Script Summary: Enabling the lights out feature on YouTube for every video.
License: GPL 2 or later
UPDATE2: There's now the option of selecting whether you want lights off by default. It can be set by the script menu. Simply right click on the Greasemonkey icon and go to "User script commands". See the last screenshot below for a picture.
UPDATE: Around 18th of June, the script stopped working due to a web page layout change at YouTube. I have since updated the script so that it works again and I hope to have made it more robust against future updates. See the discussion here, if you want.
I basically copied the features found on some YouTube videos so that I can use lights out on every video I want.
The buttons are just above the video, on the right of the video title like where YouTube originally puts it. See the screenshot image file.
Any feedback is welcome, feel free to drop me a line.
If you are interested, there's another greasemonkey script doing a similar task, found here: