LEDs enable an optimal near-infrared sensing system (MAGAZINE)

Today’s high-efficiency, low-cost, near-infrared (NIR) LEDs and lasers enable many commercial applications. A few straightforward formulas can help the designer approximate the performance of an NIR sensing system and then optimize it to best handle the real-world variables of a particular application, as ROLF WEBER explains.

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This article was published in the September 2011 issue of LEDs Magazine.

View the Table of Contents and download the PDF file of the complete September 2011 issue.

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Specifying the best near-infrared (NIR) system for a particular sensing application can be complex but, armed with an understanding of the basic principles and a few straightforward equations, the designer has a good chance of success. Systems based on the NIR range (850-950 nm) of the light spectrum are becoming increasingly popular in a variety of diverse applications such as security and surveillance, data communications, automotive and manufacturing to name a few. Some of the more interesting applications for NIR include adaptive cruise control in automobiles, fingerprint and iris recognition in security systems, and gesture recognition in gaming, medical and home-entertainment applications.

The three main areas that need to be addressed in designing a typical NIR system include:

• the emitter or light delivery system, sometimes called the radiator or irradiator, which may be based on an IR LED or a laser,
• the target, which is the object of interest irradiated by the emitter subsystem,
• the light detector or sensor (camera or photodiode based), which measures the amount of light reflected back from the target.

Successfully approximating the light intensity that will ultimately reach the sensor requires an understanding of each link in the light chain between emitter and sensor. There are three critical questions to be answered for any application. For a given emitter in a given application, how much light power or beam flux (in mW/cm2) arrives at the target? How much of that is reflected back to, and captured by, the sensor? Finally, is the level of light sufficient to reliably collect the information required for the application?

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This article was published in the September 2011 issue of LEDs Magazine. To read the full version of this article, please visit our magazine page, where you can download FREE electronic PDF versions of all issues of LEDs Magazine. You can also request a print copy of LEDs Magazine (available by paid subscription) and sign up for our free weekly email newsletter.

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