LED and Fireflies

 From Twinkling of Fireflies to LED - more on Green Light,the Millennium Light!

Twinkle Twinkle little stars. NOW I WONDER WHERE YOU ARE??  Leave aside stars; on a clear night in urban India you do not even get glimpses of fireflies nowadays. Vanished! Magician – Artificial Light Pollutant. Lighting professionals all over the world are relentless in their effort to relive the olden days of mystical star gazing experience on clear nights. The solution lies in LED as light source in general lighting. Reason being it is a tiny light source and thus can be optically controlled in a highly effective manner. Imagine a stadium lit by LED floodlight or all major thoroughfares in a city lit by LED streetlights. No untoward upward light, no glare, no pollution. LED is here and has progressed at a furiously rapid pace since the dawn of this millennium. Recently, scientists inspired by the twinkling of fireflies have modified LED to make it almost one and a half time more efficient than the original. Fireflies are bioluminescent insects and the organs on their abdomens flash light in order to attract their mates. A chemical reaction in photocytes (specialized cells in fireflies) creates light. This light is then emitted through cuticle( a part  of the insect’s exoskeleton).Mismatch in light travel which is slower in cuticle compared to air normally dims the glow as a proportion of light is reflected back into the photocytes. Researchers observed that specimens of fireflies found in Latin America and the United States have unique surface geometry of cuticles. The jagged scales resembling factory roof improve light extraction manifold and minimize internal reflections. This discovery led scientists to develop effective LED coating which could produce more efficient and brighter light output.

This image taken from LED Professionals show:

The misfit scales(bottom right) found on the lantern of the Photuris firefly (top right) are the inspiration for a GaN LED, coated with a "factory-roof" pattern (left) that increased light extraction by more than 50 percent

For more information please refer the original Papers:
• "Improved light extraction in the bioluminescent lantern of a Photuris firefly (Lampyridae),” Optics Express, Vol. 21, Issue 1, pp. 764-780 (2013).
• "An optimal light-extracting overlayer, inspired by the lantern of a Photuris firefly, to improve the external efficiency of existing light-emitting diode,” Optics Express, Vol. 21 Issue S1, pp. A179-A189 (2013).

Credits: The article was originally released on the www.osa.org website.

Reference: LED Professionals.