A. There is much confusion about how to compare traditional UV lamps to UV LED systems, often because the terminology used is inconsistent or overlapping. In particular for UV LED curing, equipment specifications can vary from manufacturer to manufacturer. This is actually two questions, so let’s take each in turn.
1. Power requirements for UV lamps describe the electrical power input the lamp consumes. You will see this written as Watts or W/inch. Traditional lamps using a quartz bulb to generate UV, specify input power in W/inch. To calculate the total electrical power required to operate the lamp, simply multiply input power by the length of the bulb in inches (30 inch x 600 W/inch = 18,000 Watts). Power is designated this way to make it easy to compare lamps of different lengths.
UV LED curing units cannot use this W/inch specification for input power, because there is no long continuous bulb like there is with traditional systems. Instead, UV LED curing lamps utilize many extremely small LED diodes which are densely packed together in multiple columns and rows called an array, so only Watts are used to specify input power. Typically, UV LED lamp size will be specified by the dimensions of the emission window, the quartz window separating the diodes from open air, and is written in terms of length and width.
In both cases, this input power is for the lamp or array only and does not indicate the total electrical power needed to operate the curing system. Some curing equipment manufacturers include a total power consumption specification, also in Watts, but not all do.
2. The UV output of a lamp is called irradiance (sometimes referred to as intensity) and describes the highest UV energy seen at a given distance from a lamp, making it a very practical value for end users. For traditional systems using elliptical reflectors, the peak irradiance is focused inches away from the bulb. For a UV LED system, the irradiance reported by most manufacturers is measured directly at the emission window face. In both cases, this irradiance is per square inch, Watts/in2, or more often, a per square centimeter value (W/cm2).
The two most important values impacting curing are typically peak irradiance (W/cm2) and total energy (J/cm2), sometimes referred to as dose, which takes into account exposure time. For a specific curing process these measurements need to be taken at the substrate, not the emission window of the UV LED curing unit. End users should take radiometry measurements themselves, using the correct radiometry measurement device for UV LED curing, to characterize the curing parameters for their process. Learn more about correctly measuring output of UV LEDs by downloading Technical Paper:
Comparing traditional UV to UV LED