This technology involves the use of an extensible array of light-emitting diodes (LEDs) as a means of sensing incident light levels. The light-sensing LED array can be used to construct highly-dynamic backlights for displays and large-format synthetic aperture cameras.

A hand casts a shadow on elements of a prototype light-sensing LED array. Elements in the shadow are illuminated, and those in the light are off.
Using an LED array that both emits and senses light allows the construction of a large format display backlight that automatically adjusts to changing ambient lighting conditions. The LED array can be used to sense reflected light and construct an image of objects passing in front of the array, allowing the creation of a large-format synthetic aperture camera. The construction of the LED array is extensible to virtually any size, meaning that an entire billboard, information display, or wall can be covered with the light-sensing array.

The principle behind sensing light with an LED is to drive the LED as a capacitor, the discharge from which can be accelerated by light. The LED is reverse-biased, then the bias is removed and the LED is allowed to discharge. By measuring the time it takes for the LED capacitor to fully discharge, the level of light incident on that LED can be calculated. By alternating between modes, the LED array can be used to both display (emit light) and sense light.

This technology is patent pending and immediately available for licensing or partnering opportunities. For more information, visit the NDSU Research Foundation.

Lighting Technology Magazine

This article first appeared in the May, 2011 issue of Lighting Technology Magazine.

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