Light switch is reversed
There are two likely possibilities here, and one a little more unusual:
Regular Switch
If this is a regular, single switch controlling the light, then it will typically have embossed on it &quot;ON&quot; and &quot;OFF&quot; indicators. If it does, and the operation seems to be opposite of what those indicate then I don't know what is going on. But if has those and they are upside down - i.e., the switch is actually functioning correctly but the labels actually indicate that &quot;ON&quot; is down instead of up, then simply remove the switch and replace it right-side up and you're done.
If it doesn't have &quot;ON&quot; and &quot;OFF&quot; marked on it, but it only has two wires attached (except for ground, of course), then it is a regular switch and you can simply remove the switch and replace it right-side up and you're done.
3-Way Switch
If the switch does not have &quot;ON&quot; and &quot;OFF&quot; marked on it then it is typically a 3-way switch. This means there is another switch somewhere that also controls the light. It might be on the other side of the room next to another room you rarely use. Or it might simply be in a hard-to-reach location so that you just don't think of using that switch. If you can find the other switch, flip it once and now this switch will be reversed and work the way you expect it.
If it is a 3-way switch and you can't find the other end, you can simply remove the switch and replace it right-side up and you're done. Or you can swap the two travelers (two of the three wires that have the same color screws), but since you have to remove and replace the switch to do that, just leave the wires as-is and turn the switch around.
3-Way Switch With One Switched Hot
There is one more wacky but safe &amp; legal possibility: You have a 3-way switch used in place of a regular switch with only one switched hot instead of two travelers. In this case, you won't find a 2nd switch and you will only see 2 wires (not counting ground) connected to the switch. This will happen if:

There was a 2nd 3-way switch and it was removed (e.g., in order to install a switch for something else in that location)
The installer ran out of regular switches and used a 3-way switch

But again, the easiest solution is still remove the switch and replace it right-side up and you're done.