Short-wave infrared illumination has moved from laboratory curiosity to production-line equipment. Optical sorters that separate foreign material from almonds, blueberries, recycled PET and potato strips now run at 3 to 8 tonnes per hour, and their accuracy is limited less by camera resolution than by the wavelength and bandwidth of the light illuminating the product. This white paper explains how to choose SWIR LED emitters by wavelength and full-width half-maximum (FWHM) bandwidth, and how QUEENDOM’s J-07 2835 SWIR (1600 nm), J-08 3535 SWIR (2000 nm) and J-09 5050 SWIR parts map onto the main sorting tasks.

1. Why SWIR, and why wavelength matters more than power

Silicon-based sensors stop responding beyond approximately 1,100 nm. By moving to extended-InGaAs focal plane arrays, machine vision systems gain access to the 900–2,500 nm band, where materials that look identical in visible light diverge sharply. Water absorbs strongly near 1,450 nm and 1,940 nm. Fat absorbs near 1,210 nm and 1,730 nm. Sugar has a broad absorption shoulder around 1,500 nm. Plastics differ by C-H bond overtones: polyethylene and polypropylene separate best near 1,700 nm, while PET has a distinct signature near 1,660 nm.

The engineering consequence is that a sorter’s contrast is set by the ratio of two reflectance curves, not by the raw brightness of the lamp. Increasing radiant power raises signal-to-noise but does not create contrast. Choosing the wrong wavelength at high power produces a bright, evenly-lit image in which the defect is still invisible.

Material pair to separateBest discrimination bandTypical contrast driver
Water-rich fruit vs. dry stem1,400–1,500 nmWater absorption
Fat / marbling vs. lean tissue1,700–1,750 nmFat C-H absorption
PET vs. PE / PP flake1,640–1,680 nmPolymer C-H overtone
Almond shell vs. kernel1,600–1,700 nmLignocellulose vs. oil
Blueberry vs. leaf / stem960–1,100 nmChlorophyll vs. anthocyanin
Potato bruise vs. sound tissue1,350–1,450 nmCell disruption / water

2. What FWHM does to sorting contrast

FWHM is the spectral width at half of peak intensity. A 1600 nm emitter specified at FWHM ≤ 60 nm concentrates its photons into a narrow band; the same die with FWHM of 150 nm spreads energy across a range in which both target and background absorb similarly, diluting the difference the camera is trying to see.

Two effects follow. First, narrow FWHM increases contrast per unit of optical power, which allows shorter exposure and higher line rate. Second, narrow FWHM reduces spectral cross-talk between adjacent sorting tasks running on the same line, important when a single camera block handles the visible and SWIR channels in sequence.

Emission spectra: narrow versus wide FWHM at the same peak wavelength 1400 1600 1800 0 100 Wavelength (nm) Relative intensity (%)
Figure. Green solid line: FWHM ≤ 60 nm emitter. Amber dashed line: FWHM ≈ 150 nm emitter at the same peak wavelength. Narrow bandwidth concentrates photons into the discrimination band, raising contrast per unit power. Representative values, for engineering reference only.

3. Selecting by application: the four dominant sorting tasks

The table below maps the three main production sorting problems onto QUEENDOM SWIR parts. Radiant flux figures are typical at the stated drive current, on a 25 °C heat-sink.

Sorting taskRecommended QUEENDOM partPackagePeak / FWHMTypical radiant fluxWhy this part
Fruit water content, potato bruiseJ-07 2835 SWIR2835 SMD1600 nm / ≤ 60 nm12–18 mW @ 100 mACompact footprint for dense linear arrays
Plastic flake (PET vs PE/PP)J-07 2835 SWIR2835 SMD1600 nm / ≤ 60 nm12–18 mW @ 100 mA1660–1680 nm shoulder accessible via bin
Fat / marbling, meat gradingJ-08 3535 SWIR3535 ceramic2000 nm / ≤ 80 nm8–14 mW @ 350 mACeramic body survives high-duty pulsing
High-flux wide-web sortingJ-09 5050 SWIR5050 ceramic1600 / 2000 nm variants30–55 mW @ 700 mAHighest flux per emitter, fewer parts per bar

3.1 Contrast versus wavelength

Contrast in a reflective sorter follows the reflectance difference divided by the summed reflectance. The curve below shows a representative almond-shell-versus-kernel contrast across the SWIR band, with the J-07 and J-08 peaks marked.

Reflectance-difference contrast versus wavelength for shell versus kernel J-07 1600 J-08 2000 1100 2300 0 high Wavelength (nm) Contrast (a.u.)
Figure. Representative reflectance-difference contrast for almond shell against kernel. Vertical markers show the J-07 (1600 nm) and J-08 (2000 nm) peak positions. Not a certified measurement.

4. Design workflow: from substrate to illuminator

A repeatable five-step workflow keeps sorting projects from becoming trial-and-error:

  1. Measure both classes. Capture reflectance spectra of target and contaminant on the actual belt, under the actual moisture state. Dry and wet product behave differently at water-absorption bands.
  2. Compute the contrast curve. For every candidate wavelength, calculate (R_target − R_contaminant) / (R_target + R_contaminant). Rank by peak contrast.
  3. Pick the emitter and FWHM. Choose the QUEENDOM part whose peak sits within the highest-contrast band, and specify FWHM as narrow as the radiant-flux budget permits.
  4. Size the illuminator. Divide the required irradiance at the camera plane by the single-emitter flux to obtain emitter count, then add 20–30 % margin for optics loss and LED degradation.
  5. Validate at line rate. Run the sorter at production speed and measure false-reject and false-accept rates. Contrast measured statically rarely predicts dynamic performance.

4.1 Emitter count versus required irradiance

For a linear illuminator, required emitter count scales linearly with belt width and target irradiance. The curves below show three irradiance targets for a 600 mm web using J-07 and J-09 emitters.

Required emitter count versus belt width at three irradiance targets 200 600 1000 0 160 Belt width (mm) Emitters required
Figure. Required emitter count versus belt width. Green solid: 20 W/m² target. Blue solid: 40 W/m². Amber dashed: 80 W/m². Representative values assuming 78 % optical efficiency.

4.2 Matching the illuminator to the camera

The illuminator and the camera are one optical system, and specifying them separately is a common source of disappointing results in the field. Three parameters must be co-designed.

Numerical aperture and collection angle. A camera lens with a small aperture collects less of the diffusely reflected SWIR energy. If the illuminator is sized for an f/2.8 lens and the integrator installs an f/5.6 lens to gain depth of field, delivered signal falls by a factor of four. Confirm the lens aperture before finalising emitter count.

Angular distribution versus field of view. Emitters with a 90° viewing angle concentrate energy into the centre of the field; 120° devices light the edges more evenly but at lower peak irradiance. For wide belts, mixing narrow-angle emitters at the centre with wide-angle parts at the edges flattens the uniformity profile without increasing part count.

Pulse timing and exposure window. In line-scan systems the exposure window is set by line rate, not by the illuminator. The emitter must reach full radiant flux within that window, which means the driver must deliver a fast rising edge. A slow driver effectively shortens the exposure and forces higher peak current, which in turn stresses the package. Specify the driver rise time alongside the LED part number.

5. Thermal and lifetime considerations

SWIR emitters are typically driven in pulsed mode at line rate. Two rules govern reliability:

  • Pulse duty must respect thermal resistance. The 3535 ceramic body of J-08 and the 5050 ceramic body of J-09 have lower junction-to-case thermal resistance than plastic SMD packages, which is why they tolerate higher peak currents at the same duty.
  • De-rate for lifetime. IES LM-80 data on SWIR packages typically show 90 % flux maintenance at 6,000 hours at rated current on a 55 °C heat-sink. Budget illuminator flux accordingly and re-validate contrast after the first 2,000 hours of production.
ParameterJ-07 2835 SWIRJ-08 3535 SWIRJ-09 5050 SWIR
Die technologyAlGaInAs / InGaAsPAlGaInAsAlGaInAs
Peak wavelength1600 nm2000 nm1600 / 2000 nm
FWHM≤ 60 nm≤ 80 nm≤ 60 / 80 nm
Tension Directe1.1–1.5 V @ 100 mA1.3–1.8 V @ 350 mA1.3–1.9 V @ 700 mA
Radiant flux (typ.)12–18 mW8–14 mW30–55 mW
Viewing angle120°90° / 120°90° / 120°
Résistance Thermique~180 K/W~45 K/W~25 K/W
Recommended heat-sinkFR-4 or MCPCBMCPCB mandatoryMCPCB + active cooling above 500 mA

6. Common mistakes and how to avoid them

MistakeConsequenceCorrection
Specifying by power instead of wavelengthBright but low-contrast imageRank candidates on contrast curve first
Using wide-FWHM parts to save costContrast loss of 20–40 % typicalSpecify FWHM as a controlled parameter
Ignoring moisture stateWorks on dry sample, fails in productionMeasure reflectance on wet product
Sizing at nominal fluxContrast decays below threshold by mid-yearBudget 20–30 % degradation margin
Reflow with wrong profilePackage cracking, wavelength shiftFollow the ceramic-body profile in the datasheet
No spectral filtering at cameraAmbient SWIR from heaters contaminates imageAdd bandpass filter matched to emitter peak

7. Verification and test methods

Three tests close the loop on an SWIR illuminator specification:

  1. Spectral characterization — measure peak wavelength and FWHM on a calibrated spectroradiometer at rated current and at the production-case temperature, since peak wavelength shifts approximately 0.3–0.4 nm/°C for these material systems.
  2. Irradiance uniformity — scan the illuminated plane with a calibrated SWIR radiometer at nine points and report maximum-to-minimum ratio; a target of ≤ 1.15:1 is realistic for a well-designed bar.
  3. End-to-end sorting trial — introduce a known quantity of contaminant into production product and measure false-accept and false-reject rates over at least three hours of continuous operation.

8. Conclusion and selection guidance

For most food-sorting retrofits, J-07 2835 SWIR at 1600 nm with FWHM ≤ 60 nm provides the best balance of flux density, footprint and optical control for belt widths below 600 mm. Move to J-08 3535 SWIR at 2000 nm when the discrimination task depends on fat or C-H overtones that peak above 1,800 nm, and to J-09 5050 SWIR when a single high-flux emitter per position is preferred over dense emitter arrays. In every case, select on the contrast curve first, then size the array on irradiance, and leave thermal and degradation margin at the end.

9. Referenced standards

  • IEC 62471 — Photobiological safety of lamps and lamp systems
  • IEC 60825-1 — Safety of laser products (applies to high-irradiance collimated SWIR sources)
  • IES LM-80 — Approved method: measuring luminous flux maintenance of LED light sources
  • IES TM-21 — Projecting long-term lumen maintenance of LED light sources
  • ISO 22000 — Food safety management systems (downstream process context)

10. Contact us

QUEENDOM supplies J-07, J-08 and J-09 SWIR emitters from stock and can provide spectral characterization data, FWHM binning statements and reference illuminator layouts on request. Contact our component engineering group for sample quantities and application support.

Related products and applications

The SWIR emitters referenced in this paper — and the packages they ship in — are listed below.