Editorials

Sensor Feedback May Be the Answer to LED Degradation and Color Shift Over Time

LEDs gradually fade in intensity, and they also shift in color over time. How quickly their brightness declines and their color shifts depends on the LEDs and their operating environment. The fabrication of LEDs gives them inherently different brightnesses even when attempting to give them the same brightness. In fact, all LED producers use binning to group LEDs based on their measured performance characteristics. As a result of this binning, LEDs luminaires and lamps can be made without a discernible difference in brightness or color temperature.

These LEDs are also tested for their useful lifetime (LM-80) to project how long until the LED has 80 percent of its original brightness. Color temperature shift is also part of the measurement. While all LEDs degrade over time and shift in color, the output of Luminaires and lamps doesn’t have to as much as it does.

The industry has the sensor technology that can monitor the brightness and color temperature of an LED light. Such sensors are not prohibitively expensive. In fact, AMS says that its brightness and color temperature monitoring sensors run just a few dollars each in bulk orders.

So not only can this technology help luminaires and lamps continue to produce the same output from an LED light, but it can also ensure that the there is no noticeable difference in output and color temperature between lights of the same type.

With the addition of sensors, an LED light engine will last longer. How much longer, depends on the reliability and LM-80 of the original light engine without the sensor feedback.

The technology for this is already available. Austrian firm AMS is one company that appears to be ahead of the curve in sensing and feedback technology for lighting. I got to speak with Tom Griffiths of AMS recently about the company’s recently released light intensity and color temperature sensor. Unlike other sensor and dimming solutions that may require a microprocessor, the AMS solution only needs to sense when the output is too high or low, or the color temperature is too high or low.

A feedback loop then makes slight adjustments up or down in either the output or color temperature to meet the specified result.

Other solutions can use complex lookup tables that differ for each LED.

This brings up another point. With the AMS solution LED luminaire makers can switch LEDs relatively easily with only minor changes in designs. In the fast moving LED lighting industry, according to Tom.

Tom says that AMS sensors work with a slightly wider range of LEDs to achieve the desired result. In theory, this can also translate to slightly less money spent on binning the LEDs.

Tom pointed out that the human eye has the ability to see even very slight differences in color and output.  With a combination of binning and techniques and sensor feedback, differences in light output from light to light and from LED to LED can be greatly reduced and when combined with superior binning can be nearly eliminated.

Such a device can enable customers to control the output and color temperature of their LED lights. And it can give the luminaires and lamps the output and color temperatures that users desire for much longer, extending their lifetimes.

Luxeon Color

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