The phosphor layer of some LEDs will stay glowing for some time just like a glow in the dark toy, even with FET drivers (no output capacitor). Some LEDs glow for longer than others, it will depend on the phosphor composition.
Wow that is very noticeable, I didn’t realize it could be that bright. I know most emitters are phosphorescent to a certain extent, but that’s something I didn’t consider very much.
Another thing to consider is the fact that some LEDs ate VERY sensitive to 365nm UV, to the point that the driver of my Q8 Pro turned on, the button backlight was responding to the switch commands, and I could even do a voltage check, and it was reading 2.3V with the battery tube removed, so if you want to use the main emitter as a sensor you could use a 365nm LED as your Tx and you would have a strong signal to work with.
