Q: What is the difference between a mercury-arc bulb and an LED bulb?
Conventional arc lamps are considered broadband light sources because they emit light over a wide range of wavelengths including short wave UV, long wave visible, and even longer wave infrared. LEDs (Light-Emitting Diodes) on the other hand, are semiconductor light sources that emit very discrete wavelengths of light energy. This results in a single, narrow, bell-shaped emission spectrum.
LEDs offer many advantages over mercury-arc bulbs. LEDs cure cooler for better thermal management and offer very stable intensity which translates into more consistent process control. LED light-curing systems start up instantly, provide immediate light energy, and have an expected operating life of 10,000 hours, which results in significantly reduced downtime and lower light replacement costs when compared to conventional lamp systems.
Q: Will bond performance be similar whether you are using an LED or a conventional lamp light source?
The direct replacement of an arc lamp spot-curing system with an LED spot-curing system—without evaluation and process adjustment—can result in substandard bond performance. Differences in LED wavelength distribution and intensity necessitates the evaluation (if not formulary modification) of the chemistry and curing-energy dosage. There are some adhesives that provide the flexibility to use both types of light sources without changes to your process. Verification is strongly recommended to ensure successful results.
Q: Do LED adhesives cure best at the 365 nm wavelength peak?
Traditional mercury arc lamps indeed emit a high level of energy at the wavelength peak of 365 nm. However, this does not mean that an LED light source with a 365 nm peak will provide the best performance. The reality is that many light-curable chemistries, including acrylated adhesives, use photo initiators that respond best to the narrow, bell-shaped spectral curve.
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