Display Technology
High efficiency phosphor converted amber LEDs for displays and signage now available for the first time with proven lifetime characteristics
By David Scott-Mackwell, director, Forge Europa A
mber and yellow LEDs have been popular in the professional display and signage industry for many years as they enable the
creation of dot-matrix display panels that are robust, reliable and provide adequate illumination to compete with natural light in outdoor applications. As such they have become commonplace in transport infrastructure worldwide and have been widely used in road, bus and rail, and passenger terminal signage and so on. The de-facto standard LED platform for these applications has long been based on compound semiconductors – specifically Aluminium Indium Gallium Phosphide, or as commonly abbreviated in the LED industry AlInGaP. This material has served the LED display industry well for almost three decades, being both efficient and robust, but it is not without shortcomings.
AlInGaP LEDs are relatively expensive to manufacture, and their very narrow wavelength emission spectrum means that very careful production batch handling is generally required in order to avoid unwanted visible colour artefacts in display screens such as mismatched colour patches.
While AlInGaP remains the dominant choice for professional amber display and signage applications there is now an alternative technology available that derives from the LED lighting industry – phosphor-converted amber, also known as PC amber.
PC amber LEDs are made in the same way as white light emitting LEDs – they generate blue light from a compound semiconductor of Indium Gallium Nitride (InGaN) and down-convert the blue light to amber via superimposed phosphors. PC amber LEDs overcome many of the weaknesses of AlInGaP – they are cheaper to manufacture due to the
24 May 2025
economies of scale attained from the general lighting industry. Plus, they are more efficient at light production for the same reasons and produce broader spectral emission, thus providing better colour consistency. Indeed, PC amber LEDs surround us every day as almost all vehicle turn indicators now use this technology to create amber light. With all these benefits surely the professional display and signage industries should be moving to PC amber straight away? Well, there lies the challenge because the one downside of PC amber and indeed all LEDs that use phosphors to down-convert light from a short wavelength (e.g. blue) to a longer one (e.g. amber) is that the phosphors degrade over time. Meaning this chronic degradation results in light output reduction and colour change. Automotive vehicle turn indicators have a whole-life on-time of the order of 1000 hours – just 6 weeks – whereas professional displays need
Components in Electronics
to operate for many tens of thousands of hours without visible degradation. Forge Europa has been deeply involved in the professional LED display and signage industry since the 1990s and has invested heavily in addressing the lifetime issue of PC amber LEDs through a programme of LED device customisation and long-term life testing. This has involved designing LED semiconductor and phosphor technologies specifically tuned to the very long service life requirements of professional LED displays, and then long-term life-testing the resulting LED designs.
LEDs have been life-tested under globally accepted and universally proven lighting industry standard accelerated environmental test conditions IESNA LM-80-20 and TM- 21-21. And the result? A range of PC amber LEDs with degradation and colour shift performance yielding lifetimes in excess of ten years in professional display and signage applications. Both off-the-shelf and semi- custom PC amber LED packages are available from the team at Forge Europa.
https://www.forge.co.uk/ www.cieonline.co.uk
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