Prevent display from sleeping
In addition to the "sleep corner" mentioned in Tetsujin's answer, there is also a small app out there called Caffeine which you can use to prevent the machine (and thus display as well) from sleeping. Note that it will even stop a laptop from sleeping when the lid is shut, so be sure to disable it. There are also alternatives like Amphetamine and Owly that seem to do the same thing, but I've only use Caffeine. All of them hit the same underlying OSX setting, apparently.