I was trying to figure out how to say something like "|undim| the light" in the meaning of "restore the previous amount of light" as an opposite of "dim the light" but have no idea what word or phrase I should use.
I was thinking of "brighten" but it implies a different feel to the phrase, something like "make it brighter than it is now".
The dictionaries give so many antonyms to dim and its synonyms (like dull, faint, darken, subdue) that makes it even harder to choose.
Best Answer
It depends on how exactly the state of the brightness of the lights needs to match the pre-dimmed state, and what level the brighter setting is. I.e. if you just want the lights set brighter than they currently are, or to be set to the highest brightness setting, you can be less specific in your instruction.
My choice for a less specific instruction would be (as mentioned in several comments):
The second of these gives the implication of returning to a previous state, but doesn't explicitly say that it must be to exactly the previous state.
Turn is especially suitable if it is a rotating dimmer switch
If there is a specific setting for the lights to be returned to (e.g. going from 1/4 brightness to 1/2 brightness, or changing to half of the lights at full brightness, half of the lights at 1/2 brightness) then you need to be more specific about it. Words like reset, restore, return or redo may be appropriate.
Note, however, that these terms do not specify that the lights are to be brightened.
Also note that just saying:
may well be understood in the context. It can also be used to mean dim the lights; for example before a slideshow you could say "do the lights" to mean dim the lights and afterwards also say "do the lights" to mean make the lights bright again.