Matching UV Wavelength to Your Adhesive (365 vs 385 vs 395 vs 405 nm)
The single most common reason a UV adhesive "won’t cure" is a wavelength mismatch, the source emits one band and the adhesive’s initiator wants another. Getting this right is the difference between a two-second cure and a joint that never hardens.
A photo-initiated adhesive only cures where the source wavelength overlaps the initiator’s absorption. Shorter UV (365 nm) drives surface cure and works with the widest range of initiators; longer bands (395, 405 nm) penetrate deeper and pass through more substrates but need an adhesive tuned to them. Match the two and cure is fast and complete; mismatch them and nothing happens no matter how long you expose.
The SkyBeam carries four independent LED channels, 365, 385, 395, and 405 nm, so you can dial in the exact band your adhesive wants, or run different chemistries on different channels. When you don’t want to commit to one band, the SunSpot 2’s 275–650 nm arc covers every UV-cure chemistry at once.
Step by Step
- 1 Read the adhesive datasheet. Find the recommended cure wavelength or the initiator’s absorption peak. This is the number the source has to hit.
- 2 Choose the matching band. Pick the LED channel closest to the datasheet band, 365 nm for surface-cure and the widest initiator compatibility, 395/405 nm for depth and curing through substrates.
- 3 Set intensity and time for the dose. The datasheet gives a target dose (mJ/cm²). Dose is intensity times time, set both to hit it, and verify intensity with a radiometer.
- 4 When in doubt, go broad. If the chemistry is unqualified or you run many adhesives, a broad-spectrum SunSpot 2 removes the matching problem entirely, it emits every band, so whatever the initiator wants is present.
Common Pitfalls
- Exposing longer to fix a wavelength mismatch, if the band is wrong, more time does nothing.
- Assuming all "UV" adhesives cure at 365 nm, many modern LED-cure adhesives are tuned to 395 or 405 nm.
- Setting time without setting intensity, dose is both; a distant guide at long time can under-dose.
Questions
What UV wavelength should I use to cure my adhesive?
The one on the adhesive datasheet. Match the source to the initiator’s absorption band: 365 nm for surface cure and the widest compatibility, 395–405 nm for deeper cure and curing through substrates. A wrong band will not cure no matter how long you expose.
What is the difference between 365 nm and 405 nm UV curing?
365 nm is shorter and more energetic, strong surface cure and compatible with the most initiators. 405 nm is longer, it penetrates deeper and passes through more clear substrates, but the adhesive must be formulated to cure at 405 nm.
When should I use a broad-spectrum arc instead of a single LED wavelength?
When the chemistry is unqualified, changes often, or you run many adhesives. A broad-spectrum SunSpot 2 emits 275–650 nm, so whatever wavelength any given initiator needs is present and you never have to match a band.
