Brake Bulb Out Warning

[roboblob]

I have a weird one , as well as a weird fault

Last night I started the car, all was good until I pressed the brake pedal , up came the brake bulb out warning ( yellow with pads around a bulb) so I used my walking stick to press the brake while I checked which one was out, to my surprise all of them were ok, including the 4 in the high level.
Has anyone had a similar issue before ?

I am wondering if one of them is ready for failing and is giving a different resistance reading to the other one, but from looking at the light given they both look the same .

I have ordered a new pair just to rule them out.