When only a small bead of adhesive needs to cure and the surrounding assembly must stay untouched, a spot curing system delivers concentrated ultraviolet energy through a light guide to a target just millimeters across. That focus is what makes selective, repeatable bonding possible on crowded assemblies.

How Spot Curing Works

A spot system pairs a UV source with one or more flexible light guides that carry the energy to the work point. The guide terminates in a lens or a bare tip that produces a defined spot, typically adjustable between 3 and 12 mm in diameter. Because the energy is concentrated, irradiance at the tip can be very high, which drives fast cure of small adhesive volumes without heating the whole part.

Two source types dominate. UV LED spot lamps such as the Incure L9000 UV LED spot lamp run at a single configured wavelength between 365 and 405 nm, switch instantly, and support up to four light guides from one controller. Mercury-arc spot lamps like the Incure S20 emit broadband output from roughly 275 to 650 nm with intensity above 21 W/cm² at the guide tip, useful when a resin needs the wider spectrum or a very high peak.

Key Benefits

• Selective cure. Energy reaches only the targeted bond, leaving nearby seals, coatings, and heat-sensitive parts unaffected.
• Speed. Small adhesive volumes at high irradiance cure in one to several seconds.
• Positioning time. The adhesive stays liquid until the light triggers it, so components can be aligned precisely before cure.
• Multi-point work. A bifurcated or four-pole guide splits one source across several bond sites fired together.

Understanding the light guide is central to using these systems well; our explainer on what a light guide does in a UV spot lamp system covers the fundamentals.

Selecting a Spot Curing System

Wavelength. Match the LED peak or arc spectrum to the adhesive’s photoinitiator. A mismatch shows up as a soft or tacky bond even at long exposure.

Irradiance at the working distance. The number that matters is the value at the actual gap between the guide tip and the bond, not at the emitter. Irradiance drops quickly as the tip is pulled back, so fixture the guide at a consistent distance.

Spot size. Choose a spot slightly larger than the adhesive footprint. Too small a spot leaves an uncured ring; too large a spot wastes energy and may reach adjacent components.

Guide count and geometry. Single guide for one bond, multi-pole for simultaneous multi-site cure. Longer guides lose some transmission, so specify the shortest length that reaches comfortably.

Duty cycle. LED sources tolerate unlimited cycling and suit robotic or indexed lines. Arc sources are kept lit with a shutter controlling exposure.

If you need help pairing a source, guide, and fixture to a specific part, Email Us with a sketch of the bond location and the adhesive data sheet.

Light Guide Care

Light guides degrade with use. Liquid-filled guides can develop bubbles or solarization; fiber bundles can suffer broken fibers at the ferrule from tight bends. Both reduce transmitted irradiance gradually, so a bond that cured in two seconds when new may need four seconds a year later if the guide is not checked. The article on what causes UV light guide degradation over time explains the mechanisms and how to catch them with a radiometer.

Handle guides with a minimum bend radius of roughly ten times the guide diameter, keep the tips clean of cured adhesive, and store them without sharp kinks.

Custom Configurations

Industrial spot curing is rarely off-the-shelf. Typical customization includes guide length and tip lens tailored to the fixture, a manifold that splits output to match the number of bond sites, an interlocked shroud for operator safety, and integration with a dispensing robot so cure fires automatically after each dot is placed. For processes where the adhesive must also survive fast handling right after cure, compare how UV adhesives and epoxy differ on cure speed for quick repairs.

Process Control

Validate a spot process by measuring tip irradiance with a small-aperture radiometer, then setting exposure to deliver the adhesive’s specified dose with a margin. Re-measure on a fixed schedule. Log source hours, guide changes, and radiometer readings so any drop in bond quality can be traced to a specific cause rather than guessed at.

Shadowed bond lines remain the main limitation. If the adhesive sits under an opaque part, reposition the guide to fire into the gap, add a second guide from another angle, or switch to a dual-cure adhesive with a secondary heat or moisture mechanism.

Summary

A spot curing system succeeds when the wavelength matches the adhesive, the irradiance is verified at the real working distance, and the spot is sized just larger than the bond. Add disciplined light guide maintenance and the process stays stable for years. Contact Our Team to configure a spot system for your assembly.

Visit www.incurelab.com for more information.