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Light Emitting Diodes (LED) - The Base Building Block
Let's start with the LED. As the base building block, this is the first choice a UV LED lamp supplier has to make. It is a critical choice that impacts the remainder of the systems architecture and design. Simply put, an LED is a solidstate device that produces light when an electrical current is allowed to flow from the positive (anode) side of the circuit to the negative (cathode) side.
Not all LEDs are built the same nor do they exhibit the same characteristics. UV LED lamp suppliers have critical choices to make as to the quality, type, material and shape of LED for their systems. Key LED characteristics considered by each UV LED lamp supplier include wavelength and UV output.
The wavelength emitted from an LED is controlled using differing amounts of dopants such as aluminum, gallium or indium derivatives during the manufacturing of the LED. The general rule of thumb is that the shorter the wavelength, the lower the peak UV output available from the die.
The UV LED supplier must weigh the trade‐offs between wavelength and the associated total energy with cure rate. Chemistry plays a significant role in this discussion. Some applications, due to their specific chemistry, require a given wavelength. However, for many applications a small shift in the peak wavelength will have no impact as the absorption of the UV by the photoinitiator which kicks‐off the reaction has a broad absorption range.
The output of a single UV LED is measured in milliwatts (mW) at a nominal input voltage and current. UV LED output has shown considerable improvement in recent years where specifications for LEDs from various vendors have improved from 2005 to 2011 with a compound annual growth of 5‐10%. This improvement shows the LED vendors have and will continue to improve the output of UV LEDs, which only provides a better foundation for the UV LED curing lamps that utilize them.