マシンビジョンにおけるNIRイメージング：850nm対940nm、バンドパスフィルター、およびIR補正レンズ
なぜ近赤外光は可視光では捉えきれないコントラストを明らかにするのか、850nmと940nmのどちらを選ぶべきか、そしてフィルター・レンズ・照明の完全な組み合わせには何が必要なのか。
850nm gives higher sensor quantum efficiency and a stronger signal for the same illuminator power, but the LEDs produce a faint visible red glow. 940nm produces no perceptible glow under normal conditions but needs more power or exposure time, because silicon sensor QE at 940nm runs at roughly half or less of its 850nm value.
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 stay invisible, 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.
850nm：センサーの量子効率が高く、かすかな可視光の発光が見られる
Silicon CMOS sensors have higher quantum efficiency at 850nm than at 940nm, so for the same drive power an 850nm source gives more usable signal, supporting shorter exposures or lower illumination power. The tradeoff is glow: 850nm sits close to the edge of human vision, where deep-red sensitivity falls off steeply but does not vanish until roughly 750nm, and the short-wavelength tail of the LED's emission puts a small fraction of its output near that edge. At high drive currents this glow is detectable in dark environments.
940nm：目に見える発光はないが、シリコンの量子効率の約半分である
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. High-throughput lines where exposure time is the binding constraint should verify this margin against the actual sensor QE curve.
大気環境および屋外での使用に関する考慮事項
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.
| 基準 | 850nm | 940nm |
|---|---|---|
| センサーの量子効率 | より明るく、照度1ワットあたりの信号強度もより高い | より低い値（通常、850nmの値の約半分以下）。センサーごとに確認してください。 |
| 目に見える輝き | 暗い環境下でかすかな赤い光が見える | 通常の状態では目立った発光は見られない |
| 必要な照明出力 | 特定の信号レベルに対して低い | Higher, to close the sensor quantum efficiency gap |
| 代表的な利用例 | 産業用検査、バーコード読み取り、光の漏れが許容される交通監視 | イルミネーターの視認性が許容できない、隠蔽型または人向けの設置環境 |
| 同等の単一帯域通過フィルタ | CBP850 | CBP940 |
| マッチング用デュアルバンドパスフィルタ | CDB850 | CDB941 |
These filters are not interchangeable: a 940nm bandpass filter blocks 850nm illumination and produces a dark image if paired wrong. See bandpass filter machine vision for how center wavelength and passband width factor into the selection.
What NIR Imaging Means in Machine Vision
NIR imaging uses wavelengths from roughly 700nm to 1000nm, just beyond visible red. 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 blocks wavelengths above roughly 650nm and stops NIR 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.
インクおよび印刷グラフィック
Carbon-based inks absorb visible light and stay dark, and 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.
NIRができないこと
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 stays invisible. 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.
フィルターの選択
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 but cannot fully reject either. An electronic switcher moves an IR-cut and a bandpass filter in and out for true day/night separation.
レンズのIR補正が重要となる場合
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 depend on a dual-bandpass filter to define the NIR passband, or leakage degrades daylight color.
Commonlands NIR Imaging Components
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, ranked by the order in which each choice locks down the rest of the design.
| ランク | コンポーネント | 種類 | 主な仕様 | こんな方に最適 |
|---|---|---|---|---|
| 1 | CIL122 | IR補正済みM12レンズ | 12mm EFL, F/2.0, 1/1.7in 8-12MP | 1つの焦点位置から可視光および近赤外（NIR）の両方で鮮明な画質を維持しなければならない、昼夜兼用およびデュアルモードシステム |
| 2 | CBP850 | 850nm単一帯域通過フィルター | 850nmを通過、可視光線を遮断；直径7.0mm、厚さ0.3mm | 850nmのアクティブ照明。LEDの微かな光が許容され、センサーの量子効率（QE）が重要となる場合 |
| 3 | CBP940 | 940nm単一帯域通過フィルター | 940nmで透過率90%以上、可視光帯を遮断する | 目に見える発光が許されない、隠蔽型または人向けの940nmシステム |
| 4 | CLA216-ICR-850BP | 電子式IRカット／850nmバンドパス・スイッチャー | IRカットフィルターと850nmバンドパスフィルターを1つの可動ホルダーに収め、高さは7.6mm | 各モードで完全なノイズ除去機能を備えたシングルカメラの昼夜兼用モデル。IR補正レンズと組み合わせて使用します。 |
| 5 | CDB850 | デュアルバンドパスフィルター（可視光＋850nm） | 1つの固定要素に、可視光ウィンドウと850nmウィンドウを組み込む | 850nmのRGBIRセンサーによるスイッチレスな昼/夜切り替え機能、可動部品なし |
| 6 | CDB941 | デュアルバンドパスフィルター（可視光＋940nm） | 1つの固定要素に、可視光ウィンドウと940nmウィンドウを組み込む | 940nmのRGBIRセンサーによるスイッチレスな昼/夜切り替え、可視光による発光なし |
The ranking follows build order, not price: 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. Confirm the lens field of view covers the illuminator beam angle with the field of view calculator before ordering.
よくある質問
マシンビジョンにおいて、850nmと940nmの違いは何ですか？
850nm and 940nm are the two standard 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 perceptible glow but needs roughly double the power or exposure to match, since silicon QE at 940nm is often half its 850nm value or less.
マシンビジョンにおけるNIRイメージングとは何ですか？
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.
エンジニアは、どのような場合に可視光の代わりにNIRイメージングを使用すべきでしょうか？
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.
NIRイメージングにはどのようなフィルターが使われていますか？
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.
NIRイメージングには、IR補正レンズが必要ですか？
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?
センサーの仕様、作動距離、照射波長、および検査目的についてご説明ください。コモンランズ・エンジニアリングでは、850nmと940nmのどちらを選ぶべきかのご提案、バンドパスフィルターまたはデュアルバンドパスフィルターの選定、およびIR補正済みM12レンズとの組み合わせについてサポートいたします。