I wonder when people first started using the visual of a light bulb to represent someone having an idea? (I’m trying really hard now to resist the urge to go and Google that.) As a child I saw light bulbs used like that in comics and cartoons all the time, so of course it became imprinted on me, and then I started using it in my own drawings and comics. I think the media I consumed during my childhood is also where I got the notion that “hot water bottle + mercury thermometer = sick person”.