correction is not required. If it must also image sharply in visible light from the same mechanical focus position, an IR-corrected lens is required. A standard lens has chromatic focus shift between visible and NIR. Removing the IR-cut filter does not fix it, because the shift is in the glass, not the filter.
Need Help Designing an NIR Imaging System?
Beschreiben Sie den Sensor, den Arbeitsabstand, die Wellenlänge der Beleuchtung und das Prüfziel. Commonlands Engineering kann Ihnen dabei helfen, zwischen 850 nm und 940 nm zu wählen, einen Bandpass- oder Dual-Bandpass-Filter auszuwählen und diesen mit einem IR-korrigierten M12-Objektiv zu kombinieren.