Hi Jim:
Your blog is the best I’ve come across on the Internet. Very useful information. Regarding the subject of [Electromagnetic Pulse] EMP, are the new Light Emitting Diode (LED) flashlights more, or less immune to EMP than those using conventional incandescent bulbs?
Modern solid-state circuitry is in grave danger of terminal damage in the event of an EMP occurrence.
LEDs are composed of a semiconductor junction, similar to transistors and integrated circuits.
Do modern LED flashlights have enough of the right characteristics to pick up sufficient EMP burst energy and become permanently useless?
Your comments please, and thank you. – Clark F. in Canada
JWR Replies: LEDs are not absolutely impervious to nuclear weapons effects, but their design makes them fairly robust. Most of the publicized vulnerability of microcircuits to EMP pertains to Metal Oxide Semiconductor (MOS) devices, which are indeed quite sensitive to fast rise-time high voltage spikes. (Everything from EMP, to lightning, to even just a the touch of a human finger transmitting static electricity.) In essence, the smaller MOS-based chip gate dimensions, the more vulnerable the chip is to EMP. But according to C.N. Ghiosh, writing in the IDSA’s Strategic Analysis Journal, “[microcircuit]…diodes, transistors, gate arrays and ICs are based on pure silicon slices [which do not have the same EMP vulnerability as MOS devices] as their electrical properties depend upon the regularity and uniformity of the basic silicon crystal lattices. The initial total damage from Neutron radiation is proportional to the neutron influence, but there is a subsequent annealing process during which there is some degree of recovery. This apart, the damage could be permanent. Also it may be made clear here that it makes no difference whether the device is working equipment or kept on the shelf for future use. However, the annealing process will be longer in such cases. According to Ghiosh, when struck by neutron radiation, “Light Emitting Diodes (LEDs) can suffer degradation in optical output by 10 to 20 per cent.” In essence, LEDs are far less vulnerable to nuclear weapons effects. Hard gamma or neutron radiation would kill you long before you noticed any degradation of LEDs due to silicon matrix disruption! And EMP waveforms themselves don’t affect the silicon structure on an LED. The scale of a LED semiconductor junction is huge compared to the junctions found in gate array chips. So even if they were MOS-based, LEDs would be an order of magnitude less vulnerable to EMP. The bottom line is that I wouldn’t worry about EMP destroying LEDs.
