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Advanced Imaging Magazine

Updated: January 12th, 2011 09:49 AM CDT

MERCRON LEDs: Tricky Little Light Sources

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LEDs are simple, but careful power management is needed to preserve their light output and to avoid the deadly combination of high current and high temperature that will cause irreversible deterioration of this expensive light source.

Fluorescent lamps and LEDs share the phenomenon of "thermal runaway," when increasing temperatures cause reduced efficiency. Proportionately, less light is generated as more power is applied and—in the extreme—light output actually declines. However, unlike fluorescents, LEDs can suffer permanent damage if thermal runaway occurs unchecked.

The LED's light output will fall as the temperature climbs, resulting in unstable light for machine vision operations. For example, an LED operated at only 60 percent of maximum current can lose 25 percent of its brightness with a 40°C temperature rise. If the LED is driven near maximum ratings, the effect is even more pronounced, with a 33 percent drop in brightness. Regulating the current, the voltage, or even the input wattage is not going to stabilize the output. And finally, LEDs age with time and need more power to keep the light intensity dependably constant long term.

To counter these problems, MERCRON's new LED Lamp Ballasts (controllers) use light feedback to stabilize and precisely regulate LED output. Moreover, the approach of thermal runaway, or diode decay, is detected by MERCRON's time-tested All's Well Monitoring System, which alerts the operator when the desired light-level cannot be maintained. This feature also prevents "false rejects" in inspection systems due to lighting hiccups or "brown-outs." A safety-start procedure is used to prevent power-up current surges that also can damage LED arrays.

Protect your investment; safeguard your system with any one of MERCRON's Lamp Controllers, either for Fluorescents, Metal Halide, IR, Tungsten, UV, high-pressure Sodium, or now—LEDs.

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