Narrow spectrum blue LED lights for fire studies, monitoring

August 03, 2018 // By Julien Happich
Researchers at the National Institute of Standards and Technology (NIST) have devised a simple method for increasing visibility through clean-burning flames, using ordinary blue LED light. By combining narrow-spectrum blue illumination (around 450nm) with matched optical filters, they were able to reduce the influence of optical emissions from a glowing hot target and a large natural gas diffusion flame, reducing the observed intensity of the flame by 10,000-fold and yielding highly detailed images of the otherwise occulted background.

The new imaging method published in the Fire Technology journal uses digital image correlation (DIC), an optical analysis technique that compares successive images of an object as it deforms under the influence of applied forces, such as strain or heat.

By precisely measuring the movement of individual pixels from one image to the next, researchers can accumulate detailed information about how the material performs over time, including behaviors such as strain, displacement, deformation, and even the microscopic beginnings of failure.
To ensure that DIC would provide high-quality images even when bright, rapidly moving flames came between the sample and the camera, NIST scientists borrowed from the methods that glass and steel manufacturers use to monitor hot and glowing materials during production.

“Glass and steel manufacturers often use blue-light lasers to contend with the red light given off by glowing hot materials that can, in essence, blind their sensors," said research structural engineer Matt Hoehler. "We figured if it works with heated materials, it could work with flaming ones.”


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