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Not all LED luminaires are created equal-SEE THE DIFFERENCE!
Date: 24/8/2011
Helpful hints for a fair LED Comparison and Quality Assurance
ArmadilloLED are committed to provide educational information so you can cut through competitive manufacturer claims and separate fact from fiction. We want to help you find products that meet your expectations.
Use Measurable Performance Data Do not be lead by data only . Many claimed manufacturers supply data from other lighting components and one time lab results. Conduct "in field" application level performance evaluations using IESNA recommended practices and standards. Utilise available design software and application engineering practices to predict application level performance. Evaluate relevant and credible case studies.
Operation at Constant Current The drive current through an LED must be controlled. High current densities within the junction of the chip cause partial overheating which damages the crystalline structure of the LED die. At these areas are so called darkline defects, where light ceases to be generated. This should not be confused with the maximum junction temperature of the LED, which is related to the higher temperature at which the optical grade epoxy starts to expand rapidly and increases the risk of catastrophic failures, such as broken wires or lifted LED dies.
To produce light, an LED must be operated in the forward-bias regime. The emitted light is a function of the forward voltage Vf and the forward current If. In the lab, LEDs are usually operated in a forward bias direction from a constant current DC power supply. At low currents, the slope of the radiant power (luminous flux) verses time rises faster than the slope of the electrical power (start-up range) verses time. At high currents, the slope becomes flatter (saturation area), which is mainly caused by heating of the LED chip. Under normal operating conditions (between the start-up range and saturation area), the optical radiation emitted by LEDs is strongly correlated to the electrical current, which is why constant current is recommended for measurements intended to characterize the optical properties of an LED.
