Curing UV Adhesives - which wavelength and lamp?
UV-curing adhesives set in seconds once the right light reaches the bond line. This guide explains how to match wavelength, light intensity and shadow zones, and how to size the LED curing lamp correctly.
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Why is wavelength the decisive factor?
A UV adhesive only cures when the light hits the wavelength its photoinitiator responds to. Common peaks are 365 nm (long-wave UV-A) and 385, 395 or 405 nm at the edge of the visible range. Lamp and adhesive must match, otherwise polymerisation never starts.
365 nm penetrates deeper into thick or pigmented bond lines and cures through where less light arrives. 405 nm suits thin, transparent joints and substrates that dislike short-wave UV. Many modern adhesives are dual-band and respond across both ranges.
How much light intensity do you need?
What matters is the light dose: irradiance (in mW/cm² or W/cm²) multiplied by exposure time. You reach the same dose with high intensity and a short time, or the other way round. The data sheet usually states a minimum dose in mJ/cm².
Spot lamps hit very high values at the light exit, but intensity falls off with the square of distance. Double the distance and irradiance drops to roughly a quarter. Keep the lamp as close to the bond line as possible and measure the real value with a radiometer.
- Measure irradiance at the workpiece, not assumed at the lamp head.
- Dose = intensity x time - fix the time with a timer in series production.
- Oxygen inhibits surface cure - beat a tacky residue with more dose or inert gas.
- Calibrate the radiometer regularly, LED output drops over its life.
What about shadow zones?
UV light only cures where it reaches. Hidden joints under opaque parts, behind metal edges or deep in bores stay liquid. Such shadow zones are the most common cause of incomplete cure and later bond failure.
Dual-cure adhesives solve this: they start with UV light and cure the light-starved areas through a second mechanism - moisture, heat or anaerobic setting under exclusion of air. Alternatively, a transparent joint partner lets the light enter.
How do I size the LED curing lamp?
Choose the lamp by wavelength, required irradiance and the area to be exposed. Spot lamps suit small, defined bond points; area lamps and LED arrays cover larger or several joints at once. LED systems are mercury-free, ready instantly and long-lived.
- Match the wavelength to the adhesive (365 vs 405 nm or dual-band).
- Pick irradiance so the target dose is reached within the cycle time.
- Fit the light field to the joint geometry - spot, line or area.
- Aim for even illumination and allow for edge fall-off of an area lamp.
- Provide cooling and spacers so the geometry stays reproducible.
Find the right UV or dual-cure adhesive for your substrate and joint.
Read the guideFrequently asked questions
Does a 405 nm lamp cure every UV adhesive?
No. The photoinitiator must respond to 405 nm. Pure 365 nm adhesives may skin over but will not cure through reliably. Always compare the peak wavelength in the data sheet.
How do I calculate the right exposure time?
Take the minimum dose from the data sheet (in mJ/cm²) and divide it by the irradiance measured at the workpiece. Add a safety margin for distance variation and LED ageing.
What happens in shadow zones?
No light reaches them and the adhesive stays liquid. Use dual-cure systems (moisture, heat or anaerobic) or cure through a transparent joint partner.
Why does the surface stay tacky?
Atmospheric oxygen inhibits surface cure. More light dose, higher intensity or inert gas removes the tacky residual layer.
Looking for the right UV bonding system?
We supply UV and dual-cure adhesives with matching LED curing lamps for 365 and 405 nm - tuned to your joint and cycle time.
Matched wavelength
Adhesive and LED tuned from 365 to 405 nm.
Process-safe
Dose and distance defined, reproducible in series.
Handles shadow zones
Dual-cure systems reliably set light-starved areas.
Expert advice
We help with adhesive choice and lamp sizing.