Using LEDs as Light-Level Sensors and Emitters

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Executive Summary

Modulating LED power based on ambient light level increases battery life, a particularly helpful feature in a device where battery life is measured in days. Using a very simple circuit, Altera's MAX II and MAX IIZ CPLDs can measure the analog light level of their environments and then drive an LED at a proportional analog intensity level. Controlling the LED intensity based on ambient light as demonstrated reduces LED energy usage by more than 47 percent without affecting appearance.

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