As I understand it, as an event parameter, you can send relative values (i.e -20 would reduce the lighting level by 20 from whatever it currently is). This would only have an effect if the light was currently on. It's not a perfect solution.
It would be great if certain events could use "states" based partly on light status. For example, I started playing a movie late last night and I already had the lights off. When the movie finished, the lights automatically came up as usual, but I would have preferred if they'd stayed off (my preference indicated by the initial condition).
In other words, turn up the lights post-media only if they were on when the media started.
I'm guessing it's not feasible given the current code, but if it were possible it would make the system quite powerful.