In the original Star Trek television series, Captain Kirk often avoided disaster with the simple command: “Scotty, we need more power!” Star Trek is science fiction (emphasis on fiction), with the original television version set in the 23rd century. Episode after episode, the electrical circuits on the U.S.S. Enterprise managed rapid, large, sustained power surges and spikes to provide “more power” without any damage. When I try consuming “more power” in the 21st century, I either trip a circuit breaker or unknowingly create a brownout in the neighborhood. It makes me wonder if the electrical grid in the US finally will get updated by the 23rd century.
UV sources have evolved since the original Star Trek first aired in 1966. Source manufacturers have responded to Captain Kirk’s command. In 2025, are there any situations in UV curing where “we need more power?”
If the UV process is properly designed, tested and validated with the formulation and the UV source sized and matched, we would not expect to see a situation where the end user is looking for more power. However, we recently ran into some examples…
Mercury-Based Sources
Mercury-based sources have evolved over the last 60 years. Early on, it felt like a reverse game of limbo. Instead of “how low can you go,” UV source manufacturers played “how high (of electrical consumption) can I go?” With mercury-based sources, there are checks and balances between the electrical power consumed, UV power delivered, heat/IR produced, cooling and the life of the system bulb. Arc or microwave technology commonly is used in mercury sources to deliver the needed UV photons. Source manufacturers utilize different approaches, including bulb types, bulb diameters, and reflector shapes and materials. Power supplies available today often are smaller, lighter, intelligent and more energy efficient, with some manufacturers offering high-frequency versions. Look for ongoing improvements to mercury-based sources, not so much in the generation of UV photons but in the monitoring of the source, power supply and other key parameters.
Mercury Sources: We Need More Power, Example One
A formulator designed a coating and established the process window on a benchtop UV system in the company’s lab. The good news is that the formulator used the same equipment in the lab as the end user has on the production line. The bad news is that the end user had challenges meeting the formulator-specified target consistently, especially in UV-C. (Full disclosure: My company was guilty until proven innocent and did our due diligence to make sure that our radiometers were calibrated and being used properly.)
The UV sources here were part of a complex production line. Further testing revealed that the process values were met consistently only when the UV sources were run. When the end user turned on the rest of the production line, a drop in UV values was noted, with the UV-C values decreasing by almost 25%. This was a situation where more power was needed to drive both the production line equipment and UV sources without a drop off in the UV produced. This example illustrates the need for communication between the UV source supplier, machine integrator and installation crew to make sure that everything is installed correctly.
Mercury Sources: We Need More Power, Example Two
UV curing takes place on a global scale, with many companies having operations on multiple continents. This situation arose when a company established a process window and ran a production line in the US, with the sources running on 60 Hz supplied electrical power. The company transferred the production line and the same UV equipment to a facility outside the US that was running on 50 Hz supplied electrical power. The process window was extremely tight to begin with, and the transfer and subsequent running of the equipment on 50 Hz added additional challenges. The UV output decreased ever so slightly, and the drop was enough to push the process outside of the established process window.
LED-Based Sources
Persistent work and a vision by a few companies over the last 20 years have resulted in the commercialization of UV LEDs for curing applications. Progress was not always smooth, and some applications were a better fit and adopted UV LEDs earlier than others. UV LED output (irradiance) increased rapidly, and it felt more like an arms race than a reverse limbo game. Claims such as, “My UV LED has an output of (insert the number) W/cm2, which is 1 W/cm2 higher than the output of my competition and means my LED is better” were common.
This arms race went on for several years, with many grand, confusing claims. Today, UV LEDs are commercially available with outputs well over 20 W/cm2 at the surface of the workpiece. In some cases, the higher Watt values were used to compensate for the monochromatic output of the UV LED source. Early on, the higher Watt values also allowed a formulation designed for a broadband source to be used with an LED.
Formulations for UV LEDs got better, and the industry realized that most commercially available UV LEDs had more than sufficient irradiance (power). Along the way, the UV LED discussion turned, and people started asking, “So what (Watt), how many Joules does your UV LED array deliver?”
LED Sources: We Need More Power, Example One
I thought that all discussions of power levels from a UV LED were outdated until we encountered a locally made 395 nm UV LED in Asia on a recent trip. The LED, installed in a formulation lab, was water-cooled and “rated” at 6-8 Watts/cm2 by the supplier. For me, this was all very reasonable by today’s technology.
Initial measurements were made at 75% power with the LED positioned 8 inches (20 cm) from the cure surface. The blue trace in Figure 1 is the initial measurement, which shows an irradiance value of just over 400 mW/cm2 (L-395 band). The LED was moved as close (2 inches/5 cm) to the cure surface as the system permitted and the applied power turned up to 100%. The red trace in Figure 1 shows the irradiance profile with the changes and an increased irradiance value of just under 800 mW/cm2 (L-395 band).
The irradiance value increased when the power was increased to 100% and the LED moved as close to the cure surface as possible. Even though the reading was not made at the quartz window, I doubt that this LED could come anywhere close to the 6-8 W/cm2 irradiance value claimed by the supplier.
The output of this system is extremely low compared to the values normally measured on 395 nm UV LEDs. The formulator will need to determine if 800 mW/cm2 on this LED will allow their product to cure sufficiently. Other LED systems offer much higher (20x+) UV output in both the irradiance and energy density values than this system. The applied power on an LED always can be reduced to replicate lower-power LED systems, but there is no way for the power on this system to be increased and for it to replicate higher-power systems.
between the two.
I also was surprised that this system was water-cooled, as most water-cooled LED systems that we see have more power (20x) before water cooling is needed. The people of this particular country have a saying – “good enough is good enough.” I hope it works out for them, but I would have asked Scotty for more power on this LED. Figure 2 compares the LED measured in Asia at 100% power (red trace) with an LED (blue trace) that we consider is more typical of the power of commercially available LEDs.
Summary
Successful UV curing happens when the correct UV spectrum, power (W/cm2) and time exposure (J/cm2) are applied per the defined and established process window. This column gave a few examples of one of the key parameters (power) falling short of what is needed or was expected. Don’t be afraid to be your own Captain Kirk and ask Scotty for more power!
Jim Raymont
Director of Sales
EIT 2.0 LLC
jraymont@eit20.com
