Ultraviolet LED illumination opens a family of industrial inspection applications that visible-wavelength lighting simply cannot reach. Many materials, inks, coatings, and biological substances fluoresce under UV excitation: they absorb UV photons and re-emit light at a longer, visible wavelength. A standard monochrome or colour camera captures that fluorescence emission with ease, making invisible features visible at very high contrast against a dark background.
The uses of UV LED illumination in machine vision span leak detection with fluorescent tracers, security marker verification on labels and documents, adhesive and sealant inspection, contamination detection on food contact surfaces, and authentication of high-value products. Each application carries its own requirements for UV wavelength, illumination intensity, illuminator geometry, and camera and filter configuration. This guide walks through the technical principles and practical design considerations for each category.
UV Wavelengths in Industrial Vision Applications
Industrial UV LED illuminators run at two primary wavelength bands: 365 nm and 395 nm. The choice between these wavelengths has a marked effect on the performance of fluorescence-based inspection.
365 nm UV Illumination
Illuminators at 365 nm produce true UVA radiation. This wavelength excites a wide range of fluorescent materials including most commercial UV-reactive dyes, fluorescent tracers used in leak detection, optical brighteners in paper and textiles, and many biological fluorophores. At 365 nm, the excitation radiation itself is completely invisible to standard silicon-based camera sensors without a UV-passing filter. The camera image shows only the fluorescence emission, giving very high contrast between fluorescent and non-fluorescent areas.
The main limitation of 365 nm LEDs is lower output power than 395 nm. LED efficiency at 365 nm is lower than at longer UV wavelengths, so more LEDs or higher drive current are needed to reach the same surface irradiance. Thermal management matters more for 365 nm illuminators because of the higher thermal load per unit of optical output.
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395 nm UV Illumination
Illuminators at 395 nm produce near-UV radiation that borders the visible spectrum. This wavelength is faintly visible to the human eye as a violet glow and is also partly detectable by standard camera sensors. The main advantage of 395 nm is higher LED efficiency and higher achievable surface irradiance for the same drive power. Many commercial fluorescent tracers and security inks respond well to 395 nm excitation.
The partial visibility of 395 nm radiation in camera images means a short-pass or band-pass filter is needed on the camera lens to block the excitation wavelength and pass only the fluorescence emission. Without it, the 395 nm background illumination partly swamps the fluorescence signal and weakens detection contrast. RODER Vision UV illuminators are available at both 365 nm and 395 nm to match the specific fluorophore excitation needs of the application.
Fluorescent Leak Detection
Leak detection with fluorescent tracers is one of the most demanding and highest-value UV inspection applications. A small quantity of UV-fluorescent dye is added to the fluid or gas in the system under test. Any leakage point is found by imaging the exterior of the system under UV illumination. The leaked fluorescent tracer fluoresces brightly under UV excitation, making even very small leak points visible against the dark background of the surrounding surface.
Applications in Hydraulic and Pneumatic Systems
Hydraulic systems in automotive, aerospace, and industrial machinery use fluorescent tracer dyes to pinpoint minute leak points on hoses, connectors, seals, and heat exchangers. The fluorescent tracer is usually added to the hydraulic fluid or coolant at a concentration of 0.1% to 0.5%. After running the system under operating pressure, the exterior is imaged under UV illumination. Even a single drop of leaked fluid fluoresces brightly and is immediately detectable.
Machine vision inspection takes over from manual UV lamp inspection in high-volume production. An automated UV inspection station images the complete exterior of the assembled component at defined camera positions. The image processing algorithm picks out fluorescent spots above a defined size and intensity threshold, classifies each detected spot, and triggers the reject mechanism for components with confirmed leak indications.
Leak Detection in Refrigeration and Air Conditioning Systems
Refrigeration and air conditioning systems require 100% leak testing before shipment. UV fluorescent tracer dyes are compatible with most refrigerant and compressor oil formulations. The assembled system is charged with refrigerant containing the UV tracer and pressurised. Leak points are found by UV machine vision inspection of the brazed joints, valve connections, and pipe penetrations.
Security Marker and Authentication Verification
Security markers that stay invisible under white light and fluoresce under UV illumination are widely used for product authentication, document security, and brand protection. Machine vision systems using UV LED illuminators can verify the presence, position, and content of these security features at production speed.
Pharmaceutical Label Authentication
Pharmaceutical labels often carry UV-fluorescent security features including UV-reactive inks, fluorescent fibres embedded in the label substrate, and UV-visible serial numbers or codes. Vision inspection under UV illumination confirms that all required security features are present and correctly positioned. This inspection is built into the label application station and runs at full packaging line speed.
Document and Banknote Verification
High-security documents including identity documents, certificates, and banknotes carry complex UV-fluorescent patterns that are impossible to reproduce without access to the original fluorescent ink formulations. Machine vision inspection under UV illumination can confirm the presence and correct pattern of these features and reject counterfeit or tampered documents in automated processing systems.
Adhesive, Sealant, and Coating Inspection
Many adhesives, sealants, and coatings used in manufacturing are formulated with UV-fluorescent additives. That lets the presence, coverage, and bead continuity of the adhesive or sealant be verified by UV machine vision after application and before assembly.
Adhesive Bead Presence and Continuity
Structural adhesive applied to automotive body panels, door seals, and bonded assemblies has to be continuous and within the specified width and position tolerance. UV-fluorescent adhesive formulations let the complete bead be imaged under UV illumination. The image processing algorithm measures bead width, catches gaps or skip sections, and confirms the bead sits within the permitted positional tolerance relative to the part geometry.
Gasket and Seal Compound Verification
Sealing compounds applied to gasket faces, threaded connections, and flange surfaces can be verified by UV inspection if the compound carries a UV-fluorescent additive. The presence of the compound on the critical sealing surfaces is confirmed by the fluorescence image before assembly. Missing or wrongly positioned compound is caught before the joint is made, sparing the cost and effort of disassembly and rework.
UV Illuminator Design and Integration Considerations
UV LED illuminators for machine vision call for careful design and integration to reach reliable, stable, and safe operation.
Thermal Management for UV LEDs
UV LED junction temperature strongly affects both output intensity and wavelength stability. As the junction temperature climbs, the optical output falls and the emission peak drifts slightly toward longer wavelengths. For fluorescence-based inspection, wavelength stability is critical because a shift in the excitation wavelength changes the fluorescence excitation efficiency and alters the apparent brightness of the fluorescent feature in the image. RODER Vision UV illuminators build in HTTM thermal management technology to control LED junction temperature and hold UV output intensity and wavelength stable across all operating conditions.
Camera Filter Requirements
Fluorescence imaging needs a long-pass or band-pass filter on the camera lens to block the UV excitation wavelength and pass only the fluorescence emission at visible wavelengths. Without it, the reflected UV illumination from the scene background partly swamps the weaker fluorescence signal. The filter cut-on wavelength has to be chosen to fully block the UV excitation wavelength while passing the fluorescence emission band of the specific fluorophore used.
For 365 nm illumination, a long-pass filter with cut-on at 400 nm to 420 nm is used. For 395 nm illumination, a filter with cut-on at 420 nm to 450 nm is needed to block the stronger near-UV background adequately. RODER Vision optical filter accessories are available to complete the UV fluorescence inspection system.
Operator Safety
UV radiation at 365 nm and 395 nm can cause eye and skin damage with sustained exposure. Industrial UV LED illuminators for machine vision are usually installed inside enclosed inspection cells where operator exposure is removed during operation. When maintenance or setup work calls for operation with open guards, appropriate UV-protective eyewear has to be worn. RODER Vision UV illuminators comply with CE marking requirements for electrical and optical safety.
Products and Technologies
RODER Vision Illuminator Families for UV Applications
The RODER Vision product families below support UV illumination for fluorescent leak detection, security marker verification, and adhesive inspection.
DL6 — High Density LED Matrix
Available with UV 365 nm and 395 nm LEDs. High-density matrix for area UV illumination. HTTM thermal management for stable UV output. Ideal for label and security feature inspection.
DC6 — High Density LED Ring
UV ring illumination for top-view fluorescence inspection of adhesive beads, seals, and surface coatings. Multi-wavelength options including 365 nm and 395 nm UV.
DL5 — High Intensity LED Matrix
High peak UV intensity in strobe mode for leak detection at high inspection speed. Strong UV excitation to detect minimal fluorescent tracer concentrations.
FD2 — Flat Dome LED Illuminators
Diffuse UV illumination for uniform fluorescence excitation on flat labels and documents. Clears directional shadows. UV 365 nm and 395 nm options available.
Frequently Asked Questions
365 nm produces true UVA radiation that excites a wider range of fluorescent materials with no background visibility in camera images, though it needs a filter to block the UV reflection. 395 nm LEDs are more efficient and reach higher surface irradiance but are partly visible to cameras and need a tighter cut-on filter. For the most demanding fluorescence work, 365 nm gives better contrast; for general fluorescence inspection, 395 nm is adequate and more cost-effective.
A small amount of UV-fluorescent dye tracer is added to the fluid or gas in the system. After pressurisation, the exterior is imaged under UV illumination, and any leaked fluid fluoresces brightly against the dark surrounding surface. The machine vision algorithm picks out fluorescent spots above a defined size and intensity threshold and triggers rejection of leaking components. The method catches very small leaks that stay invisible under white light.
Yes. A long-pass or band-pass filter on the camera lens is needed to block the UV excitation wavelength and pass only the visible fluorescence emission. Without it, reflected UV from the scene background swamps the weaker fluorescence signal. For 365 nm illumination, use a filter with cut-on at 400-420 nm; for 395 nm illumination, use a filter with cut-on at 420-450 nm.
Yes, as long as the adhesive or sealant carries a UV-fluorescent additive. The cured or uncured bead fluoresces under UV illumination, and the machine vision system confirms bead presence, width, continuity, and position. Gaps, skip sections, and positional deviations are caught before assembly. Many structural adhesive and sealant makers offer UV-fluorescent formulations specifically for machine vision process verification.
UV radiation at 365-395 nm causes eye and skin damage with sustained direct exposure. Industrial UV illuminators should sit inside enclosed inspection cells that prevent operator exposure during normal operation. UV-protective eyewear rated for UVA wavelengths has to be worn during setup and maintenance work with open guards. RODER Vision UV illuminators comply with CE marking requirements for electrical and optical safety.
Contacts & Information
Contact for general information : info@roder.it
Systems and Sensor Integration Partner : www.roder.it
RODER Artificial Vision Division : www.rodervision.com
RODER Instruments Division : www.innovacheck.com
More information about RODER VISION : about us
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Please note: Some images on this website have been intentionally generated using Artificial Intelligence (AI). This is due to the fact that, for many applications and projects, it is not possible to disclose photographs of the actual installation or system due to confidentiality agreements, contractual clauses, and Non-Disclosure Agreements (NDAs).
