Turn Display Off But Prevent Computer From Sleeping

I'd like to keep my computer running at full processor speed to finish a task (say disk encryption) before going to "sleep". But I don't want to burn the monitor and so would like just the display to be off while the computer hums away in the background. I know Caffeine can keep the computer running but it keeps the display on as well.

I tried the below but the machine seemingly goes to sleep (because it asks me to log in once the display has turned off):

1. System Preferences > FileVault > Advanced  and unchecked the "Log out after XX minutes of inactivity"
2. System Preferences > Screen Saver > Start after = Never
3. System Preferences > Energy Saver >
   1. Turn display off after 1 min
   2. check "Prevent computer from sleeping..."
   3. uncheck "Put hard disks to sleep when possible"
   4. uncheck "Enable Power Nap"
   5. nothing setup in "Schedule" to turn off

Is there anyway to keep the display off but the computer from not going to sleep?