DISPLAYS & UIs
Transitioning to high efficiency Phosphor Converted Amber LEDs
for displays and signage With high efficiency Phosphor Converted Amber LEDs now available with proven lifetime characteristics, David Scott- Maxwell, director at Forge Europa, explores the benefits and considerations of this technology for the display
T
he professional display and signage sector has relied heavily on amber and yellow LEDs for many years. This is primarily because this technology enables the creation of dot-matrix panels that are robust and reliable. Furthermore, they provide adequate illumination to compete with natural light in outdoor applications.
Taking these benefits into account, it is unsurprising that amber and yellow LEDs have been popular for transport infrastructure across the globe.
The LED platform for these applications has long been based on compound semiconductors - specifically Aluminium Indium Gallium Phosphide, commonly abbreviated in the LED industry to AlInGaP. Due to the popularity of these semiconductors, they have in effect become the industry standard. While this efficient and robust material has served the LED display industry well for almost three decades, it does have some limitations.
Firstly, AlInGaP LEDs are relatively expensive to manufacture. Adding to their drawbacks, their very narrow wavelength emission spectrum means that careful production batch handling is generally required to avoid unwanted visible colour artefacts in display screens such as mismatched colour patches. In spite of these issues, given their prevalence, AlInGaP has remained the dominant choice for professional amber display and signage applications. This said, developments have been in the pipeline. 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. They overcome many of the weaknesses of AlInGaP –
24 MAY 2025 | ELECTRONICS FOR ENGINEERS
being cheaper to manufacture due to the economies of scale attained from the general lighting industry. For the same reasons, they also offer better efficiency in respect of light production and produce broader spectral emission – delivering better colour consistency. Demonstrating their rising use, PC amber LEDs can be seen in our everyday activities as almost all vehicle turn indicators now use this technology to generate amber light.
Understanding all of these benefits would suggest that the professional display and signage industries should be transitioning to the use of PC amber as a matter of course. Yet this has not happened for one main reason. The challenge with PC amber, and in fact all LEDs that use phosphors to down-convert light from a short wavelength (eg blue) to a longer one (eg amber), is that the phosphors degrade over time.
This chronic degradation results in light output reduction and colour change. While in some settings this is unproblematic, for the professional display sector it presents a real issue. To put this in context, automotive vehicle turn indicators have a whole-life on- time of the order of 1000 hours – just 6 weeks
– whereas professional displays need to operate for many tens of thousands of hours without visible degradation.
Forge Europa has been involved in the professional LED display and signage industry since the 1990s. The company has invested heavily in addressing the lifetime issue of PC amber LEDs. This has involved designing LED semiconductor and phosphor technologies specifically tuned to the very long service life requirements of professional LED displays. The resulting LED designs have then been life-tested under globally accepted and universally proven lighting industry standard accelerated environmental test conditions IESNA LM-80-20 and TM-21-21.
The result is a range of PC amber LEDs with degradation and colour shift performance yielding lifetimes in excess of 10 years in professional display and signage applications. This commitment to R&D has opened up new opportunities for the display and signage sector to embrace PC amber technology, paving the way for greater efficiency, better colour consistency, and lower financial outlays.
https://www.forge.co.uk/
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