@patosawa
Possibly you can install the screensavers from the proper FreeBSD project and activate them: FreeBSD Manual Pages > Screensaver
However, non of them will be able to shut off the display. You can use blank screen at best, which will not provide any notable power savings.
As mentioned, shutting off the screen is a hardware feature and usually notebooks do this when closing the lid. Possibly you can get a BIOS upgrade which has this ability.