Lighting : Lighting October 2016 - Vol 36 Issue 5
22 LIGHTING MAGAZINE | October/November 2016 (CCT=3000K, CRI=85). The FWHM data in Table 2 and Figure 3 are from the DoE Solid State Lighting R&D Plan published last year4. There are many other possibilities using phosphor conversion, determined by economics, desired CCT and CRIs. In a few words, all LERs are obtained based on presumptions. Hence there is no universal maximum LER for the LED family but only conditional ones. That’s where the paradox lies. THE PAST – A BRIEF LED HISTORY, HAITZ’S LAW AND EFFICACY PREDICTION To understand what might happen in the future, it is always good to look back into the history. LED technology was first discovered and discussed a long time ago. The invention of Table 2. Phosphor-converted white LED peak wavelengths and spectral widths Parameter Blue LED Green Dip Red Dip Peak wavelength (nm) 453 538 608 FWHM width (nm) 20 70 30 LEDs dates back to 1961 when the first infra-red LED was invented by Texas Instruments. There was slow development with applications restricted largely as signal indicators, even though some major breakthroughs had emerged that enabled the invention of white LEDs. In 1999, Dr Roland Haitz, a senior engineer, with three scientists, published their report, The case for a national research program on semiconductor lighting. In 2000, the report was released to the general public. The authors made very bold predictions of LEDs’ future trends regarding price and lumen output per lamp. The predictions were so attractive that they acted as a beacon that drew government and industry funds into solid-state lighting (SSL) R&D. Table 1. RGB source peak wavelengths and spectral widths Parameter Blue LED Green LED Red LED Peak wavelength (nm) 463 545 610 FWHM width (nm) 20 30 20 Figure 3. The output spectrum of the pc-LED Haitz’s law for LEDs is the counterpart of Moore’s famous law of the integrated circuit industry. The 2003 version of the law says: ‘The lumen output per package for red LEDs would increase by a factor of 20 per decade while the cost per lumen would still decrease in a pace of a factor of 10 per decade’5 . This can be seen in Figure 4 for red and white LEDs. Besides Haitz’s law, another far- reaching claim the authors made regarded luminous efficacy: they believed it would rise to 150-180 lm/W by 2020 (10 times higher than incandescent lamps). It was actually the high efficacy, energy saving and low price promised in the paper that thrilled governments and the industry. From 2000, the world has raced towards a LED-led future. To understand what might happen in the future, it is always good to look back into the history. LED technology was first discovered and discussed a long time ago. The invention of LEDs dates back to 1961 when the first infra-red LED was invented by Texas Instruments.
Lighting August 2016 - Vol 36 Issue 4
Lighting December 2016