I’ve put together an exaggerated scenario with a Nikon SB-900 flash 1 inch from a PCB with very large traces attached to my scope, effectively forming a dipole antenna.
Test #1: GN 1/1 flash 25mm from PCB
For those not into photography, GN refers to “Guide Number” – an industry standard measurement of flash power. GN 1/1 is effectively full power for most flash guns. It’s so much power that it can be painful to trigger with your hand over the lens.
Wow. Ouch. The scope registered a 44V pk-pk spike. Definitely enough to damage sensitive electronics.
Test #2: GN 1/1 flash 300mm from PCB
With this test the voltage spike measured is significantly less, just 4.3V pk-pk. Not enough to damage most electronics.
Test 3: GN 1/128 flash 300mm from PCB
For this test I left the flash at the same distance, but backed the power off to the minimum for my unit.
The voltage spike measured (5.1V) is actually very similar to the previous, within the shot-to-shot margin of error. The amplitude is the same because the distance and dimensions of the arc are unchanged from the previous test. The potential current induced will be less however I am not in a position to easily test this.
I was tempted to hook some components up to the test connections to see whether or not they survive but realistically there’s no point as such tests would not correlate to any realistic real world scenario.
Suffice to say that the point has been proven. Pointing high powered flash guns at sensitive electronics can induce voltages in the circuit large enough to do damage. It is important to point out however that this only applies to very close exposure to bare circuit boards. A device inside a metal case is well protected against flash induced damage.