many of the fruit machines also do it to do dimmer / brighter effects.

there's one that does a 'photo finish' (can't remember which) by holding the lamps on for an excessive amount of time to make them much brighter, apparently not popular with the ops because it was both distracting, and burnt them out.

we need some generic simulation code for bulbs / leds with attack / decay / max saturation parameters etc. at that point you make the lamps in the artwork not on/off things, but ones that take a parameter. IMHO that code lives outside the actual artwork system, much like any other discrete simulation. The actual artwork just takes a value.

of course MAME is still limited, there are cases where coloured lamps close together need to mix to form new colours, another issue entirely tho, the basic lamp sim needs to live somewhere.