Feature: Optoelectronics and LEDs
Whilst mercury lamps still maintain an advantage in
absolute electrical efficiency at high power, the efficiency gap is no longer prohibitive, especially in low-power, duty-cycled or sensor-driven applications. A more relevant metric than raw optical output in UV
systems is cost per emitted joule ($/J). Whilst mercury lamps may still offer lower $/J at very high continuous power, UVC LEDs can be pulsed, enabling these new solid-state UV light sources to compete favourably in low- to mid-dose systems, especially in intermittently operated systems or those requiring precise dose control. When evaluated on a delivered dose basis, UVC LEDs
benefit from directional emission, since there is less wasted light, there is pulsing or instant on/off control, with reduced optical losses, and lower maintenance and downtime. Mercury vapour lamps typically achieve 8,000-12,000 hours
of usable life, but this figure depends heavily on operating conditions and duty cycle. Pulsing or rapid on/off cycling dramatically reduces Hg lamp life due to electrode wear and thermal stress. In comparison, UVC LEDs tolerate rapid cycling without degradation, and can exceed 10,000-20,000 hours at rated conditions – potentially higher with pulsing and active cooling. In pulsed or duty-cycled operation, UVC LEDs can outlast mercury lamps by a wide margin, delivering a higher cumulative dose over their operational lifetimes.
Figure 2: ATLAS hermetic SMD 230nm UVC LED on starboards
Pulsing, modulation and smart control Table 1 shows the comparison between UVC LEDs and mercury vapour lamps. One of the most decisive advantages of UVC LEDs is their native ability to pulse and modulate output: their on/off switching is in the microseconds range, there’s no warm-up or re-strike time, and they easily synchronise with various sensors. These advantages compare to mercury vapour lamps that need several minutes to warm up and can’t be rapidly cycled without shortening their lifespan. These capabilities unlock many applications for UVC LEDs where mercury lamps are fundamentally unsuitable.
Table 1: UVC LED (280nm) vs mercury vapour lamp
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