SWIR LED Food Sorting Application

Nut and grain processors face a stubborn inspection problem: shell fragments, insect damage, and foreign matter that look identical to good product under visible light. This project shows how 1470nm SWIR LEDs solved it — raising foreign-matter rejection accuracy to 99.2% on a high-throughput sorting line.

Application Background

A nut processing company supplying retail brands in Europe and North America needed to upgrade its optical sorting line. The existing color-camera system reliably removed visibly discolored kernels, but three defect classes kept escaping to the customer’s incoming inspection:

• Shell fragments — thin, pale pieces that match almond flesh under RGB imaging
• Concealed insect damage — internal cavities with no external color signature
• Plastic and rubber debris — from conveyor wear, often similar in color to product

Each escaped defect risked chargebacks and audit findings under the customer’s food-safety program. Manual re-inspection of flagged lots was costing the plant 40+ labor hours per week.

Engineering Challenge

The physics of the problem pointed to the short-wave infrared band. Water and organic materials interact with SWIR light very differently than with visible light:

• At 1470nm — close to a strong water absorption peak — the moisture contrast between sound nut flesh and damaged or foreign material produces a dark-bright signature invisible to RGB cameras
• Shell, plastic, and insect-damaged tissue show clearly differentiated reflectance against healthy kernels at this wavelength

Three constraints shaped the illumination design: the sensors needed uniform line illumination across a 1200mm scan width; the LEDs had to deliver sustained radiant power under continuous duty at 40°C ambient inside the sorter housing; and the source lifetime had to match the machine’s 5-year service interval to avoid mid-season teardowns.

Solution & Key Components

Queendom supplied SWIR LED arrays built on the 3535 high-radiance platform, configured for line-scan illumination:

Parameter	Value	Design Note
Peak wavelength	1470 nm (SWIR)	Matches water-absorption contrast band
Package	3535 ceramic SMD	Thermal stability under continuous duty
Line coverage	1200 mm (8 modules × 150 mm)	Overlap eliminates dark seams
Illumination uniformity	> 90% across scan width	Critical for line-scan cameras
Drive	Constant current, closed-loop thermal foldback	Protects radiant output at 40°C ambient
Service lifetime target	50,000 h (L70)	Exceeds machine service interval

Integration notes for sorting-machine builders: the modules mount behind protective sapphire windows (SWIR transmits well; glass absorbs partially), and the constant-current zones map one-to-one to the camera’s pixel banks so intensity can be trimmed per zone during commissioning.

Results

After a two-week validation run, the SWIR channel caught shell fragments and plastic debris that the RGB stage missed, while the false-reject rate stayed below the 0.5% contract threshold — keeping yield losses acceptable.

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Frequently Asked Questions

Why 1470nm instead of 1550nm for food sorting?

Both wavelengths sit in the SWIR water-contrast band. 1470nm offers a practical balance: strong moisture contrast, available high-radiance LED sources, and better sensor compatibility than longer SWIR wavelengths, which increasingly require costlier InGaAs detector options.

Can SWIR LEDs replace RGB cameras entirely?

No — the two channels are complementary. RGB removes visibly discolored product; SWIR catches moisture, shell, and foreign-material contrast invisible to color imaging. Most modern sorters run both channels in sequence.

How are the arrays protected in wash-down environments?

Modules sit behind sapphire or SWIR-transmissive windows in IP65-rated housings, with gasketed cable glands — the same enclosure discipline used in the food-washdown lighting described in our waterproof lighting applications.