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What's responsible for the recent LED advances?

21 May 2013  | Jon Domingo

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Traditionally LEDs were perceived as an excellent lighting alternative offering significant energy savings, albeit with inferior visual performance compared to some lighting options.

Over the past few years, the energy savings LEDs provide have continued to grow at an impressive pace. In fact today's LEDs are more than twice as efficient as LEDs from just five years ago, offering 25-30% energy savings compared to CCFLs and up to 80% savings compared to incandescent bulbs. These eye-catching energy savings have been accompanied by significant space savings and enhanced visual performance.

Key developments in LED manufacturing, specifically enhanced equipment, improved processes and superior materials, have allowed the latest generation of LEDs to provide a powerful combination of excellent light output, visual performance and space savings. Let's look at each development closer.

LED manufacturing trends
Enhanced equipment: Over the past 10 years, equipment used to manufacture LED dies has undergone dramatic improvements. LED manufacturers have shifted from class 10,000 clean room to highly sophisticated class 1,000 clean rooms for all production processes. This change ensures that no particles bigger than .5um per cubic foot are allowed inside the room as opposed to a class 10,000 clean room, where up to 70 such particles would enter the same space. A Laminar Flow Clean Room consistently pushes airflow from top to bottom from an air purified HEPA filtered machine, refreshing the air inside and further preventing contamination.

Vapor Phase Epitaxy has also helped advance LED performance. Metalorganic Chemical Vapor Deposition (MOCVD) machines are no used to create die substrates. The multi-reactors systems that have replaced them provide up to 20% superior wavelength uniformity, while generating more consistent colour performance and cost savings.

Due in large part to this enhanced equipment, the structural efficiency of LEDs has improved from 50 to 70% ten years ago to over 90% today. The enhanced structural efficiency in turn creates superior visual performance.

Improved processes: Two major process improvements have led to a significant increase in visual performance particularly for white LEDs. Five years ago, LEDs could only achieve a colour-rendering index (CRI) of 50 to 60. In particular, there were issues with producing warm white light. Improvements in manufacturing processes and in binning have dramatically enhanced visual performance.

To create visually appealing warm white light, several steps were added to the manufacturing process. A red die is placed in the same package as the blue die, which is then coated with a highly engineered phosphor coating, resulting in significantly better visual performance. Tweaking the thickness and consistency of the phosphor coating delivers specific gradients of white.

A second significant process improvement was the shift from sapphire substrate to thin-film based die production. Rather than growing dies in a crystal format, they are now made via a thin film process, which can be controlled on a molecular level, greatly enhancing wavelength uniformity and thus visual performance.

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