UVA LED in Anti-Counterfeiting Detection
Fluorescence Excitation Principle
Photons in the UVA band (320–400 nm) match the excitation peaks of most security inks and specialty fibers. When 365 nm, 385 nm, or 395 nm photons are absorbed by fluorescent dyes containing rare-earth, benzoxazole, or pyrazoline structures, electrons jump from ground to excited states and then release energy as 420–650 nm visible light, instantly emitting bright green, blue, or red fluorescence detectable by eye or camera. Thanks to a large Stokes shift, a simple 420 nm long-pass filter in front of the camera completely blocks the excitation light while passing only the fluorescence, yielding high-contrast images. Under 365 nm at 20 mW cm⁻², ordinary colorless fluorescent fibers in RMB banknotes emit >200 cd m⁻² blue-white light within 0.2 s, tripling contrast and providing sufficient SNR for high-speed on-line inspection.
Wavelength Selection Guide for UVA LED Anti-Counterfeiting Detection
365 nm
Highest fluorescence efficiency; matches peak absorption of official security inks in banknotes (RMB, EUR), ID cards, etc. Ideal for high-end documents, tobacco & alcohol caps, cosmetics.
385 nm
15 % higher wall-plug efficiency and ~30 % lower cost than 365 nm; suited for high-volume packaging inspection (toothpaste, medicine, milk-powder cans).
395 nm
Least visible violet, minimal visual disturbance; preferred for “invisible” codes on concert tickets, luxury bags, jewelry certificates that require dark-field imaging.
Rule of thumb:
☑ Paper securities → 365 nm first.
☑ Plastic films or dark inks → 385 nm.
☑ Totally “light-free” setting → 395 nm plus a 420 nm short-pass filter.
System Optimization Tips
Irradiance (I) & Working Distance
☑ Too low I → dim fluorescence; intensity drops 30–50 % per extra cm.
☑ Recommend: surface inspection at 10–30 mm; line-scan camera tilted 30°; uniformity >85 %.
Viewing Angle & Filtering
☑ Direct LED light swamps fluorescence; use 420 nm high-pass filter to block excitation and pass 450–700 nm emission.
Thermal Management
☑ 365 nm chips have only ~40 % WPE; 2 nm wavelength drift at Tj>80 °C cuts fluorescence by 20 %.
☑ Solution: MCPCB + forced air, housing <60 °C, <5 % output drop after 24 h continuous run.
Common Problems & Fixes
-
☑ Problem: Weak or no fluorescence
☑ Causes: Wavelength mismatch, ink covered by UV varnish, insufficient dose
☑ Fixes: Check ink absorption peak and switch to 365 nm; raise I to 20 mW cm⁻²; remove varnish or use 395 nm-transmissive coating -
☑ Problem: Image over-exposed, purple background.
☑ Causes: Excitation leakage, shallow filter cut-off.
☑ Fixes: Stack 420 nm long-pass + 550 nm short-pass filters; cut camera gain by 6 dB. -
☑ Problem: 30 % output drop after 6 months.
☑ Causes: High junction temp, over-current, sulfur contamination.
☑ Fixes: De-rate to 80 % rated current; constant-current accuracy ±3 %; cover exit window with quartz glass to block sulfur/acid mist.
Materials & Accessories
Exit window
Synthetic quartz (JGS-1) transmits >92 % at 365 nm; ordinary soda-lime glass cuts off below 350 nm—do not use.
Lens
PC or PMMA absorbs 365 nm; choose quartz or optical glass.
Filters
420 nm long-pass + 550 nm short-pass combo blocks 99.5 % of excitation light.
Camera
Mono industrial camera, pixel ≥2.2 µm, QE >60 % at 500 nm.
Typical Application Cases
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☑ Case 1: RMB banknote sorter (on-line).
☑ Requirement: 1,200 notes/min, false-negative <0.01 %.
☑ Solution: 365 nm linear module 50 mW cm⁻², 4k line-scan camera + 420 nm long-pass filter; contrast improved 3×, false-negative 0.006 %. -
☑ Case 1: Premium liquor cap inner-code inspection.
☑ Requirement: 60,000 bottles/8 h, cap coated with UV varnish.
☑ Solution: 385 nm area array, 15° incident angle, camera equipped with 550 nm short-pass filter; read rate 99.8 %, cost 40 % lower than laser coding. -
☑ Case 1: Luxury handbag stitching authentication.
☑ Requirement: In-store verification within 30 s, no leather damage.
☑ Solution: 395 nm handheld pen, 1 W, housing <45 °C after 10 min continuous use; fluorescent dots combined with RFID, on-site complaint rate down 90 %.
Conclusion
UVA LEDs deliver “precise wavelength, cold emission, long lifetime, and mercury-free” in one package, moving anti-counterfeiting detection from labs and bank counters to production lines and everyday consumers. Follow the three golden rules—“wavelength first, filter matched, heat managed”—and a tiny bead can make invisible inks flash into view, giving brands, customs, and shoppers a low-cost, reliable, and sustainable “counterfeit-spotting flashlight.”