I once conducted a test with a 4W UHF transceiver and a grain of wheat bulb. The wires needed to be the right length (obviously) and oriented in a particular way for there to be a substantial illumination. If the wires were next to each other, there would be no illumination of the bulb.
www,propulsionlabs.com.au/Misc_Video_And_Images/RF_Test.MOV
Mind you, transmitting on 1W+ can have a have a considerable detrimental effect to your electronics. I found that out the hard way when I used to communicate via audio DTMF tones through a standard hand held transceiver. Threw a lot of time and energy at that problem before giving up on DTMF some years ago - Faraday cages, wire shielding, bypass caps, etc etc…
My current electronics transmits on 2W (that’s Chinese watts, not necessarily real watts) and utilises UART serial comms throughout which at least made the RF issues quite manageable with bypass caps. However, all my recovery is 100% non-pyro and one problem I never finished up finding a complete solution for was that whenever I transmitted, the miniature geared motor in my main chute latch device would rotate a bit. After (say) 5-10 transmissions, it (via a 60ish:1 gear ratio) would fully rotate the 90 degrees needed to open the latch. Fortunately it wasn’t an issue that occurred on my gas device for deploying my drogue, but still, it was a problem I only ever finished up finding a band-aid solution for (so far).
I’m certainly no RF expert, but FWIW, I’ve always used 1W+ to transmit and I generally agree with John. It would take particularly clumsy or bad luck wiring to initiate an Ematch from >1W transmission.
As for flash bulbs, I’ve never gone near them since one of our club members had one go off in his hands – no wires, no electronics – just the flash bulb.
TP